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Journal of Power Sources 289 (2015) 71e80

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Journal of Power Sources

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Review

Chitosan and alginate types of bio-membrane in fuel cell application:An overview

N. Shaari a, S.K. Kamarudin a, b, *

a Fuel Cell Institute, Universiti Kebangsaan Malaysia, 43600, UKM Bangi, Selangor, Malaysiab Department of Chemical and Process Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600, UKM Bangi,Selangor, Malaysia

h i g h l i g h t s

� Fuel crossover is the major problems in polymer electrolyte membrane fuel cell.� Chitosan and alginate-based biopolymer membranes are proposed to solve the problems.� This review performs the state-of-the-art chitosan and alginate-based membranes for fuel cell.

a r t i c l e i n f o

Article history:Received 15 October 2014Received in revised form27 March 2015Accepted 5 April 2015

Keywords:Fuel cellBio-membraneChitosanAlginate

* Corresponding author. Department of Chemical aulty of Engineering and Built Environment, UniversitiUKM Bangi, Selangor, Malaysia.

E-mail address: ctie@eng.ukm.my (S.K. Kamarudin

http://dx.doi.org/10.1016/j.jpowsour.2015.04.0270378-7753/© 2015 Elsevier B.V. All rights reserved.

a b s t r a c t

The major problems of polymer electrolyte membrane fuel cell technology that need to be highlightedare fuel crossovers (e.g., methanol or hydrogen leaking across fuel cell membranes), CO poisoning, lowdurability, and high cost. Chitosan and alginate-based biopolymer membranes have recently been usedto solve these problems with promising results. Current research in biopolymer membrane materials andsystems has focused on the following: 1) the development of novel and efficient biopolymer materials;and 2) increasing the processing capacity of membrane operations. Consequently, chitosan and alginate-based biopolymers seek to enhance fuel cell performance by improving proton conductivity, membranedurability, and reducing fuel crossover and electro-osmotic drag. There are four groups of chitosan-basedmembranes (categorized according to their reaction and preparation): self-cross-linked and salt-complexed chitosans, chitosan-based polymer blends, chitosan/inorganic filler composites, and chito-san/polymer composites. There are only three alginate-based membranes that have been synthesized forfuel cell application. This work aims to review the state-of-the-art in the growth of chitosan and alginate-based biopolymer membranes for fuel cell applications.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

Membrane separation technology utilizes membranes to serveas barriers or filters for target species within liquid, gas or colloidalparticle mixtures [1e4]. Non-conventional separation methodsoffer certain advantages, including higher separation efficiency,increased energy conversion and environmental protection, andincreased versatility. Non-traditional membrane separation tech-nology utilizes enhanced selectivity and affinity membrane layers

nd Process Engineering, Fac-Kebangsaan Malaysia, 43600,

).

to increase separation efficiencies and reduce environmentalproblems due to a wider range of applications, which include waterand contaminants treatment and processing and hazardous organicrecovery. Membrane separation technology has played an impor-tant role in industry and daily lives because of its flexible andversatile features. Its use is more prominent when in the large-scalepetroleum industry, but its effects can be seen even in small tech-nologies, such as drinking water filters, batteries, biomedical pu-rifications and controlled drug delivery.

The composition and structure of the material in a membrane isthe most important component in any membrane-based technol-ogy. Membrane performance can be optimized using multi-component or composite membrane materials, a practice whichhas been successfully implemented in the past decade [5e8]. This isimportant because basic materials, whether natural or synthesized,

N. Shaari, S.K. Kamarudin / Journal of Power Sources 289 (2015) 71e8072

typically do not meet all conditions necessary for a fully capableseparation process. Various components that are combined to formnew attributes can more readily achieve optimum membrane ca-pacity and performance [8].

Polysaccharide-based composites need to be considered in thecontext of the environment and ecosystems. Until now, the com-posites industry is dominated by synthetic polymer, but recently,their popularity has waned due to their non-biocompatibility [9].The use of polysaccharides, such as cellulose, has supplantedtraditional “green” synthetic polymers, such as polylactic acid (PLA)and poly-3-hydroxybutyrate (PHB). The textile and energy in-dustries and science, medical and engineering fields have rapidlyadapted to use biopolymer materials in their applications [10].However, due to strict environmental regulations, the biopolymerchoice must meet stringent requirements to replace syntheticpolymers. Recent studies have investigated simple biopolymersderived from natural raw materials with a clear structure to pro-duce new membrane materials. It has already been shown thatbiopolymers have desirable properties, such as sustainability andcarbon-neutral and renewable production processes, because theyare sourced directly from natural plant organisms and can be usedfrom year-to-year or in some cases, indefinitely [11].

Alginate, cellulose, and chitosan are examples of biopolymersderived from natural substances and have been applied to polymernetworks (e.g., carriers for controlled drug release, membraneswith regulated permeability, sensor devices, and artificial muscles).To achieve excellent functional properties, polymers should exhibitefficient responses to any changes in the internal or externalphysicochemical microstructure. Research on biopolymer mem-brane materials and systems has focused on the development ofnovel and efficient biopolymers and increasing their membraneprocessing capacity and operation [11].

In this review paper, we focus on chitosan and alginate bio-membranes applications in fuel cells. This review includes a gen-eral overview of fuel cell mechanisms, chitosan and alginate bio-polymers, a list of chitosan and alginate-based membranescurrently used in fuel cells and lastly, a summary and perspective.

2. Fundamental of fuel cell membranes

2.1. Fuel cell

Research on fuel cells began in the 19th century with studiesfocusing on the direct conversion of fossil fuel chemical energy intoelectrical energy. Due to its significant potential, different types offuel cells have since been developed [12]. A “fuel cell is an elec-trochemical cell that is able to continuously convert the chemicalenergy of a fuel and an oxidizing agent into electrical energy by theprocess basically involves changing the electrolyte electrode sys-tem”. The principles of an electrochemical battery are similar tothose of a fuel cell. The only identifiable difference is that chemicalenergy is stored outside the cell of a fuel cell, whereas chemicalenergy of an electrochemical battery is stored within the cell. Fuelcells are more efficient than conventional methods of generatingelectrical power, which require many conversion steps before theproduction of actual electrical power. Fuel cells can achieve up to60% efficiency by converting chemical energy directly to usablepower and thermal energy. Fuel cells can be categorized by theelectrolyte type and operation temperature. Low temperature fuelcells include alkaline fuel cells (AFCs), phosphoric acid fuel cells(PAFCs), polymer electrolyte fuel cells (PEFCs) and direct methanolfuel cells (DMFCs). High temperature fuel cells include solid oxidefuel cells (SOFCs) and molten carbonate fuel cells (MCFCs).

In proton exchange membrane fuel cell, proton-conductingmembrane is located in the middle of the fuel cell between anode

and cathode. Generally, the structure of fuel cell containing a flowfield (including collector ribs and channels), a diffusion layer (DL),and a catalyst layer (CL) on the anode and cathode sides and apolymer conducting membrane. It functions as an ion conductor,electron flow controller, and reaction barrier for maintainingchemical and mechanical stability [13]. The membrane thicknessranges from 30 to 200 mm. Various types of membranes have beendeveloped in the literature. Traditionally, there are four major typesof membranes often used in fuel cells: Nafion, non-Nafion-fluorinated, composite fluorinated and non-fluorinated mem-branes [14].

Nafion is the most popular membrane material and is used as aproton exchange membrane based on its ability to conduct protons,high chemical stability and structural and mechanical strengths.However, Nafion membranes are expensive to produce. In addition,methanol crossover through the Nafion membrane is a significantissue that has yet to be resolved. Recent studies have attempted todevelop substitute polymer electrolytemembranes that exhibit lowmethanol permeabilities and high ionic conductivities, are notexpensive to produce, have environmental design considerations,and are made of biomaterials. However, despite these goals, twomajor fuel problems persist.

2.1.1. Methanol crossoverThe separation distance between the anode and cathode is very

important in preventing direct fuel access to the cathode (i.e.,preventing oxidation). Current membranes are able to allow protonexchange but are inefficient as fuel separators, especially given theevidence of crossover phenomenon [15], which may lead to thedestruction of the reduction catalyst. There are three mechanismsby which methanol crossover could occur: electro-osmotic dragand methanol permeation and diffusion [24]. Methanol crosses themembrane and directly reacts with oxygen. Consequently, this re-action produces electrons and oxidizes the cathode and thus, de-creases the current production of the fuel cell. In addition, Ptcatalysts are poisoned by the oxidation byproduct, CO. Hydratedprotons are transferred from the anode to the cathode duringelectro-osmotic drag. Methanol diffuses across the membrane if asufficient concentration gradient exists. The crossover could bereduced by regulating the fuel feed concentration at the anode,using effective methanol-oxidizing anode catalysts and using afunctional proton exchange membrane. Xiao et al. [35] reportedthat cesium phosphotungstate salts in a chitosan membrane hasthe low methanol permeability is 5.6 � 10�7 cm2 s�1 which 90%lower than that of a Nafion-212 membrane under the same tem-perature and pressure condition.

Among the factors involved in the regulation of methanolcrossover was membrane material, membrane structure, mem-brane thickness and cell operating parameters such as temperatureand concentration of the methanol feed [55]. High methanol con-centration will increase the permeability of methanol moleculesagitated due to the existence of high methanol in methanolewaterassociation. The size of the radius of a single molecule is 0.19 nm.When the size of the cavity free number can be generated smallerthan the size of the radius of methanol, the barriers of methanol isincreased. Several studies have combined the filler in the matrix ofchitosan, which aims to shrink the size of the radius of the freevolume cavity, for example, zeolite, sorbitol, and modernite [51,56].The introduction of sorbitol and mordenite in chitosan matrixmembrane exhibit the 44% decrease in methanol permeabilitycompare to pure chitosan membrane. This is evidenced by thedecrease in free volume changes in the membrane cavity size whensobitol and modernite in increasing the chitosan matrix. The littleamount of free volume cavity and rigid good chitosan will be anexcellent barrier for methanol [51]. The hydrophilic characteristics

N. Shaari, S.K. Kamarudin / Journal of Power Sources 289 (2015) 71e80 73

of chitosan is very helpful in determining water absorption bypriority and so on, it is very suitable as a barrier to methanol as thehydrophilic nature of this [67]. A combination of two homopoly-mers, chitosan and alginate as a membrane gave good results in thepermeability of methanol, which is as low as 4.6 � 10�8 cm2 s�1.Polyion involved in the merger of these two polymers exhibit animportant function, where it reduces the interaction between theioneion polymers with methanol. Therefore, the methanolpermeability can be reduced [71].

2.1.2. Durability and costTo successfully commercialize fuel cells, their durability and

high production costs must be addressed. Recent studies haveinvestigated water and heat management and the development ofnew membrane materials [16]. Nafion membranes are veryexpensive (approximately 1000 USD m�2) and have low perfor-mance ratings at temperatures above 120 �C [17]. Their preparationalso involves environmentally hazardous chemicals, namely fluo-rine. Thus, the use of Nafion membranes contributes toward envi-ronmental pollution. Additionally, the corrosion of a Nafionmembrane harms a fuel cell system. Undeniably, Chitosan andAlginate have won in a much lower price than Nafion. This isbecause; chitosan is a product from dumping of marine products,which involves a process that delighted in its production. Mean-while, alginate is extracted from brown seaweed. Given theseconsiderations, a biopolymer membrane is ideal for replacingNafion membranes to realize a more environmentally-friendlytechnology.

3. Overview of biomembrane (chitosan and alginate)

3.1. Chitosan

Chitosan is one of the most environmentally-friendly materialsand can be found in crustacean shells, insects, molluscan organs,and fungi. Table 1 lists common sources of chitin and chitosan.Chitosan consists of b-(1,4)-linked 2-amino-deoxy-D-glucopyr-anose; thus, CS is a copolymer of glucosamine and N-acetylglu-cosamine [18e20]. The amino and hydroxyl groups of chitosan canact as electron donors. The application of chitosan as a biomaterialis verywidespread and is found in areas such as the pharmaceuticalindustry, fuel cells, and wastewater treatment. Interestingly, it isalso used in food packaging because of its biodegradable, biocom-patible, antimicrobial, and hydrophilic properties [21]. Chitosan hasbeen produced in various forms, such as membranes, films, andfibrous mats and spans [22]. Despite its advantages, chitosan hasdrawbacks that limit its application. Chitosan has low mechanicalstrength and low electrical conductivity. It is also very brittle due toa high glass transition temperature [23]. The disadvantage of chi-tosan can be overcome by blending chitosan with other polymers,doping inorganic fillers in the chitosan matrix, creating chitosan-

Table 1Sources of chitin and chitosan [18].

Sea animals Insects Microorganisms

Annelida Scorpions Green algaeMollusca Spiders Yeast (b-type)Coelenterata Brachiopods Fungi (cell walls)Crustaceans Ants Mycelia PenicilliumLobster Cockroaches Brown algaeCrab Beetles SporesShrimp ChytridiaceaePrawn AscomydesKrill Blastocladiaceae

based organiceinorganic hybrids [24], or chemically modifyingchitosan. Fig. 1 shows the chemical structure of chitin and chitosan.Chitosan is insoluble in most organic solvents, alkalis and water butis soluble in dilute organic acids, such as acetic, formic, and lacticacids. CS has a very high degree of water solubility because itconsists of three different polar groups, i.e., hydroxyl (OH), amine(NH2), and ether (COC).

3.2. Alginates

Alginate is a prominent water-soluble polysaccharide found inbrown seaweed. It consists of (1-4)-linked b-D-mannuronic acid(M) and a-L-gluronic acid (G) units. Fig. 2 shows representativealginate structures: (a) in a chain conformation and (b) as a blockdistribution. Alginates have a number of advantageous properties,including excellent biocompatibility, non-toxicity, non-immuno-genicity, biodegradability, relatively low costs and easy combina-tion with divalent cations (e.g., calcium) [25,26]. As such, alginateshave great potential in various fields and uses, such as textileprinting, dehydration, biomedical and tissue engineering, and drugdelivery vehicles. It has very high water absorption capacity,absorbing 200e300 times its own weight. Alginate can be manu-factured into a variety forms, such as film, microspheres and fibers,because of their reversible solubility [26]. Sodium alginate is thesodium salt of alginic acid. Alginate can be easily cross-linked withglutaraldehyde, 1,6-hexane diamine, and other bi-functionalorganic compounds. It can also dissolve in a solution of multiva-lent ions [27]. However, like chitosans, alginates have certain limitsto their applications due to several weaknesses, which include highwater solubility and low mechanical strength [28].

Alginate has a six-membered ring structure backbone; there-fore, it is difficult to increase the rigidity or to compact. Thisstructure creates larger void volumes and allows the absorption ofwater molecules. Unfortunately, excessive water absorption causesmembrane swelling and thereby decreases membrane selectivity[29]. It is very important to balance between membrane perme-ability and selectivity to water or gas [30]. To address this short-coming, alginate has been modified using various methods, whichcan be categorized as covalent crosslinking, ionic crosslinking, andnon-bond interactions [31]. It has been shown that covalentcrosslinking to polymers with polar groups increases the stability ofmembrane structure due to the polymer polar groups reducing thehydrophilic nature of the polymer. Ionic crosslinking providesbetter results because the produced polymer electrolyte complex isboth robust and hydrophilic [32].

4. Polyelectrolyte complexes e membranes for fuel cell

4.1. Chitosan-based membrane

There are four groups of chitosan-based membrane that arecategorized based on their reaction and preparation methods.Ramirez-Salgado [33] selected a biopolymer as the basic content todevelop a low-cost proton electrolyte membrane.

4.1.1. Salt-complexed and self-cross-linked chitosanNeat CS is a poor proton conductor. The introduction of salt

complexes the CS matrix and improves its amorphous nature. Maet al. [34] synthesized a chitosan membrane with phosphate andtriphosphate salts. It has been reported that a triphosphate chito-san membrane has more advantages than a phosphate chitosanmembrane in a direct borohydride fuel cell (DBFC). The powerdensity of a triphosphate chitosan membrane was over 50% higherthan that of commercial Nafion. Additionally, a chitosan-baseddirect borohydride fuel cell (DBFC) has been shown to have

Fig. 1. Structure of chitin and chitosan [21].

Fig. 2. Representative alginate structure: (a) chain conformation and (b) block distri-bution [25].

N. Shaari, S.K. Kamarudin / Journal of Power Sources 289 (2015) 71e8074

similar stability and efficiency as those of a Nafion-based directborohydride fuel cell (DBFC). Xiao et al. [35] reported that cesiumphosphotungstate salts in a chitosan membrane was the majorfactor to lowering methanol permeability, which was approxi-mately 90% lower than that of a Nafion-212 membrane.

Cross-linking is projected to diminish the crystallinity of a CSmembrane and improve the ionic conductivity [36]. Mukoma et al.[37] found that sulfuric acid cross-linked chitosan membranes hadhigher proton conductivity compared with un-crosslinked chito-san. Amino groups in chitosan and sulfate ions have a coulombicinteraction, which makes the ionic crossing of the main chainspossible, as shown in Fig. 3. Xiang et al. [38] reported that thechitosan sulfate membrane reached the highest proton conduc-tivity value of 0.03 S cm�1 at 80 �C. Ma et al. [39] prepared sulfuricacid cross-linked chitosan (CCS) membranes for a direct borohy-dride fuel cell (DBFC). The CCS membrane displayed higher ionicconductivity than an N212 membrane. Mukoma et al. [17] investi-gated the methanol permeability of crosslinked-chitosan mem-branes at medium to high methanol concentrations; the resultswere compared with methanol permeability in Nafion 117 mem-branes. Wan et al. [40] fabricated a three-layer structure ofchitosan-based ion-immobilized membranes with a porous inter-mediate layer and two solid surface layers cross-linked withglutaraldehyde. Chavez et al. [41] investigated the ionic conduc-tivity of glutaraldehyde-crosslinked chitosan membranes by mo-lecular modeling and simulation. The results revealed that the

conductivity of the system was enhanced, and the crystallinity ofglutaraldehyde-crosslinked chitosan membranes was reduced.

The mechanical stability of chitosan can be enhanced throughcross-linking and quaternization [42]. Wan et al. [43] prepared aseries of quaternized-chitosan derivatives (QCDs) at various de-grees of quaternization using glycidyl trimethyl ammonium chlo-ride as the main quaternization reagent. The thermal stability wasenhanced, but the crystallinity and swelling index of the mem-branes decreased with increasing crosslinking density. Increasingthe degree of quaternization increased the ion exchange capacityand ionic conductivity of the membranes. Choudhury et al. [44]prepared a Cs membrane by ionic cross-linking with sulfate andhydrogen phosphate salts of sodium for use in direct borohydridefuel cells (DBFCs) (2012). The results show that a cross-linked Csmembrane has good mechanical strength. A double cross-linkingprocess also improved proton conductivity and reduced themethanol cross-over phenomenon. Hasani-Sadrabadi et al. [36]prepared a triple layer composite Nafion 105 membrane. Bothsides of the membrane were coated with glutaraldehyde/sulfo-succinic acid cross-linked chitosan. The proton conductivity andmethanol permeability was improved compared with those of aconventional Nafion 117 membrane. Furthermore, the cross-linkedtriple layer membrane exhibited higher open circuit voltage, powerdensity output, and an overall increased fuel cell efficiencycompared with those of a Nafion 117 membrane. Osifo and Masala[45] prepared a modified Chs flaked membrane cross-linked withH2SO4 for direct methanol fuel cells. The Chs membrane showedgood thermal stability relative to a Nafion 117membrane. However,Chs membranes presented a lower proton resistance (204 s cm�1)than that of a Nafion 117 membrane (284 s cm�1). Ramadhan et al.[46] improved the proton conductivity in a proton exchangemembrane for fuel cell by preparing an acid-based complexedmembrane. N-Succinylchitosan-chitosan complexes were used formembrane preparations. The results showed that N-succinylchi-tosan-chitosan membrane achieved higher proton conductivity ofabout one order of magnitude compared with that of chitosan-onlymembranes. The amino groups in chitosan and sulfate ions have acoulombic interaction which makes possible the ionic crossing ofthe main chains [37].

4.1.2. Chitosan-based polymer blendThe main objective of manufactured polymer blends is to inte-

grate desired characteristics of each element while simultaneously

Fig. 3. Chemical structure of ionically cross-linked chitosan.

N. Shaari, S.K. Kamarudin / Journal of Power Sources 289 (2015) 71e80 75

compensating for their undesirable traits [47]. Buraidah and Arof[48] used a solution cast method to prepare chitosaneNH4I elec-trolytes blended with PVA. High amounts of PVA unfortunately ledto a reduced conductivity as shown in Fig. 4. Ions likely resurfacedand crystallized on the film surface due to a high content of PVA inthe electrolytes. Yang and Chiu (2012) [18] fabricated a PVA and CS-blended membrane with glutaraldehyde as the crosslinking agent.It was found that glutaraldehyde increased themechanical strengthof the membrane. Seo et al. [49] combined chitosan and PSSA-MAto form a blended polymer membrane, which was crosslinked byesterification and complex formation. The increased concentration

Fig. 4. The room temperature ionic conductivity of chitosaneNH4I with various con-centrations of PVA [48].

of ionic groups in the membrane led to an increased ion exchangecapacity (IEC). However, crosslinking and complex formation in themembrane also increased the proton conductivity, which resultedin a low level of water uptake.

4.1.3. Chitosan-based composite membrane4.1.3.1. Chitosan/inorganic filler composite. An inorganic filler wasrepeatedly combined with polymeric material. The properties ofthe composite membrane were influenced by the conditions underwhich the combination was performed, including the type ofpolymer and inorganic filler used, total solids used, diffusion ho-mogeneity, and the size and orientation of solid particles dispersedin the polymer matrix [50]. As reported by Yuan et al. [51], twostrategies to implement the combination process between inor-ganic and polymer materials include an in situ formation of inor-ganic particles in a polymer matrix using a solegel reaction orcrystallization and a physical mixing of an organic solution andwith fillers followed by simple casting. The formation of chitosan-

Fig. 5. Schematic of structure of SPSF obtained by surface modification of PSF withsulfuric acid [66].

Fig. 6. A model depicting the formation of semi-IPN and interaction of the blend with crosslinking agents [67].

N. Shaari, S.K. Kamarudin / Journal of Power Sources 289 (2015) 71e8076

inorganic composite membranes aims to achieve a stable balancebetween the hydrophilic and hydrophobic nature of chitosan; toeliminate the fuel crossover phenomenon; to enhance the me-chanical strength and durability; and to increase the proton con-ductivity by incorporating solid inorganic proton conductors [52].

Several studies have revealed that an increase in the amount ofinorganic filler reduced the proton conductivity. This phenomenonwas attributed to the relatively low proton conductivity of thefillers and their significant dilution of proton exchange groups inthe host polymermatrix. As shown byWang et al. [53], an inorganicfiller, silica particles, when used to fill in a polymer membrane, thecomposite membrane exhibited reduced proton conductivity. Tri-pathi and Shahi [54] reported the functionalization of inorganicfiller before incorporation into a polymer matrix to decrease themethanol permeability and enhance proton conductivity.

Zeolite is another common inorganic filler used in polymeric

membranes. They represent a group of aluminosilicates with abasic structure composed of multiple voids that can be filled bywatermolecules or huge ions [51]. Zeolite particle pore sizes and itscontent has a significant impact on CS/zeolite properties [55].Additionally, thermal and mechanical stabilities were at appro-priate levels due to the presence of hydrogen bonds between CSand zeolites [56]. As reported by Yuan et al. [57] an appropriatezeolite content results in an increased mechanical strength.Furthermore, the addition of a plasticizer into a CS/zeolite mem-brane resulted in reductions of the glass transition temperature (Tg)and the crystallinity of the hybrid membrane. CS/zeolite mem-branes were enhanced when the zeolite was sulfonated by threedifferent approaches. The presence of a sulfonic group increasedthe interaction interface between the zeolite and chitosan matrixand reduced methanol permeability [58].

Solid superacids are used to increase the proton conductivity

Fig. 7. Cross-sectional SEM image of pure PAAm-graft-chitosan matrix. The mass ratioof NMBA to AA is 0.06/10 [69].

N. Shaari, S.K. Kamarudin / Journal of Power Sources 289 (2015) 71e80 77

and mechanical properties of the CS membrane. Universally, thereare three types of solid superacids: metal oxide-supported sulfates(MxOyeSO4

2�), heteropolyacids (HPAs) and zeolite solid superacids.Wang et al. [59] inserted a nanosized solid superacid, TiO2eSO4

2�

(STiO2) into a chitosan (CS) matrix to fabricate a hybrid membrane.The results revealed that the superacid fillers in the hybrid mem-brane reduced the fractional free volume (FFV) of the membrane.This phenomenon indirectly reduced the methanol diffusionpathway in the membrane and consequently, reduced the meth-anol permeability. Unfortunately, the incorporation of STiO2 parti-cles also reduced the proton conductivity of the membrane due tothe drop in water uptake volume. Cui et al. [60] reported that HPAsformed strong electrostatic interactions with a chitosan matrix toform insoluble complexes. Wua et al. [61] incorporated organo-phosphorylated titania submicrospheres (OPTi) as possible fillersinto a chitosan matrix; in this composite membrane, the methanolpermeability was reduced and the proton conductivity increased. Itcan be observed that ionic crosslinking agents, such as the PO3H2

andNH2 groups on OPTi and CS, respectively, enhanced thecompatibility between inorganic fillers and the polymer matrix. Cuiet al. [62] prepared a novel membrane consisting of chitosan andphosphotungstic acid for direct methanol fuel cells. The use of

Fig. 8. Structural representation of chitosanesodium alginate ion complex formation reacti(eNH3C) of chitosan [71].

phosphotungstic acid filler enabled membrane conductivity to bemaintained. A three-layer structured membrane developed byWanet al. [63] with potassium hydroxide as ionic functionality wasinserted into chitosanmatrices. Themembrane comprised a porousintermediate layer and two crosslinked solid surface layers. It wasreported that proton conductivity was increased. O�glu et al. [64]prepared chitosan (CHI) and poly(acrylic acid) (PAA) with salt andacid treatments. This method reduced the methanol permeabilityof the membrane.

4.1.3.2. Chitosan/polymer composite. Nafion can be replaced byseveral economical synthetic polymers, such as polysulfone, pol-ybenzimidazole, or poly(aryl ether ketone), due to their desiredstability. The sulfonation of these polymers enhanced their protonconductor ability [65]. In 2008, microporous poly-sulfone (PSF)was used as a substrate with a thin chitosan layer to form acomposite membrane. Fewer weaknesses were observed for thiscomposite. However, a weak interaction between the two poly-mers was observed; an attempt to overcome this problem usingsurface modifications which forms an SPSF/CS composite mem-brane is shown in Fig. 5. High thermal stability indicates that it canfunction as a membrane for high temperature fuel cells [66].Smitha et al. (2006) [67] attempted to overcome the drawback ofits hydrophilic nature by mixing CS with a strong polymer (e.g.,PVP). As shown in Fig. 6, a mixture of glutaraldehyde-crosslinkedCS and PVP produced a semi-interpenetrating network. Cross-linking with glutaraldehyde and sulfuric acid has high membraneconductivity as 0.024 S cm�1 and lower methanol permeability as7.3 � 10�8 cm2 s�1 than Nafion membrane.

Hasani-Sadrabadi et al. [68] fabricated a double layer mem-brane encompassing a layer of physically-altered chitosan as amethanol barrier layer, coated on Nafion. The double layermembrane exhibited diminished methanol permeability as1.67 � 10�6 cm2 s�1 and considerably higher membrane selec-tivity when compared with Nafion 117. High stability, good protonconductivity (0.13 S cm�1) and excellent proton transfer has beenshown by a three-dimensional (3D) polyacrylamide-graft-chitosan (PAAm-graft-chitosan) membrane with which H3PO4serves as a placeholder. Fig. 7 shows the cross-sectional SEMimage of a pure PAAm-graft-chitosan matrix [69]. Nafionionomer-implanted PVA/CS membranes was prepared by Zhang

on between anion group (eCOO�) of sodium alginate and the protonated cation group

Table 2List of membrane with Ionic conductivity, ion exchange capacity and methanol permeability values.

Membrane Ionic conductivity, Scm�1 Ion exchange capacity (IEC), mmol g�1 Methanol permeability cm2 s�1 Remarkably Reference

Nafion 117 14 � 10�3 e 18 � 10�7 DMFC [17]PCS 20 � 10�3 e 16.24 � 10�7 DMFC [18]CsTP 0.114 e e DBFC [34]CTS/Csx-PTA 6 � 10�3 e 5.6 � 10�7 DMFC [35]CCS 1.1 � 10�1 e e DBFC [39]GA/C 1 � 10�2 e e PMFC [40]Chitosan-H2SO4 1.83 � 10�2 e e FC [41]QCDs �10�2 0.83 e PEFC [43]ICCSHMEs 1.5 � 10�3 e e DBFC [44]Ch flakes e e 1.4 � 10�6 DMFC [45]ChitosanePVAeNH4I 1.77 � 10�6 e e FC [48]CS/PSSA-MA 10�2 0.55 e FC [49]CS/mordenite e e 4.9 � 10�7 DMFC [51]Cs-zeolite filling 2.58 � 10�2 0.168 3.90 � 10�7 DMFC [55]Cs-zeolite 0.024 e 0.624 � 10�6 DMFC [56]CS/PMA 0.015 0.46 2.7 � 10�7 DMFC [60]CH-K7 3.14 � 10�2 0.53 e AFM [63]CS/PVP 0.024 e 7.3 � 10�8 DMFC [67]CGS-12/Nafion 112 0.075 e 1.67 � 10�6 DMFC [68]PAAm-graft-chitosan 0.13 e e PEMFC [69]CS/SHNT 0.0076 0.134 2.08 � 10�6 DMFC [70]Chitosanesodium alginate 0.042 1.4 4.6 � 10�8 DMFC [71]Alg/Car 3.16 � 10�2 e 4.89 � 10�6 DMFC [73]

N. Shaari, S.K. Kamarudin / Journal of Power Sources 289 (2015) 71e8078

et al. [23]. Bai et al. [70] provided halloysite nanotubes containingsulfonate polyelectrolyte brushes (SHNTs). The presence of SHNTsgenerates a strong electrostatic attraction for the CS chain. Thiseffectively immobilizes the chain, and therefore, the thermal andmechanical stability of nanohybrid membranes can be improved.

4.2. Alginate-based membrane

Smitha et al. [71] fabricated a blend membrane consisting ofchitosan and sodium alginate biopolymers and formed a polyioncomplex (PIC) for DMFC applications. The prepared membraneshowed great potential in terms of lowmethanol permeability, highmechanical stability and high proton conductivity (0.042 S cm�1).Fig. 8 shows a structural representation of the chitosanesodiumalginate ion complex formation reaction between an anion group(eCOO�) of the sodium alginate and a protonated cation group(eNH3C) of chitosan.

The major weakness of alginate is its low mechanical strengthdue to its hydrophilic nature. An inorganic filler can overcome thisproblem. To this end, sodium alginate/graphene oxide (Al/GO)nanocomposite films were prepared. The results revealed thathydrogen bonding and high interfacial adhesion between the GOfiller and the Al matrix significantly changed the thermal stabilityandmechanical properties of the nanocomposite film. A TG analysisshowed that the thermal stability of the Al/GO composite film wasbetter than that of neat Al film [72]. Novel polyelectrolyte mem-branes were prepared from pure solutions of alginate (Alg) andcarrageenan (Car) and their mixtures. The films were crosslinkedand sulfonated. The methanol permeability (4.89 � 10�6 cm2 s�1)and proton conductivity (3.16 � 10�2 S cm�1) of Alg/Car mem-branes increased with increasing carrageenan content [73].

5. Summary and perspective

Chitosan and alginate compounds have been employed invarious applications due to their plentiful quantity in nature. In fuelcells, they were shown to have potential use as substitutes forpolyelectrolyte membranes, especially in low to intermediatetemperature polymer electrolyte fuel cells, direct methanol fuelcells, alkaline polymer electrolyte fuel cells, and biofuel cells. Chi-tosan and alginate compounds are hydrophilic and easily

modifiable to develop needed superficial properties, such as lowmethanol permeability and proton conductivity (similar to those ofNafion membranes). These two biopolymers play important rolesin polyelectrolyte complexes (PECs) and have always shown betterperformances with all modifications. In addition, chitosan andalginate compounds are relatively inexpensive to produce. How-ever, further studies need to be conducted in order to better char-acterize the properties of chitosan and alginate-based membranes.Table 2 presents the comparison between the membranes.

In future studies, three major properties should be investigatedfor improvements in fuel cell performance: i) Increasing the protonconductivity to the levels of Nafion membranes. ii) Increasing themembrane mechanical strength. Blended polymer membraneshave shown enhancedmechanical and chemical stability. However,the chemical modifications (e.g., sulfonation and phosphorylation)required to fabricate such composites polymers may negativelyaffect the mechanical strength. iii) Decreasing methanol perme-ability. While the levels are comparable or even better than that forthe Nafion membrane, likely because of the enhanced hydrophilicproperties of the biomembrane, there is room for improvement.

There are several investigations proposed for future works.

(i) Preparation of PECs biomembranes: due to the rapid reactionduring the preparation of biomembranes, there was greatdifficulty in controlling the membrane structure and inter-action. Furthermore, the application of biomembranes inPECs has not reached a large enough scale due to thesomewhat complicated processing technique.

(ii) Additional studies of alginate-basedmembranes: advantagesof metals, inorganic fillers, surfactants and crosslinkingagents need to be exploited to produce more membranesbased on alginate biomaterials.

(iii) Biopolymers with the capability to form films at low cost andwith minimal environmental concerns have to be furtherexplored to maximize their benefits in various applications(e.g., controlled drug delivery and sensors).

Acknowledgment

The authors gratefully acknowledge the financial support givenfor this work by the Universiti Kebangsaan Malaysia (UKM) under

N. Shaari, S.K. Kamarudin / Journal of Power Sources 289 (2015) 71e80 79

GUP-2013-031 and Ministry of Education FRGS/2/2013/TK06/UKM/01/1.

Appendix A. Supplementary data

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.jpowsour.2015.04.027.

References

[1] M. Mulder, Basic Principles of Membrane Technology, second ed., KluwerAcademic Publishers, Netherlands, 1998.

[2] K.K. Sirkar, Membranes, phase interfaces, and separations: novel techniquesand membranes e an overview, Ind. Eng. Chem. Res. 47 (2008) 5250e5266.

[3] W.J. Koros, Evolving beyond the thermal age of separation processes: mem-branes can lead the way, AIChE J. 50 (2004) 2326e2334.

[4] R.W. Baker, Research needs in the membrane separation industry: lookingback, looking forward, J. Membr. Sci. 362 (2010) 134e136.

[5] M. Ulbricht, Advanced functional polymer membranes, Polymer 47 (2006)2217e2262.

[6] V. Abetz, T. Brinkmann, M. Dijkstra, K. Ebert, D. Fritsch, K. Ohlrogge, D. Paul,K.V. Peinemann, S.P. Nunes, N. Scharnagl, M. Schossig, Developments inmembrane research: from material via process design to industrial applica-tion, Adv. Eng. Mater. 8 (2006) 328e358.

[7] R.V. Klitzing, B. Tieke, Polyelectrolyte membranes, Adv. Polym. Sci. 165 (2004)177e210.

[8] A.F. Ismail, P.S. Goh, S.M. Sanip, M. Aziz, Transport and separation propertiesof carbon nanotube-mixed matrix membrane, Sep. Purif. Technol. 70 (2009)12e26.

[9] I. �Simkovic, What could be greener than composites made from poly-saccharides? Carbohydr. Polym. 74 (2008) 759e762.

[10] F. Vilaplana, E. Stromberg, S. Karlsson, Environmental and resource aspects ofsustainable biocomposites, Polym. Degrad. Stab. 95 (2010) 2147e2161.

[11] Available on http://dx.doi.org/10.5772/50697.[12] S.K. Kamarudin, W.R.W. Daud, A. Md. Som, A.W. Mohammad, S. Takriff,

M.S. Masdar, The conceptual design of PEMFC system via simulation, Chem.Eng. J. 103 (2004) 99e113.

[13] M.M. Ahmad, S.K. Kamarudin, W.R.W. Daud, Z. Yaakub, High power passiveDMFC with low catalyst loading for small power generation, Energy Convers.Manag. 51 (2010) 821e825.

[14] L. Zhang, S.-R. Chae, Z. Hendren, J.-S. Park, M.R. Wiesner, Recent advances inproton exchange membranes for fuel cell applications, Chem. Eng. J. 204e206(2012) 87e97.

[15] Q. Liu, L. Song, Z. Zhang, X. Liu, Preparation and characterization of the PVDF-based composite membrane for direct methanol fuel cells, Int. J. Energy En-viron. 1 (2010) 643e656.

[16] B.P. Tripathi, V.K. Shahi, Organiceinorganic nanocomposite polymer electro-lyte membranes for fuel cell applications, Prog. Polym. Sci. 36 (2011)945e979.

[17] P. Mukoma, B.R. Jooste, H.C.M. Vosloo, A comparison of methanol permeabilityin Chitosan and Nafion 117 membranes at high to medium methanol con-centrations, J. Membr. Sci. 243 (2004) 293e299.

[18] J.M. Yang, H.C. Chiu, Preparation and characterization of polyvinyl alcohol/chitosan blended membrane for alkaline direct methanol fuel cells, J. Membr.Sci. 419e420 (2012) 65e71.

[19] F.C. de Go, E.R. -Castellon, E. Guibal, M.M. Beppu, An XPS study of chromateand vanadate sorption mechanism by chitosan membrane containing coppernanoparticles, Chem. Eng. J. 234 (2013) 423e429.

[20] H. Susanto, A.M. Samsudin, N. Rokhati, I.N. Widiasa, Immobilization of glucoseoxidase on chitosan-based porous composite membranes and their potentialuse in biosensors, Enzyme Microb. Technol. 52 (2013) 386e392.

[21] J. Ma, Y. Sahai, Chitosan biopolymer for fuel cell applications, Carbohydr.Polym. 92 (2013) 955e975.

[22] R.T. De Silva, P. Pasbakhsh, K.L. Goh, S.-P. Chai, H. Ismail, Physico-chemicalcharacterisation of chitosan/halloysite composite membranes, Polym. Test. 32(2013) 265e271.

[23] Y. Zhang, Z. Cui, C. Liu, W. Xing, J. Zhang, Implantation of nafion ionomer intopolyvinyl alcohol/chitosan composites to form novel proton-conductingmembranes for direct methanol fuel cells, J. Power Sources 194 (2009)730e736.

[24] M.A. de Moraesa, D.S. Cocenza, F. da Cruz Vasconcellos, L.F. Fraceto,M.M. Beppu, Chitosan and alginate biopolymer membranes for remediation ofcontaminated water with herbicides, J. Environ. Manag. 131 (2013) 222e227.

[25] S.N. Pawar, K.J. Edgar, Alginate derivatization: a review of chemistry, prop-erties and applications, Biomaterials 33 (2012) 3279e3305.

[26] M.A. de Moraesa, D.S. Cocenza, F. da Cruz Vasconcellos, Chitosan and alginatebiopolymer membranes for remediation of contaminated water with herbi-cides, J. Environ. Manag. 131 (2013) 222e227.

[27] Y. Mo, K. Xiao, Y. Shen, X. Huang, A new perspective on the effect ofcomplexation between calcium and alginate on fouling during nanofiltration,Sep. Purif. Technol. 82 (2011) 121e127.

[28] K. Listiarini, L. Tan, D.D. Sun, J.O. Leckie, Systematic study on calciumealginate

interaction in a hybrid coagulation-nanofiltration system, J. Membr. Sci. 370(2011) 109e115.

[29] K. Listiarini, W. Chun, D.D. Sun, J.O. Leckie, Fouling mechanism and resistanceanalyses of systems containing sodium alginate, calcium, alum and theircombination in dead-end fouling of nanofiltration membranes, J. Membr. Sci.344 (2009) 244e251.

[30] K. Listiarini, W. Chun, D.D. Sun, J.O. Leckie, Fouling mechanism and resistanceanalyses of systems containing sodium alginate, calcium, alum and theircombination in dead-end fouling of nanofiltration membranes, J. Membr. Sci.344 (2009) 244e251.

[31] G. Li, W. Li, H. Deng, Y. Du, Structure and properties of chitin/alginate blendmembranes from NaOH/urea aqueous solution, Int. J. Biol. Macromol. 51(2012) 1121e1126.

[32] Y. Li, H. Jia, F. Pan, Z. Jiang, Q. Cheng, Enhanced anti-swelling property anddehumidification performance by sodium alginateepoly(vinyl alcohol)/poly-sulfone composite hollow fiber membranes, J. Membr. Sci 407e408 (2012)211e220.

[33] J.R. -Salgado, Study of basic biopolymer as proton membrane for fuel cellsystems, Electrochim. Acta 52 (2007) 3766e3778.

[34] J. Ma, Y. Sahai, R.G. Buchheit, Evaluation of multivalent phosphate cross-linked chitosan biopolymer membrane for direct borohydride fuel cells,J. Power Sources 202 (2012) 18e27.

[35] Y. Xiao, Y. Xiang, R. Xiu, S. Lu, Development of cesium phosphotungstate saltand chitosan composite membrane for direct methanol fuel cells, Carbohydr.Polym. 98 (2013) 233e240.

[36] M.M. Hasani-Sadrabadia, E. Dashtimoghadam, N. Mokarram, F.S. Majedi,K.I. Jacob, Triple-layer proton exchange membranes based on chitosanbiopolymer with reduced methanol crossover for high-performance directmethanol fuel cells application, Polymer 53 (2012) 2643e2651.

[37] P. Mukoma, B.R. Jooste, H.C.M. Vosloo, Synthesis and characterization of cross-linked chitosan membranes for application as alternative proton exchangemembrane materials in fuel cells, J. Power Sources 136 (2004) 16e23.

[38] Y. Xiang, M. Yang, Z. Guo, Z. Cui, Alternatively chitosan sulfate blendingmembrane as methanol-blocking polymer electrolyte membrane for directmethanol fuel cell, J. Membr. Sci. 337 (2009) 318e323.

[39] J. Ma, N.A. Choudhury, Y. Sahai, R.G. Buchheit, A high performance directborohydride fuel cell employing cross-linked chitosan Membrane, J. PowerSources 196 (2011) 8257e8264.

[40] Y. Wan, K.A.M. Creber, B. Peppley, V.T. Bui, Chitosan-based electrolyte com-posite membranes II. Mechanical properties and ionic conductivity, J. Membr.Sci. 284 (2006) 331e338.

[41] E.L. Chavez, R.O. -Roa, G.C. -P�erez, J.M.M. -Magad�an, F.L.C. -Alvarado, Theo-retical studies of ionic conductivity of crosslinked chitosan membranes, Int. J.Hydrog. Energy 35 (2010) 12141e12146.

[42] Y. Wan, B. Peppley, K.A.M. Creber, V.T. Bui, E. Halliop, Quaternized-chitosanmembranes for possible applications in alkaline fuel cells, J. Power Sources185 (2008) 183e187.

[43] Y. Wan, B. Peppley, K.A.M. Creber, V.T. Bui, Anion-exchange membranescomposed of quaternized-chitosan derivatives for alkaline fuel cells, J. PowerSources 195 (2010) 3785e3793.

[44] N.A. Choudhury, J. Ma, Y. Sahai, High performance and eco-friendly chitosanhydrogel membrane electrolytes for direct borohydride fuel cells, J. PowerSources 210 (2012) 358e365.

[45] P.O. Osifo, A. Masala, Characterization of direct methanol fuel cell (DMFC)applications with H2SO4 modified chitosan membrane, J. Power Sources 195(2010) 4915e4922.

[46] L.O.A.N. Ramadhan, C.L. Radiman, V. Suendo, D. Wahyuningrum,S. Valiyaveettil, Synthesis and Characterization of Polyelectrolyte Complex N-Succinylchitosan-chitosan for Proton Exchange Membranes, Procedia Chem. 4(2012) 114e122.

[47] L. Chikh, V. Delhorbe, O. Fiche, (Semi-)interpenetrating polymer networks asfuel cell membranes, J. Membr. Sci. 368 (2011) 1e17.

[48] M.H. Buraidah, A.K. Arof, Characterization of chitosan/PVA blended electrolytedoped with NH4I, J. Non-Cryst. Solids 357 (2011) 3261e3266.

[49] J.A. Seo, J.H. Koh, D.K. Roh, J.H. Kim, Preparation and characterization ofcrosslinked proton conducting membranes based on chitosan and PSSA-MAcopolymer, Solid State Ionics 180 (2009) 998e1002.

[50] A. Dupuis, Proton exchange membranes for fuel cells operated at mediumtemperatures: materials and experimental techniques, Prog. Mater. Sci. 56(2011) 289e327.

[51] W. Yuan, H. Wu, B. Zheng, X. Zheng, Z. Jiang, X. Hao, Sorbitol-plasticizedchitosan/zeolite hybrid membrane for direct methanol fuel cell, J. PowerSources 172 (2007) 604e612.

[52] B.P. Tripathi, V.K. Shahi, Organiceinorganic nanocomposite polymer electro-lyte membranes for fuel cell applications, Prog. Polym. Sci. 36 (2011)945e979.

[53] J. Wang, H. Zhang, Z. Jiang, X. Yang, L. Xiao, Tuning the performance of directmethanol fuel cell membranes by embedding multifunctional inorganic sub-microspheres into polymer matrix, J. Power Sources 188 (2009) 64e74.

[54] B.P. Tripathi, V.K. Shahi, Functionalized organic-inorganic nanostructured N-p-carboxy benzyl chitosan-silica-PVA hybrid polyelectrolyte complex asproton exchange membrane for DMFC applications, J. Phys. Chem. B 112(2008) 15678e15690.

[55] H. Wu, B. Zheng, X. Zheng, J. Wang, W. Yuan, Z. Jiang, Surface-modified Yzeolite-filled chitosan membrane for direct methanol fuel cell, J. Power

N. Shaari, S.K. Kamarudin / Journal of Power Sources 289 (2015) 71e8080

Sources 173 (2007) 842e852.[56] J. Wang, X. Zheng, H. Wu, B. Zheng, Z. Jiang, X. Hao, B. Wang, Effect of zeolites

on chitosan/zeolite hybrid membranes for direct methanol fuel cell, J. PowerSources 178 (2008) 9e19.

[57] W. Yuan, H. Wu, B. Zheng, X. Zheng, Z. Jiang, X. Hao, B. Wang, Sorbitol-plas-ticized chitosan/zeolite hybrid membrane for direct methanol fuel cell,J. Power Sources 172 (2007) 604e612.

[58] Y. Wang, D. Yang, X. Zheng, Z. Jiang, J. Li, Zeolite beta-filled chitosan mem-brane with low methanol permeability for direct methanol fuel cell, J. PowerSources 183 (2008) 454e463.

[59] J. Wang, Y. Zhang, H. Wu, L. Xiao, Z. Jiang, Fabrication and performances ofsolid superacid embedded chitosan hybrid membranes for direct methanolfuel cell, J. Power Sources 195 (2010) 2526e2533.

[60] Z. Cui, W. Xing, C. Liu, J. Liao, H. Zhang, Chitosan/heteropolyacid compositemembranes for direct methanol fuel cell, J. Power Sources 188 (2009) 24e29.

[61] H. Wua, W. Hou, J. Wang, L. Xiao, Z. Jiang, Preparation and properties of hybriddirect methanol fuel cell membranes by embedding organophosphorylatedtitania submicrospheres into a chitosan polymer matrix, J. Power Sources 195(2010) 4104e4113.

[62] Z. Cui, C. Liu, T. Lu, W. Xing, Polyelectrolyte complexes of chitosan andphosphotungstic acid as proton-conducting membranes for direct methanolfuel cells, J. Power Sources 167 (2007) 94e99.

[63] Y. Wan, B. Peppley, K.A.M. Creber, V.T. Bui, E. Halliop, Preliminary evaluationof an alkaline chitosan-based membrane fuel cell, J. Power Sources 162 (2006)105e113.

[64] T. Gümüso�glu Güls, Gülsen Albayrak Arı, H. Delig€oz, Investigation of saltaddition and acid treatment effects on the transport properties of ionicallycross-linked polyelectrolyte complex membranes based on chitosan andpolyacrylic acid, J. Membr. Sci. 376 (2011) 25e34.

[65] H. Ahmad, S.K. Kamarudin, U.A. Hasran, W.R.W. Daud, Overview of hybridmembranes for direct-methanol fuel-cell applications, Int. J. Hydrog. Energy35 (2010) 2160e2175.

[66] B. Smitha, D. Anjali Devi, S. Sridhar, Proton-conducting composite membranesof chitosan and sulfonated polysulfone for fuel cell application, Int. J. Hydrog.Energy 33 (2008) 4138e4146.

[67] B. Smitha, S. Sridhar, A.A. Khan, Chitosanepoly(vinyl pyrrolidone) blends asmembranes for direct methanol fuel cell applications, J. Power Sources 159(2006) 846e854.

[68] M.M.H. -Sadrabadi, E. Dashtimoghadam, F.S. Majedi, S.H. Emami, H. Moaddel,A high-performance chitosan-based double layer proton exchange membranewith reduced methanol crossover, Int. J. Hydrog. Energy 36 (2011)6105e6111.

[69] S. Yuan, Q. Tang, B. He, H. Chen, Q. Li, C. Ma, S. Jin, Z. Liu, H3PO4 imbibedpolyacrylamide-graft-chitosan frameworks for high-temperature proton ex-change membranes, J. Power Sources 249 (2014) 277e284.

[70] H. Bai, H. Zhang, Y. He, J. Liu, B. Zhang, J. Wang, Enhanced proton conductionof chitosan membrane enabled by halloysite nanotubes bearing sulfonatepolyelectrolyte brushes, J. Membr. Sci. 454 (2014) 220e232.

[71] B. Smitha, S. Sridhar, A.A. Khan, Chitosanesodium alginate polyion complexesas fuel cell membranes, Eur. Polym. J. 41 (2005) 1859e1866.

[72] M. Ionita, M.A. Pandele, H. Iovu, Sodium alginate/graphene oxide compositefilms with enhanced thermal and mechanical properties, Carbohydr. Polym.94 (2013) 339e344.

[73] S.D. Pasini Cabello, S. Moll�a, N.A. Ochoa, J. Marchese, E. Gim�enez, V. Compa~n,New bio-polymeric membranes composed of alginate-carrageenan to beapplied as polymer electrolyte membranes for DMFC, J. Power Sources (2014)345e355.