A Halted Photodeposition Technique Controls Co‐Catalyst Loading and Morphology on Organic Semiconductor Nanoparticles for Solar H ₂ Production

Abstract Solar hydrogen production with semiconductor photocatalyst particles typically requires co‐catalysts, but since co‐catalysts are often deposited in situ, the rate of their nucleation/growth and role in parasitic light absorption are not well controlled. Herein a halted photodeposition‐dialysis method is introduced that affords unprecedented control over platinum (Pt) co‐catalyst loading and morphology on bulk heterojunction organic semiconductor photocatalyst nanoparticles. Pt loading and surface distribution are controlled by tuning the initial Pt precursor concentration and photodeposition time followed by removal of unreacted Pt precursor via dialysis. Applying this method with typical Pt deposition conditions gives a max H ₂ evolution rate of 140 mmol h ⁻¹ g ⁻¹ (based on semiconductor mass) with only 15.2 wt.% Pt deposited and suggests an optimum loading of <20 wt.% Pt, above which parasitic light absorption decreases the H ₂ evolution rate. Moreover, a peak H ₂ evolution >30 mmol h ⁻¹ g ⁻¹ is achieved with a Pt loading of only 1.01 wt.% by tuning the deposition conditions to favor a more uniform Pt coverage with small clusters and single atoms over larger Pt NPs. This represents a performance more than eight times higher compared to typical Pt photodepositions (based on Pt) and gives critical insights into optimizing performance.