Photochemically‐Driven CO₂ Release Using a Metastable‐State Photoacid for Energy Efficient Direct Air Capture

Abstract

One of the grand challenges underlying current direct air capture (DAC) technologies relates to the intensive energy cost for sorbent regeneration and CO2 release, making the massive scale (GtCO2/year) deployment required to have a positive impact on climate change economically unfeasible. This challenge underscores the critical need to develop new DAC processes with substantially reduced regeneration energies. Here, we report a photochemically‐driven approach for CO2 release by exploiting the unique properties of an indazole metastable‐state photoacid (mPAH). Our measurements on simulated and amino acid‐based DAC systems revealed the potential of mPAH to be used for CO2 release cycles by regulating pH changes and associated isomers driven by light. Upon irradiating with moderate intensity light, a ≈55 % and ≈68 % to ≈78 % conversion of total inorganic carbon to CO2 was found for the simulated and amino acid‐based DAC systems, respectively. Our results confirm the feasibility of on‐demand CO2 release under ambient conditions using light instead of heat, thereby providing an energy efficient pathway for the regeneration of DAC sorbents.

Unravelling photoisomerization dynamics in a metastable-state photoacid

“…Photoisomerization represents the first step in the complex photoreaction of an mPAH, a novel class of photoacid capable of producing a large proton concentration with high efficiency, good reversibility, and an extremely long-lived acidic state with a half-life ranging from seconds to hours. 1–3 The mPAHs have enabled the successful demonstration of various chemical, energy, materials, and biomedical applications, such as photochemically-driven CO 2 release 4,5 and dissipative assembly. 2,6 While multiple isomers with various connected pathways during a photoreaction cycle are often considered to promote their unique functionalities, the transient intermediates and associated structural dynamics of mPAHs remain poorly understood.…”

“…It remains unclear if the early time dynamics identified for a merocyanine photoacid would occur in an indazole photoacid, a different type of mPAH that has attracted much attention in recent years. 1,5…”

“…So far, there have been only a few studies on indazole mPAHs, 5,11–13 and their photoreactions remain poorly understood. First, the origin of photoacidity has not been determined for this class of mPAH.…”

Reversible CO2 Capture and On-Demand Release by an Acidity-Matched Organic Photoswitch

“…Previous research has demonstrated photoacid-triggered formation of carbonic acid for spectroscopic characterization and photoacid-accelerated CO 2 release from acidic conditions . Very recently, an elegant strategy using an indazole photoacid to promote CO 2 release from amino acid sorbents was also reported . However, identification of a single-component solute that can recurrently capture and release according to dark/light cycles remains a highly desirable goal.…”

“…24 Very recently, an elegant strategy using an indazole photoacid to promote CO 2 release from amino acid sorbents was also reported. 25 However, identification of a single-component solute that can recurrently capture and release according to dark/light cycles remains a highly desirable goal. Further, a systematic framework for analyzing the thermodynamic requirements and experimental investigation of the precise mechanism of the photochemical process is needed to provide a theoretical foundation for the development of this novel approach to reversible carbon capture.…”