Electron Transfer via Unoccupied e g Orbitals at Photoelectrochemical Interfaces

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Abstract
Unraveling electron transfer (ET) mechanisms at photoelectrochemical (PEC) interfaces is crucial for advancing device efficiency. Contrary to the established paradigm of redox‐mediated ET, we report a nonredox mechanism operating at photoelectrode/cocatalyst/electrolyte interfaces. This mechanism utilizes unoccupied orbitals within the cocatalyst's active centers to enable direct, conductor‐like ET without valence change during catalysis. Specifically, using a Ni(OH) 2 ‐modified Fe 2 O 3 photoanode, we demonstrate that applied photovoltage transforms Ni(OH) 2 into NiOOH, generating Ni 3+ active sites ( t 2g 6 e g 1 ) with an unoccupied e g orbital. Crucially, this transformation induces a substantial energy level downshift of these sites (from −4.95 to −7.40 eV vs. vacuum), definitively excluding redox mediation under constant photovoltage. Within these Ni 3+ sites, the unoccupied e g orbital serves as the direct conduit for ET without valence variation. This non‐redox, unoccupied orbital‐mediated mechanism provides a rational explanation for electron transfer at PEC interfaces and serves as a fundamental descriptor to guide the rational design of efficient active centers in PEC devices.
Funding Information
  • National Natural Science Foundation of China (52272217)
  • National Natural Science Foundation of China (51872135)
  • National Natural Science Foundation of China (51572121)
  • National Natural Science Foundation of China (21633004)

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