New directions for the photocatalytic reduction of CO₂: Supramolecular, scCO₂ or biphasic ionic liquid-ScCO₂ systems

There is an urgent need for the discovery of carbon-neutral sources of energy to avoid the consequences of global warming caused by ever-increasing atmospheric CO₂ levels. An attractive possibility is to use CO ₂ captured from industrial emissions as a feedstock for the production of useful fuels and precursors such as carbon monoxide and methanol. An active field of research to achieve this goal is the development of catalysts capable of harnessing solar energy for use in artificial photosynthetic processes for CO₂ reduction. Transition-metal complexes are excellent candidates, and it has already been shown that they can be used to reduce CO₂ with high quantum efficiency. However, they generally suffer from poor visible light absorption, short catalyst lifetimes, and poor reaction rates. In this Perspective, the field of photocatalytic CO₂ reduction is introduced, and recent developments that seek to improve the efficiency of such catalytic processes are highlighted, especially CO₂ reduction with supramolecules and molecular systems in supercritical CO₂ (scCO₂) or biphasic ionic liquid-ScCO₂ mixtures.