Synergistic proton conduction via Ca-vacancy coupled with Li⁺-bridge in Ca₅(PO₄)₃OH

Proton conductivity plays a crucial role in the advancement of materials for proton ceramic fuel cells (PCFCs) and a variety of electrochemical devices. Traditional approaches to enhancing proton conductivity in perovskites have largely relied on doping strategies to induce structural oxygen vacancies. However, these methods have yet to overcome the challenges associated with achieving desired proton conductivity. Here, we introduce an approach wherein intermediate Li⁺ ions act as a bridge linked to Ca vacancies, fostering a mechanism for accelerated proton transport. Utilizing protonated Ca₅(PO₄)₃OH-H(Li) as an electrolyte, we achieve a proton conductivity of 0.1 S cm⁻¹ and a fuel cell performance of 661 mW cm⁻² at an operational temperature of 550 °C for realizing low temperature PCFCs. This proton transport synergy overcomes traditional doping limitations, enabling the advancement of proton-conducting electrolytes and enhancing the efficiency of proton conducting electrolyte fuel cells, with implications in energy conversion and storage technologies.