Layered ammonium metal phosphate based heterostructure with phosphate–sulfide interfacial synergy for efficient oxygen evolution and urea oxidation reactions†

Abstract

This study unveils a highly efficient electrocatalyst based on hydrated ammonium metal phosphates (NH₄MPO₄·H₂O) with a layered crystal structure and expanded interlayer spacing, facilitating rapid electron and ion transport for advanced oxygen evolution reaction (OER) applications. Addressing inherent limitations in conductivity and electroactive surface area, we engineered a heterostructured electrocatalyst by combining NH₄NiPO₄·H₂O with CdIn₂S₄ and in situ formed Ni₃S₂ on nickel foam (NF) through a two-step hydrothermal process. The resulting NH₄NiPO₄·H₂O/CdIn₂S₄/Ni₃S₂ (NPO/CINS) system leverages phosphate–sulfide interfacial interactions, significantly enhancing catalytic performance. Electrochemical tests reveal impressive OER and urea oxidation reaction (UOR) activities, achieving low overpotentials of 245 mV and 1.26 V at 10 mA cm⁻², respectively. The obtained exceptional UOR efficiency exceeds that of previously reported oxide and sulfide-based heterostructure electrocatalysts. The NPO/CINS heterostructure demonstrates remarkable stability towards OER, with only 2% degradation over 65 hours of continuous operation, affirming its durability for high-performance applications. This work emphasizes the power of synergistic interfacial bonding, optimized electron transfer, and strategic structural design, positioning the NPO/CINS heterostructure as a pioneering catalyst for scalable energy solutions.