Control strategy of Ni and Co at the B-site to improve oxygen reduction reaction activity of the Li[NixCo2/3-xMn1/3]O2 symmetrical electrode

Abstract

Symmetric solid oxide fuel cells (SSOFCs) are attracting much attention due to their ability to improve chemical and thermal compatibility between electrolytes and electrodes and reduce manufacturing costs. The in-situ precipitating of electrode in reduction atmosphere has been proved to be an effective strategy to improve the maximum power density of SSOFCs. Herein, we use the Li(Ni_xCo_2/3-xMn_1/3)O₂ (LNCM) serial material as the symmetrical electrodes to fabricate SSOFCs, which are operated in normal and reverse mode. In reverse operation, the LNCM is firstly reduced by hydrogen and in-situ precipitates the Ni–Co alloy and Li₂MnO₃. The electrochemical impedance spectra (EIS) indicates that the reduced product delivers excellent oxygen reducing activity as well as promising catalytic activity toward hydrogen oxidation reaction. Thus, the SSOFCs based on LNCM symmetric electrodes present superior electrochemical performance in the reverse operation. Moreover, in the LNCM serial samples, the atomic ratio of Ni and Co at the B site is adjusted to control the contents of in-situ precipitation for further optimizing the cell performance. Using Li[Ni_1/2Co_1/6Mn_1/3]O₂ as symmetric electrodes shows outstanding performance of 923 mW cm⁻² at 550 °C. This work provides a reference scheme for electrode design of SSOFCs.