A descriptor for the design of 2D MXene hydrogen evolution reaction electrocatalysts

Abstract

The two-dimensional metal carbide semiconductor, Ti₂CO₂, is recognized as having considerable potential as a cost-effective basal plane electrocatalyst for the hydrogen evolution reaction (HER). However, challenges in terms of both catalytic activity and conductivity still remain. The HER catalytic activity of 2D Ti₂CO₂ can be tuned by Ti vacancies (V_Ti) anchoring single transition metal (STM) atoms. Herein, 27 different Ti₂CO₂-STMs (STM = 3d, 4d, 5d metals) and 81 HER catalytic active sites are screened by computational methods. The results indicate that STM doping not only optimizes the Gibbs free energy of hydrogen adsorption (ΔG_H), but also converts semiconductors into conductors. Several new and promising nonprecious HER electrocatalysts are identified, including Ti₂CO₂–W. The excellent catalytic activity (ΔG_H ≈ 0 eV), conductivity, and stability make it an ideal potential catalyst for the HER. The p–d orbital hybridization between STM and C and O atoms leads to a rearrangement of electrons near the Fermi level, which plays a crucial mechanism in regulating HER activity. We apply machine learning methods to build a physical descriptor to uncover trends in Ti₂CO₂-STM HER catalysis, and the descriptor can also be applied to Zr₂CO₂-STM and Ta₂CO₂-STM HER catalysis. This work provides a promising strategy for improving the HER performance of 2D Ti₂CO₂, and more importantly, develops simple descriptors to efficiently search for highly active HER catalysts.