Boosting Oxygen Evolution Kinetics by Mn–N–C Motifs with Tunable Spin State for Highly Efficient Solar‐Driven Water Splitting

Abstract Solar‐driven water splitting is in urgent need for sustainable energy research, for which accelerating oxygen evolution kinetics along with charge migration is the key issue. Herein, Mn 3+ within π‐conjugated carbon nitride (C 3 N 4 ) in form of Mn–N–C motifs is coordinated. The spin state ( e g orbital filling) of Mn centers is regulated by controlling the bond strength of Mn–N. It is demonstrated that Mn serves as intrinsic oxygen evolution reaction (OER) site and the kinetics is dependent on its spin state with an optimized e g occupancy of ≈0.95. Specifically, the governing role of e g occupancy originates from the varied binding strength between Mn and OER intermediates. Benefiting from the rapid spin state‐mediated OER kinetics, as well as extended optical absorption (to 600 nm) and accelerated charge separation by intercalated metal‐to‐ligand state, Mn–C 3 N 4 stoichiometrically splits pure water with H 2 production rate up to 695.1 µmol g −1 h −1 under simulated sunlight irradiation (AM1.5), and achieves an apparent quantum efficiency of 4.0% at 420 nm, superior to most solid‐state based photocatalysts to date. This work for the first time correlates photocatalytic redox kinetics with the spin state of active sites, and suggests a nexus between photocatalysis and spin theory.