# Heavy is the Crown: Crown Ether Modulation of Cobalt Porphyrin CO2 Electroreduction in Zero‐Gap Electrolyzers

## TL;DR

This paper explores how adding crown ethers to cobalt porphyrins improves the electrochemical reduction of CO2 in a type of industrial electrolyzer.

## Contribution

The study introduces crown ether-modified cobalt porphyrins and demonstrates their enhanced performance in CO2 electroreduction under industrial conditions.

## Key findings

- Crown ether-modified cobalt porphyrins achieved 96% CO selectivity at 100 mA/cm2 in zero-gap electrolyzers.
- Crown ether positioning affects catalytic performance and stability in electrochemical CO2 reduction.
- High potassium concentration improves CO selectivity up to 43% at 300 mA/cm2.

## Abstract

Since decades, metalloporphyrins have been studied to catalyze the electrochemical CO2 reduction (eCO2R) with the most recent studies focusing on immobilized complexes aiming for heterogeneous, scalable catalysis. However, reports for the application in industrially relevant zero‐gap type electrolyzer cells (ZGEs) are especially rare. Herein we present the synthesis of four novel crown ether (CE) substituted cobalt porphyrins to benefit from an increased local cation concentration. Following their electrochemical characterization all catalysts have been tested in ZGEs. Experiments under laboratory‐scale conditions (≤100 mA/cm2) revealed that the positioning of the CE influences the catalytic performance in terms of Faradaic Efficiency for CO (FECO) as well as cell voltage. A maximum selectivity for CO of 96% at 100 mA/cm2 is reached, ranking the ortho substituted complex among the best state of the art systems. Post‐mortem analysis of the prepared electrodes proved that the introduction of CEs enhances the complex stability significantly. At higher current densities (≤500 mA/cm2) the positioning of the CEs is less impactful. Instead, the type and concentration of cations in the reactor play a dominant role determining reaction performance, achieving up to 43% FECO at 300 mA/cm2 with a high potassium concentration.

The implementation of crown ethers into the ligand of cobalt porphyrins benefits the electrochemical CO2 reduction in the several ways: (1) the reduction potential is lowered in presence of K+; (2) it boosts the CO generation in Zero‐Gap Electrolyzers and (3) ensures complex stability during electrolysis.