Cogeneration of electricity and organic chemicals using a polymer electrolyte fuel cell

Abstract

Several unsaturated organic alcohols (allyl alcohol, propargyl alcohol, 2-butin-1,4-diol, 2- buten-1,4-diol) and acids (maleic acid, acrylic acid, crotonic acid, acetylendicarboxylic acid) were used as oxidants together with hydrogen as fuel in a polymer electrolyte fuel cell (PEFC). The standard free enthalpies ( Δ R G θ ) of the overall fuel cell reactions H 2/oxidant were calculated to be negative and the equilibrium voltages of such systems are in the range of U 00 = 0.4–0.6 V. In this way, the cogeneration of electric energy and desired hydrogenated products in a fuel cell reactor is apparent. Nafion ® 117, as polymer electrolyte, and commercial gas diffusion electrodes (ETEK) with carbon supported Pt were used in a PEFC reactor. The aqueous solutions of unsaturated alcohols and organic acids ( c = 1–2 mol dm −3) were pumped under ambient pressure through the cathode compartment of the cell whereas hydrogen was fed into the cell at p = 0.15 MPa. The open circuit voltages were measured to be in the range of 0.1–0.25 V. Current densities up to 50 mA cm −2 and maximum power densities of around 1 mW cm −2 has been achieved in the case of allyl alcohol, 2-butene-1,4-diol and acrylic acid. HPLC analysis indicates that the double or triple bond in unsaturated alcohols and organic acids is selectively hydrogenated. In addition, the electrochemical behaviour of the alcohols and acids was studied by means of cyclic voltammetry at a smooth polycrystalline Pt electrode in H 2SO 4. Reduction reactions were observed at potentials of E < 200 mV versus RHE. It was found that the onset potential for electrochemical hydrogenation of the double and triple bond in the cyclic voltamogram correlates well with the fuel cell performances using these compounds as oxidants.