Reaction‐Specific Ultralow‐Pt‐Integrated CuCo Carbonate Hydroxide Nanoneedles for Durable Alkaline Seawater Electrolysis

ABSTRACT Developing bifunctional electrocatalysts that combine high activity, low noble‐metal usage, and durability in alkaline seawater‐containing electrolytes is important for sustainable hydrogen production. Herein, Pt‐integrated copper cobalt carbonate hydroxide nanoneedle arrays grown on Ni foam were prepared by hydrothermal synthesis followed by controlled Pt electrodeposition. The Pt deposition cycle was found to govern the balance between accessible CuCo–CH sites and Pt‐derived interfacial activity: Pt@CuCo–CH–7C delivered the best OER performance, whereas Pt@CuCo–CH–3C was optimal for the HER. In 1.0 M KOH, Pt@CuCo–CH–7C required overpotentials of 213 and 332 mV to reach 10 and 100 mA cm − 2 , respectively, for the OER, while Pt@CuCo–CH–3C achieved HER overpotentials of 11.9 and 181 mV at the same current densities. Electrochemical impedance (EIS), double‐layer capacitance, and DFT free‐energy analysis indicate that Pt incorporation improves interfacial charge transfer, increases accessible catalytic sites, and lowers the free‐energy requirement of the OER potential‐determining step. A two‐electrode Pt@CuCo–CH–7C||Pt@CuCo–CH–3C electrolyzer achieved 10 mA cm − 2 at 1.47 V in alkaline seawater‐containing electrolytes and maintained stable operation for 250 h at 100 mA cm − 2 , with Faradaic efficiencies of 97%–99%. These results suggest that controlled noble‐metal integration into multimetal carbonate hydroxide frameworks is an effective strategy for durable alkaline seawater electrolysis.