Optimizing hydrogen evolution reaction: Computational screening of single metal atom impurities in 2D MXene Nb₄C₃O₂

MXenes, a novel class of 2D transition metal carbides and nitrides, have recently emerged as a promising candidate in the quest for efficient catalysts for the hydrogen evolution reaction. To enhance the performance of 2D MXenes with modest or poor catalytic efficiency, a particularly prosperous strategy involves doping with transition and noble metal atoms. Taking the Nb₄C₃O₂ monolayer as a model, we explore substitutional metallic impurities, which serve as single-atom catalysts embedded within the Nb₄C₃O₂ surface. Our findings demonstrate the ability to finely tune the atomic H binding energy within a 0.6 eV range, showing the potential for precise control in catalytic applications. Across different transition and noble metals, the single atoms integrated into Nb₄C₃O₂ effectively adjust the free energy of H adsorption at nearby O atoms, achieving values comparable to or superior to Pt catalysts. A comprehensive examination of the electronic properties around the impurities reveals a correlation between changes in local reactivity and charge transfer to neighboring O atoms, where H atoms bind.