Efficient CO₂ Conversion through a Novel Dual-Fiber Reactor System

Carbon dioxide (CO₂) can be converted to valuable organic chemicals using light irradiation and photocatalysis. Today, light-energy loss, poor conversion efficiency, and low quantum efficiency (QE) hamper the application of photocatalytic CO₂ reduction. To overcome these drawbacks, we developed an efficient photocatalytic reactor platform for producing formic acid (HCOOH) by coating an iron-based metal-organic framework (Fe-MOF) onto side-emitting polymeric optical fibers (POFs) and using hollow-fiber membranes (HFMs) to deliver bubble-free CO₂. The photocatalyst, Fe-MOF with amine-group (-NH₂) decoration, provided exceptional dissolved inorganic carbon (DIC) absorption. The dual-fiber system gave a CO₂-to-HCOOH conversion rate of 116 ± 1.2 mM h^-1 g^-1, which is ≥18-fold higher than the rates in photocatalytic slurry systems. The 12% QE obtained using the POF was 18-fold greater than the QE obtained by a photocatalytic slurry. The conversion efficiency and product selectivity of CO₂-to-HCOOH were up to 22 and 99%, respectively. Due to the dual efficiencies of bubble-free CO₂ delivery and the high QE achieved using the POF platform, the dual-fiber system had energy consumption of only 0.60 ± 0.05 kWh mol^-1, 3000-fold better than photocatalysis using slurry-based systems. This innovative dual-fiber design enables efficient CO₂ valorization without the use of platinum group metals or rare earth elements.