Role of Graphene on Ni/NiO for the Hydrogen Evolution Reaction

The hydrogen evolution reaction (HER) in alkaline electrolytes is an effective and environmentally friendly strategy for producing H2; however, challenges relating to catalyst efficiency and longevity remain. Herein, density functional theory (DFT) is used to help explain why a protective graphitic layer on Ni0/NiOx nanoparticles helps prevent surface oxidation at ambient and anodic conditions and reduction (NiOx-* Ni0) at the cathodic potential. We find that the work of adhesion of the graphitic layer to nickel-terminated surfaces is 2-3 times stronger than that to oxygen-or hydroxylated-terminated surfaces. Furthermore, we determined the additional energy required to remove a surface group/ atom (O, OH and Ni) when protected by a graphitic layer. Our findings lead us to conclude that the graphitic layer will limit oxidation, help minimize the reduction of NiOx and favor the formation of Ni-rich surfaces. These findings provide a plausible explanation of how an ideal Ni0/NiOx ratio is maintained during HER, which is crucial for enhanced device performance and stability.