Cost-Effective Surface Engineering Strategy for the NiCoP/Activated Carbon Heterostructure toward High-Performance Overall Water Splitting

Developing low-cost electrocatalysts for efficient hydrogen production via water splitting is highly desirable but remains a significant challenge. Herein, a novel dual-waste-derived NiCoP/AC electrocatalyst is synthesized from a NiCo–metal–organic framework (NiCo–MOF) via a two-step synthesis process. The high-surface-area activated carbon (AC) (1829 m 2 g –1 ) is derived from dried waste papaya petioles via chemical activation and pyrolysis, while the benzene-1,2-dicarboxylic acid (BDC) linker for the MOF is recovered from waste PET bottles. Owing to the large surface area and porosity of the carbon support, the NiCo–MOF grows uniformly over the AC surface, and subsequent phosphidation generates abundant, accessible NiCoP active sites favorable for electrochemical water splitting. The optimized NiCoP/AC catalyst delivers overpotentials of 248 mV for the hydrogen evolution reaction (HER) and 405 mV for the oxygen evolution reaction (OER) at 100 mA cm –2, requires only 1.52 V to achieve 10 mA cm –2 in a two-electrode configuration, and demonstrates excellent durability, maintaining stable performance for 41 h at a high current density of 400 mA cm –2 . Furthermore, faradaic efficiencies of 96% for HER and 94% for OER are achieved, confirming the catalyst’s high selectivity. This work presents a sustainable and practical strategy for efficient overall water splitting by employing a cost-effective, waste-derived NiCoP/AC electrocatalyst.