Heterogeneous single-cluster catalysts (Ni4, Fe4) supported on 2D materials (ZnO monolayer, graphene and borophene) for efficient hydrogen evolution reaction

Catalysts based on non-noble and cost-effective metals are crucial for the hydrogen evolution reaction (HER) to obtain viable renewable energy in the form of hydrogen. ZnO monolayer (ZnO-m), graphene and borophene are 2D materials that have attracted much interest due to their intriguing honeycomb-like structures with various electronic properties (semiconducting, semimetallic and metallic). In this work, we employ density functional theory to systematically investigate and compare the HER activities of the above three 2D materials with Ni and Fe clusters adsorbed on top. Our results indicate that all model composites exhibit significantly enhanced catalytic activity toward HER. The Gibbs free energies of hydrogen adsorption (ΔG_H) of Fe cluster@graphene and Fe cluster@ZnO-m were found to be 0.053 and 0.011 eV, respectively, which are close to the ideal value, suggesting that the catalytic activity is better than that of platinum. Water dissociation occurs for all studied composites with energy barriers close to zero. In addition, Fe cluster@borophene exhibited strong acidic HER activity with the widest pH range, and Ni cluster@graphene and Ni cluster@borophene showed excellent HER activity with the widest pH range and acid-alkali resistance. These insights provide important strategies for designing low-cost water-splitting catalysts with high HER activity.