Microbial electrolysis cells: Hydrogen production from glycerol and alternative cathode materials

Microbial electrolysis cells (MECs) are promising systems for producing sustainable energy while treating organic waste. MECs contain exoelectrogenic bacteria that produce hydrogen from organic matter via electrohydrogenesis. Glycerol is a low cost commodity, major byproduct of biodiesel production and a potential source of organic matter for MECs. Glycerol was used for hydrogen production via anaerobic fermentation or electrohydrogenesis. MECs have to be affordable to be commercialized. Low cost transition metals were evaluated as alternatives to platinum catalysts for use in MEC cathodes.;Hydrogen was produced at 0.28 mol-H2/mol-glycerol from glycerol fermentation while 1.06 mol-H2/mol-glucose (0.53 mol-H2/mol-3C) was obtained from glucose fermentation. The main product of glycerol fermentation was 1,3-propanediol which adversely affects H2 gas yields. Higher hydrogen yields were achieved using MECs from glycerol (3.9 mol-H2/mol-glycerol) with efficiencies similar to those achieved with glucose (7.2 mol-H2 /mol-glucose or 3.6 mol-H2/mol-3C, Eap=0.9V). 1,3-propanediol was produced in MEC but subsequently consumed, achieving better substrate utilization than fermentation. Hydrogen production from the glycerol byproduct from biodiesel was higher via electrohydrogenesis (1.8 mol-H 2/mol-glycerol) than fermentation (0.31 mol-H2/mol-glycerol), but lower than pure glycerol due to the presence of methanol and soaps.;Stainless steel and nickel alloys were compared to platinum sheet metal for use as cathodes in MECs. SS A286 was superior to platinum in cathodic and energy recovery, and hydrogen production rate (1.5 m3/m 3d SSA286, 0.68 m3/m3d Pt, Eap=0.9V). Performance was further increased by nickel oxide electrodeposition. Smaller particles reduce total mass of the material and material costs. Commercially available nickel and stainless steel powders were applied to cathodes and compared to typical Pt cathodes (0.002 microm). Cathodes made with Ni (0.5--1 microm) had similar Coulombic efficiencies, cathodic, hydrogen and energy recoveries in MECs compared to Pt-cathodes but slightly lower hydrogen production rates (1.2--1.3 m3/m 3/d Ni; 1.6 m3/m3/d Pt, E ap=0.6V). Avoiding exposure of the Ni catalyst to air minimized Ni dissolution. Analysis of the anodic biofilms showed that G. sulfurreducens and P. propionicus were the most abundant bacteria. Non-precious metals can therefore achieve higher hydrogen production rates than those obtained with platinum and can be used in MEC cathodes allowing large scale production.