Boosting CO₂ solar-to-fuel efficiency

Using solar energy to convert carbon dioxide (CO₂) into synthetic fuel as a renewable energy resource is seen as a promising technology for mitigating the effects of the greenhouse gas.

Yuan et al. focus on recent advancements in this technology, known as photocatalytic CO₂ reduction, and highlight the most important factors to consider in addressing the biggest hurdles faced by the materials, including low light absorption, undesired charge combination, and a high CO₂ activation barrier that affects material surface reactions.

The authors identified the particle size of the thin films used to make the photoelectrochemical cells (PECs) as a critical factor. Notable research to increase light absorption has been with quantum dots, such as cadmium sulfide dots on which nickel terpyridine complexes are anchored, as well as with nanorods and nanoparticles of various materials.

For undesired charge combination, the authors pointed to ultrathin structures as a solution for reducing recombination. For example, adding an ultrathin carbon layer on tin disulfide increases charge separation and improves carrier lifetime.

To enhance the PEC efficiency, additives that increase positive charges, or metals, can be incorporated into the material. For example, cation doping narrows the bandgap with enhanced light absorption at long wavelengths and also improves charge separation and migration. Similarly, adding platinum nanoparticles to titanium dioxide films increases charge separation and enhances methane formation.

Regarding future research, the authors highlighted one main challenge that remains largely unaddressed — the rapid release of hydrogen when water as a byproduct begins to emerge. This hydrogen evolution reaction competes with CO₂ reduction to consume the active photoelectrons, causing poor efficiency and low selectivity.

Source: “Recent advances on visible-light-driven CO₂ reduction: strategies for boosting solar energy transformation,” by Jin Yuan, Yaping Du, and Hongbo Zhang, APL Materials (2020). The article can be accessed at https://doi.org/10.1063/5.0003215 .