Surface stabilities of 3C–SiC and H₂O adsorption on the (110) surface

Abstract

First‐principles calculations and thermodynamics analyses were combined to study the surface stabilities of 3C–SiC and H2O adsorption on the (110) surface. The stoichiometric (110) surface was predicted to be generally the most stable. Only at the extremely C‐poor condition, the nonstoichiometric Si‐terminated (100) could become more energetically favored. The adsorption and dissociation of single H2O molecule on the 3C–SiC (110) were then comparatively investigated. Calculations show that H2O molecules prefer to partially dissociate into one hydroxyl OH and one H adsorbed at the top‐most Si and C sites, respectively, leading to the formation of a hydrogen network on the surface. The calculated equilibrium adsorption diagram further suggested that the 3C–SiC (110) surface can be only either completely clean or fully covered by the partially dissociated species of H2O, for a wide range of temperature and the partial potential of H2O.

Density Functional Theory Modeling of Photo-electrochemical Reactions on Semiconductors: H2 Evolution on 3C-SiC

“…However, a recent study by Peng et al derived the thermodynamic phase diagram for various SiC facets, which revealed that the stoichiometric (110) surface is the most stable under the range of operating conditions relevant to our study. They found that water readily dissociates on the clean SiC (110) surface (Figure a), such that surface hydroxyl and hydrogen adsorb on Si and C surface sites, respectively, forming a hydrogen-bonded network on the surface . Accordingly, we employed a SiC (110) surface slab model with a dissociated water layer on both sides of the SiC (110) slab (Figure b).…”

“…Earlier studies of HER on SiC employed SiC (111) and (100) surfaces that either were clean or covered with hydrogen . However, a recent study by Peng et al derived the thermodynamic phase diagram for various SiC facets, which revealed that the stoichiometric (110) surface is the most stable under the range of operating conditions relevant to our study. They found that water readily dissociates on the clean SiC (110) surface (Figure a), such that surface hydroxyl and hydrogen adsorb on Si and C surface sites, respectively, forming a hydrogen-bonded network on the surface .…”

“…The Volmer reaction is highly favorable and is exothermic even for negligible charge density on SiC (110) surface. Moreover, since the dissociative adsorption of water on SiC (110) is quite favorable, the spontaneous nature of the reaction of a hydronium cation with a bare C site is not surprising. Furthermore, on metal electrodes the variation in electrode potential changes the hydrogen coverage because water dissociation typically is not spontaneous .…”

“…Using the E BGC and E g , the position of the valence band maximum ( E VBM ) and conduction band minimum ( E CBM ) were calculated using eqs and : Because our calculation for band edge positions was performed with a neutral surface, the band edge positions correspond to positions at the pH of zero charge (pH zc ). We assume that pH zc = 7 for the SiC (110) surface in this work because there is an even coverage of protons and hydroxides predicted under neutral conditions, , and in Section we test the sensitivity of our results with respect to this assumption. We utilized the Nernst relation, as formulated in eqs and , to compensate for the shifts in band edge positions caused by the difference between the electrolyte pH and the pH zc .…”

“…They found that water readily dissociates on the clean SiC (110) surface (Figure 1a), such that surface hydroxyl and hydrogen adsorb on Si and C surface sites, respectively, forming a hydrogen-bonded network on the surface. 48 Accordingly, we employed a SiC (110) surface slab model with a dissociated water layer on both sides of the SiC (110) slab (Figure 1b). This arrangement also saturates all dangling bonds on the surface, so there are no defect states present in the semiconductor bandgap.…”