Electrochemical Degradation in Protonic-Ceramic Cells and Stacks

Abstract

Proton-conducting ceramics are emerging as a promising material for efficient electricity generation, energy storage, and fuels synthesis. While recent developments of this material are highly encouraging in terms of performance at the lab-scale level, there are limited studies focused on the long-term stability and scalability of the device. In this work, we report our development of protonic-ceramic electrochemical cells and stacks and their corresponding long-term performance. We find that the degradation rates in protonic-ceramic fuel cells (PCFCs) are orders-of-magnitude higher than that found in protonic-ceramic electrolysis cells (PCECs), especially at low-temperature (below 600 oC), high-bias conditions. While this behavior is counterintuitive to expectations of solid-oxide devices, our studies show that by modifying the air/steam electrode – electrolyte interface, excellent performance and stability can be achieved for both PCFCs and PCECs (Figure 1).The degradation behaviors of protonic-ceramic electrochemical cells are investigated using Electrochemical Impedance Spectroscopy (EIS). A hypothesis of the protonic-ceramic degradation mechanism has been proposed based on the EIS analysis. It has been shown that the charge-transfer and oxygen-transport processes at the air/steam electrode – electrolyte interface play important roles to maintain a stable cell performance. Several fuel cell and electrolyzer stacks have been optimized to facilitate these electrochemical processes. As will be shown, the excellent performance and stability improvements of these stacks confirm the validity of our hypothesis. Figure 1