Copper Catalysis-Based Amperometric Microsensors for Carbon Dioxide Monitoring

A fast response microsensor that can detect the distribution of CO₂ at the microscale level is essential for the observation of biophysiological activity, carbon flux, and carbon burial. Inspired by the previous success of Cu catalysis, we attempted to use this metal Cu material to develop an amperometric microsensor that can meet the requirements. Specifically, the ambient gases diffuse through a silicone membrane into a trap casing filled with an acidic CrCl₂ solution, where the otherwise interfering O₂ interferent is removed by a redox with Cr²⁺. The gases then diffuse through a second silicone membrane into an electrolyte, where CO₂ is selectively reduced to methanol (CH₃OH) at a Cu cathode through a carbon monoxide (CO) pathway. Due to the use of Cu catalysis at the WE tip, CO₂ can be reduced at a less negative polarization (-470 mV) instead of the previously reported -1200 mV, thus avoiding hydrogen-evolution interference due to water from the byproduct or from water diffusion through the silicone membrane. This moderate polarization results in a stable baseline, making the microsensor suitable for long-term monitoring. Interferences from other gases, such as N₂O, which may be of much concern in environmental monitoring, can be ignored. Applications and limitations are also discussed with a view to further improvement in the future.