Understanding the impact of catholyte flow compartment design on the efficiency of CO2 electrolyzers

Abstract

This work explores and provides new understanding how catholyte flow compartment design and catholyte bubble flow characteristics of a gas diffusion electrode inside a CO₂ flow cell electrolyzer affect its electrocatalytic reactivity and product selectivity. Focusing on Cu-based GDEs for CO₂ electroreduction to hydrocarbons at high current densities (50–700 mA cm⁻²), four basic compartment designs were selected, 3D printed and investigated. Experiments were coupled to computational fluid dynamics simulation of catholyte flow and bubble dynamics. The findings from this work suggest a homogenous fluid velocity distribution combined with fluid velocity in the range between 0.1–0.01 m s⁻¹ to be optimal for high yields in C₂₊ products at high current densities. Special focus was placed on the role and relation between gas bubble dynamics and local pH, both strongly affected by the design architecture. From our experimental observations and simulations, we propose a hydrodynamic “volcano” model addressing the competition between bubble release rate and local pH, both controlled by catholyte flow velocity. The balance between fast bubble release and high enough local pH across the electrode surface puts the electrolyzer operation at the top of the performance volcano.