Taking advantage of Li-evaporation in LiCoO₂ as cathode for proton-conducting solid oxide fuel cells

LiCoO₂, a widely used electrode material for Li-ion batteries, was found to be suitable as a cathode material for proton-conducting solid oxide fuel cells (H-SOFCs). Although the evaporation of Li in LiCoO₂ was detrimental to the Li-ion battery performance, the Li-evaporation was found to be beneficial for the H-SOFCs. The partial evaporation of Li in the LiCoO₂ material preparation procedure led to the in-situ formation of the LiCoO₂+Co₃O₄ composite. Compared to the cell using the pure phase LiCoO₂ cathode that only generated moderate fuel cell performance, the H-SOFCs using the LiCoO₂+Co₃O₄ cathode showed a high fuel cell performance of 1160 mW·cm^–2 at 700 ℃, suggesting that the formation of Co₃O₄ was critical for enhancing the performance of the LiCoO₂ cathode. The first-principles calculation gave insights into the performance improvements, indicating that the in-situ formation of Co₃O₄ due to the Li-evaporation in LiCoO₂ could dramatically decrease the formation energy of oxygen vacancies that is essential for the high cathode performance. The evaporation of Li in LiCoO₂, which is regarded as a drawback for the Li-ion batteries, is demonstrated to be advantageous for the H-SOFCs, offering new selections of cathode candidates for the H-SOFCs.