A wide range usage of carbon monoxide (CO) makes carbon dioxide reduction reaction (CO₂RR) to CO become indispensable.^[1] Previous studies have shown that reduced graphene oxide-copper nanoparticles (rGO-CuNPs)-based electrocatalyst had promising results for the electrochemical CO₂RR, including good production rate of CO, efficiency, and stability.^[2] In the past few years, continuous-flow micro-fluidic electrolyzers have been regarded as the state-of-the-art for processing electrochemical CO₂RR. Most of the typical flow electrolyzers are composed of anode, cathode, membranes, catalyst layers, and liquid electrolytes. Recently, zero-gap electrolyzer setup has gained more attention, because of its lower cell resistance and no liquid electrolytes needed at the cathode side. Liquid electrolytes-free system can not only minimize the mass-transport losses that stem from CO₂ being dissolving in liquid electrolyte but also can enable pressurized CO₂ operation.^[3]

In this work, zero-gap electrolyzer was used for CO2RR. Our innovation was introduced by mixing rGO-CuNPs with alkaline ionomer, Sustainion, and spraying the well-mixed catalyst ink on the gas diffusion layer (GDL) at the cathode side. The cathodic gas diffusion electrodes (GDE), Nafion 212, proton exchange membrane (PEM), and the anodic catalyst layer based on iridium oxide (IrO₂), were mechanical compressed and applied as our membrane electrolytes assembly (MEA). This novel assembly was used to replace the conventional anion exchange membrane (AEM). Compared with conventional bipolar membrane (BPM) setup, this innovative MEA design overcame several problems, including eliminating the interfacial junction between membranes and improving the low ionic conductivity and poor stability of AEM at the high pH condition. The most important purpose is to suppress the hydrogen evolution (HER), which competes with CO₂RR at the cathode side. We did several characterization experiments to confirm the morphology, particle sizes, and the surface element containments of MEA and catalyst by using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopes (TEM), and X-ray photoelectron spectroscopy (XPS). Potentiostat (Gamry Interface 1010E) and the power supply were utilized to do the electrochemical testing. Based on our new MEA strategy, the breakthrough electrochemical performance was accomplished. The current density of 2 A cm^-2 was recorded, which was a significantly higher than in other studies, enabling high rate of CO production. Also, the overall cell voltage was recorded to be below 3V. The maximum faradaic efficiency (FE%) was able to reach up to 95%. In 7-days stability test, the result has shown that all the efficiencies and voltage kept in extremely stable values at the current density 1 A cm^-2 (Figure 1).

References

[1] B. Endrődi, E. Kecsenovity, A. Samu, T. Halmágyi, S. Rojas-Carbonell, L. Wang, Y. Yan, and C. Janáky, Energy Environ. Sci., (2020), 13, 4098-4105.

[2] S. Ozden, L. Delafontaine, T. Asset, S. Guo, K. A. Filsinger, R. D. Priestley, P. Atanassov, C. B. Arnold, Journal of Catalysis, (2021), 404, 512-517.

[3] B. Endrődi, E. Kecsenovity, A. Samu, F. Darvas, R. V. Jones, V. Török, A. Danyi, and C. Janáky, ACS Energy Lett., (2019), 4, 1770–1777.