Rationally Designed Solid Sorbent Electrolyte Exhibits Dual CO ₂ / H ₂ O Sorption and Enables Full Gas Phase CO ₂ Reduction

Efficient CO₂ electrolysis hinges on high CO₂ availability and controlled water transport toward and away from the catalyst. Traditional methods, such as direct CO₂ supply in the gas form or using CO₂ sorbent liquid electrolytes face significant limitations. In this study, a pioneering approach is presented using a rationally designed CO₂/H₂O sorbent composite electrolyte, enabling low-temperature aqueous CO₂ electroreduction without liquid catholyte nor anolyte. The development of a multi-functional electrolyte in the form of a solid sorbent ionogel is introduced in this work. This novel material is designed to perform several tasks at once, namely 1) ensuring ionic conductivity (1.5-3 mScm^-1) in a solid material, thereby removing salt precipitation issues linked to liquid aqueous electrolytes, 2) serving as local CO₂ concentrator (0.03-0.13 mmol CO₂/g for P_CO2 0.1-1 bar at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mn>30</mml:mn> <mml:msup><mml:mspace></mml:mspace> <mml:mo>∘</mml:mo></mml:msup> <mml:mi>C</mml:mi></mml:mrow> <mml:annotation>$30 \,^{\circ }\mathrm{C}$</mml:annotation></mml:semantics> </mml:math> ) to pave the way for flue gas based feed streams at lower CO₂ partial pressures and 3) regulating water supply and removal (0.3-2.3 mmol H₂O/g range at 85 % relative humidity depending on degree of methyl functionalization), to prevent preferential hydrogen evolution. This work offers a proof-of-concept for full-vapor phase CO₂ reduction, where methyl-functionalization of an ionic liquid-silica nanocomposite enable to steer the selectivity from H₂ to CO production.