A targeted ionic iron/platinum-based precatalyst for bias-dependent reconstruction in alkaline water splitting

Abstract Efficient alkaline water splitting requires catalysts for both the oxygen-evolution reaction (OER) and the hydrogen-evolution reaction (HER). Precatalyst reconstruction offers a route to generating active surfaces under operating conditions. Here, we report an ionic iron/platinum-based precatalyst reservoir for alkaline water splitting, prepared by combining anionic iron(III) phthalocyanine-4,4′,4″,4‴-tetrasulfonate (FeTSPc³⁻) with cationic [Pt(NH₃)₄]²⁺ (TP²⁺) species. The resulting FeTSPc/TP ionic solid has limited solubility in alkaline electrolyte and supplies Fe- and Pt-derived species under electrochemical bias. Rather than acting as a persistent molecular bifunctional catalyst, FeTSPc/TP undergoes bias-dependent reconstruction on nickel-foam electrodes. Under anodic conditions, Fe-derived species are associated with the nickel surface, producing a Ni–Fe (oxy)hydroxide-type OER-active layer. Under cathodic conditions, Pt-derived species generate Pt-containing deposits that promote the HER. Compared with bare Ni foam, the FeTSPc/TP system decreases the OER overpotential by approximately 200 mV and the HER overpotential by approximately 80 mV under the tested conditions. The analyses support the formation of distinct catalyst-derived surface deposits at the two electrodes. These results show that a single ionic precatalyst reservoir can deliver different catalyst-forming components to anodic and cathodic surfaces, providing a proof-of-concept strategy for bias-dependent reconstruction during alkaline water splitting.