NiFe co-doped TiO2 as a high-performance bifunctional photocatalyst for enhanced oxygen evolution and reduction reactions in efficient zinc-air battery systems

This study underscores the significant influence of Ni and Fe transition metal doping, as well as NiFe co-doping, on enhancing the properties of TiO₂ to address the critical challenges in developing high-performance photo-assisted Zn-air batteries, particularly the need for improved light absorption, charge carrier separation, and catalytic efficiency. The doping process notably enhances light absorption and charge carrier separation, while the reduction in TiO₂ crystallite size increases the surface area and shortens charge carrier diffusion paths, thereby minimizing recombination rates and improving photocatalytic efficiency. Moreover, the higher redox potentials of Ni and Fe oxidation states relative to TiO₂'s conduction band enable them to function as efficient electron acceptors, stabilizing charge carriers and accelerating reduction reactions. Electrochemical analysis reveals that NiFe-doped TiO₂ exhibits superior conductivity and reduced charge transfer resistance compared to its single-element-doped counterparts, facilitating faster reaction kinetics. For OER, the overpotential decreases from 307 mV to 221 mV, while for ORR, illumination improves the half-wave potential to 0.65 V and increases the diffusion-plateau current density from 3.96 mA/cm² to 4.6 mA/cm². Battery performance testing demonstrates that under light irradiation, the charging potential is reduced to 1.63–1.66 V, and the discharge voltage is stabilized at 1.56–1.60 V, resulting in a round-trip efficiency of 96.34 %, compared to 77.59 % under dark conditions. These performance metrics approach the theoretical redox potential of 1.64 V, outperforming the capabilities of the state-of-the-art catalysts for photo-assisted Zn-air systems. Overall, this work establishes NiFe-doped TiO₂ as a highly effective bifunctional photocatalyst, highlighting its potential to optimize oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) processes, thereby contributing to advancements in sustainable energy storage technologies.