(Invited) Electrolyzer Development and Process Optimization: Paving the Road for Industrial Carbon-Dioxide Electroreduction

Abstract

Electrochemical reduction of CO2 is a promising method for converting a greenhouse gas into value-added products, utilizing renewable energy. Novel catalysts, electrode assemblies, and cell configurations are all necessary to achieve economically appealing performance. In this talk, I am going to present a zero gap electrolyzer cell, which converts gas phase CO2 to products without the need for any liquid catholyte. This is the first report of a CO2 electrolyzer cell, where multiple stacks are connected, thus scaling up the electrolysis process. The operation of the cell was validated using both silver nanoparticle and copper nanocube catalysts, and the first was employed for the optimization of the electrolysis conditions. Upon this, CO formation with partial current densities above 250 mA cm−2 were achieved routinely, which was further increased to 300 mA cm−2 (with ~95 % Faradaic efficiency) by pressurizing the CO2 inlet. Evenly distributing the CO2 gas among the stacks (parallel connection), the operation of the multi-stack cell was identical to the sum of multiple single-stack cells. When passing the CO2 gas through the stacks one after the other (serial gas connection), the CO2 conversion efficiency was increased remarkably. Importantly, the presented electrolyzer simultaneously provides high partial current density, low cell voltage (−3.0 V), high conversion efficiency (up to 40 %), and high selectivity for CO production; while operating at up to 10 bar differential pressure.In the second part of the talk I will show how the cell can operate with pure water feed on the anode side, therefore avoiding the use of alkaline anolyte. A carefully designed activation protocol will be presented, which allows the cell to operate at high current density, using pure water feed. The effect of temperature and flow rate on the operation will also be presented. Finally, the nature of ion-transport through the anion exchange membrane as a function of the operational conditions will be discussed.