Functionalization-Mediated Synthesis of Bridge-Coordinated Fe Atoms on MoS₂ Nanosheets for PEM Water Electrolyzers

Transition metal chalcogenides are among the most promising platinum group metal-free (PGM-free) catalysts for hydrogen production in a proton exchange membrane water electrolyzer (PEMWE). However, achieving both high activity and long-term stability remains a critical challenge for their practical deployment. Here, we report a functionalization-mediated synthesis of molybdenum sulfide, containing bridge-coordinated Fe atoms (b-Fe-MoS₂), achieving enhanced catalytic performance for the hydrogen evolution reaction (HER). Combined detailed spectroscopic and electrochemical characterizations revealed that cysteine functionalization promotes the anchoring of Fe atoms in a bridge-like coordination environment on the MoS₂ nanosheets, resulting in tunable electron density near the Fe sites and improved robustness of the atomic sites, as supported by our operando and post-mortem investigations. The experimental results are complemented with density functional theory (DFT) calculations revealing that the unique coordination environment of Fe atoms modulates the hydrogen adsorption free energy. When integrated in a 25 cm² catalyst-coated membrane PEM water electrolyzer, b-Fe-MoS₂ achieved remarkable performance, delivering 1.55 A cm^-2 at 2 V and showed stable operation over 360 h following initial activation. These results demonstrate the effectiveness of the functionalization-mediated approach for preparing robust HER catalysts and highlight the potential of bridge-coordinated Fe-MoS₂ cathodes for PGM-free PEM water electrolyzers.