The α-WC(0001) Surface as a Hydrogen Sponge: A First Principle Study of H₂ Dissociation and Formation of Low and High Coverages

Tungsten carbide (WC) displays a Pt-like behavior in catalysis, applied in hydrogenation processes. Numerous theoretical studies have modeled the behavior and use of adsorbed hydrogen without obtaining a general picture, missing basic links between H₂ dissociation and generation of high surface coverage (Θ_H>0.5 ML). Here, the capability of C- and W-terminations of the α-WC(0001) surface is analyzed to dissociate several H₂ molecules to produce coverages, Θ_H, ranging from low to very high values (0.13<Θ_H<2.00 ML). Density functional theory and an ab initio atomistic thermodynamic were used to achieve the conditions for H₂ dissociation. The WC−C surface has higher capacity to dissociate H₂ molecules than WC−W. However, both surfaces can reach full surface coverage, Θ_H=1 ML, at mild ambient conditions, T=300 K and P=1 atm, and even up to 500 K at low and high pressures. The H-adatoms on WC−W are more labile than on WC−C. The binding of adsorbates is hindered at high Θ_H, implying a need to modulate Θ_H according to the application. The results give the basis to understand the capabilities of WC-based catalysts in hydrogenation-related reactions, with the advantage of WC being a hydrogen reservoir at mild practical catalytic conditions.