Theoretical Exploration of the Thermodynamic Process Competition between NRR and HER on Transition-Metal-Doped CoP (101) Facets

Abstract

Transition-metal phosphides are a series of potential electrocatalysts in many electrochemical processes, among which CoP attracts the most attention because of its high stability, abundance, and low cost. In this article, we calculate both the hydrogen evolution reaction (HER) and the nitrogen reduction reaction (NRR) processes on a series of (101) facets of M-doped CoP (M = Mn, Fe, Ni, and Cu). Mn and Fe doping leads to higher d band centers of metal sites on the surface, in which all of the adsorptions are stronger than those on nondoped CoP. Ni and Cu doping causes lower d band centers of metal sites and weakens all of the adsorptions on the CoP surface. The competition of reaction thermodynamics between HER and NRR could be understood by the theoretical onset potential, which is evaluated by the maximum energy request in the electrochemical process. In our calculations, there is a linear relationship between the adsorption energy of H* and energy requirement of the NRR’s potential-limiting step. It is revealed that when CoP is doped with metals which show weaker electronegativity, N2 adsorption is intensified and more electrons are injected into N2 during NRR, for which the NN triple bond is weakened and the catalyst performs better NRR activity and selectivity. Therefore, Mn and Fe perform better in promoting NRR. This theoretical exploration helps understand the relationship between the HER and NRR processes on the CoP (101) plane and gives a guide to design improved CoP with greater HER or NRR catalytic activity by transition-metal doping.

Structural characteristics of metal (Ni, Cu) doped cobalt phosphide catalysts and mechanism of catalytic hydrogen evolution of NH3BH3

“…The energy gap value of the Cu-doped CoP was the smallest, and the energy gap value of the three catalysts was inversely proportional to their catalytic activity: the smaller the energy gap value means the stronger the catalytic activity. This was similar to the results of Fu et al[57].4 | CONCLUSIONIn this paper, the catalyst model of CoP and its Cu-and Ni-doped counterparts were optimized by density functional theory, and the corresponding stable catalyst structures were obtained. Based on these structures, we respectively studied the hydrogen evolution reaction mechanism of ammonia borane (NH 3 BH 3 , AB) on the surface of three catalysts and explored four feasible reaction paths for hydrogen evolution reaction on the catalyst surface.…”

Self-supported electrocatalysts for the hydrogen evolution reaction

“…In addition to CoS 2 , the CoP electrocatalyst has also received great attention for the HER. [182][183][184][185][186] Likewise, Wang's group utilized a synergistic electronic and geometric tailoring strategy to rationally fabricate hierarchically porous N-doped carbon incorporated Mo-doped CoP nanosheet arrays on the titanium foil (Mo-CoP/NC/TF) via etching Co-based MOFs (Fig. 7g-j).…”

The electronic structures of non-metal (N, S) doped cobalt phosphide catalysts and the catalytic mechanism for the hydrogen evolution reaction of ammonia borane: a theoretical study

“…All the structure optimizations, band structures and DOS calculations were carried out using the Dmol 3 module implemented in the Material Studio 8.0 program. 35 The construction of the CoP model followed a similar procedure to the six-layer slab model used by Bahamon et al , 36 and the selection of the (101) crystal plane of the CoP catalyst refers to the theory of the thermodynamic process of transition metal doped CoP by Fu et al 37 We built a six-layer slab and studied 101 sides of the model. The activity of CoP (101) (lattice parameters are a = 7.473 Å, b = 12.805 Å, c = 20.942 Å, α = β = γ = 90°) has been evaluated by using a supercell containing a six-layer (2 × 3) CoP (101) slab.…”