Enhanced acidic hydrogen evolution stability and activity in CoP through S doping for proton exchange membrane electrolyzers

Abstract

The development of cost-effective, highly efficient, and stable electrocatalysts for the acidic hydrogen evolution reaction (HER) is essential for advancing clean and renewable hydrogen energy technologies. This is particularly critical for proton exchange membrane (PEM) electrolyzers powered by renewable energy sources. Among various candidates, cobalt-based phosphide (CoP) has emerged as a promising catalyst for the HER in acidic media, owing to the synergistic interaction between Co and P, as well as its inherent stability. Despite significant efforts to enhance its catalytic activity, the critical issue of stability has often been overlooked. Herein, sulfur (S), which has a higher electronegativity than P, is selectively incorporated into CoP nanowire arrays through a simple vulcanization method. This strategy aims to enhance stability without altering catalytic activity. The optimized S-CoP/CC electrocatalyst shows an overpotential of 96 mV at 10 mA cm⁻² in acid electrolyte, showing a slight improvement over the initial CoP/CC (114 mV). Remarkably, it shows exceptional durability, maintaining excellent stability over 150 h of testing in acid solution. The incorporation of sulfur serves a dual role: it enhances electronic conductivity and increases the electrochemical surface area, thereby improving catalytic activity, while simultaneously strengthening the CoP bond energy, leading to outstanding acid stability. Furthermore, when employed as the cathode in a PEM electrolyzer, S-CoP/CC achieves a current density of 500 mA cm⁻² at 1.70 V, demonstrating excellent stability over 140 h at 60 °C. Our findings present a new approach for enhancing both the stability and activity of acidic HER by incorporating higher-electronegativity anions into the CoP lattice. This strategy is applicable not only to Co-based phosphides but also to other non-precious metal-based transition metal compounds, paving the way for the development of high-performance PEM electrolyzers.