Electrode Degradation in Proton-Conducting Ceramic Electrochemical Devices

Abstract

We present our efforts to identify, quantify, and mitigate sources of degradation in proton-conducting ceramic electrochemical devices. As described in another presentation, researchers at the Colorado School of Mines are currently scaling up proton-conducting ceramics into multi-cell stacks for both fuel-cell and electrolyzer applications. This integration of novel protonic-ceramic materials with stack packaging materials brings questions regarding materials compatibility and stack-level degradation. The lower operating temperature (500 – 600 ºC) of protonic-ceramic devices presents promise for reducing the driving forces behind several well-established degradation mechanisms found in more-prevalent oxygen-ion conducting ceramics. Nickel sintering in the anode support should decrease, as should chromia-scale growth and electrode poisoning from metallic interconnects. That said, other aspects of protonic ceramics could enhance degradation. For example, under fuel-cell operation, water vapor is formed at the cathode, increasing oxygen partial pressure and promoting chromia poisoning. Further, these degradation mechanisms are presented over thousands of hours of stack operation, often happening simultaneously, clouding our understanding.In this presentation, we describe our efforts to identify and mitigate the key degradation mechanisms found in proton-conducting ceramic electrochemical devices and stacks. Through collaboration with the University of Bordeaux, we have developed unique device packaging and experimentation to enable careful measurement of electrochemical performance at electrode-electrolyte interfaces over thousands of hours of operation. As shown in the figure, a ~ 2-mm-thick BaCe0.4Zr0.4Y0.1Yb0.1O3-δ (BCZYYb4411) electrolyte is sandwiched between two identical BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) air electrodes to form an electrolyte-supported symmetric cell. Fuel electrodes can also be studied. The cell is packaged, perhaps with metallic interconnects, within carefully designed alumina fixturing that maintains consistent electrical connections throughout the long testing periods. The assembly is sealed within a quartz reactor and placed within a furnace, and enables exploration of a wide range of operating conditions, gas compositions, and temperatures.In this talk, we will present results focusing on degradation at the cathode-electrolyte interface. The effect of H2O concentration, and the role of metallic interconnects in cathode degradation will be presented. Figure 1