Enhanced photocatalytic hydrogen evolution and stability from highly de-mixed all-polymer bulk heterojunction nanoparticles

Organic bulk heterojunction photocatalysts show great potential for solar fuel production, yet controlling their nanoscale morphology remains a key challenge. Here, we show that allpolymer blends undergo pronounced de-mixing during nanoparticle formation, producing larger length-scale phase segregation as pseudo-Janus structures. Such morphologies enhance both photocatalytic activity and photostability by suppressing bulk and surface non-geminate charge recombination and providing continuous charge percolation pathways to Pt cocatalysts. Optimised all-polymer binary nanoparticles achieve hydrogen evolution rates of over 25 µmol h⁻¹ cm⁻² and when fabricated as a ternary all-polymer particle, exhibit external quantum efficiencies of over 12% across the visible and into the near IR spectrum (16.4 % at 850 nm), achieving unprecedented mass normalised hydrogen evolution rates of over 1 mol g-1 h-1. These findings underscore the critical role of phase-segregation length scale in achieving efficient and stable organic photocatalysts.