SUMMARYFuel cells are an emerging technology with applications in transportation, stationary and portable power generation, with outputs ranging from mW to MW. The most promising and most widely researched, developed and demonstrated type of fuel cells is proton exchange membrane (PEM) fuel cell. State of the art in PEM fuel cell technology and challenges in their development and widespread applications are discussed.

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Ferrocene-functionalized polyethylenimine and multiwalled carbon nanotubes were attached covalently by glutaraldehyde onto a carbon cloth to develop an immobilized enzyme (glucose oxidase) electrode for biofuel cell applications. Developed enzymatic anode was characterized by electrochemical methods to determine electrochemical performance. Anodic open-circuit potential was measured as within 0-20 mV range. Cyclic voltammetry showed anodic peak for glucose oxidation around 400-600 mV (vs. sat. Ag/AgCl) varying with scan rate. An enzyme fuel cell with 2.5 mg/cm 2 glucose oxidase-loaded bioanode and 0.70 mg/cm 2 Pt-loaded cathode attached to Nafion™ 115 membrane has provided around 2.5 mA/cm 2 current density at short-circuit conditions. Enzymatic kinetic parameters of prepared anode were determined by electrochemical methods that surprisingly indicated less K M (i.e., better substrate affinity) than that of determined by conventional enzymatic methods. Enzymatic stability determined by electrochemical methods moreover indicated longer enzyme half-life.

A high power enzymatic fuel‐cell was anticipated by using a recently developed glucose oxidase (GOx) immobilized bio‐anode, a conventional platinum−carbon based cathode and a popular high performance 125 μ‐thick perfluorosulfonic acid‐type proton exchange membrane (i. e. Nafion® 115). Unexpected current density decay from 2.13 mA cm−2 to 0.28 mA cm−2 was observed within 2 hours. Polarization measurements and AC impedance analysis indicated that loss of performance was linked to the membrane behavior. Ion exchange between buffer solution and membrane was perceived as the main cause for the fast performance loss. Saturation of the membrane with the cation in the buffer solution diminished proton transfer needed for cathode reaction. Charge transfer resistances, obtained from AC impedance data, increased with time substantially due to cation exchange within membrane. Replacement of membrane with the same enzyme electrode and cathode has resulted 100 % current density recovery on the fuel cell performance. It was concluded that a membrane, not affected by the buffer cations, was required for successful enzymatic fuel cell applications.

Mixed-oxide coated Ti 0.8 Mo 0.2 O 2-C composite supported 20 wt.% Pt electrocatalysts with Ti 0.8 Mo 0.2 O 2 /C= 75/25 mass ratio were developed for CO tolerance of polymer electrolyte membrane fuel cell (PEMFC) anode. Studies of the structure, composition and stability, as well as the results of CO ads stripping confirmed that the mixed oxide composite support and the electrocatalyst prepared for this study show the well-documented characteristics of the Pt/Ti 1x Mo x O 2-C systems and Pt/Ti 0.8 Mo 0.2 O 2-C catalyst with enhanced CO tolerance compared to the Pt/C catalyst is suitable for further investigation as an anode in reformate-fed PEMFCs. Dilution of hydrogen with CO 2 and CH 4 had negligible negative impact on the fuel cell performance. Switching gas composition between hydrogen and reformate shows recovery of potential after CO poisoning. Nevertheless, anode catalyst loading of 0.25 and 0.5 mgPt/cm 2 was not enough to give reasonable performance when CO impurity was present. Loading of 0.85 mgPt/cm 2 Ti 0.8 Mo 0.2 O 2-C supported catalyst was effective to give 1000 mA/cm 2 current density at 0.6 V under 25 ppm CO and 30 psig. Higher loading was needed at mass transfer limited region to overcome poisoning. However, loadings higher than 0.85 mgPt/cm 2 caused mass transfer limitations. Hence higher loadings is proposed with 40 wt.% Pt/Ti 0.8 Mo 0.2 O 2-C support catalyst.

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Silica impregnated expanded graphite–epoxy composites are developed as bipolar plates for proton exchange membrane (PEM) fuel cells. These composite plates were prepared by solution impregnation, followed by compression molding and curing. Mechanical properties, electrical conductivities, corrosion resistance, and contact angles were determined as a function of impregnated content. The plates show high flexural strength with 5% methyltrimethoxysilane (MTMS) addition (20 MPa) and in‐plane conductivity of 131 S cm−1 that meet the DOE target (>100 S cm−1). Corrosion current values as low as 1.09 μA cm−2 were obtained. The contact angle was found to be 80°. Power density of 1 W cm−2 was achieved with custom made expanded graphite–polymer composite plates. High efficiency values were obtained at low current regions.