Bipolar Membranes for Photoelectrochemical CO2 Conversion

Abstract

CO2 capture and conversion represent one of the most critical challenges of our society. One sustainable approach to tackle it is the development of electrochemical processes coupling a solar-driven carbon dioxide reduction to CO/water oxidation to O2 with reactions leading tohigh-value products. In such photoelectrochemical reactors, (photo)electrocatalysts and membranes play a crucial role to achieve high CO2 conversion with minimum energy.The aim of this study is developing polymer membranes with high stability, mechanical resistance and ion conductivity, that can work in the broad pH operation range of CO2/H2O co-electrolysis cells. Consistently with the use of KOH at the anode, the used membrane is often an anion exchange membrane (AEM). However, carbonate crossover through AEM occurs during CO2 electrolysis via diffusion and migration. [1] The use of a bipolar membrane (BPM) allows to mitigate this issue, bringing novel challenges of stability and performance.The BPM consists in a cation exchange layer (CEL) and an anion exchange layer (AEL), with a bipolar junction formed at their interface. Such membrane must guarantee a constant pH level generating H+ and OH- by water dissociation at the junction, avoid product crossover, and optimize mass transfer and reactivity of coupled anodic and cathodic reactions. A crucial point is the control of the electrochemical behavior at the CEL/AEL interface. With this aim, a 3D-structure made of a network of fibers was developed [2, 3] providing a great interfacial area and mechanical interlocking of the anion and cation exchange ionomers preventing delamination and facilitating the exchange of ions and matter at the interface. Furthermore, such fiber webs allow the controlled deposition of inorganic or organic catalysts to enhance the water dissociation rate at the bipolar junction.The bipolar membrane was prepared interposing a web of electrospun fibers bearing water dissociation nanocatalysts at the interface between anion and cation exchange polymer layers. The prepared BPMs were characterized for their morphology, composition, ion conductivity, and performance.This work has been performed with the financial support of the European Union’s Horizon 2020 Research and Innovation Action Program under the project SunCoChem (Grant agreement No 862192).