Lead-Free Tin-Based Halide Perovskites: A Bifunctional Catalyst for Oxygen Evolution and Oxygen Reduction Suitable for Sustainable Energy Applications

Developing bifunctional electrocatalysts capable of efficiently driving the interconversion between oxygen and water molecules via oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for establishing renewable-driven energy infrastructure. A series of lead-free halide perovskites Cs<inf>2</inf>SnX<inf>6</inf> (X = Cl, Br, I) is designed, along with their mixed halide derivatives Cs<inf>2</inf>SnCl<inf>x</inf>Br<inf>6-x</inf> (where x = 2, 3, 4), to probe bifunctional OER/ORR activity. Measurements reveal the influence of halide ions on the morphology and unravel the unique halide-electronegativity-tunable electronic properties. Further, these materials are immobilized on carbon paper and utilized as anode, where Cs<inf>2</inf>SnCl<inf>6</inf> and Cs<inf>2</inf>SnCl<inf>2</inf>Br<inf>4</inf> displayed the best OER activity and appreciable Faradic efficiency. The photophysical properties of the perovskites lead to a distinct enhancement (≈0.24–0.72 mA cm⁻²) in the OER current response for Cs<inf>2</inf>SnCl<inf>6</inf> and Cs<inf>2</inf>SnCl<inf>2</inf>Br<inf>4</inf> under white-light irradiation. The perovskites maintain their structural and chemical integrity during the (photo)electrocatalysis, as demonstrated by in-depth post-electrolytic surface analysis. The electrocatalysts continue to demonstrate active ORR during the cathodic scan (onset potential of ≈0.6 V vs RHE); however, with minimal influence of photoirradiation. Overall, the Cs<inf>2</inf>SnX<inf>6</inf>-based perovskite electrocatalysts exhibit promising bidirectional OER/ORR activity with competitive catalytic efficiency and stability, suitable for developing sustainable devices for O<inf>2</inf>/H<inf>2</inf>O redox chemistry-mediated energy transduction applications.