Electrochemical CO₂ Reduction – In search of new catalysts with high throughput online analysis

Abstract

CO₂ neutral energy sources like wind or solar energy already contribute deeply to our energy landscape. Unfortunately those renewable energy sources do not provide energy with the stability that we are used to from conventional energy sources. Also a demand dependent supply of energy remains difficult and one key question needs to be answered: Where will our energy come from, when the sun doesn’t shine and the wind doesn’t blow? 

The idea behind electrochemical CO₂ reduction is to convert CO₂ into chemical compounds like methane, methanol or carbon monoxide (for Syngas), that can serve as energy storage and can be used to compensate energy fluctuations from renewable energy sources by classical combustion or in combination with fuel cells. Therefore this approach is also referred as the artificial carbon dioxide cycle.

Advantages in contrast to classical heterogeneous gas catalysis are the direct use of electrical energy, a potential dependent and therefore customizable product distribution and operation at ambient pressure and temperature.  Despite these high prospects and over 50 years of research in this field, there is still no commercial application available.

Main reasons for this are (1) the broad product distribution on hydrocarbon producing electrodes and thereby a more or less costly product separation, (2) the low energy efficiency due to the high overpotential on the working electrode and (3)  oxygen evolution as counter reaction, that also shows high overpotential and in addition to that catalyst degradation by dissolution. 

The search for new catalysts, which can address these issues, is one of the most important tasks to make electrochemical CO₂ reduction successful. We developed new techniques to approach these issues, by utilizing the scanning flow cell (SFC), with all its advantages concerning the screening of parameters, to determine overpotentials and couple it (I) to an online electrochemical mass spectrometer (OLEMS) for direct correlation of product distribution to applied potential/current and (II) combine it with an inductively coupled plasma mass spectrometer (ICP-MS) to study dissolution behavior.^1–3 The use of special alloy electrodes, which show a longitudinal concentration gradient, in our systems allows  efficient screening of different catalysts.⁴ In addition to that the SFC enables us to screen temperature, different electrolytes and potential or current fully automated.

This new approach is the first realization of a high-throughput screening solution, covering activity, selectivity and stability. Utilized to deepen our understanding of fundamental processes and improve performance of electrochemical CO₂ reduction, this technique shows its high potential.