Highly active oxygen‐evolving Mn3+ centers are incorporated into photoresponsive carbon nitride (C3N4) as Mn–N–C motif for solar‐driven water splitting. For the first time, the spin state of Mn is tuned to boost oxygen evolution with an optimized e g ≈0.95 occupancy. The extended optical absorption, accelerated charge migration, and spin‐mediated fast redox kinetics endow Mn–C3N4 with superior activity.
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, Mn3+ within π‐conjugated carbon nitride (C3N4) 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–C3N4 stoichiometrically splits pure water with H2 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.