2D Bismuthene as a Functional Interlayer between BiVO ₄ and NiFeOOH for Enhanced Oxygen‐Evolution Photoanodes

Abstract BiVO 4 has attracted wide attention for oxygen‐evolution photoanodes in water‐splitting photoelectrochemical devices. However, its performance is hampered by electron‐hole recombination at surface states. Herein, partially oxidized two‐dimensional (2D) bismuthene is developed as an effective, stable, functional interlayer between BiVO 4 and the archetypal NiFeOOH co‐catalyst. Comprehensive (photo)electrochemical and surface photovoltage characterizations show that NiFeOOH can effectively increase the lifetime of photogenerated holes by passivating hole trap states of BiVO 4 ; however, it is limited in influencing electron trap states related to oxygen vacancies ( V O ). Loading bismuthene on BiVO 4 photoanodes increases the density of V O that are beneficial for the oxygen evolution reaction via the formation of oxy/hydroxyl‐based water oxidation intermediates at the surface. Moreover, bismuthene increases interfacial band bending and fills the V O ‐related electron traps, leading to more efficient charge extraction. With the synergistic interaction of bismuthene and NiFeOOH on BiVO 4 , this composite photoanode achieves a 5.8‐fold increase in photocurrent compared to bare BiVO 4 reaching a stable 3.4 (±0.2) mA cm –2 at a low bias of +0.8 V RHE or 4.7(±0.2) mA cm –2 at +1.23 V RHE . The use of 2D bismuthene as functional interlayer provides a new strategy to enhance the performance of photoanodes.