Bio-electrochemical production of hydrogen by using electroactive materials

Abstract

Due to the thermodynamic barrier, volatile fatty acids formed during dark fermentation cannot be oxidized further to produce hydrogen. In this work, we have designed an H-type bio-electrochemical cell to oxidize the acetate, a common intermediate product of dark fermentation reaction, to produce energy in the form of electricity and hydrogen gas. The hydrogen gas can be used as a fuel source and as an energy vector to supply the energy during the drought season. The inoculation was done on carbon felt and carbon cloth electrodes by daily replacing the medium for up to 7 weeks. Acetate was used as a model. The generation of voltage in the cells suggested successful degradation of the organic matter by microorganisms. The overpotential existing in the cells was determined by modelling the polarization behaviour, and the internal resistance of the cells was found in the range 405 Ω-715 Ω. The system was efficient in reducing the COD level by 80% in a batch operation. The electrochemical characterization of the cathode materials was done in a half-cell setup, and Nickel foam catalyzed with platinum (0.5 mg/cm2) exhibited better performance in the reduction zone. The coulombic efficiencies of the cells ranged from 2.28% to 15.80%. The coulombic efficiency was determined as a function of charge transferred in the circuit due to the oxidation of substrate at the anode. The influence of competing microorganisms at the anode and the internal resistance on the efficiency of the cells were also studied. The hydrogen production rate was determined by translating the charge available in the circuit using Faraday’s law. Voltage and Concentration were linearly increased to see their effect on the hydrogen production. At lower voltage (0.5 V, 0.8 V) and lower concentrations (5 mM, 10 mM), the production of hydrogen was almost insignificant; while at higher concentrations (20 mM) and voltage (1.0 V), hydrogen gas was produced at a rate of 0.005-0.006 m3/m3/day.