(405f) Evaluating the Accuracy of Volcano Plots for Hydrogen Evolution on Mxenes

Hydrogen (H₂) is a promising clean energy carrier due to its high energy density and zero carbon emissions when used as fuel. The electrocatalytic hydrogen evolution reaction (HER), a key half-reaction in water electrolysis, offers a promising and sustainable route for large-scale H₂ production. However, improved efficiency and/or cost are needed to improve the viability of electrolytic H₂. Layered two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, known as MXenes (M_n+1X_nT_x: M = early transition metal, n=1-3, X = C or/and N, and T_x = surface functional groups), have emerged as potential HER catalysts due to their tunable electronic structures and surface chemistries. Their relatively well-defined structure makes them an excellent platform for design, and for testing the accuracy of catalytic design principles like the volcano plot.

In this study, we conduct a systematic DFT-based screening of experimentally synthesized MXenes, M_n+1X_nT_x (M = Ti, V, Nb, Cr, Mo; X = C and/or N; T_x = O) to evaluate the accuracy of the well-known volcano plot in predicting their experimental overpotential. Thus, we plotted the experimental overpotential as a function of the hydrogen adsorption free energy (ΔG_H), a widely accepted descriptor where values near zero are thought to indicate optimal catalytic performance. To capture the coverage-dependent behaviour of hydrogen adsorption on MXenes, we incrementally increase hydrogen coverage and evaluate ΔG_H at each step. We find that the theoretical volcano plot is quantitatively inaccurate in predicting experimental overpotentials, but the volcano plot is qualitatively useful for a rough initial screening. Our findings provide guidance for the rational design of MXene-base electrocatalysts with minimal overpotential and improved hydrogen production efficiency.