Amorphization and Defect Engineering of Ternary Metal Pyrophosphates toward High-Performance Oxygen Evolution Reaction Catalysts

Hydrogen production via water electrolysis has received great attention as a clean and sustainable alternative to conventional steam reforming, which requires high temperature and pressure and generates significant CO 2 emissions. However, the sluggish four-electron kinetics of the oxygen evolution reaction (OER) remains a major bottleneck, limiting overall energy efficiency, and the challenge becomes even more severe when replacing noble-metal catalysts with transition-metal-based alternatives for cost-effective hydrogen production. To address these challenges, the development of non-noble-metal-based OER catalysts with low overpotential and long-term stability is highly desired. In this paper, we report the synthesis of ternary metal (Co, Ni, and Fe) phosphonate derivatives that exhibit significantly enhanced OER activity and durability in an alkaline electrolyte compared to previously reported bimetallic phosphonates. In particular, oxygen vacancy (O v )-rich CoNiFe pyrophosphate (O v -CNF-P 2 O 7 ) obtained by calcination and subsequent reduction shows accelerated electron transfer and stronger hydroxide adsorption relative to pristine CNF-P 2 O 7, resulting in excellent OER performance with an overpotential of 227 mV at 10 mA cm –2 and a Tafel slope of 42 mV dec –1 .