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.