Breaking Barriers to a Sustainable Future: Enhancing CO2 Reduction through Advanced Voltage Diagnosis
Authors: Arabyarmohammadi Fatemeh , Shayesteh Ali , Miao Rui Kai , O'Brien Colin P. , Alkayyali Tartela , Lee Geonhui , Dorakhan Roham , Zargartalebi Mohammad , Sargent Edward H. , Sinton David 
Published: February 2024

Electrochemical conversion of CO2 is a promising technology that uses renewable electricity to produce valuable chemicals with lower emissions than traditional methods. However, to make this technology commercially viable, it is crucial to run CO2RR at current densities higher than 200 mA/cm2, as determined by techno-economic analysis. This enables the amortization of electrolyzer capital costs over the typical operating lifetime of a potential commercial CO2RR facility. While the field has made progress in meeting this reaction rate target for many products of interest, reducing the operating voltage of CO2 electrolyzers remains a significant challenge. Addressing this challenge could pave the way for more efficient and cost-effective CO2RR technologies.

The economic viability of CO2 electrolyzers heavily relies on their operating voltage, which is a crucial performance metric as it defines the energy efficiency of electrolyzers. Despite the importance of this metric, there is insufficient information on the distribution of voltage losses, especially in the membrane electrode assembly (MEA) electrolyzers as it is challenging to place a reference electrode in these configurations. Current research eﬀorts focus on improving the performance of CO2 electrolyzers. Achieving industrially relevant current densities with high energy efficiency (EE) remains a challenge because full cell performance is impacted by several factors under the operating conditions. There is a need for cell diagnostics applicable to standard cell configurations that analyze each cell component (i.e., cathode, anode, and membrane) running under relevant conditions. In this study we aim to optimize the performance of the MEA systems and reduce operational voltage to enhance energy efficiency, which can address the high full-cell voltages of conventional CO2 electrolyzers and make them commercially viable and sustainable.

In this study, we developed an analytical cell to measure voltage losses in a zero-gap MEA electrolyzer. This cell design incorporates reference electrodes on each side of the membrane, enabling it to measure both cathodic and anodic overpotentials. Electrochemical Impedance Spectroscopy (EIS) was also conducted to analyze the ohmic overpotential across the electrolyte. In the next step, the diagnostic platform was utilized to assess the performance of major CO2/COR approaches, including conventional Neutral CO2R in MEA and emerging high single pass aproaches COR, Acidic CO2R cell and CO2 Reactive capture system cell. In our analysis, we evaluated each system and identified the specific overpotentials associated with each cell component in each system. The voltage distribution plot highlights the key energy losses in each cell, indicating excess voltages required for each component. It reveals that CO2R in acidic media incurs significant voltage losses, primarily at the cathode/membrane interface. This finding emphasizes the need for optimization of this interface to reduce the overall energy loss and improve CO2RR efficiency. Additionally, we found that further optimization of the cathode and anode is essential to reduce the full cell voltage in CO2 reactive capture approach. Our analysis also demonstrates that COR approach is a very promising approach as it exhibits the lowest cathode and anode overpotentials.

In conclusion, our study highlights the significance of minimizing energy losses in CO2RR for enhanced efficiency and feasibility. The voltage distribution plot can serve as a useful tool for identifying and addressing critical energy losses in each cell component.

Figure 1