Floating Carbon Nitride Composites for Practical Solar Reforming of Pre-treated Wastes to Hydrogen Gas

Photoreforming (PR) is a promising green-energy technology that can use sunlight to mitigate biomass and plastic waste while producing hydrogen gas at ambient pressure and temperature. However, practical challenges including photocatalyst lifetime, recyclability, and low production rates in turbid waste suspensions limit PR’s industrial potential. By immobilising PR catalyst materials (carbon nitride/platinum; CNx|Pt and carbon nitride/nickel phosphide; CNx|Ni2P) on hollow glass microspheres, which act as floating supports enabling practical composite recycling, such limitations can be overcome. Substrates derived from plastic and biomass, including poly(ethylene terephthalate) (PET) and cellulose, are reformed by floating PR composites, which are reused for up to 10 consecutive cycles under realistic, vertical simulated solar irradiation (AM1.5G), reaching activities of 921 ± 166 µmolH2 m−2 h−1 on pre-treated PET. Floating PR composites are also advantageous in realistic waste where turbidity prevents light absorption by non-floating catalyst powders, achieving 503.2 ± 1.9 µmolH2 m−2 h−1 using floating CNx versus non-detectable H2 production with non-floating CNx. Low Pt loadings (0.033 ± 0.0013 % m/m) demonstrate consistent performance and recyclability, allowing efficient use of precious metals for PR hydrogen production at the largest areal scale (217 cm2) reported to date, taking an important step toward practical PR implementation.