Solar fuels and electrofuels

Production of fuels from water and CO₂ using renewable energy could provide energy storage solutions and reduce our dependence on fossil fuels. This month, we showcase recent efforts to advance understanding in this area.

A wealth of candidates are being investigated to improve the catalysts found in acidic and alkaline electrolysers. However, attention should be focused on developing stable water oxidation catalysts with improved intrinsic activity — not only increased geometric activity — alongside best practice for data collection.

Solar-driven photocatalytic water splitting provides a clean pathway for production of hydrogen fuel. This Review examines both amorphous and crystalline polymeric materials for water splitting, exploring polymer design strategies, theoretical understanding and challenges for the field.

Electrocatalytic reduction of CO₂ to fuels could be used as an approach to store renewable energy in the form of chemical energy. Here, Birdja et al. review current understanding of electrocatalytic systems and reaction pathways for these conversions.

While the two individual half-reactions involved in visible-light-driven water splitting are well studied, producing H₂ and O₂ simultaneously on a single particle remains challenging. Here, the authors achieve this by decorating CdS nanorods with both Pt nanoparticles and molecular Ru complexes to catalyse the evolution of H₂ and O₂, respectively.

Semi-artificial photosynthetic systems combine natural and synthetic features to overcome limitations of each approach to produce solar fuels. Sokol et al. integrate a dye-sensitized TiO₂ photoanode with the natural machineries, photosystem II and hydrogenase, to split water without additional applied bias.

For photo-electrochemical hydrogen production to become viable on a large scale, not only efficiency but also power density must be optimized. Here, the authors explore the impact of thermal integration on photo-electrochemical devices driven by concentrated solar irradiation and design one that operates with high efficiency and power density output.

Conventionally, the two half reactions involved in water electrolysis occur simultaneously, presenting materials and process challenges. Here, the authors decouple these to split water efficiently in two steps: electrochemical hydrogen evolution, followed by spontaneous oxygen evolution at elevated temperature.

Electrochemical CO₂ reduction to fuels and chemicals is typically accompanied by oxygen evolution as the anodic half reaction. Here, Verma et al. identify glycerol oxidation as a viable alternative half reaction, reducing cradle-to-gate CO₂ emissions and improving the economics of CO₂ conversion.

Liquid products from electrocatalytic CO₂ reduction are often mixed with additional solutes in the electrolyte, meaning that downstream separation is required. Here, the authors design cells that use solid electrolytes to generate flows of CO₂-derived liquid fuels with high concentrations that are free of extraneous ions.