Enhanced catalytic activity of SO-incorporated graphene for the hydrogen evolution reaction

Sulfur defects have been used to enhance the catalytic activity of carbon-based nanostructures in the hydrogen evolution reaction (HER). This is accomplished by increase in the hydrogen adsorption ability due to the large size of sulfur atoms, which increases the sp 3 character of graphene carbons. However, the effect of sulfur oxidation on the HER activity has not yet been discussed, even though sulfur can easily be oxidized to sulfur oxide (SO x ) in acidic environments, which may decrease the metallicity of graphene by opening the bandgap. Herein, we systematically investigate the HER activity of SO x -incorporated graphene, SO x @G ( x = 2, 3 or 4), based on electronic, thermodynamic and kinetic viewpoints. Our results reveal that SO 3 @G on the basal plane has superior HER catalytic activity due to its metallic nature and ability to stabilize adsorbed hydrogen (H*) which results from electrostatic interactions between SO 3 and H* in an intermediate state. As a thermodynamic descriptor of the HER activity, the hydrogen binding Gibbs free energy (Δ G Volmer H* ) is calculated to be −0.04 eV for SO 3 @G in the Volmer step. In addition, the activation energies in both the Volmer and Tafel steps (Δ E Volmer a and Δ E Tafel a , respectively) of SO 3 @G show the lowest energy barriers among SO x @G, taking values of 0.005 eV and 0.14 eV, respectively. Thus, these values can be used as kinetic descriptors and are close to those of conventional Pt catalysts. SO x incorporation enhances the catalytic activity of carbon-based nanostructures in the hydrogen evolution reaction (HER).