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Review

An overview of cathode material and catalysts suitable forgenerating hydrogen in microbial electrolysis cell

Anirban Kundu a, Jaya Narayan Sahu b,*, Ghufran Redzwan a, M.A. Hashim b

a Institute of Biological Sciences, University of Malaya, 50603 Kuala Lumpur, MalaysiabDepartment of Chemical Engineering, University of Malaya, 50603 Kula Lumpur, Malaysia

a r t i c l e i n f o

Article history:

Received 12 September 2012

Received in revised form

3 November 2012

Accepted 5 November 2012

Available online xxx

Keywords:

MEC

Cathode

Cathode catalyst for hydrogen

evolution

* Corresponding author. Tel.: þ60 3 79675295E-mail addresses: [email protected], ja

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0360-3199/$ e see front matter Copyright ªhttp://dx.doi.org/10.1016/j.ijhydene.2012.11.0

a b s t r a c t

Bio-electrohydrogenesis through Microbial Electrolysis Cell (MEC) is one of the promising

technologies for generating hydrogen from wastewater through degradation of organic

waste by microbes. While microbial activity occurs at anode, hydrogen gas is evolved at the

cathode. Identifying a highly efficient and low cost cathode is very important for practical

implication of MEC. In this review, we have summarized the efforts of different research

groups to develop different types of efficient and low cost cathodes or cathode catalysts for

hydrogen generation. Among all the materials used, stainless steel, Ni alloys Pd nano-

particle decorated cathode are worth mentioning and have very good efficiency. Industrial

application of MEC should consider a balance of availability and efficiency of the cathode

material.

Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

1. Introduction through the external circuit. There are two aspects of this BES.

Energy is considered as the lifeline of modern era. Non-

renewable energy sources like coal, oil and natural gas are

excessively used to meet the world’s energy requirements.

This has come out with an increased rate of depletion of the

natural resources. This is a global concern as the future

generations would definitely be at threat if the natural

resource is depleted at this alarming rate. There are of course

alternatives for non-renewable energies. Utilization of solar

energy, wind, tidal, geothermic and bio energy, which in

principle are renewable, are possible alternatives.

Bio-electrochemical system (BES) possesses a tremendous

potential for energy generation and simultaneous treatment

of wastewater containing organic substances. Microbes

present in the anode degrade the organic substance and

release electron to the solid anode surface which travel

; fax: þ60 3 [email protected] (J.N.

u A, et al., An overviewll, International Journ

2012, Hydrogen Energy P31

One in which electricity is produced known as MFC and

another where hydrogen is produced known as Microbial

Electrolysis Cell (MEC) [1]. Cathode is one of the most impor-

tant parts of the MEC where hydrogen as well as different

chemical compounds are produced. In recent time numbers of

researches are directed toward development and application

of a low cost cathode or cathode catalyst for practical utili-

zation in MECs for hydrogen generation. In this article the

material and catalyst used by different research groups for

hydrogen generation and result obtained are discussed.

2. Hydrogen as fuel

Recently interest on hydrogen as a fuel has increased a lot

mainly due to the reason that hydrogen has the highest

Sahu).

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ublications, LLC. Published by Elsevier Ltd. All rights reserved.

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i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 2 ) 1e1 32

gravimetric energy density of any known fuel and is compat-

ible with electrochemical and combustion processes for

energy conversion without creating environmental pollution

and contributing to climate change by producing carbon-based

emissions. Hydrogen has a high energy density by weight yet

when it is burnt in engines produces almost no pollution. An

Otto cycle internal-combustion engine has a maximum effi-

ciency of about 38%, 8% higher than a gasoline internal-

combustion engine when the former is run on hydrogen [2].

Hydrogen is a colorless, odorless gas that accounts for almost

75 percent of the entire universes’ mass. However it is avail-

able on Earth only in combination with other elements like

oxygen, carbon and nitrogen and must be separated from

these other elements to obtain pure hydrogen to be used.

Although, hydrogen is not a primary source of energy like coal,

rather it is an energy carrier like electricity. Hydrogen fuel cells

and related hydrogen technologies provide the essential link

between renewable energy sources and sustainable energy

services. NASA has used liquid hydrogen as fuel for space

shuttle and rockets since the 1970s [3,4]. Hydrogen is used

there as fuel to power the electrical systems and as byproduct

pure water is produced, used by the crew as drinking water.

The market of hydrogen fuel is increasing and according to

a market research company the total world production of

hydrogen as a chemical constituent and as an energy source

was valued at $120 billion in 2010. An expected increase at

a 6.3% compound annual growth rate it may reach a value of

$163 billion in 2015 [5]. This seems to be very promising not

only for the business but also for the academicians because

a chunk of this money will be invested in the R&D section

where the researcher can research on novel technology to

increase the power output and machineries to use the

hydrogen as fuel at lesser cost. There are different types of

processes for hydrogen production like steam reforming,

partial oxidation, plasma reforming, water electrolysis, water

thermolysis, photocatalytic water splitting, sulfureiodine

Fig. 1 e Schematic d

Please cite this article in press as: Kundu A, et al., An overviehydrogen in microbial electrolysis cell, International Journj.ijhydene.2012.11.031

cycle. Biomass and waste streams can in principle be con-

verted into bio-hydrogen with biomass gasification, steam

reforming or biological conversion like biocatalysed electrol-

ysis or fermentative hydrogen production. Fermentative

hydrogen production is a well-known process. Besides dark

and photo fermentation, bio-electrohydrogenesis (electrolysis

using microbes) is another possibility. The biocatalysed elec-

trolysis process is based on a biological anode where electro-

chemically active microorganisms transfer electrons from

organic substrate directly to a solid surface and the get

combined with Hþ ions at cathode in absence of oxygen.

Microbial electrohydrogenesis provides a completely new

approach for hydrogen generation from biomass, such as bio-

waste andwastewater, and accomplishing waste treatment at

the same time.

3. MEC system

Microbial Electrolysis Cell (MEC) technology represents

a new form of clean and green energy by generating elec-

tricity and hydrogen from what would otherwise be

considered waste. In bio-electrochemical systems bacteria

oxidize organic matter and release carbon dioxide and

protons into solution and electrons to anode [6]. The elec-

trons released in anode flows through an external electrical

circuit to the cathode where they are used in reduction of

oxygen. When oxygen is supplied to the cathode, current

can be produced and the system is known as MFC. However,

in absence of oxygen, and electrochemically enhancing the

cathode potential in an MFC circuit it is possible to produce

hydrogen (Fig. 1) directly by reduction of protons and elec-

trons produced by the bacteria [3,7e9]. This approach greatly

reduces the energy needed to make hydrogen directly from

organic matter compared to that required for hydrogen

production from water via electrolysis. In a typical MFC, the

iagram of MEC.

w of cathode material and catalysts suitable for generatingal of Hydrogen Energy (2012), http://dx.doi.org/10.1016/



i n t e r n a t i o n a l j o u r n a l o f h yd r o g e n e n e r g y x x x ( 2 0 1 2 ) 1e1 3 3

open circuit potential of the anode is 0.30 V [10,11]. When

hydrogen production occurred at the cathode, the half

reactions occurring at the anode and cathode, with acetate

oxidized at the anode, is as follows [7]:

Anode : C2H4O2 þ 2H2O/2CO2 þ 8e� þ 8Hþ (1)

Cathode : 8Hþ þ 8e�/4H2 (2)

Producing hydrogen at the cathode requires a potential of at

least E0 ¼ 0.41 V (NHE) at pH 7.0 [12], so hydrogen can theo-

retically be produced at the cathode by applying a circuit

voltage greater than 0.11 V (i.e., 0. 41e0.30 V). This voltage is

substantially lower than that needed for hydrogen derived

from the electrolysis of water, which is theoretically 1.21 V at

neutral pH. In practice, 1.8e2.0 V is needed for water hydro-

lysis under alkaline solution conditions due to overpotential

at the electrodes [7].

Hence, thermodynamic analysis shows that, the addition

of greater than 0.11 V to the power that generated by bacteria

(0.3 V) will generate hydrogen gas at the cathode. However it

is observed that voltages of 0.2 V are needed because of

electrode over potentials. This hydrogen evolution process

provides a route for extending bio-hydrogen production past

the endothermic barrier imposed by the microbial formation

of fermentation dead-end products, such as acetic acid

and same exoelectrogenic bacteria can be used that was

used in MFCs and not exposing the cathode to oxygen

[7,10,13]. Although, some researchers [7e9,14] referred to the

MEC as a biocatalyzed electrolysis cell (BEC) or a bio-

electrochemically assisted microbial reactor (BEAMR) but

Logan et al. [1] defined the process as electrohydrogenesis or

microbial electrolysis to emphasize that in an MEC there is an

electrically driven hydrogen evolution process that is distinct

from fermentation.

4. Cathode material and catalyst used inMEC for hydrogen evolution

The hydrogen evaluation reaction (HER) reaction occurs at

the cathode. MEC construction includes one anodic chamber

with the anode; one cathodic chamber with cathode; or

a single chamber with both anode and cathode [15]; an

external electrical power source; and an electronic separator.

Cathode acts as the primary electron donor in an MEC system

[7,8,16].

A variety of parameters can limit current density in MECs,

for example, distance between the anode and cathode, elec-

trolyte resistivity (including the membrane), ARB (Anode-

respiring bacteria) density on the anode, and the specific

surface area of the electrodes, cathode material and catalyst

[17e20]. The base material of cathode and the catalyst

applied on it have significant effect on the performance of the

MECs. The base material of the cathode may be graphite,

titanium of other conductive materials. The hydrogen

evolution reaction (HER) on plain carbon electrodes is very

slow, requiring a high overpotential to drive hydrogen

production. To reduce the over potential a catalyst is used on

the cathodes [1].

Please cite this article in press as: Kundu A, et al., An overviewhydrogen in microbial electrolysis cell, International Journj.ijhydene.2012.11.031

4.1. Platinum as cathode catalyst

Platinum is commonly used as the catalyst due to its low

overpotential (�0.05 V at 15 Am�2) for the HER under opti-

mized conditions (for phosphate buffer at pH 6.2, for ammonia

it was at pH 9.0) of mass transport [21]. Platinum catalyzed

electrodes are commercially available e.g., E-TEK, USA;

Magneto Special Anodes, The Netherlands; Alfa Aesar,

Germany but can easily be prepared in the laboratory [22,23]

by mixing commercially available platinum (e.g., 10 wt% Pt/

C, E-TEK) with a chemical binder (5% Nafion solution or 2%

PTFE solution). Hydrogen production rates obtained

3.12 � 0.02 m3 m�3 reactor liquid day �1at Eap ¼ 0.8 V with

a cathodic hydrogen recovery rH2, cat ¼ 96% and an overall

energy efficiency of hEþS ¼ 75% by using Pt catalyst on carbon

cloth in a single chamber MEC of volume 28 ml [24]. Titanium

mesh having surface area 400 cm2, thickness 1 mm, specific

surface area 1.7 m2m�2 with platinum catalyst were used by

Rozendal et al. (2007) in two-chamber and one-chamber

configurations, with hydrogen production rates up to

0.3 m3 m�3 reactor liquid day�1at an applied voltage of 1.0 V

[8,15]. Selembo et al. (2010) applied platinum catalyst of

particle size 0.002 mm mixing with 400 mL and 50 mg carbon

black on carbon cloth using a brush to obtain hydrogen

production rate 1.6 � 0.0 m3 m�3 reactor liquid day�1,

Columbic efficiency 85.0 � 6.4% [25].

However, there aremany disadvantages to using platinum,

including the high cost and the negative environmental

impacts incurred during mining/extraction [26]. Platinum can

also be poisoned by chemicals such as sulfide, which is

a common constituent of wastewater [1]. Therefore, finding

out alternative of Pt catalyst for commercialization of the MEC

systemwas very important. Differentmaterials were tested as

cathode in MECs. In the following sections different alterna-

tives of platinum which has been used by different research

groups has been discussed in detail.

4.2. Microbial biocathode

Concepts of a cathode where microorganism will act as the

catalyst were first developed in the 1960s but no significant

progress was made [27]. In the recent years researchers have

studied and explored several metabolic processes present in

the cathode, stepping toward a possibility to develop

a cathode catalyzed by microorganisms or biocathode [28].

Microorganisms that can produce hydrogen are found in

a large variety of environments [29] and contain hydrogenases

that catalyze the reversible reaction given in Eq. (3).

2Hþ þ 2e�4H2 (3)

Purified hydrogenases have been successfully used on carbon

electrodes as a catalyst for hydrogen production [30e33].

Rozendal et al. [34] describes thedevelopmentof amicrobial

biocathode for hydrogen production from a naturally selected

mixed culture of electrochemically active microorganisms. An

MEC half cell with carbon felt electrodes was constructed with

a biological anode and fed with acetate and hydrogen at the

initial phase. The operation started in a batch mode and latter

shifted to continuousmode.Hexacyanoferrate(III)was reduced





at the cathode. Once the anodic current was stable, the acetate

and hydrogen supply was stopped, and the polarities of anode

and cathode were reversed, resulting in a biocathode and

chemical anode as schematically described in Fig. 2.

At a cathode potential of �0.7 V, the average current

generation of the biocathode was about �1.2 Am�2, average

volumetric hydrogen production rate during the hydrogen

yield tests was about 0.63 m3 H2/m3 cathode liquid volume/

day for the biocathode chamber and 0.08 m3 H2m�3 cathode

liquid volume/day for the control electrode chamber. A carbon

monoxide inhibition test was conducted to prove that the

biocathode is microbial in origin and expected microbial bio-

cathode behavior was observed.

Jeremiasse et al. [35] studied a full biological MEC where

both the anodic as well as cathodic reactions were catalyzed

by microorganisms to understand the difference of perfor-

mance predicted from the electrochemical half cell by

Rozendal et al. [34] using the same experimental set up. Two

set ups (MEC1 and MEC2) were used in this 1600 h study. The

cathode chamberwas inoculated 600 h after the inoculation of

anode chamber. During the 52-h yield test, MEC 1 had an

average current density of 0.79 Am�2 and produced 0.08 L of

hydrogen; and MEC 2 had an average current density of

0.84 Am�2 and produced 0.11 L of hydrogen. Hydrogen

production rate was 0.03 Nm3/m3 reactor liquid/day to

0.04 Nm3m�3 reactor liquidday�1. At an applied cell voltage of

0.8 V, both MECs had a current density of 3.3 Am�2. According

to the authors this result is compatible with the result of

Tartakovsky et al. (3.2 A m�2 at 0.85 V) [36].

Jeremiasse et al. [37] further investigated for the faster

start-up of microbial biocathode. Two attributes were studied,

the effects of cathode potential and carbon source. The former

attribute had no effect on the start-up time but the latter

reduced the start-up time almost 2 folds. According to the

researchers of this study higher biomass yield from acetate

may have helped the faster start-up of the microbial bio-

cathode which was supported by thermodynamic calcula-

tions. To increase the H2 production rate, a flow through

biocathode fed with acetate was investigated. This biocathode

produced 2.2m3 H2 m�3 reactor day�1 at a cathode potential of

�0.7 V versus NHE. In Table 1 the experimental conditions

used for biocathodes are tabulated.

Fig. 2 e Three phase biocathode start-up procedure. A) Start-up

inoculation with a mixed culture of electrochemically active mi

polarity reversal to a hydrogen-producing biocathode and adap


4.3. Use of stainless steel as cathode

In the research to find out alternative for expensive Platinum

catalyst it was found that first row transition metals are very

useful due to their stability, abundance in nature, low cost,

and low toxicity to living organisms. The most promising

materials identified so far are nickel and stainless steel alloys

for their low cost, easy availability, low overpotentials, and

stability in highly alkaline solutions [39].

Olivares-Ramırez et al. [40] worked on three different type

of stainless steel each with different metal composition. SS

304, SS 316 and SS 430 containing 9.25%, 12%, and 0.75% of

nickel respectively were used for hydrogen evaluation reac-

tion (HER) in the alkaline electrohydrolyzer. From the cyclic

voltametry experiments modification of active surface of the

stainless steel and cyclic voltammograms well defined

cathode and anode peaks corresponding to hydrogen and

oxygen evolution zones in the cathodic (�1500 mV to

�1350 mV/NHE) and anodic (400e500 mV/NHE) regions

respectively were reported. The hydrogen evolution rate

which was analyzed by means of the graphical mineral oil

volume displacement as a function of time reveals that SS 316

is the best cathode electrode at various applied voltage among

SS 304, SS 316 and SS 430 and it was attributed to its higher

nickel content than the others used in the experiment.

Selembo et al. [39] studied different stainless steel alloys

304, 316, 420 and A286 and nickel alloys 201, 400, 625 and HX at

neutral pHcondition. Thecathodesweremadebycutting sheet

metal in to 3.8 cm diameter disks. Sheet metal of flat surface

was used to eliminate the influence of factors like catalyst

particle size, binding efficiency etc. The experiments were

conductedat either 0.6Vor 0.9 V at 30 �Cconstant temperature.

According to the results obtained SS A286 is the best

alloy in terms of overall hydrogen recovery (rH2,

COD ¼ 62 � 6%), cathodic hydrogen recovery (rH2,

cat ¼ 61 � 3%), energy efficiency relative to electrical input

(hE¼ 107� 5%), overall energy recovery based both electric and

substrate inputs (hEþS ¼ 46 � 3%), Current density

(IV ¼ 222 � 4 A m�3), hydrogen production rate

(Q¼ 1.50� 0.04m3m�3 day�1), andH2 content (80� 2%) at 0.9 V.

SS 304 also showed better result in comparison to platinum

sheet metal. SS alloys A286 (21.2 � 2.2 ml) and 304 produced

of an acetate and hydrogen-oxidizing bioanode after

croorganisms, B) adaptation to hydrogen oxidation only, C)

tation. Adopted from Ref. [34].




Table

1e

Experim

entalco

nditionsforth

etestin

gofbioca

thode.

MECsy

stem

Typeofelectro

deuse

dTypeofelectro

lyte

use

dTem

peratu

re(�C)

pH

Modeofoperation

Reference

Anode

Cath

odeandca

thode

catalyst

Anodech

am

ber

Cath

odech

amber

Electro

chemical

halfce

ll

Graphitefelt

Electro

chemically

activatedmicro

bes

ongraphitefelt

100mM

potassium

ferricyanide/

ferrocy

anide

solution

Standard

micro

bial

nutrientso

lutiona

e7

Initiallyfed-batch

modelater

continuousmode

[34]

Twoch

ambered

Electro

chemically

micro

beson

graphitefelt

Electro

chemically

activatedmicro

bes

ongraphitefelt

Standard

micro

bial

nutrientso

lutionaþ

1.36gL�1

NaCH

3COO$3

H2O

Standard

micro

bial

nutrientso

lutionaþ

0.84gL�1

NaHCO

3

30

7Continuous

mode

[35]

a0.74gL�1KCl,0.58gL�1NaCl,0.68gL�1KH

2PO

4,0.87gL�1K2HPO

4,0.28gL�1NH

4Cl,0.1

gL�1MgSO

4$7H

2O,0.1

gL�1CaCl 2$2H

2O,and1mLL�1ofatrace

elementmixtu

re[38].


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, An overviewtional Journ

19.1 � 1.1ml hydrogen at an applied voltage of 0.9 V compared

to Platinum sheet metal producing18.9 � 5.4 ml. Ni 625 per-

formed better than the othermetals in terms of total hydrogen

gas production at 0.6 V applied voltage by producing 6.61mlH2.

Performance of SSA268 andNi 625were enhancedwhennickel

oxide was electrodeposited on the surface of the sheet metal.

Gas production increased from 9.4 to 25 ml for SS A286 and

from 16.2 to 25 ml for Ni 625 at an applied voltage of 0.6 V.

Energy recovery based on electrical input (hE) increased from

3.1% (SS A286) and 31% (Ni 625) to 137% for SS A286 and Ni 625

both with nickel oxide coating. Volumetric hydrogen produc-

tion rates (Q) also improved from 0.01 (SS A286) and 0.1 (Ni 625)

to 0.76m3H2m�3 day�1 for bothnickel oxidemodifiedmetals at

0.6 V. Methane gas production was reduced from 6.8 to 4.1 ml

for SS A286 and from 7.7 to 4.2 ml for Ni 625. These results are

very promising in terms of good performance and at low cost

which is an absolute requirement for large scale application.

Call et al. [41] selected high nickel containing SS 304 to use

in an MEC. They compared the performance of high surface

area SS brush with Pt-catalyzed carbon cloth (Pt/C) cathodes

and also examined the effect of material composition on

current productionwith SS brush and graphite brush cathode.

Hydrogen production rates and overall energy recoveries ob-

tained here for a reactor with 100% loaded SS brush oriented

vertically above and parallel to the core of the anode was

Q ¼ 1.7 � 0.1 m3H2m�3d�1 and overall energy recovery was

hEþS ¼ 78 � 5%.

Stainless steel mesh SS 304 woven and expanded mesh

having composition 0.08%C, 2%Mn, 1%Si, 18e20%Cr, and

8e11%Ni, was tested for their suitability as cathodes in MECs

as cathode [42]. SSmesh has higher surface area as well as flat

nature like flat sheet therefore closer space between anode

and cathode can be arranged. Linear sweep voltammetry (LSV)

result shows that �0.67 � 0.01 V of voltage is required to

generate substantial current and cyclic voltammetry (CV)

tests results measured that electrochemically active areas for

all mesh ranged from 12.23 to 23.26 cm2. Matsuda’s equation

(Eq. (4)) was applied to obtain the peak current, ip (A) and

effective surface area of the working electrodes:

ip ¼ 0:4464� 10�3n3=2F3=2AðRTÞ�1=2DR1=2C�Rv

1=2 (4)

where n ¼ 1 is the number of electrons transferred,

F ¼ 96,487 C/mol e� Faraday’s constant, R ¼ 8.314 J mol�1 K�1

the gas constant, T ¼ 303 K the temperature, CR* ¼ the initial

ferrocyanide concentration, and v ¼ the scan rate.

SS mesh no 60 with a wire diameter of 0.019 cm and a pore

size of 0.023 cm produced the highest current densities and

hydrogen production rate (3.3 � 0.4 m3H2/m3d, 2.1 � 0.3 m3H2/

m3d, and 0.8 � 0.1 m3H2m�3d�1) at the three different applied

voltages of 1.2 V, 0.9 V, 0.6 V respectively with respect to other

different meshes. When tested in MEC SS mesh no 60 was

used the Coulombic efficiency obtained was 101 � 1%. At

applied voltage 0.9 Ve1.2 V the cathodic hydrogen recoveries

(rcat) was almost 100%. The energy recovery relative to elec-

tricity input (hw%) reached the highest value of 232 � 9% at

0.6 V and the highest overall energy efficiency (hwþs%) of

74 � 4% at 0.9 V. A similar overall efficiency of 72 � 11% was

reached at 0.6 V. The SS mesh showed good stability as the

SEM-EDSmeasurement shows little variation the composition

of the SS after 15 cycles at applied voltage of 0.9 V.





Study on microbial corrosion showed that hydrogen

evolution reaction enhanced due to deprotonation of phos-

phate species on stainless steel [43,44]. When stainless steel

was combined with phosphate species it was found that the

cathodic deprotonation of phosphate identified in corrosion

could be exploited to enhance H2 production in neutral pH

electrolysis. The high concentration of phosphate species

used in combination with a stainless steel cathode allowed

high current density for hydrogen evolution and hydrogen

evolution rates of up to 4.9 Lh�1m�2 in saline solutions at pH

8.0, a relevant pH value for MEC operation [45]. The presence

of phosphate species and other weak acids has recently been

shown to have a beneficial effect in MEC, because the charged

species increase the electrolyte conductivity and also reduce

the overpotential on Pt-graphite cathodes [46]. The cathode

was tested in an MEC that used a microbial anode formed

from marine sediment and operated at high salinity.

Combination of bicarbonate buffer and SS 304 cathodes

with mesh no 60 provided good performance compared to

MECs containing Pt catalysts or phosphate buffers [47]. The

maximum volumetric hydrogen production rate of

Q ¼ 1.40 � 0.13 m3 H2-m�3 d�1, electrical energy efficiency of

hE ¼ 155 � 8%, overall energy efficiency of hEþS ¼ 68 � 3%, and

a Coulombic Efficiency (CE) ¼ 87 � 5% with MECs using SS

cathodes and BBS were similar to values produced with either

PBS or a Pt catalyst at Eap ¼ 0.9 V. Hence inexpensive SS

catalysts and carbonate buffers can achieve performance

similar to those achievedwith Pt and phosphate bufferswhich

are expensive as well as there is discharge limit of phosphate

in the environment which make phosphate buffer unsuitable

to be used for wastewater treatment. A comparison of the

testing conditions of stainless steel as cathode is tabulated in

Table 2.

4.4. Use of other metals and materials as cathode andcathode catalyst

Tungsten carbide (WC), inspite of performing less than plat-

inum as catalyst, is considered as catalyst material since

1960s because of its low price and insensitivity toward catalyst

poisons like H2S and CO [48]. In an half cell experiment with

conventional three electrode system maximum current

density of �118 mA cm�2 at overpotential 760 mV and

26 mA cm�2 at overpotential 300 mV the electrocatalytic

activity for tungsten carbidewas observed. Interestingly when

different composition of the tungsten carbide was tested

a significant relation between WC content and HER current

densities obtained [49].

Nickel and Ni-alloy for hydrogen production in MECs was

tested for the development of efficient, stable and cost-

effective cathodes by different research groups. Hu et al. [50]

developed cathodes by electrodepositing NiMo and NiW onto

a three-dimensional carbon-fiber-weaved cloth material and

were evaluated at neutral pH using electrochemical cells.

These electrodeswere also examined for hydrogen production

in single chamber tubular MECs with cloth electrode assem-

blies (CEA). While similar performances were observed in

electrochemical cells, NiMo cathode exhibited better perfor-

mances than NiW cathode in MECs. At an applied voltage of

0.6 V, the MECs with NiMo cathode accomplished a hydrogen


production rate of 2.0 m3 m�3 reactor liquid day�1at current

density of 270 Am�3 (12 A m�2), which was 33% higher than

that of the NiW MECs producing 1.5 m3 m�3 reactor liquid

day �1and slightly lower than that of the MECswith Pt catalyst

producing 2.3 m3 m�3 reactor liquid day�1. The overall

hydrogen recoveries were 65%, 55% and 48% for theMECswith

NiMo, NiW, and Pt catalysts, respectively at the applied

voltage of 0.6 V. NiMo and NiW MECs ran for over 30 h and no

methane was detected by the end of the batches.

The possible reason for higher HER activity may be attrib-

uted to the higher loading of the catalysts than the Pt catalyst

[50]. According to the authors the uniform deposition of NiW

or NiMo increase the surface area of catalyst coating and

decrease cathodic over potential [51,52]. In a further study the

research group has shown that the optimal condition for

electrodeposition of NiMo on carbon cloth is Mo/Ni mass ratio

of 0.65 in electrolyte bath, an applied current density of

50 mA cm�2and electrodeposition duration of 10 min and

under this condition, the NiMo catalyst has a formula of

Ni6MoO3 with a nodular morphology [53].

Commercially available Nickel and stainless steel powder

with different sizes at different metal loadings were used on

carbon cloth to construct cathodes by Selembo et al. [25]. Two

cathode namely Ni 210 with 60 mg Ni in 267 mLN afion and Ni

210 þ CB with 60 mg Ni in 400 mL Nafion had the low over-

potential of �0.500 V and �0.683 V at this current density

range (�0.63 mAcm�2 ¼ �3.2 log Acm�2). Very similar current

densities produced with these two materials over the

complete range of applied voltages. These two metal powder

and binder combinations were used as cathodes in MECs.

Single chamber MECs made of Lexan were 4 cm long con-

taining 3 cmdiameter cylindrical-shaped chamberswere used

and anodes were ammonia treated graphite fibre brushes

(25 mm diameter � 25 mm length, 0.22 m2 surface area) made

with a titanium wire twisted core. The maximum current

increased for the two Ni cathodes over the first 6 cycles by as

much as 4.7 mA for Ni 210 and 4.1 mA for Ni 210 þ CB. The

surfaces of the Ni 210-based cathodesmaintained very similar

structures before and after 12 MEC cycles [25]. Nickel powder

was relatively stable with respect to corrosion when MECs

were continuously maintained under anaerobic conditions

but if exposed to air a nickel oxide layer is formed and can

become hydroxylated, forming Ni(OH)2 in water, and may get

dissolved. Different types of Ni alloy with different composi-

tion, chemically deposited on a GDL 25BC carbon paper was

evaluated by Manuel et al. [54]. A stable H2 production at rates

of 2.8e3.7 L LR�1 D�1 was obtained at a total catalyst load of

1 mg cm�2 containing Ni, Mo, Cr, and Fe on cathode. Only 5%

methane was present in the gas stream. When Ni loading was

of 0.6 mg cm�2 hydrogen production reached volumetric rate

of 4.1 L LR�1 D�1.

An optimized composition of 150 mM NiSO4$7H2O, 25 mM

NiCl2$6H2O, 500 mM H3BO3, and 1 mM CTAB at pH 4.5 was

used for Ni electrodeposition onto a porous carbon paper to

develop a low cost cathode capable of prolonged hydrogen

generation [55]. Hydrogen production as high as 5.4 L LR�1 d�1

with a corresponding current density of 5.7 A m�2 was ach-

ieved at a Ni load of 0.2e0.4 mg cm�2 under acetate non-

limiting conditions. The optimized Ni load and high porosity

of gas diffusion cathode providing higher surface area and




Table 2 e Experimental conditions for the testing of stainless steel cathode.

MEC system Type of electrode used Type of electrolyte used Temperature(�C)

pH Mode ofoperation

Reference

Anode Cathode andcathode catalyst

Anode chamber Cathode chamber

Electrochemical

half cell

Graphite felt Electrochemically

activated microbes

on graphite felt

100 mM potassium

ferricyanide/

ferrocyanide solution

Standard microbial

nutrient solution*

e 7 Initially fed-batch

mode later

continuous mode

[34]

Two chambered Electrochemically

microbes on

graphite felt

Electrochemically

activated microbes

on graphite felt

Standard microbial

nutrient solution*

þ 1.36 gL�1

NaCH3COO$3H2O

Standard microbial

nutrient solution*

þ 0.84 gL�1 NaHCO3

30 7 Continuous mode [35]

Single chamber Ammonia treated

graphite brushes

(25 mm diameter

� 25 mm

length, 0.22 m2

surface area)

Stainless steel alloys

and nickel alloys

(sheet metal cut

into 3.8 cm diameter

disks).

50-mM phosphate buffer solution (4.58 gL�1

Na2HPO4 and 2.45 gL�1 NaH2PO4$H2O),

0.31 gL�1 NH4Cl, 0.13 gL�1 KCl, and

trace vitamins and minerals.

30 7 Fed-batch [39]


graphite brushes

The SS brush

cathodes

(grade 304 SS)

1 gL�1 Sodium acetate in a 50 mM

phosphate buffer medium (PBS; Na2HPO4,

4.58 gL�1; and NaH2PO4$H2O, 2.45 gL�1)

and nutrient solution (NH4Cl, 0.31 gL�1; KCl,

0.13 gL�1; trace vitamins and minerals.

30 7 Fed-batch [41]


graphite brushes

(25 mm diameter

� 25 mm

length, 0.22 m2

surface area)

SS 304 woven and

expanded mesh

1 gL�1 of sodium acetate; 50 mM PBS

phosphate buffer (4.58 gL�1 Na2HPO4, and

2.45 gL�1 NaH2PO4$H2O), 0.31 gL�1 NH4Cl,

0.13 gL�1 KCl; and trace vitamins and

minerals

30 7 Fed-batch [42]

Double chamber Cylindrical felt

carbon anode

(0.25 m2

projected

surface area).

254SMO stainless

steel

Seawater at pH 7.5

added with marine

sediments from the

Atlantic Ocea

Water

containing

0.5 M sodium

phosphate

Room

temperature

8 Fed-batch [45]


graphite brushes

(25 mm diameter

� 25 mm

length, 0.22 m2

surface area)

The SS brush

cathodes

(grade 304 SS)

1 gL�1 sodium acetate and Bicarbonate

buffer (BBS, 80 mM; 6.71 gL�1 NaHCO3,

0.31 gL�1 NH4Cl, 0.05 gL�1 Na2HPO4,

0.03 gL�1 NaH2PO4$H2O, pKa ¼ 8.34,

pH ¼ 8.9 as prepared)

30 8.9 Fed-batch [47]

* 0.74 gL�1 KCl, 0.58 gL�1 NaCl, 0.68 gL�1 KH2PO4, 0.87 gL�1 K2HPO4, 0.28 gL�1 NH4Cl, 0.1 gL�1 MgSO4$7H2O, 0.1 gL�1 CaCl2$2H2O, and 1 mLL�1 of a trace element mixture [38].

internatio

naljo

urnalofhydrogen

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(2012)1e13

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Please

citeth

isarticle

inpress

as:

Kundu

A,etal.,

An

overview

ofca

thodem

ateria

land

catalysts

suita

ble

forgeneratin

ghydro

gen

inm

icrobial

electro

lysis

cell,

Intern

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al

of

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Energy

(2012),

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j.ijhydene.201

2.11.031



Table 3 e Experimental conditions for the testing of other metals and materials as cathode and cathode catalyst.

MEC system Type of electrode used Type of electrolyte used Temperature(�C)

pH Mode ofoperation

Reference

Anode Cathode and cathodecatalyst

Anode chamber Cathode chamber

Electrochemical

half cell

Platinum electrodes

served as the

counter electrodes

Tungsten carbide

powder mixed

with 5% Nafion�

solution and hand-

pressed onto the

graphite disc.

100 mM H2SO4, and 100 mM sodiume

phosphate-buffer,

22e23 �C 7 e [49]

Single chamber Carbon cloth type A NiMo and NiW

on carbon cloth

5 gL�1 of sodium acetate trihydrate, 100 mM

phosphate buffer and other nutrients.

30 � 2 7 Fed-batch [50]


graphite brushes

(25 mm diameter

� 25 mm length,

0.22 m2 surface area)

Nickel (2e10 mm),

nickel oxide NiOx

87302 (�74 mm),

and stainless steel

powder on carbon

cloth (Nafion used

as binder)

1 gL�1 acetate and a 50 mM phosphate buffer

nutrient medium

30 7 Fed-batch [25]

Double chamber

(membrane less)

Carbon felt measuring

(10 cm � 5 cm and

5-mm thick)

Ni-alloy catalyst ink

with 30% Nafion on

GDL 25BC

carbon paper

Sodium acetate (90.7 gL�1), yeast extract

(6.7 gL�1), NH4Cl (18.7 gL�1), KCl (148.1 gL�1),

K2HPO4 (64.0 gL�1), and KH2PO4 (40.7 gL�1).

30 e Continuous

flow

[54]

Double chamber

(membrane less)

Carbon felt measuring

(10 cm � 5 cm and

5-mm thick)

Ni-salts

electrodeposited

on GDL 25BC

carbon paper

Sodium acetate (90.7 gL�1), yeast extract

(6.7 gL�1), NH4Cl (18.7 gL�1), KCl (148.1 gL�1),

K2HPO4 (64.0 gL�1), and KH2PO4 (40.7 gL�1).

30 e Continuous

flow

[55]

Double Chamber

with anion

exchange

membrane

Graphite felt

(10 � 10 � 0.25 cm)

Ni foam

(10 � 10 � 0.2 cm,

1360 kg m�3)

2.72 gL�1

NaCH3COO$3H2O,

0.68 gL�1 KH2PO4,

0.87 gL�1 K2HPO4,

0.74 gL�1 KCl,

0.58 gL�1 NaCl,

0.28 gL�1 NH4Cl,

0.1 gL�1 CaCl2$2H2O,

0.01 gL�1 MgSO4$7H2O

and 0.1 mLL�1 of

a trace element mixture

0.1 M KCl 30 � 1 �C Not

controlled

Continuous

flow

[56]

Double chamber

with heterogeneous

anion exchange

membrane

Graphite felt of

(10 � 10 � 0.25 cm)

Alloys with

nickeleirone

molybdenum

(NiFeMo) and

cobaltemolybdenum

(CoMo) electrodeposited

on Cu sheet

2.72 gL�1 NaCH3COO$3H2O,

0.68 gL�1 KH2PO4, 0.87 gL�1

K2HPO4, 0.74 gL�1 KCl,

0.58 gL�1 NaCl, 0.28 gL�1

NH4Cl, 0.1 gL�1 CaCl2$2H2O,

0.01 gL�1 MgSO4$7H2O

and 0.1 mLL�1 of a trace

element mixture

0.1 M KCl 30 � 1 �C 6 Continuous

flow

[60]

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isarticle

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Kundu

A,etal.,

An

overview

ofca

thodem

ateria

land

catalysts

suita

ble

forgeneratin

ghydro

gen

inm

icrobial

electro

lysis

cell,

Intern

atio

nal

Journ

al

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Hydro

gen

Energy

(2012),

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j.ijhydene.2

012.11.031



Double

chamber

withpro

ton

exch

ange

membrane

Activatedca

rbon

fibers

with

enrich

edbacteria

Pdnanoparticle

depositedonplain

carb

onpaper

NaAc,

0.1

gL�1;NH

4Cl,

0.310gL�1;KCl,0.130gL�1;

CaCl 2,0.010gL�1;MgCl 2$6H

2O,

0.020gL�1;NaCl,0.002gL�1;

FeCl 2,0.005gL�1;CoCl 2$2

H2O,

0.001gL�1;MnCl 2$4H

2O,

0.001gL�1;AlCl 3,0.0005gL�1;

(NH

4) 6Mo7O,0.003gL�1;H

3BO

3,

0.0001gL�1;NiCl 2$6H

2O,

0.0001gL�1;CuSO

4$5H

2O,

0.001gL�1;ZnCl 2,0.001gL�1.

50mM

phosp

hate

buffer

e7

Fed-batch

[66]

Single

chamber

Ammonia

treated

graphitebru

shes

(25mm

diameter

�25mm

length

,

0.22m

2su

rface

area)

MoS2ca

talyst

powderon

stainless

steel

andca

rboncloth

1gL�1so

dium

ace

tate,

50mM

phosp

hate

buffer

aswellastrace

vitamins

andminerals

e7

Fed-batch

[72]


Please cite this article in press as: Kundu A, et al., An ovehydrogen in microbial electrolysis cell, Internationalj.ijhydene.2012.11.031

rviewJourn

better transport of hydrogen improved the hydrogen produc-

tion rate not allowing themicrobial conversion of hydrogen to

methane. The highly reproducible procedure of electrodepo-

sition could be effectively used for manufacturing large scale

cathodes for pilot scale and industrial scale MECs. The size

and density of Ni particles could be easily controlled by elec-

trodeposition time and/or the concentration of Ni salt. The

authorsmade the observation that Ni nuclei of 200 nm formed

nodular Ni structure of about 10 mm and after 45 days the

characteristics were unchanged [55]. They attribute the

stability of the electrode to the nodular structure of Ni

deposition.

Jeremiasse et al. [56] used Ni foam as cathode for gener-

ating high purity hydrogen at high volumetric production rate.

Ni foam was found to have high HER catalytic activity under

alkaline condition [57,58] and low electrical resistivity than

graphite or titanium [59]. It is also cheap and easily available.

The pH was not controlled to observe the change in over-

potential due to pH change if any. The performance of the

MEC was found to be 50 m3 m�3 MEC d�1 of hydrogen

production at current density 22.8 � 0.1 A m�2 and electrical

energy input of 2.6 kWhm�3 H2 at applied cell voltage 1 V. The

cathodic overpotential was found to be low and the authors

suggested that this may be due to a large specific surface area

of Ni foam (128 m2 m�2 projected area). The measured over-

potential for Ni foam was �0.14 V at 10.5 A m�2. Due to large

surface area the true surface current density decreased and

consequently the activation overpotential was lowered. It was

found that the cathode overpotential increased during long

term operation but the reason for that is unclear to the

authors. Thismay be due to poisoning of active surface area of

cathode, formation of Nickel hydride or due to hydrogen gas

bubbles, clogging the pores but it needs further investigation.

Jeremiasse et al. [60] investigated with nickel-

eironemolybdenum (NiFeMo) and cobaltemolybdenum

(CoMo) range of alloys as possible HER catalysts in an MEC

around neutral andmild alkaline pH although these alloys are

known to have a high catalytic activity under strong alkaline

conditions in water electrolysers [60e62]. The catalytic

activity of these alloys was compared in a 0.1 M phosphate

buffered electrolyte of pH 6. Near neutral pH, Cu sheet cath-

odes coated with NiMo, NiFeMo or CoMo alloy showed a high

catalytic activity for the HER compared to cathodes that

consist of only Ni. Mass transport limitation at near neutral pH

becomes a hindrance for catalytic activity. Their catalytic

activity is best exploited at alkaline pH where mass transport

is not limiting. This was demonstrated in an MEC with CoMo

coated Cu cathode and anion exchange membrane, which

reached a production rate of 50 m3 H2 m�3 MEC d�1 (at STP) at

an electricity input of 2.5 kWh m�3 H2. A Ni-based gas diffu-

sion cathode having Ni loading of 0.4 mg cm�2was used to

treat domestic wastewater in a continuous flow microbial

electrolysis cell. Wastewater treatment efficiency observed

was maximum of 76% COD reduction at organic load 441 mg

La�1 d�1 and applied voltage Vapp ¼ 0.75 V. The energy

consumption at high organic loading of 3120 mg La�1 d�1 was

0.77 Wh g COD�1 and at lowest organic load 243 mg La�1 d�1 it

became 2.20 Wh g COD�1 [63] which is comparable with the

work of Cusick et al. which was done with Pt-based Microbial

Electrolysis Cell [64].




Table 4 e Performance of different cathode materials and cathode catalysts used in MEC.

Cathode materialsand catalyst

Cathodepotential (V)

H2 yield (%) Currentgenerated (I )

A m�3

(unless otherwisestated)

Q ¼ hydrogenproductionrate m3 m�3

reactorliquid day�1

(unless otherwisestated)

Columbicefficiency (%)

Cathodichydrogen

recovery rH2,cat (%)

Overallhydrogen

recovery rH2,COD (%)

Energyefficiencyrelative toelectrical

input hE (%)

Overallenergy recovery

based bothelectric andsubstrate

inputs hEþS (%)

Reference

Biocathode �0.7 e �1.2 Am�2 0.63 e 49 e e e [34]

Biocathode 0.8 e 3.3 Am�2 0.03e0.04 e 17e21 e e e [35]

Biocathode �0.7 e e 2.2 e [37]

Stainless steel A286 0.9 80 � 2 222 � 4 1.50 � 0.04 e 61 � 3 62 � 6 107 � 5 46 � 3 [39]

Stainless steel 304 0.9 77 � 1 100 � 4 0.59 � 0.01 e 53 � 1 49 � 0 90 � 2 38 � 1 [39]

Ni 625 0.9 67 � 9 160 � 22 0.79 � 0.27 e 43 � 9 41 � 13 75 � 16 31 � 8 [39]

SS A286 þ NiOx 0.6 76 � 2 130 � 21 0.76 � 0.16 e 52 � 4 56 � 2 137 � 12 48 � 3 [39]

Ni 625 þ NiOx 0.6 76 � 5 131 � 7 0.76 � 0.15 e 52 � 9 56 � 10 137 � 24 48 � 9 [39]

Stainless steel-brush 0.6 e 188 1.7 e 84 e 221 78 [41]

Stainless Steel

304 mesh þbicarbonate

buffer

0.9 e e 1.40 � 0.13 87 � 5 e e 155 � 8 68 � 3 [47]

NiMo on carbon-

fiber-weaved cloth

0.6 2.6 mol mol�1 270 2.0 75 86 e 182 65 [50]

NiW on carbon-fiber-

weaved cloth

0.6 2.2 mol mol�1 200 1.5 73 e 114 55 [50]

Ni 210 (60 mg Ni in

267 mL Nafion on

carbon cloth)

0.6 92 � 0 160 � 31 1.3 � 0.3 92.7 � 15.8 79 � 10 73 � 3 210 � 40 65 � 2 [25]

Ni 210 þ CB (60 mg

Ni in 400 mL Nafion

on carbon cloth)

0.6 92 � 1 139 � 2 1.2 � 0.1 83.8 � 1.2 94 � 5 79 � 5 252 � 12 73 � 4 [25]

Ni (0.6 gm chemically

deposited on a GDL

25BC carbon paper)

1.0 2.8 mol mol�1 3.60 Am�2 4.14 68.0 103.3 e e e [54]

Pd nanoparticle on

carbon cloth

0.6 e e 2.6 � 0.5 L m�2 d�1 56.0 � 10.2 46.4 � 8.5 26.0 � 4.8 e e [66]

MoS2 on carbon cloth e 92 � 3 10.7 � 1.2 Am�2 e e e 90 � 2 123 � 7 57 � 3 [72]

internatio

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urnalofhydrogen

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(2012)1e13

10Please

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isarticle

inpress

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Kundu

A,etal.,

An

overview

ofca

thodem

ateria

land

catalysts

suita

ble

forgeneratin

ghydro

gen

inm

icrobial

electro

lysis

cell,

Intern

atio

nal

Journ

al

of

Hydro

gen

Energy

(2012),

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://dx.doi.o

rg/10.101

6/

j.ijhydene.2

012.11.031




Recent extensive works in the field of nanofabrication

provide a unique opportunity to develop efficient electrode

materials due to the fact that nanomaterial’s are very stable

not only structurally but also have stable electrical and

chemical properties [65].

Palladium, being the most platinum like metal and with

excellent catalytic property and high abundance, is of prime

importance. Huang et al. [66] investigated the feasibility of

using Pd nanoparticles for hydrogen evolution in MEC. Elec-

trochemical deposition of Pd was conducted in 0.1 M NaCl

solution containing 1.26 mM K2PdCl6 as the precursor on

a carbon clothwith amaximum loading calculated as 0.17mg,

or 0.0106 mg cm�2 assuming 100% electrodeposition. A low

surface density of Pd nanoparticles with uniform shape was

formed under the tested conditions. The Pd nanoparticles

coated cathode performed better with coulombic efficiency of

56.0 � 10.2% and hydrogen generation of 2.6 � 0.5 L m�2 d�1

than the Pt catalyst used in this study with coulombic effi-

ciency of 52.0 � 7.4% and hydrogen production of

2.1� 0.3 Lm�2 d�1. The catalytic efficiency of Pdwas almost 50

timesmore than Pt. Thismuch higher catalytic activity inMEC

for hydrogen evolution may be due to the surface nano-sized

morphology of Pd deposition and deposition condition [67].

The Ni-based nanomodified materials are promising elec-

trocatalysts for HER in near neutral electrolytes and could be

applied as cathodes in MECs [68]. The electrocatalytic prop-

erties of electrodeposited NiFe-, NiFeP- and NiFeCoP-

nanostructures onto carbon felt toward HER in neutral and

weak acidic solutions show higher catalytic activity than bare

carbon felt. The voltage needed to initiate hydrogen produc-

tion and the current production rates were in the range of

�0.60 and �0.75 V vs. Ag/AgCl as estimated from obtained

linear voltammograms. The highest current production rate

corresponding to 1.7 � 0.1 m3 m�3 reactor liquid day�1was

achieved with NiFeCoP/carbon felt electrodes. These nano-

structure modification results in improvement of the corro-

sion resistance in neutral phosphate buffer and weak acidic

(pH 5.5) acetate buffer solutions.

Research work on enzymes and quantum chemical simu-

lations suggested that molybdenum disulfide (MoS2) would

have a small free energy difference for HER [69e71]. Use of

MoS2 as a photocatalyst for hydrogen evolution is well-known

but it was used in electrochemical studies for HER by Tokash

et al. [72]. Based on LSV study in sodium perchlorate and

a phosphate buffer solution optimumMoS2 loading was 54mg

MoS2 and 60 mg carbon black, or 47 wt.% MoS2, with a surface

density of 45 gm�2 but considering the cost with the perfor-

mance of LSV and galvanostatic polarization tests the 33 wt.%

MoS2 composite cathode was chosen for tests in MECs. The

performance was compared with a typical Pt catalyst on

carbon cloth which maintained the same amount of carbon

black and Nafion binder as used in the MoS2 composite cath-

odes. At average current density of 10.0 � 1.6 Am�2 for Pt and

10.7� 1.2 Am�2 for MoS2, and the average fed-batch cycle time

14.7 � 0.4 h the gas compositions were H2 ¼ 90 � 6%,

CH4 ¼ 1 � 0.6%, and CO2 ¼ 8.7 � 5.4% for the Pt cathodes, and

H2¼ 92� 3%, CH4¼ 1� 0.8%, and CO2¼ 6.7� 2.3% for theMoS2cathodes. COD removals were 88 � 2% for MECs with Pt-based

cathodes and 90 � 2% for the MECs with MoS2 based cathodes.

Electrical energy efficiency for cathodeswas 123� 7%which is


less than platinum-based cathodes (158 � 14%). However,

overall efficiency of MoS2 cathodes was similar to platinum-

based cathodes with 61 � 5%. Considering the cost MoS2composite cathodes costs one fifth of the typical platinum

cathode. Table 3 describes the experimental conditions for

testing different material as cathode and cathode catalyst

other than stainless steel or bio-cathode.

5. Summary

Cathode is one of themost important parts of theMEC system.

Toward the practical implication ofMEC system the cost of the

cathode along with its higher efficiency are two very impor-

tant parameters which are of immense importance. Cathode

along with its catalyst may contribute almost 47%, which is

a substantial amount toward the total cost of the MEC system

[73]. Although it was well-known that platinum is a good

catalyst for hydrogen generation its cost prevented it to be

used in practical situation. In search of material having same

or more efficiency at much lower cost it was found out that

stainless steel or nickel alloys are good alternatives. Gas

diffusion cathode prepared by chemical deposition of Ni alone

can successfully be used for hydrogen production. Molyb-

denum disulfide, tungsten carbide, Ni alloys like NiMo, NiW,

NiFeMo are successfully used by different research groups for

hydrogen generation. Application of nanotechnology has

shown a new area of research. Electrodeposited palladium

nanoparticles as cathode catalyst for hydrogen generation

was successfully operated. Ni-based nanomodified materials

are also very promising electrlocatalyst for hydrogen

production. The comparison done in Table 4 disclose that

among all the cathode materials stainless steel, MoS2 and

nickel foam are worth mentioning owing to their easy avail-

ability, low cost and comparative efficiency with platinum

cathode catalyst. Stainless steel is probably the bettermaterial

in terms of its durability, structural strength and easy adapt-

ability to mass-manufacturing approaches. Although, pilot

scale application of these cathodes and cathode catalysts are

yet to be tested for their performance in real wastewater

treatment, this development of different low cost material to

be used as cathode or cathode catalyst has taken the possi-

bility of MECs to be used more and more in practical purposes

a step closer to be reality.

Acknowledgments

The authors are grateful to University of Malaya (Project no:

UM.C/HIR/MOHE/ENG/20) for providing the fund for the

research work.

r e f e r e n c e s

[1] Logan BE, Call D, Cheng S, Hamelers HVM, Sleutels THJA,Jeremiasse AW, et al. Microbial electrolysis cells for highyield hydrogen gas production from organic matter. EnvironSci Technol 2008;42:8630e40.





[2] Berger E. BMW hydrogen near zero emission vehicledevelopment. BMW Clean Energy CARB ZEV TechnologySymposium 2006, p. 12.

[3] Wrana N, Sparling R, Cicek N, Levin DB. Hydrogen gasproduction in a microbial electrolysis cell byelectrohydrogenesis. J Cleaner Production 2010;18(Suppl. 1):S105e11.

[4] Bullen RA, Arnot TC, Lakeman JB, Walsh FC. Biofuel cellsand their development. Biosens Bioelectron 2006;21:2015e45.

[5] Gainer K. Hydrogen as a chemical constituent and as anenergy source. BCC Research; 2011.

[6] Logan BE, Hamelers B, Rozendal R, Schroder U, Keller J,Freguia S, et al. Microbial fuel cells: methodology andtechnology. Environ Sci Technol 2006;40:5181e92.

[7] Liu H, Grot S, Logan BE. Electrochemically assisted microbialproduction of hydrogen from acetate. Environ Sci Technol2005;39:4317e20.

[8] Rozendal RA, Hamelers HVM, Euverink GJW, Metz SJ,Buisman CJN. Principle and perspectives of hydrogenproduction through biocatalyzed electrolysis. Int J HydrogenEnergy 2006;31:1632e40.

[9] Logan BE, Liu H, Grot S, Mallouk T. A bioelectrochemicallyassisted microbial reactor (BEAMR) that generates hydrogengas; 2009.

[10] Liu H, Logan BE. Electricity generation using an air-cathodesingle chamber microbial fuel cell in the presence andabsence of a proton exchange membrane. Environ SciTechnol 2004;38:4040e6.

[11] Liu H, Ramnarayanan R, Logan BE. Production of electricityduring wastewater treatment using a single chambermicrobial fuel cell. Environ Sci Technol 2004;38:2281e5.

[12] Plambeck JA. Hydrogen electrodes, oxygen electrodes, andpH; 1995.

[13] Cheng S, Logan BE. Sustainable and efficient biohydrogenproduction via electrohydrogenesis. Proc Natl Acad Sci USA2007;104:18871e3.

[14] Ditzig J, Liu H, Logan BE. Production of hydrogen fromdomestic wastewater using a bioelectrochemically assistedmicrobial reactor (BEAMR). Int J Hydrogen Energy 2007;32:2296e304.

[15] Rozendal RA, Hamelers HVM, Molenkamp RJ, Buisman CJN.Performance of single chamber biocatalyzed electrolysiswith different types of ion exchange membranes. Water Res2007;41:1984e94.

[16] Geelhoed JS, Hamelers HVM, Stams AJM. Electricity-mediated biological hydrogen production. Curr OpinMicrobiol 2010;13:307e15.

[17] Lee H-S, Rittmann BE. Significance of biological hydrogenoxidation in a continuous single-chamber microbialelectrolysis cell. Environ Sci Technol 2009;44:948e54.

[18] Kato Marcus A, Torres CI, Rittmann BE. Conduction-basedmodeling of the biofilm anode of a microbial fuel cell.Biotechnol Bioeng 2007;98:1171e82.

[19] Cheng S, Liu H, Logan BE. Increased power generation ina continuous flow MFC with advective flow through theporous anode and reduced electrode spacing. Environ SciTechnol 2006;40:2426e32.

[20] Bard AJ, Faulkner LR. Electrochemical methods:fundamentals and applications. 2nd ed. John Wiley & Sons;2001.

[21] Jeremiasse AW, Hamelers HVM, Kleijn JM, Buisman CJN. Useof biocompatible buffers to reduce the concentrationoverpotential for hydrogen evolution. Environ Sci Technol2009;43:6882e7.

[22] Cheng S, Liu H, Logan BE. Increased performance of single-chamber microbial fuel cells using an improved cathodestructure. Electrochem Commun 2006;8:489e94.


[23] Cheng S, Liu H, Logan BE. Power densities using differentcathode catalysts (Pt and CoTMPP) and polymer binders(Nafion and PTFE) in single chamber microbial fuel cells.Environ Sci Technol 2005;40:364e9.

[24] Call D, Logan BE. Hydrogen production in a single chambermicrobial electrolysis cell lacking a membrane. Environ SciTechnol 2008;42:3401e6.

[25] Selembo PA, Merrill MD, Logan BE. Hydrogen productionwith nickel powder cathode catalysts in microbialelectrolysis cells. Int J Hydrogen Energy 2010;35:428e37.

[26] Freguia S, Rabaey K, Yuan Z, Keller J. Non-catalyzed cathodicoxygen reduction at graphite granules in microbial fuel cells.Electrochim Acta 2007;53:598e603.

[27] Lewis K. Biochemical fuel cells. Bacteriol Rev 1966;30:101e13.[28] He Z, Angenent LT. Application of bacterial biocathodes in

microbial fuel cells. Electroanalysis 2006;18:2009e15.[29] Schwartz E, Friedrich B. The H2-metabolizing prokaryotes. In:

Dworkin M, Falkow S, Rosenberg E, Schleifer K-H,Stackebrandt E, editors. The prokaryotes. New York:Springer; 2006. p. 496e563.

[30] Vincent KA, Parkin A, Armstrong FA. Investigating andexploiting the electrocatalytic properties of hydrogenases.Chem Rev 2007;107:4366e413.

[31] Lojou E, Bianco P. Electrocatalytic reactions at hydrogenase-modified electrodes and their applications to biosensors:from the isolated enzymes to the whole cells. Electroanalysis2004;16:1093e100.

[32] Croese E, Pereira M, Euverink G-J, Stams A, Geelhoed J.Analysis of the microbial community of the biocathode ofa hydrogen-producing microbial electrolysis cell. ApplMicrobiol Biotechnol 2011;92:1083e93.

[33] Vignais PM, Billoud B, Meyer J. Classification andphylogeny of hydrogenases1. FEMS Microbiol Rev 2001;25:455e501.

[34] Rozendal RA, Jeremiasse AW, Hamelers HVM, Buisman CJN.Hydrogen production with a microbial biocathode. EnvironSci Technol 2007;42:629e34.

[35] Jeremiasse AW, Hamelers HVM, Buisman CJN. Microbialelectrolysis cell with a microbial biocathode.Bioelectrochemistry 2010;78:39e43.

[36] Tartakovsky B, Manuel MF, Wang H, Guiot SR. High ratemembrane-less microbial electrolysis cell for continuoushydrogen production. Int J Hydrogen Energy 2009;34:672e7.

[37] Jeremiasse AW, Hamelers HVM, Croese E, Buisman CJN.Acetate enhances startup of a H2-producing microbialbiocathode. Biotechnol Bioeng 2012;109:657e64.

[38] Zehnder AJB, Huser BA, Brock TD, Wuhrmann K.Characterization of an acetate-decarboxylating, non-hydrogen-oxidizing methane bacterium. Arch Microbiol1980;124:1e11.

[39] Selembo PA, Merrill MD, Logan BE. The use of stainless steeland nickel alloys as low-cost cathodes in microbialelectrolysis cells. J Power Sources 2009;190:271e8.

[40] Olivares-Ramırez JM, Campos-Cornelio ML, Uribe Godınez J,Borja-Arco E, Castellanos RH. Studies on the hydrogenevolution reaction on different stainless steels. Int JHydrogen Energy 2007;32:3170e3.

[41] Call DF, Merrill MD, Logan BE. High surface area stainlesssteel brushes as cathodes in microbial electrolysis cells.Environ Sci Technol 2009;43:2179e83.

[42] Zhang Y, Merrill MD, Logan BE. The use and optimization ofstainless steel mesh cathodes in microbial electrolysis cells.Int J Hydrogen Energy 2010;35:12020e8.

[43] Da Silva S, Basseguy R, Bergel A. Electrochemicaldeprotonation of phosphate on stainless steel. ElectrochimActa 2004;49:4553e61.

[44] De Silva Munoz L, Bergel A, Basseguy R. Role of the reversibleelectrochemical deprotonation of phosphate species in





anaerobic biocorrosion of steels. Corros Sci 2007;49:3988e4004.

[45] Munoz LD, Erable B, Etcheverry L, Riess J, Basseguy R,Bergel A. Combining phosphate species and stainless steelcathode to enhance hydrogen evolution in microbialelectrolysis cell (MEC). Electrochem Commun 2010;12:183e6.

[46] Merrill MD, Logan BE. Electrolyte effects on hydrogenevolution and solution resistance in microbial electrolysiscells. J Power Sources 2009;191:203e8.

[47] Ambler JR, Logan BE. Evaluation of stainless steel cathodesand a bicarbonate buffer for hydrogen production inmicrobial electrolysis cells using a new method formeasuring gas production. Int J Hydrogen Energy 2011;36:160e6.

[48] Harnisch F, Schroder U, Quaas M, Scholz F. Electrocatalyticand corrosion behaviour of tungsten carbide in near-neutralpH electrolytes. Appl Catal B Environ 2009;87:63e9.

[49] Harnisch F, Sievers G, Schroder U. Tungsten carbide aselectrocatalyst for the hydrogen evolution reaction in pHneutral electrolyte solutions. Appl Catal B Environ 2009;89:455e8.

[50] Hu H, Fan Y, Liu H. Hydrogen production in single-chambertubular microbial electrolysis cells using non-precious-metalcatalysts. Int J Hydrogen Energy 2009;34:8535e42.

[51] Navarro-Flores E, Chong Z, Omanovic S. Characterization ofNi, NiMo, NiW and NiFe electroactive coatings aselectrocatalysts for hydrogen evolution in an acidic medium.J Mol Catal A Chem 2005;226:179e97.

[52] �Simpraga R, Tremiliosi-Filho G, Qian SY, Conway BE. In situdetermination of the ‘real are factor’ in H2 evolutionelectrocatalysis at porous NiFe composite electrodes. JElectroanal Chem 1997;424:141e51.

[53] Hu H, Fan Y, Liu H. Optimization of NiMo catalyst forhydrogen production in microbial electrolysis cells. Int JHydrogen Energy 2010;35:3227e33.

[54] Manuel MF, Neburchilov V, Wang H, Guiot SR, Tartakovsky B.Hydrogen production in a microbial electrolysis cell withnickel-based gas diffusion cathodes. J Power Sources 2010;195:5514e9.

[55] Hrapovic S, Manuel MF, Luong JHT, Guiot SR, Tartakovsky B.Electrodeposition of nickel particles on a gas diffusioncathode for hydrogen production in a microbial electrolysiscell. Int J Hydrogen Energy 2010;35:7313e20.

[56] Jeremiasse AW, Hamelers HVM, Saakes M, Buisman CJN. Nifoam cathode enables high volumetric H2 production ina microbial electrolysis cell. Int J Hydrogen Energy 2010;35:12716e23.

[57] Marracino JM, Coeuret F, Langlois S. A first investigation offlow-through porous electrodes made of metallic felts orfoams. Electrochim Acta 1987;32:1303e9.

[58] Rausch S, Wendt H. Morphology and utilization of smoothhydrogen-evolving raney nickel cathode coatings and poroussintered-nickel cathodes. J Electrochem Soc 1996;143:2852e62.

[59] Rozendal RA, Harnisch F, Jeremiasse AW, Schroder U.Chemically catalyzed cathodes in bioelectrochemicalsystems. In: Rabaey K, Angenent L, Schroder U, Keller J,editors. Bioelectrochemical systems: from extracellular


electron transfer to biotechnological application London, UK.New York, USA: IWA Publishing; 2010. p. 22.

[60] Jeremiasse AW, Bergsma J, Kleijn JM, Saakes M, Buisman CJN,Cohen Stuart M, et al. Performance of metal alloys ashydrogen evolution reaction catalysts in a microbialelectrolysis cell. Int J Hydrogen Energy 2011;36:10482e9.

[61] Fan C, Piron DL, Sleb A, Paradis P. Study of electrodepositednickelemolybdenum, nickeletungsten,cobaltemolybdenum, and cobaltetungsten as hydrogenelectrodes in alkaline water electrolysis. J Electrochem Soc1994;141:382e7.

[62] Arul Raj I. On the catalytic activity of NiMoFe compositesurface coatings for the hydrogen cathodes in the industrialelectrochemical production of hydrogen. Appl Surf Sci 1992;59:245e52.

[63] Escapa A, Gil-Carrera L, Garcıa V, Moran A. Performance ofa continuous flow microbial electrolysis cell (MEC) fedwith domestic wastewater. Bioresour Technol 2012;117:55e62.

[64] Cusick RD, Kiely PD, Logan BE. A monetary comparison ofenergy recovered from microbial fuel cells and microbialelectrolysis cells fed winery or domestic wastewaters. Int JHydrogen Energy 2010;35:8855e61.

[65] Fan Y, Xu S, Schaller R, Jiao J, Chaplen F, Liu H. Nanoparticledecorated anodes for enhanced current generation inmicrobial electrochemical cells. Biosens Bioelectron 2011;26:1908e12.

[66] Huang Y-X, Liu X-W, Sun X-F, Sheng G-P, Zhang Y-Y, Yan G-M, et al. A new cathodic electrode deposit with palladiumnanoparticles for cost-effective hydrogen production ina microbial electrolysis cell. Int J Hydrogen Energy 2011;36:2773e6.

[67] Polcaro AM, Palmas S. Electrodeposition of catalysts forhydrogenation of organic molecules: deposition mechanismof Pd on carbon felt. Electrochim Acta 1991;36:921e6.

[68] Mitov M, Chorbadzhiyska E, Rashkov R, Hubenova Y. Novelnanostructured electrocatalysts for hydrogen evolutionreaction in neutral and weak acidic solutions. Int J HydrogenEnergy 2012.

[69] Sobczynski A. Molybdenum disulfide as a hydrogenevolution catalyst for water photodecomposition onsemiconductors. J Catal 1991;131:156e66.

[70] Zong X, Yan H, Wu G, Ma G, Wen F, Wang L, et al.Enhancement of photocatalytic H2 evolution on CdS byloading MoS2 as Co catalyst under visible light irradiation.J Am Chem Soc 2008;130:7176e7.

[71] Hinnemann B, Moses PG, Bonde J, Jørgensen KP, Nielsen JH,Horch S, et al. Biomimetic hydrogen evolution: MoS2nanoparticles as catalyst for hydrogen evolution. J Am ChemSoc 2005;127:5308e9.

[72] Tokash JC, Logan BE. Electrochemical evaluation ofmolybdenum disulfide as a catalyst for hydrogen evolutionin microbial electrolysis cells. Int J Hydrogen Energy 2011;36:9439e45.

[73] Rozendal RA, Hamelers HVM, Rabaey K, Keller J,Buisman CJN. Towards practical implementation ofbioelectrochemical wastewater treatment. TrendsBiotechnol 2008;26:450e9.




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An overview of cathode material and catalysts suitable for ... · PDF fileReview An overview of cathode material and catalysts suitable for generating hydrogen in microbial electrolysis