Electrochemical conversion of H2O/CO2 to fuel in a proton-conducting solid oxide electrolyser

In this paper, we demonstrate the direct conversion of CO2/H2O into fuel in a proton-conducting solid oxide electrolyser with the configuration (La0.75Sr0.25)(0.95)Mn0.5Cr0.5O3-delta (LSCM, oxygen electrode)/BaCe0.5Zr0.3Y0.16Zn0.04O3-delta (BCZYZ, proton-conducting electrolyte)/Ni (fuel electrode) at 600 degrees C, where 5% H2O/Ar and 100% CO2 are fed into the oxygen electrode and fuel electrode, respectively. AC impedance spectroscopy and I-V testing demonstrate two main processes in the electrochemical process from 0 to 2 V: (1) the reoxidation of the LSCM electrode (Mn-3 +/- -> Mn-4 +/-) below 1.2 V (iR-corrected voltage) and (2) the oxidation of H2O (H2O - 2e -> H-+/- +/- 1/2O(2)) above 1.2 V (iR-corrected voltage). The current density reaches similar to 0.1 Acm(-2) at 2 V versus open circuit voltage (OCV) with a total polarisation resistance of 7.5 Omega cm(2). Steam is steadily electrolysed under a 2 V load at 600 degrees C, and the generated protons in the fuel electrode are simultaneously and completely utilised to electrochemically reduce CO2 with 100% selectivity and similar to 90% current efficiency to CO fuel. However, the carbon deposition, poisoning and oxidation of Ni metal in the fuel electrode degrade the cell performance. (C) 2013 Elsevier B.V. All rights reserved.