Low doping strategy in amorphous alumina: Harnessing oxygen vacancies and retaining structural disorder for advanced...

Amorphous alumina has emerged as a compelling candidate for ceramic fuel cells (CFCs) due to its intrinsic structural disorder, which promotes low-energy ionic transport pathways. However, generating oxygen vacancies without altering the amorphous nature is critical for practical applications. In this study, we report a low-doping strategy using cobalt (3 % and 6 %) to enhance the ionic conductivity of amorphous alumina without compromising its disordered structure. Advanced structural and chemical characterizations confirm the retention of the amorphous phase and reveal the role of cobalt doping in inducing oxygen vacancies, respectively. Electrochemical performance evaluations demonstrate a significant leap in power density of the fuel cell, with pure alumina delivering 512 mW cm^-2, while 3 % and 6 % cobalt-doped alumina (3-CAO & 6-CAO) achieve 672 mW cm^-2 and 773 mW cm^-2, respectively, at 550 °C. Enhanced ionic conductivity, reaching 0.17 S cm^-1 for 6-CAO compared to 0.078 S cm^-1 for pure alumina at 550 °C, underscores the efficacy of this approach. The functionality of dual oxidation states of cobalt and alternating oxidation states of Co between Co²⁺ and Co³⁺ assists subcutaneously in generating oxygen vacancies that enhance ionic transport while retaining the beneficial disorder of the amorphous matrix. The dominant presence of proton conductivity in 6-CAO electrolytes and their experimental confirmation assures the superior electrolytic functionality. This innovative low-doping strategy advances high-performance low-temperature CFCs, showcasing the potential of disordered ionic conductors for next-generation energy technologies.