A Theoretical Inquest of Atomically Injected Ni-Atom over Graphene and Analogous Substrates for Hydrogen Evolution Reaction

A rational catalyst for electrocatalytic hydrogen evolution reaction (HER) is a long-standing challenge that researchers are confronted with. In view of this, tiny particles of transition metals (TMs) spread over a substrate acting as an active site for the reaction, scientifically known as single-atom catalysts is seen as an efficacious way for designing an efficient catalyst. Herein, we comprehensively investigated catalytic activity of Ni-atoms spread over various kinds of two-dimensional (2D) substrates like graphene, AlC, AlN, h-BN, BeO, and MgO (Ni@2D) towards HER using density functional theory calculations. All the considered 2D substrates have various inequivalent anchoring sites like top, hollow, bridge, and vacancy sites for Ni-atoms. So, there are total 34 anchoring sites, and we computed binding energy (E\(_b\)) of Ni-atom over all the sites. Having large number of configurations, we first applied a screener on stability of Ni@2D and only considered those configurations for which the E\(_b\) value is <\(-\)3.00 eV for further calculations. Out of 34, 17 configurations were falling in this range. Further, we computed the differential Gibbs free energy of H-adsorption (\(\Delta\)G\(_H\)) and generated volcano plot between \(\Delta\)G\(_H\) and exchange current density (\(i_0\)) as a prime indicators of HER activity. Then, we screened these configurations based on \(\Delta\)G\(_H\) values that \(|\Delta\)G\(_H|\) \(\le\) to 0.5 eV, and out of 17, 10 systems were falling in this region. At last, we examined complete reaction profile of HER via Volmer-Heyrovsky (VH) and Volmer-Tafel (VT) mechanisms over the remaining 10 configurations, and the lowest activation energy for HER are 0.12 eV and 0.21 eV for Ni@AlN and 0.28 eV and 0.36 eV for Ni@h-BN via VT and VH mechanism, respectively. Our findings show Ni@AlN and Ni@h-BN could be a non-noble TM candidate for eco-operational HER catalyst.