Enhanced hydrogen generation by cocatalytic Ni and NiO nanoparticles loaded on graphene oxide sheets

Enhanced hydrogen generation by cocatalytic Ni and

NiO nanoparticles loaded on graphene oxide sheets

Abiye Kebede Agegnehu1, Chun-Jern Pan1, John Rick1, Jyh-Fu Lee3, Wei-Nien Su2, John Rick, Bing-Joe Hwang1,3

1Nanoelectrochemistry Laboratory, Department of Chemical Engineering, National Taiwan University of Science and Technology,

2Graduate Institute of Applied Science and Technology #43 Keelung Road, Section 4,Taipei, 106. National Taiwan University of

Science and Technology

3. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan

WHEC2012- Toronto June 04, 2012

Presenter: Abiye Kebede Agegnehu

(Doctoral student)

Outline

Introduction

Experimental

Results and discussion

Conclusions

WHEC2012- Toronto June 4, 2012 2

Introduction


H2 evolution from light-induced decomposition of water is emerging

as an option to simultaneously solve energy & environmental problems.

Since the pioneering work of Fujishima and Honda on the light induced

decomposition of water by TiO2 (Nature 238 (1972) 37–38)) .

researchers have given considerable attention.

underlying thermodynamic principles have been resolved.

TiO2 is the most studied and a bench mark photocatalyst material.

Conventional photocatalysts have disadvantages:

Need high temperature to achieve good crystallinity.

Band gap engineering requires anion or cation doping.

Thus, graphene based photocatalysts are promising low cost alternatives.

Cont’d Graphene based materials have diverse applications:

Reports on photocatalytic application of GO:

H2 from aqueous methanol Reduction of resazurin in to resorufin


reaction time (h)

GO + hv → e- + h+

RZ + e - → RF.

RZ RF cleavage of N-O bonds

Experimental Section


Experimental

I. GO by modified Hummers’ method

2g graphite and 2g NaNO3 in to 92 ml Conc. H2SO4 (ice bath)

6g KMnO4 gradually added and stirred for 90 min

The ice bath removed and stirred at 34 ⁰C for 30 min

92 ml DI water was slowly added and stirred at 98 ⁰C for 15 min

Diluted by adding 280 ml DI water slowly

Terminated by adding 17 ml H2O2

Multiple washing in DI water using membrane

Dried by using freeze drier

Cont’d

II. Loading Ni and NiO


0.1g GO dispersed in

10 ml DI water

Ni(NO3)2 ·6H2O (3 % ) added

and stirred (1 hr).

Ni2+/GO solution

2.5mM solution of NaBH4

added while stirring washed

with DI water after 8 hrs.

Ni/GO

Dried at 80 ⁰ & sintered in

air at 200 ⁰C for 1 hr.

NiO/GO

Results and discusion


Fig. (a) XRD pattern of PG, and GO;

(b) plot of (αE)1/2 vs photon energy

(eV) for GO; (c) C1s XPS of GO

(d) Raman of PG and GO.

XRD at 2θ= 26.3⁰ is characteristic PG

A new peak at 2θ = 12⁰ appears

Indicates GO formation

UV –Vis shows band gap of 2 - 2.8 eV

C 1s XPS: three main C-components

(C-C : 284.6 eV), (C-O: 286.6 eV), &

(C(O)O: 288.0 eV).

The ID/IG of GO > ID/IG of PG

also depicts the its oxidation.

(d)

Cont’d


(d) Low magnification HRTEM and (e) HR TEM images

of GO, (f) SAED pattern of random GO sheets.

Wrinkled GO sheets (d) have a d- spacing of 0.43

nm (e &f).

consistently indicate moderate oxidation

Cont’d


Fig. (a)TEM image and (b) SAED pattern of Ni/GO.

~ 2 nm Ni nanoparticles uniformly dispersed on GO.

The ring pattern corresponds to the characteristic

(111) and (220) plans of Ni.

Cont’d


Fig. (c) TEM image and SAED pattern of NiO/GO

~ 2.5 nm NiO nanoparticles dispersed on GO.

SAED pattern exhibits characteristic plans of NiO.

Cont’d


Fig. Ni K-edge XANES spectra

The lower intensity of Ni/GO peak (b)

compared to (a), & (d) shows

the effective reduction of Ni2+.

Rather similar features with that of Ni

metal foil (e).

Spectra (c) shows the formation of

NiO after annealing

(a, d, and e are used as references).

Cont’d


Fig. Ni K-edge FT-EXAFS spectra.

EXAFS data also confirms Ni & NiO formation

Ni-Ni peak at 2.5 Å (b) has similar features

with Ni metal foil (e).

Two main peaks below 3.5 Å are typical

of NiO.

Ni-Ni bonds at 2.9 Å (d) &

Ni-O bonds at 2 Å (d)

H2 evolution activity

13

Fig. (a) Total H2 produced, (b) H2 evolution rate per hour

The cocatalyst loading enhanced the rate.

Ni: ~ 7 fold compared to GO

NiO: ~ 4 fold

Attributed to the difference in the barrier for the electron

Crossing the interface.

the interface.


Cont’d

14

Band structure and proposed Mechanism:

Fig. (a) Schematics of Ni/GO band structure;

(b) Proposed mechanism for H2 evolution.

CB = - 0.52 V & VB = 1.48 – 2.28 V

(vs. NHE).

The Fermi level of Ni = 0.51 V (vs. NHE).

However; shifts to more negative potential

The photogenerated e- react with H+

The holes scavenged by methanol.

no H2 evolution observed from pure water

implying more efficient Catalyst is probably

required.


Conclusions

Photocatalytic H2 evolution from aqueous methanol can be enhanced by

loading cocatalysts Ni and NiO.

Ni /GO exhibited the highest activity attributed to easy trapping of the

photogenerated electrons by Ni than by NiO.

The lowest activity of GO may be due to electron-hole recombination.

The study indicated that the cocatalyst loading on graphene based

materials can be utilized to design noble composite materials possessing

unique properties.


16

Documents

Enhanced hydrogen generation by cocatalytic Ni and NiO nanoparticles loaded on graphene oxide sheets