Efficient Hole Extraction and *OH Alleviation by Pd Nanoparticles on GaN Nanowires in Seawater for Solar‐Driven H ₂ and H ₂ O ₂ Generation

Abstract Photocatalytic seawater splitting into hydrogen and hydrogen peroxide (2H 2 O→H 2 ↑ + H 2 O 2 ) offers an ultimate solution for simultaneously generating green fuel and value‐added chemicals by the two most earth‐abundant resources i.e., solar energy and natural seawater. In this study, Pd nanoparticles are integrated with one‐dimensional gallium nitride nanowires (Pd NPs/GaN NWs) on a silicon wafer to produce H 2 and H 2 O 2 from seawater powered by sunlight. In situ spectroscopic characterizations combined with computational investigations reveal that in this nanohybrid, Pd NPs function as an efficient hole extractor and *OH alleviator during photocatalysis. Meanwhile, the chloride ions in seawater facilitate the H 2 O→ H 2 + H 2 O 2 conversion by improving the charge dynamics and lowering the energy barrier of the key *OH self‐coupling step over Pd sites in the catalytic system. As a result, the photocatalyst delivers an appreciable hydrogen production rate of 2.5 mmol⋅cm −2 ⋅h −1 with a light‐to‐hydrogen (LTH) efficiency of 4.38 % in natural seawater under concentrated light irradiation of 3 W⋅cm −2 without sacrificial agents and external energies. Notably, the water oxidation reaction produces 300 μmol/L of valuable H 2 O 2 over a duration of 2 hours under a light intensity of 3 W/cm 2 using a 20 mL water sample, achieving a light‐to‐chemical efficiency of 0.53 %. The photocatalyst shows excellent stability for up to 60 hours with a considerable turnover number of 1.42×10 7 moles H 2 per mole of Pd. The outdoor test further suggests the great potential for solar‐driven seawater splitting into green fuels and chemicals.