Electrochemical oxidation of carbon at high temperature : principles and applications

Abstract

Carbon is an important energy carrier. It is abundant in the world, existing richly in coal and biomass. Its energy is released mainly through oxidation. A heat energy of ∼393 kJ may be obtained from the complete oxidation of 1 mol of carbon. The most conventional method of carbon oxidation is combustion, which has the problems of pollutant emission and low efficiency. However, through electrochemical oxidation, the chemical energy of carbon can be converted into electricity with high efficiency and low pollution. Herein, we give a brief review of our work on a novel technology of generating electricity and carbon monoxide from electrochemical oxidation of carbon through a solid oxide fuel cell (SOFC) at high temperature. This so-called direct carbon SOFC (DC-SOFC) has an all-solid-state configuration without any purging gas or liquid medium. Electricity is generated by coupling of the electrochemical oxidation of CO at the anode and the reverse Boudouard reaction at the carbon fuel. Meanwhile, gaseous CO and CO2 are produced. We prepared electrolyte-supported and anode-supported SOFC single cells and stacks and operated them directly with Fe-loaded activated carbon, biochar derived from orchid leaf and corn cob, respectively, as the fuel. In particular, we investigated their potential applications in portable power supplies and electricity-gas cogeneration. Our experimental results show that the output performance of a DC-SOFC is comparable to that of a SOFC operated on hydrogen. A 3-cell stack of tubular anode-supported segmented-in-series DC-SOFC gives a peak areal power density of 465 mW cm–2 and a volumetric power density of 710 mW cm–3 at 850 °C. Furthermore, the composition of the gas emission can be controlled by tuning the operating electrical current and the catalysts applied for the Boudouard reaction so that CO gas and electricity cogeneration can be realized.