▎ 摘　　要

The poor oxygen evolution reaction (OER) activity of two-dimensional (2D) transition metal carbides (MXenes) is a major obstacle to their application in high-performance water splitting and fuel cells due to the high energy barriers for the absorption of intermediates. Here, we demonstrate that the lattice oxygen of MnXn-1O2 MXenes can be activated by 0D graphene quantum dots (GQDs), thereby activating the OER via the lattice-oxygen oxidation mechanism (LOM) instead of the conventional adsorbate evolving mechanism. The pH-dependent OER activity of MnXn-1O2@GQDs and O-18 isotope-labelling experiments with time-of-flight secondary-ion mass spectrometry (TOF-SIMS) provide the direct evidence of LOM. Interestingly, the activated lattice oxygen amount can be controlled by the GQDs. The as-prepared 0D/2D Ti3C2O2@GQDs heterostructure delivers a highly reduced overpotential of 390 mV (bare Ti3C2O2: 530 mV) at a benchmark current density of 10 mA cm(-2). Through optimizing the thickness and the additional conductive substrate, the overpotential at 10 mA cm(-2) decreases to 250 mV, while the Tafel slope is reduced to 39 mV dec(-1); these values indicate the as-prepared heterostructure is superior to the state-of-the-art MXene-based OER catalysts. This work provides a new strategy to enhance the OER activity of MnXn-1O2 and extends the application of LOM from perovskite to MXenes.