Heterogeneous catalysis relies on advanced, tunable materials offering structurally defined active sites and large accessible surface areas. Among the various material types, two-dimensional nanomaterials with high aspect ratios feature a high fraction of exposed atoms and thus efficient atom utilization. After more than a decade since the first report of MXene synthesis, these two-dimensional transition-metal carbides and nitrides, composed of alternating one-atom-thick metal and carbide/nitrid