Efficient Ni-NC Gas Diffusion Electrodes for CO2 Electrolyzer with High Utilization Efficiencies and Single Pass Conversions Towards CO

The electrochemical CO2 reduction in membrane electrolyzer devices can become a key technology to close the anthropologic carbon cycle. For industrialisation of CO2 electrolyzers, however, performance shortcomings of today’s state-of-art electrolyzer designs and cathodes have to be addressed. Alkaline Membrane CO2 electrolyzers suffer from low utilization efficiency of CO2 due to an acid-base CO2 loss to carbonates, which limits the CO2 utilization efficiency and single pass conversion to 50% in AEM CO2-to-CO electrolyzer. Bipolar Membrane CO2 electrolyzers suffer from high cell voltage and lower Faradic efficiencies due to the acidic environment. All thoses designs suffer from layer flooding or salting events which limit the durability of the cells. New cell designs and new diagnostic tools are needed to predict, diagnose, and eliminate detrimental operating regimes of CO2 electrolyzers. In this work, we report on NiNC catalyst-based cathode GDEs for CO2 reduction to CO in a zero-gap membrane electrolyzer cell. We compare AEM and BPM cell designs. We propose the carbon crossover coefficient, CCC, as a new diagnostic analysis tool to monitor and understand through- or in-plane mass transport limitations in AEM and BPM cells. We also demonstrate how N2 bleeds can be used as diagnostic tools to recognize salting inside the electrolyzer cell. In our AEM studies, we show that sufficient CO2 access to the catalyst surface sites is important to achieve a high performance. Under near neutral conditions on the anode we report 85% FE towards CO at 300 mA cm-2 at 3.6 V with single pass conversion of 40% which is very close to the theoretical maximum. In addition, we can report high energy efficiency but only a utilization efficiency of around 50%. In our BPM studies, we show that NiNC GDEs are active and stable cathodes in zero-gap membrane electrolyzer. Protons raise the utilization efficiency as the carbonate will decompose into CO2 and water. To handle the changed electro osmotic water drag we replaced the ionomer with PTFE and could achieve 82% FE and 69% single pass conversion at 500 mA cm-2 with close to 100% CO2 utilization efficiency towards CO. We show that using a either an AEM or BPM electrolyzer design we can reach over 100h stable performance at 100 mA cm-2. Figure caption: CO2 singel pass conversion and lambda comparison of AEM and BPM CO2 reduction electrolyzer cells. Figure 1