Switching Water Oxidation Pathway via NiFe Dual-Atoms on BiVO₄: An *O─O* Coupling Mechanism Route to Bypass Adsorbate Evolution Mechanism Limitations.

Abstract

Dual-atom catalysts (DACs) with heterogeneous active sites represent an emerging frontier in photoelectrochemical (PEC) water splitting. However, the corresponding reaction mechanism on DACs is still unclear. Herein, we present a photoanode architecture comprising NiFe dual atoms (DAs) anchored on a TiO_x-coated BiVO₄ photoanode (NiFe DAs/TiO_x/BiVO₄), which delivers an impressive photocurrent density of 6.13 mA cm^-2 at 1.23 V_RHE, sustained stability exceeding 150 h, and an applied bias photon-to-current efficiency of 2.2%. Our investigation reveals a dual functionality of the NiFe DAs which serve as an efficient oxygen evolution cocatalyst and enhance charge separation-an aspect largely overlooked in previous studies. Through in situ spectroscopic investigations combined with density functional theory calculations, we elucidate that the NiFe DAs/TiO_x/BiVO₄ enables a mechanistic shift from the conventional adsorbate evolution mechanism (AEM) observed in single atom-modified-TiO_x/BiVO₄ to an *O─O* coupling mechanism (OCM). Specifically, this OCM pathway bypasses the formation of *OOH and produces the *O─O* bridging species, broking the *OOH/*OH scaling limitation in the AEM pathway. This work uncovers PEC water oxidation mechanism at the atomic level, establishing a foundational framework for designing high-performance photoelectrodes through precise atomic-scale engineering.