Three-Dimensional Amorphous Cobalt Phosphate Nanosheets for Efficient Overall Water Splitting in Neutral Electrolytes

The development of highly active, economically viable, bifunctional electrocatalysts is crucial for achieving efficient and robust neutral water electrolysis. Herein, a three-dimensional, highly uniform amorphous cobalt phosphate (a-Co₃(PO₄)₂) nanosheet array was fabricated directly on cobalt foam via an in situ growth strategy. The a-Co₃(PO₄)₂ catalyst demonstrates overpotentials of only 109 mV for the hydrogen evolution reaction (HER) and 513 mV for the oxygen evolution reaction (OER) to achieve a current density of 10 mA cm^-2 in neutral electrolyte. Remarkably, it enables a neutral electrolyzer with a current density of 10 mA cm^-2 at a low cell voltage of 1.97 V. The electrode also demonstrates exceptional sustained stability, retaining the target current density with only 1.5% voltage augmentation over 80 h of uninterrupted operation. The remarkable performance stems from the distinctive architecture featuring vertically interconnected amorphous nanosheet arrays grown directly on Co foam, which ensures efficient interfacial electron transfer. The amorphous nature provides a high density of active sites and enhanced carrier density, as confirmed by Mott-Schottky analysis, while three-dimensional architecture facilitates mass transport and promotes bubble detachment. These integrated features collectively contribute to the superior catalytic kinetics. This study offers an economical and controllable synthesis route for designing nanoarray electrodes with superior HER and OER performance, thereby providing a promising strategy toward efficient and economically viable neutral overall water splitting.