Reforming of biogas using electrochemical cell

Abstract

This review reports the recent research results of solid oxide fuel cells using biogas (typical composition, 60% CH440% CO2), reforming of CH4 with CO2 (CH4 + CO2=2CO + 2H2) and shift reaction of CO with H2O (CO + H 2O=H2 + CO2). Solid oxide fuel cells using dense yttria-stabilized zirconia and gadolinium-doped ceria electrolytes were operated with biogas containing CH4 of 7-63 vol% at 630-875 ° C. A maximum power density of 20-160mW/cm2 was measured and this value was 1/10-1/3 of that for the cells with a H2 fuel. The reforming of CH4 with CO2 proceeds over a Ni-based catalyst at 700-900°C to produce a H2-CO fuel. The carbon deposition due to the pyrolysis of CH4 as a parallel reaction is suppressed by addition of second phase such as K2O or Ru to Ni catalyst. Electrochemical reforming of CH4 with CO2 using a porous Gd-doped ceria (GDC) cell is an attractive process to produce a H2-CO fuel at 400-800°C. The supplied CO2 is changed to CO and O2- ions by the reaction with electrons at the cathode (CO2 + 2e -=O + O2-). The produced CO and O2- ions are transported to the anode through a porous mixed conductor GDC film. In the anode CH4 reacts with O2- ions to produce CO, H2 and electrons (CH4 + O2-=CO + 2H2 + 2e -). This process suppresses the carbon deposition from CH 4. Ni in the anode accelerated the pyrolysis of CH4 but Ru promoted the oxidation of CH4 with transported O2- ions. Ni and Ru in the cathode worked well to change CO2 to CO plus O 2-. Furthermore, shift reaction of reformed gas with H2O vapor proceeded to produce a H2 fuel using a porous GDC electrochemical cell with Co2O3 catalyst at 400-500 ° C. © 2011 The Ceramic Society of Japan.