Spatially Segregated Pt/Co Dual Single-Atoms on Janus MXene Synergistically Boost Electrocatalytic Overall Water Splitting

Spatial precision in the organization of active sites enables high-performance bifunctional electrocatalysts for overall water splitting. Herein, a stepwise defect-induced in situ intercalation strategy is developed to anchor Pt and Co single atoms on the two opposing facets of Ti₃C₂T_y MXene, respectively, realizing separate-sided functionalization of monolayer Ti₃C₂T_y with Pt/Co dual single atoms (Pt/Co DSA-Ti_3-xC₂T_y). The fabricated Janus Pt/Co DSA-Ti_3-xC₂T_y exhibits superior bifunctional electrocatalytic performance in an alkaline electrolyte, originating from the distinct roles of the two facets: Pt SAs on one side drive the HER (20.0 mV @ 10 mA cm^-2), whereas Co single atoms on the other side deliver the impressive OER performance (195.0 mV @ 10 mA cm^-2). The Janus electrocatalyst exhibits an ultralow overall water splitting overpotential of only 1.45 V to achieve 10 mA cm^-2. Additionally, as bifunctional electrodes in AEMWE, Pt/Co DSA-Ti_3-xC₂T_y demonstrates a low voltage of 1.81 V at 1.0 A cm^-2 with a 200 h stability. In situ/operando spectroscopy and DFT calculations unveil that Pt/Co DSAs synergistically induce charge redistribution on the MXene surface, thus optimizing the active-site electronic states and intermediate adsorption to lower the reaction energy barrier. Our strategy serves as a pathway for atomically precise control of MXene-supported single-atom sites toward selective electrocatalysis.