A Carbon-Neutral CO₂ Capture, Conversion, and Utilization Cycle with Low-Temperature Regeneration of Sodium Hydroxide

A highly efficient recyclable system for capture and subsequent conversion of CO₂ to formate salts is reported that utilizes aqueous inorganic hydroxide solutions for CO₂ capture along with homogeneous pincer catalysts for hydrogenation. The produced aqueous solutions of formate salts are directly utilized, without any purification, in a direct formate fuel cell to produce electricity and regenerate the hydroxide base, achieving an overall carbon-neutral cycle. The catalysts and organic solvent are recycled by employing a biphasic solvent system (2-MTHF/H₂O) with no significant decrease in turnover frequency (TOF) over five cycles. Among different hydroxides, NaOH and KOH performed best in tandem CO₂ capture and conversion due to their rapid rate of capture, high formate conversion yield, and high catalytic TOF to their corresponding formate salts. Among various catalysts, Ru- and Fe-based PNP complexes were the most active for hydrogenation. The extremely low vapor pressure, nontoxic nature, easy regenerability, and high reactivity of NaOH/KOH toward CO₂ make them ideal for scrubbing CO₂ even from low-concentration sources-such as ambient air-and converting it to value-added products.