Cobalt–Iron–Phosphate Hydrogen Evolution Reaction Electrocatalyst for Solar-Driven Alkaline Seawater Electrolyzer

Seawater splitting represents an inexpensive and attractive route for producing hydrogen, which does not require a desalination process. Highly active and durable electrocatalysts are required to sustain seawater splitting. Herein we report the phosphidation-based synthesis of a cobalt–iron–phosphate ((Co,Fe)PO(4)) electrocatalyst for hydrogen evolution reaction (HER) toward alkaline seawater splitting. (Co,Fe)PO(4) demonstrates high HER activity and durability in alkaline natural seawater (1 M KOH + seawater), delivering a current density of 10 mA/cm(2) at an overpotential of 137 mV. Furthermore, the measured potential of the electrocatalyst ((Co,Fe)PO(4)) at a constant current density of −100 mA/cm(2) remains very stable without noticeable degradation for 72 h during the continuous operation in alkaline natural seawater, demonstrating its suitability for seawater applications. Furthermore, an alkaline seawater electrolyzer employing the non-precious-metal catalysts demonstrates better performance (1.625 V at 10 mA/cm(2)) than one employing precious metal ones (1.653 V at 10 mA/cm(2)). The non-precious-metal-based alkaline seawater electrolyzer exhibits a high solar-to-hydrogen (STH) efficiency (12.8%) in a commercial silicon solar cell.