Nickel–Iron Clusters on Bismuth Vanadate for Efficient Photoelectrochemical Water Splitting

ABSTRACT In this study, an ultrathin catalytic layer of nickel–iron (NiFe) nanoclusters is deposited onto an electrodeposited bismuth vanadate (BiVO 4 ) photoanode via pulsed laser ablation. The nanoclusters are synthesized from bimetallic Ni x Fe 1‐x (x = 0.25, 0.5, 0.75) alloy targets, resulting in cluster loadings between 0.55 and 1.74 µg cm −2 , equivalent to 3–9 atomic monolayers. By varying the atomic Ni:Fe ratio (25:75, 50:50, and 75:25), both photoelectrochemical (PEC) activity and stability are optimized while minimizing total catalyst loading on pristine BiVO 4 . The BiVO 4 photoanode with 6 atomic monolayer equivalents of Ni 0.75 Fe 0.25 (1.16 µg cm −2 ) delivers a photocurrent density of 3.1 mA cm −2 at 1.23 V versus RHE, a 2.05‐fold improvement over pristine BiVO 4 (1.51 mA cm −2 ), along with a sixfold increase in applied bias photon‐to‐current efficiency (ABPE) reaching 1%. To assess robustness, both pristine and 6‐Ni 0.75 Fe 0.25 BiVO 4 are evaluated under variable electrolyte temperature (∼6°C–≥60°C) and concentrated illumination (1–6 suns). Under all tested conditions, the Ni 0.75 Fe 0.25 BiVO 4 exhibits improved PEC performance and operational stability. These findings highlight the effectiveness of ultrathin (<1.7 µg cm −2 ) NiFe nanoclusters in significantly enhancing PEC performance and operational stability of BiVO 4 photoanodes across a range of challenging operational conditions.