Toru Hatae

Effect of proton-conduction in electrolyte on electric efficiency of multi-stage solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are promising electrochemical devices that enable the highest fuel-to-electricity conversion efficiencies under high operating temperatures. The concept of multi-stage electrochemical oxidation using SOFCs has been proposed and studied over the past several decades for further improving the electrical efficiency. However, the improvement is limited by fuel dilution downstream of the fuel flow. Therefore, evolved technologies are required to achieve considerably higher electrical efficiencies. Here we present an innovative concept for a critically-high fuel-to-electricity conversion efficiency of up to 85% based on the lower heating value (LHV), in which a high-temperature multi-stage electrochemical oxidation is combined with a proton-conducting solid electrolyte. Switching a solid electrolyte material from a conventional oxide-ion conducting material to a proton-conducting material under the high-temperature multi-stage electrochemical oxidation mechanism has proven to be highly advantageous for the electrical efficiency. The DC efficiency of 85% (LHV) corresponds to a net AC efficiency of approximately 76% (LHV), where the net AC efficiency refers to the transmission-end AC efficiency. This evolved concept will yield a considerably higher efficiency with a much smaller generation capacity than the state-of-the-art several tens-of-MW-class most advanced combined cycle (MACC).

Initial Damage to Anode Microstructure Caused by Partial Redox Cycles during Electrochemical Oxidation

Cell damage caused by redox cycling in which the anode is electrochemically oxidized was investigated in order to detect the initial damage before cell failure. In order to prevent catastrophic destruction of the cell, partial electrochemical oxidation was used in the redox treatment and controlled at a very low degree of oxidation of the anode. As a result, the cell performance degraded because of the partial redox cycles without a decrease in open-circuit voltage, and no mechanical damage was observed in the electrolyte. However, microcracks at the interfaces between ScSZ particles and Ni particles in the anode layer in active cell area were observed. These results indicated that the microcracks in the anode layer were the initial damage caused by partial redox cycles in which the anode was electrochemically oxidized and caused the degradation of the cell performance.