The Pure-water-Fed MEA System: The pure-water-fed membrane-electrode-assembly (MEA) system consists of an anion-exchange membrane (AEM) and a proton-exchange membrane (PEM) assembly (APMA, Figure 1). This innovative system maintains an alkaline cathode environment necessary for effective ECO₂R. Under forward bias, water dissociation occurs at the cathode and anode, participating in ECO₂R and oxygen evolution reaction (OER). The remaining OH^- and H⁺ ions are transported through AEM and PEM, respectively, forming water at their interface.

Fig. 1. (a) Schematic of the pure-water-fed APMA-MEA system architecture for ECO₂R. (b) ECO₂R performance on SS-Cu in the pure-H₂O-fed APMA-MEA cell, and the corresponding cell voltages without iR compensation.

 Results: Using a high-performance surface-step-rich Cu (SS-Cu), the ECO₂R product distribution in the pure-water-fed APMA-MEA system was examined (Figure 1b). The results were remarkable, with a peak Faradaic efficiency (FE) of approximately 66%, including a significant 43% FE towards C₂H₄ (ethylene). The cell voltage was around 4.3 V, and the full-cell energy efficiency reached 18.2% for ECO₂R.

Preventing Carbonate Formation: One of the major challenges in ECO₂R is the formation of carbonates and salt precipitation. However, the pure-water-fed APMA-MEA system architecture drastically reduces the probability of these reactions. The absence of cations, under the influence of the electrostatic field, effectively suppresses (bi)carbonate salt formation and prevents salt precipitation.

Experimental Evidence: In-situ Raman measurements directly demonstrated the effective suppression of carbonate formation on the SS-Cu surface in the pure-H₂O-fed APMA system (Figure 2a). Additionally, an isotope labeling experiment using H₂¹⁸O as the anolyte confirmed that CO₂ did not react with the electrogenerated OH^- into carbonate (Figure 2b). These findings provide strong evidence that the pure-water-fed APMA-MEA system configuration successfully prevents carbonate formation and anion crossover.

Fig. 2. (a) In-situ Raman spectra of ECO₂R on SS-Cu in 0.1 M KOH, pure H₂O and bare electrode after ~20 min of ECO₂R. (b) Mass spectra of ECO₂R using H₂¹⁸O as the anolyte in the APMA system. (c) System stability performance of ECO₂R-to-C₂H₄ on SS-Cu in a pure-H₂O-fed APMA-MEA cell stack containing 6 APMA-MEA cells at a constant current of 10 A.

Durability and Practicality: To evaluate the durability and practicality of the pure-water-fed APMA-MEA architecture, a cell stack containing six MEA cells was designed (Figure 2c). The results were highly promising, with a ~50% FE towards C₂H₄ achieved at a total current of 10 A (Figure 2d). The system remained stable for over 1000 hours, demonstrating its long-term viability and potential for industrial-scale implementation.

Conclusion: The pure-water-fed MEA system represents a significant breakthrough in the field of CO₂ reduction. By effectively suppressing carbonate formation and salt precipitation, this innovative technology offers a more stable and efficient approach to ECO₂R. With its potential to bridge the gap between fossil fuels and sustainable energy, this system brings us one step closer to a greener and more sustainable future.

To learn more about this research, please refer to our recent publication in Nature Energy: "Pure-water-fed electrocatalytic CO₂ reduction to ethylene beyond 1000 h stability at 10 A".

https://www.nature.com/articles/s41560-023-01415-4.pdf

https://doi.org/10.1038/s41560-023-01415-4