Transition metal-doped FeP nanoparticles for hydrogen evolution reaction catalysis

Transition-metal phosphides have been investigated as promising materials for hydrogen evolution reaction (HER) catalysts because of their cost efficiency, high catalytic activity, and good stability. Here, we report the spherical iron phosphide nanoparticles (FeP NPs) doped with various transition metals (Mn, Co, and Ni) via a phosphorization process from Fe-based bimetallic NPs and characterize the changes in their HER activity as a result of doping with different elements. Electrochemical measurements indicated that the Co-FeP NPs exhibited an overpotential of 126 mV to achieve a 10 mA cm−2, demonstrating higher activity than the FeP, Ni-FeP, and Mn-FeP NPs because of their large active surface area and fast charge transfer. X-ray photoelectron spectroscopy analysis showed that the Co-FeP NPs exhibit a significantly tuned chemical state through the presence of more metal–P bonds and fewer oxidized species compared with the other doped products. In addition, X-ray diffraction and X-ray absorption spectroscopy analysis revealed substitutional doping of Fe atoms by Co atoms in the FeP crystalline structure. This study provides new insights for the efficient synthesis of doped transition-metal phosphides and for designing nanocatalysts with enhanced catalytic activity.