Sulfonated Silica Particles as Proton-Conductive Porous Solid Electrolytes for CO₂ Electrolysis

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Carbon dioxide reduction reaction (CO2RR) converts CO2 into valuable chemicals but often yields products mixed with aqueous electrolytes.
• Existing CO2RR methods require energy-intensive separation processes to isolate products.
• Porous solid electrolytes (PSEs) offer a route to direct production of electrolyte-free liquid fuels and chemicals from CO2.

Purpose of the Study:

• To develop and characterize novel silica-based porous solid electrolytes (PSEs) for CO2 electrolysis.
• To investigate the impact of particle size and ligand chemistry on ionic conductivity and performance.
• To demonstrate the efficacy of these PSEs in a continuous-flow CO2 electrolyzer.

Main Methods:

• Grafting sulfonated silane ligands onto mesoporous silica particles to create PSEs.
• Synthesizing silica particles with varying sizes (20 nm to 40 μm) and two distinct sulfonated ligands.
• Evaluating ionic conductivity and performance in a continuous-flow CO2 electrolysis setup.

Main Results:

• Optimized silica PSEs achieved high ionic conductivity (up to 5.31 × 10^-2 S cm^-1).
• Smaller particle sizes enhanced ionic conductivity but posed challenges in flow stability.
• The CO2 electrolyzer utilizing these silica PSEs demonstrated >90% Faradaic efficiency for formic acid production.

Conclusions:

• Silica-based particles are effective PSEs for CO2 electrolysis, enabling electrolyte-free product generation.
• Particle size and ligand functionalization are critical parameters for optimizing PSE performance and stability.
• This work presents a versatile approach for designing solid-state electrolytes for various electrochemical applications, including CO2 conversion.