Improved catalytic activity of non-metallic elements doped two-dimensional Hittorf's violet phosphorene for the hydrogen evolution reaction: A DFT study

The search for high-efficiency and low-cost metal-free catalysts for the hydrogen evolution reaction (HER) is vital to promote the recycling of natural materials and sustainable development. With the aid of density functional theory, an evaluation of a series of non-metallic elements B-, C-, N-, O-, S-, and Si-doped Hittorf's violet phosphorene (HP) as HER catalysts are reported. Our results demonstrate that the incorporation of these non-metallic dopants can effectively improve the HER performance for the HP, implying that the doping can indeed break the inertia of the HP basal plane and enhance the interaction between the H atom and active sites. The improved HER activities are ascribed to suitable hydrogen adsorption abilities which are well correlated with the p_z-band center and charge transfer of the dopant. According to calculated exchange current density i₀ and pH-dependent H adsorption ΔG_H∗, in an acidic environment, seven doped systems own high i₀ (>0.1 mA/cm²) and the N/Si-codoping (configuration I, site N) has the best HER activity with 1.520 mA/cm². Especially, combined with the high HER activity and experimental feasibility, the O-doped HP at site 2 is the most promising candidate as the electrocatalyst for HER. This work would pave the way for designing high-performance tunable metal-free catalysts for HER and also shed light on the catalytic application of HP-based materials.