Mn-Doped Cobalt Phosphide Non-Noble Catalyst: Boosting HER for Stable and High-performance Zn-CO2 system

Abstract

Carbon capture, utilization, and storage (CCUS) is recognized as a critical pathway for decarbonization, but current approaches are limited by energy-intensive operation and suboptimal conversion efficiency. In this context, the Zn-CO2 system holds immense promise for simultaneous electricity generation, green hydrogen production, and efficient CO2 utilization. However, further improvement of the overall system efficiency hinges on enhancing the hydrogen evolution reaction (HER) in quasi-neutral media. Herein, we report a Mn-doped cobalt phosphide (Mn-CoP/NF) catalyst grown on nickel foam via a facile one-step electrodeposition, designed to promote water dissociation and enhance HER activity in neutral electrolytes. Structural characterizations reveal that Mn doping induces an amorphous transformation with a cauliflower-like morphology, markedly increasing the electrochemical active surface area (ECSA) and exposing abundant active sites. XPS analysis further confirms that Mn functions as an electron donor, generating electron-rich Co/P surfaces that favor optimized adsorption of reaction intermediates. Kinetic analysis demonstrates that the incorporation of oxyphilic Mn substantially lowers the Tafel slope from 158.7 mV dec -1 to 62.0 mV dec -1 , evidencing accelerated water dissociation in the Volmer step. Density functional theory (DFT) calculations reveal that Mn incorporation lowers the water dissociation energy barrier and optimizes the hydrogen adsorption free energy (ΔGH*). Consequently, the Mn-CoP/NF catalyst exhibits outstanding HER activity in saturated KHCO3 solution, with an overpotential of 149.9 mV at 50 mA cm-2 , similar to commercial 1 mg cm-2 Pt/C (146.4 mV). Furthermore, the Zn-CO2 system assembled with Mn-CoP/NF as the HER electrode achieves a maximum current density of 378 mA cm -2 and sustains stable operation for over 300 hours at -100 mA cm-2 .