# Effect of Channel Height on CO2-to-CH4 Reduction in Microchannel Electrocatalysis

## TL;DR

This study shows how adjusting the channel height in microchannel electrocatalytic devices can improve CO2-to-CH4 conversion efficiency.

## Contribution

The paper introduces a novel design using microchannel geometry to enhance CO2 reduction efficiency through optimized electrode spacing and bubble dynamics.

## Key findings

- A 50 μm channel height achieved 56% Faradaic efficiency for CH4 production, significantly higher than larger gaps.
- Smaller CO2 bubbles at 0.75 mL/min flow rate increased gas-liquid interfacial area and CO2 dissolution.
- Larger electrode gaps reduced efficiency due to limited CO2 availability at the cathode surface.

## Abstract

Electrocatalytic CO2 reduction is a promising approach to mitigate rising atmospheric CO2 levels while converting CO2 into valuable products such as CH4. Conversion into other useful substances further expands its potential applications. However, the efficiency of the CO2 reduction reaction (CO2RR) is strongly influenced by device geometry and CO2 mass transfer in the electrolyte. In this work, we present and evaluate microchannel electrocatalytic devices consisting of a porous Cu cathode and a Pt anode, fabricated via metal-assisted chemical etching (MACE). The porous surfaces generated through MACE enhanced reaction activity. To study the impact of the distance between electrodes, several devices with different channel heights were fabricated and tested. The device with the highest CH4 selectivity had a narrow inter-electrode gap of 50 μm and achieved a Faradaic efficiency of 56 ± 11% at an applied potential of −5 V versus an Ag/AgCl reference electrode. This efficiency was considerably higher than that of the device with larger inter-electrode gaps (300 and 480 μm). This reduced efficiency in the larger channel was attributed to limited CO2 availability at the cathode surface. Bubble visualization experiments further demonstrated that the electrolyte flow rate had a strong impact on supplied CO2 bubble morphology and mass transfer. At a flow rate of 0.75 mL/min, smaller CO2 bubbles were formed, increasing the gas–liquid interfacial area and thereby enhancing CO2 dissolution into the electrolyte. These results underline the critical role of electrode gap design and bubble dynamics in optimizing microchannel electrocatalytic devices for efficient CO2RR.