| Summary: | We systematically investigated the hydrogen evolution reaction (HER) of six facets of <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mrow> <mi>MoP</mi> </mrow> <mn>2</mn> </msub> </mrow> </semantics> </math> </inline-formula> based on the periodic density functional theory (DFT). The calculated values of Gibbs free energy of hydrogen adsorption (<inline-formula> <math display="inline"> <semantics> <mrow> <mi mathvariant="sans-serif">Δ</mi> <msub> <mi>G</mi> <mi mathvariant="normal">H</mi> </msub> </mrow> </semantics> </math> </inline-formula>) indicated that the (111) facet has a good HER activity for a large range of hydrogen coverages. The zigzagged patterns before 75% hydrogen coverage suggest a facilitation among Mo1, P1 and Mo2 sites, which are attributed to repeat occupancy sites of H atoms. From ab initial atomistic thermodynamics analysis of hydrogen coverage, we gained that the most stable coverage of hydrogen is 18.75% at 1 atm <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mi>H</mi> <mn>2</mn> </msub> </mrow> </semantics> </math> </inline-formula> and 298 K. Finally, the doping effects on HER activity were investigated and found that catalytic performance can be improved by substituting P with an S or N atom, as well as substituting the Mo atom with an Fe atom, respectively. We hope this work can provide new insights on further understanding of HER for <inline-formula> <math display="inline"> <semantics> <mrow> <msub> <mrow> <mi>MoP</mi> </mrow> <mn>2</mn> </msub> </mrow> </semantics> </math> </inline-formula> and give instructions for the experimental design and synthesis of transition metal phosphides (TMPs)-based high-performance catalysts.
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