The Combined Role of Faceting and Heteroatom Doping for Hydrogen Evolution on a WC Electrocatalyst in Aqueous Solution: A Density Functional Theory Study

Abstract

Tungsten carbide (WC) is an established model electrocatalyst for the hydrogen evolution reaction (HER) in aqueous solutions. In spite of extensive interest in and work on this material, systematic atomistic understanding of the combined role of faceting and hetero-atom doping for hydrogen evolution on WC electrocatalysts in aqueous solution is not available. To fill this knowledge gap, here we explore the interplay of these parameters for the electrocatalytic performance of WC by means of Density Functional Theory (DFT) simulations. In our simulations, we explicitly account for solvent (water) effects and related electrochemical, potential dependent oxygen or hydroxyl (co-)adsorption on the WC surfaces as determined by analysis of surface Pourbaix diagrams. Among the several low-index WC surfaces screened, the DFT simulations indicate that the W-terminated (-100) and (111) surfaces of WC show comparable exchange currents of 3.908 and 0.133 mA/cm 2 , respectively. The simulations also suggest that V or N doping can substantially increase the HER activity of some WCsurfaces to levels comparable to commercial Pt/C electrocatalysts, with current densities as large as 10.555, 1.730, and 0.636 mA/cm 2 for the V-doped W-terminated (001), V-doped (101), and N-doped (101) WC-surfaces, respectively. The improved HER activities are rationalized in terms of the d-band or p-band center, which are both shown to be related to the capability of tuning the hydrogen adsorption, thence HER performance. The calculated strong dependence of the HER activity on the presence of electrochemical adsorption of oxygen and hydroxyls reiterates the importance of modeling realistic electrochemical conditions for WC pristine or doped surfaces. We expect the DFT results presented to provide timely and original guidelines for further theoretical and experimental studies of HER activity on WC-related electrocatalysts.

Interface engineering of tungsten carbide/phosphide heterostructures anchored on N,P-codoped carbon for high-efficiency hydrogen evolution reaction

“…S18a), which is the most stable hydrogen adsorption configuration (denoted as WC (B-H) ). The calculated ΔG H* value of WC (B-H) was −0.81 eV, which is consistent with the value (−0.84 eV) reported by Yu et al [54]. Such a negative ΔG H* signified a large barrier for hydrogen desorption during HER owing to the strong W-H bond.…”

Which Is Better for Hydrogen Evolution on Metal@MoS2 Heterostructures from a Theoretical Perspective: Single Atom or Monolayer?

“…The SPD is a feasible approach to provide detailed coverages of *O and *OH on a catalyst at a given potential and pH in water, which has been successfully used to determine the realistic surfaces for hydrogen evolution and oxygen reduction. 34,37,38 The evidence of *O or *OH adsorbed on the surfaces of catalysts has been reported in previous experimental and theoretical work. 37,38,55−57 Here, the SPDs of 12 kinds of stable M S @ and M M @ in the last section are calculated and we mainly focus on adsorbates on the surfaces at U RHE = 0 V for the HER, as shown in Figures 3, 4, and S8.…”

“…In experiments, while considering water in the electrolyte, the realistic catalytic surfaces may be covered by adsorbates such as oxygen (*O) and hydroxyl (*OH), which will in turn affect the stabilities, real catalytic sites, and catalytic activities of the catalysts. The SPD is a feasible approach to provide detailed coverages of *O and *OH on a catalyst at a given potential and pH in water, which has been successfully used to determine the realistic surfaces for hydrogen evolution and oxygen reduction. ,, The evidence of *O or *OH adsorbed on the surfaces of catalysts has been reported in previous experimental and theoretical work. ,,− Here, the SPDs of 12 kinds of stable M S @ and M M @ in the last section are calculated and we mainly focus on adsorbates on the surfaces at U RHE = 0 V for the HER, as shown in Figures , , and S8.…”

“…Since oxygen and hydroxyl from liquid water may be adsorbed on the surfaces and thus to influence the structures and properties, the surface Pourbaix diagram (SPD) was constructed to obtain the structures with the lowest free energy at a given potential ( U SHE ) and pH, ,, and Cu M @ is taken as an example to describe the method for building SPDs, as shown in Figure S1.…”

“…The interaction between metal atoms and substrates influences not only the atomic structures but also the electronic structures and then the catalytic performance of the surfaces. − Besides, adsorbates such as oxygen (*O) and hydroxyl (*OH) species from the electrolytes may change the electronic structures of the active sites, which indeed impact the catalytic activities. − Thus, it is important to investigate the catalysts from the view of synergistic mechanism of the metal–support interaction and the water effects.…”