Electrochemical CO2 Reduction: Screening of Material Libraries and Improving Selectivity of Cu By Mixing It with Co

Abstract

Using CO2 and converting it into useful products or even fuels is considered as a “dream reaction”. However even after over 30 years of research in the field of electrochemical CO2 reduction the “dream” didn’t come true and still remains a scientific and technical challenge. Two main applications can be considered for the electrochemical CO2 reduction: (1) The operation as storage technology to compensate the unavoidable energy fluctuations produced by renewable energy source like wind or sun and (2) the syntheses of valuable products like ethylene. Whilst in gas-phase heterogeneous catalysis the conceptual understanding about converting CO2 into fuels and the applied processes are well developed, electrochemical CO2 reduction is still in a stage where fundamental research is inevitably necessary to prove feasibility before large-scale implementation. On the contrary distinct advantages are the direct use of electrical energy, a potential dependent and therefore customizable product distribution and operation at ambient pressure and temperature. Main reasons for a so far not realized commercial application are (1) the low selectivity for valuable products on hydrocarbon producing electrodes and thereby a costly product separation, (2) the low energy efficiency as a cause of high overpotential on the working electrode and (3) the oxygen evolution as counter reaction, that also shows high overpotential and in addition to that catalyst degradation by dissolution. In order to address the fundamental understanding of the reduction processes on various types of material combinations, we have developed an electrochemical technique that enables (1) screening of thin-film material libraries with different experimental parameters, (2) investigating catalyst activity and stability of electrodes in parallel by inductively coupled plasma mass spectrometry (ICP-MS) and (3) analyzing the selectivity of catalysts for certain products via online electrochemical mass spectrometry (OLEMS). First results utilizing this approach will be presented; the focus will be in particular on the shift in selectivity towards C2 products of the electrochemical CO2 reduction on Cu-Co thin film composition spread samples at ambient temperature and pressure. Due to a high resolution composition analysis we were able to find a composition where production of C1 species is suppressed, while in return C2 production is enhanced. Utilization of this technique deepens understanding of fundamental processes and shows its high potential for improving performance of electrochemical CO2 reduction.