Carbon dioxide reduction

A promising approach involves the use of a zero-gap electrolyser with the carbon dioxide (CO₂) reduction catalyst loaded onto a gas-diffusion electrode (GDE) directly contacting a cation exchange membrane (CEM), bipolar membrane (BPM), or anion exchange membrane (AEM).

These zero-gap structures have been proposed as a route to high current densities and to reduce manufacturing costs. This is due to the catalyst being in close contact with the membrane allowing it to strongly influence the local environment of the catalyst.

When scaling up electrochemical CO₂ reduction, it becomes crucial to address the issue of CO₂ loss as carbonates under alkaline conditions. However, zero-gap cell structures with a reverse-bias bipolar membrane (BPM) offer a possible solution, although the catalyst layer in direct contact with the acidic environment of a BP usually leads to a domination of hydrogen.

Our findings

In this study, we demonstrate that by using acid-tolerant Ni molecular electrocatalysts, we can achieve a selective CO₂ reduction of over 60% in a zero-gap BPM setup using pure water and CO₂ feed. Even at higher densities, such as 100 mA cm–2, the carbon selectivity remains above 30%, although it may decrease due to reversible product inhibition.

This study demonstrates the importance of developing acid-tolerant catalysts, especially for large-scale CO₂ utilisation efforts.