Effect of Microstructure on Performance of Double-Layer Hydrogen Electrodes for Reversible SOEC/SOFC

Abstract

We have developed high-performance double-layer (DL) hydrogen electrodes for reversible solid oxide cells. The DL hydrogen electrode consisted of mixed conductor, samaria-doped ceria (SDC), with highly dispersed Ni or Ni-Co nanocatalysts as the catalyst layer (CL) and, on top of it, a thin Ni-SDC cermet as the current collecting layer (CCL). The performance of the DL hydrogen electrode was appreciably improved by controlling the microstructure. The use of a thin, porous CCL increased the electronic conducting path to and from the CL, while maintaining sufficient gas-diffusion rates of H2 and H2O, and enlarging the effective reaction zone at the CL. The optimum CCL thickness was found to be 5 μm. The IR-free overpotentials η at the optimized DL hydrogen electrode in humidified hydrogen (p[H2O] = 0.4 atm) and Tcell = 800°C were 0.20 and -0.20 V at j = 0.5 and -0.5 A cm-2, respectively, indicating a highly reversible operation. The use of a full cell with the configuration of Ni0.9Co0.1/SDC DL hydrogen electrode|YSZ electrolyte|SDC interlayer|LSCF-SDC O2 electrode led to very promising results for the SOEC operation in which an IR-free electrolytic cell potential of 1.21 V at j=.0.5 A cm-2 and 800°C was achieved.