Multiscale-particle organic hybrid materials as electrolyte additives for electrocatalytic reactive carbon capture

The integration of CO₂ capture and conversion into a single system has been suggested as an efficient and transformative approach for enabling the conversion of CO₂ to high-value chemicals and fuels to reduce the reliance of hard-to-decarbonize industries on fossil fuels. One of the challenges of the electrochemical reduction of CO₂ is the low solubility of CO₂ in aqueous electrolyte. In this study, we synthesized a variety of multiscale-particle organic hybrid materials (MOHMs) composed of varying SiO₂ core sizes across 5 orders of magnitude, containing two distinct polymer canopies (HPE and PEI) with varying CO₂ binding strengths, and investigated their effect on CO₂RR over a nanoparticle Ag catalyst. MOHM-I-HPE-containing electrolytes were observed to exhibit a reverse volcano relationship between CO faradaic efficiency (FE) and core size, with 7 nm MOHM-I-HPE achieving similar CO FE to 0.1 molal KHCO₃ though at reduced current densities, while 10 µm MOHM-I-HPE exceeded the performance of the conventional electrolyte (76% vs. 65% FE for CO), while simultaneously exhibiting increased CO current density and decreased H₂ current density relative to the conventional electrolyte. Structural investigations of the electrodes after CO₂RR indicate that the small-core sizes form a persistent adlayer that facilitates CO₂ transport to the surface, while large-core sizes transiently deliver CO₂ to the electrode. In contrast, MOHM-I-PEI additives drastically reduced CO₂RR as the strong chemisorption prevents effective conversion of the bound CO₂. These findings provide valuable insight into the effective design of particle-based electrolyte additives and how CO₂ can be captured and delivered to the surface of catalysts, while tuning the local reaction environment.