Cobalt metal organic framework (Co-MOF) derived CoSe2/C hybrid nanostructures for the electrochemical hydrogen evolution reaction supported by DFT studies

Abstract

Generation of molecular hydrogen by electrochemical water splitting is a promising approach, and its efficiency strictly depends on the electrocatalyst used. Therefore, it is an ongoing challenge to design materials having improved the electrocatalytic behaviour towards hydrogen evolution reaction. Here, using Co-MOF [Co₄(BTC)₃(BIm)₆] as starting precursor, graphitic carbon encapsulated CoSe₂ nanorods have been prepared through a single step selenization method. The carbon network in the CoSe₂/C hybrid nanostructure forms channels, facilitating the accessibility of the electrolyte ions and maximizing the utilization of catalytic active centers. This makes the hybrid to show higher electrochemical accessible surface area, lower charge transfer resistance, and improved catalytic durability towards the electrocatalytic hydrogen evolution reaction with respect to the non-noble metal (graphite rod) counter electrode. Specifically, it needs only 253 mV of overpotential to reach the benchmarked current density (10 mA cm⁻²) with a lower Tafel slope. Further, the experimental findings have been supported by the theoretical analysis of the structure and electronic properties of CoSe₂ and CoSe₂/C hybrid by density functional theory (DFT) simulations. The interaction between CoSe₂ and C is due to charge transfer from Co 3d orbital and Se 4p orbital of CoSe₂ to the 2p orbital of carbon. Also, populated electronic states near Fermi level for C doped CoSe₂ may infer towards increased conductivity of the material. Computed overpotentials for HER activities show a qualitative order of CoSe₂/C < CoSe₂, matching nicely with the experimental data. The synergic effect of increased conductivity, improved surface area, and superior electrocatalytic activity due to C doping is responsible for the superior HER catalytic performance.