To replace Pt electrocatalysts for the HER in acidic electrolytes, several approaches have been exploited on transition metals through modifying the d–states at the Fermi level of the metal center by the alloying nonmetal elements such has sulfur, nitrogen and carbon.¹ To further reduce the overpotential and enhance the stability, ternary compounds such as nickel molybdenum nitride² have been shown enhanced performance in the HER. Very recently, metal phosphides, known as efficient hydrotreating catalysts, have also been demonstrated as HER catalysts, such as MoP,³ CoP,⁴ and Ni₂P.⁵ Unlike bulk molybdenum dichalcogenides, which show poor activity, hexagonal molybdenum phosphide (MoP) exhibits good HER activity in bulk form, however, its performance is still limited by the intrinsic strong hydrogen binding energy.

In this study, attempts to synergize the electronic properties of cobalt phosphide and molybdenum phosphide by synthesizing ternary cobalt molybdenum diphosphide lead to the formation of an efficient electrocatalyst for the HER. X-ray diffraction data and high-resolution transmission electron microscopy show that this cobalt molybdenum phosphide crystallizes in space group P63/mmc and a formula of CoMoP₂ (Figure 1). Incorporation of the sequentially stacked layers of CoP₆ and MoP₆ prisms on a single CoMoP₂ structure brings about a significant enhancement in the HER kinetics and fast charge transfer. Characterization using X-ray absorption, electrochemical impedance analysis and electrochemical activity and Tafel behavior will be discussed.

References

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Acknowledgement

This work was carried out at National Taiwan University, and financially supported by Ministry of Science and Technology (Taiwan) and Academia Sinica (Taiwan).