An ideal direct air capture process using solvents must include means to release captured CO₂ in parallel to solvent regeneration in an energy efficient way. A potential solution is to use light-driven solution chemistry. Herein a metastable-state photoacid can alter the solution pH to convert captured CO₂ in the form of bicarbonate ions to CO₂ under ambient conditions.

Abstract

The intensive energy demands associated with solvent regeneration and CO₂ release in current direct air capture (DAC) technologies makes their deployment at the massive scales (GtCO₂/year) required to positively impact the climate economically unfeasible. This challenge underscores the critical need to develop new DAC processes with significantly reduced energy costs. Recently, we developed a new approach to photochemically drive efficient release of CO₂ through an intermolecular proton transfer reaction by exploiting the unique properties of an indazole metastable-state photoacid (mPAH), opening a new avenue towards energy efficient on-demand CO₂ release and solvent regeneration using abundant solar energy instead of heat. In this Concept Article, we will describe the principle of our photochemically-driven CO₂ release approach for solvent-based DAC systems, discuss the essential prerequisites and conditions to realize this cyclable CO₂ release chemistry under ambient conditions. We outline the key findings of our approach, discuss the latest developments from other research laboratories, detail approaches used to monitor DAC systems in situ, and highlight experimental procedures for validating its feasibility. We conclude with a summary and outlook into the immediate challenges that must be addressed in order to fully exploit this novel photochemically-driven approach to DAC solvent regeneration.