MXenes have exhibited great potential as cost-effective electrocatalysts for hydrogen evolution reaction (HER). However, insight into the origin of activity is still missing. Herein, on the basis of a systematical investigation of the HER performance of 20 MXenes (M₂NO₂ and M₂CO₂, M = Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W), a Fermi-abundance model is proposed to understand variation of the activity in different MXenes. It is found that the occupied p electronic states of surface O atoms play a decisive role in the HER activity of MXenes. More importantly, Ti₂NO₂ and Nb₂NO₂ are found to be promising HER electrocatalysts with the free energy for hydrogen adsorption close to zero. This work not only provides possible catalysts for HER, the developed Fermi-abundance model but also is applicable to other two-dimensional materials and may serve as a simple descriptor of the intrinsic HER activity.

MXenes 作为具有成本效益的析氢反应 (HER) 电催化剂显示出巨大的潜力。然而，仍然缺乏对活动起源的洞察力。在此，在系统研究20种MXenes（M ₂ NO ₂和M ₂ CO ₂，​​M = Sc、Ti、V、Cr、Zr、Nb、Mo、Hf、Ta和W）的HER性能的基础上，提出了费米丰度模型来理解不同 MXenes 中活性的变化。发现表面O原子的占据p电子态对MXenes的HER活性起着决定性作用。更重要的是，Ti ₂ NO ₂和Nb ₂ NO ₂被发现是有前途的 HER 电催化剂，氢吸附的自由能接近于零。这项工作不仅为 HER、开发的费米丰度模型提供了可能的催化剂，而且还适用于其他二维材料，并可作为内在 HER 活性的简单描述符。