Efficient Hole Extraction and *OH Alleviation by Pd Nanoparticles on GaN Nanowires in Seawater for Solar-Driven H2 and H2O2 Generation

Abstract

Photocatalytic seawater splitting into hydrogen and hydrogen peroxide (2H₂O→H₂↑ + H₂O₂) 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 H₂ and H₂O₂ 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 H₂O→ H₂ + H₂O₂ 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 H₂O₂ over a duration of 2 hours under a light intensity of 3 W/cm² 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 1.42×10⁷ moles H₂ per mole of Pd. The outdoor test further suggests the great potential for solar-driven seawater splitting into green fuels and chemicals.