Decoupling Internal‐External Junction Competition in p‐InGaN/n‐BiVO 4 Photocathodes on Silicon Wafers for Efficient Neutral PEC Water Splitting

ABSTRACT Photoelectrochemical (PEC) water splitting offers a sustainable route for solar‐to‐hydrogen conversion, with neutral conditions being particularly attractive due to their safety, mild reaction environments, and material compatibility. However, achieving high PEC efficiency under neutral conditions remains challenging. Here, we demonstrate a wafer‐scale p–n heterojunction photocathode comprising p‐type InGaN nanowires integrated with n‐type BiVO 4 , achieving highly efficient water splitting without any cocatalysts under neutral conditions. By engineering a gradient oxygen vacancy distribution within BiVO 4 , the internal semiconductor junction field and the external semiconductor/electrolyte field are spatially decoupled, thereby unlocking the intrinsic potential of the heterojunction photoelectrode. The optimized Gradient Ov‐BiVO 4 /InGaN photocathode achieves a photocurrent density of 5.68 mA cm − 2 at 0 V RHE , corresponding to an 87 % improvement over conventional Ov‐BiVO 4 /InGaN, and an onset potential of 1.21 V RHE , the highest reported under neutral conditions. Remarkably, it retains 93.4 % of its initial activity after 100 h of continuous operation and enables unbiased solar water splitting when coupled with a CoRuOx/n‐InGaN photoanode. This work establishes spatially decoupled heterojunction engineering as a generalizable strategy for designing highly efficient, durable, and cost‐effective catalyst‐free PEC photoelectrodes.