Managing Hydration at the Cathode Enables Efficient CO₂ Electrolysis at Commercially Relevant Current Densities

Abstract

Gas-fed CO2 electrochemical flow reactors are appealing platforms for the electrolytic conversion of CO2 into fuels and chemical feedstocks at commercially relevant current densities (≥100 mA/cm2). An inherent challenge in the development of these reactors is delivering sufficient water to the cathode to sustain the CO2 reduction reaction, while also preventing accumulation of excess water at the porous cathode (i.e., flooding). We present herein experimental evidence showing cathode flooding in a zero-gap electrolyzer at 200 mA/cm2. This flooding causes a 37% decrease in partial current density for CO production (j CO) along with a 450 mV increase in cell voltage (E cell). We show that the detrimental effects associated with this flooding can be mitigated by pairing thin membranes (i.e., ≤40 μm) with hydrophobic cathodes to enable CO2 electrolysis at commercially relevant conditions (j CO ≥ 100 mA/cm2 and E cell < 3 V).

Investigation and Optimisation of Operating Conditions for Low-Temperature CO2Reduction to CO in a Forward-Bias Bipolar-Membrane Electrolyser

“…2. For this reason, a closer investigation of the H 2 O influence on performance is needed with some first experimental results about the impact of cathode flooding on CO 2 RR in an all-alkaline MEA cell having recently been published by Reyes et al 67 Since the Journal of The Electrochemical Society, 2021 168 043506 BPM system is more complex, some initial conceptual considerations are required before investigating this phenomenon experimentally.…”

Liquid–Solid Boundaries Dominate Activity of CO2 Reduction on Gas-Diffusion Electrodes

“…5 Here, the reaction of CO2 indisputably occurs at the liquid-solid interface of the electrolyte and the electrocatalyst. GDE-based cells have three common configurations: microfluidic cells, 6 hybrid cells, 7 and zero-gap cells, 8,9 respectively characterized by a flowing liquid electrolyte between the cathode and anode (Figure S1a), flowing liquid electrolyte between the cathode and anode separated by a membrane (Figure 1a, S1b), and a cathode and anode pressed directly against a membrane with no macroscopic gap for liquid flow (Figure S1c). The GDL, often made of a macroporous carbon paper topped by a microporous layer (MPL) of PTFE and carbon particles, is hydrophobic and provides a barrier to liquid, allowing for it to be filled by gaseous CO2.…”

Water Activity Regulates CO2 Reduction in Gas-Diffusion Electrodes

“…Further work has assessed the effect of water flooding in the GDE, a common mode for GDE deactivation during long duration stability tests. 14 These advances have moved the field towards more stable GDEs, with control over water distribution in the GDE to ensure robust pathways for CO2 to diffuse and react with protons and electrons at catalytic active sites.…”