Lignocellulose is Earth's most abundant form of biomass and its valorisation to H 2 is a key objective for the generation of renewable fuels. Solar-driven photocatalytic reforming of lignocellulose to H 2 at ambient temperature offers a sustainable route towards this goal, but this reaction is currently limited to noble metal containing systems that operate with low activity under UV light. Here, we report the light-driven photoreforming of cellulose, hemicellulose and lignin to H 2 using semiconducting cadmium sulfide quantum dots in alkaline aqueous solution. We show that basic conditions cause these dots to become coated with oxide/hydroxide in situ, presenting a strategy to improve their photocatalytic performance. The system operates under visible light, is stable beyond 6 days and is even able to reform unprocessed lignocellulose, such as wood and paper, under solar irradiation at room temperature, presenting an inexpensive route to drive aqueous proton reduction to H 2 through waste biomass oxidation.

Photocatalytic conversion of CO into carbonaceous feedstock chemicals is a promising strategy to mitigate greenhouse gas emissions and simultaneously store solar energy in chemical form. Photocatalysts for this transformation are typically based on precious metals and operate in nonaqueous solvents to suppress competing H generation. In this work, we demonstrate selective visible-light-driven CO reduction in water using a synthetic photocatalyst system that is entirely free of precious metals. We present a series of self-assembled nickel terpyridine complexes as electrocatalysts for the reduction of CO to CO in organic media. Immobilization on CdS quantum dots allows these catalysts to be active in purely aqueous solution and photocatalytically reduce CO with >90% selectivity under UV-filtered simulated solar light irradiation (AM 1.5G, 100 mW cm, λ > 400 nm, pH 6.7, 25 °C). Correlation between catalyst immobilization efficiency and product selectivity shows that anchoring the molecular catalyst on the semiconductor surface is key in controlling the selectivity for CO reduction over H evolution in aqueous solution.

The development of synthetic systems for the conversion of solar energy into chemical fuels is a research goal that continues to attract growing interest owing to its potential to provide renewable and storable energy in the form of a 'solar fuel'. Dye-sensitised photocatalysis (DSP) with molecular catalysts is a relatively new approach to convert sunlight into a fuel such as H2 and is based on the self-assembly of a molecular dye and electrocatalyst on a semiconductor nanoparticle. DSP systems combine advantages of both homogenous and heterogeneous photocatalysis, with the molecular components providing an excellent platform for tuning activity and understanding performance at defined catalytic sites, whereas the semiconductor bridge ensures favourable multi-electron transfer kinetics between the dye and the fuel-forming electrocatalyst. In this tutorial review, strategies and challenges for the assembly of functional molecular DSP systems and experimental techniques for their evaluation are explained. Current understanding of the factors governing electron transfer across inorganic-molecular interfaces is described and future directions and challenges for this field are outlined.

Several application fields can benefit from solar-hydrogen technologies via specific short-term and long-term pathways.