Durable electrocatalytic CO2 reduction to ethylene system via eliminating carbonate formation

Efficient CO2 reduction is crucial in fighting climate change. Electrocatalytic CO2 reduction (ECO2R) with renewable energy is promising, but alkaline conditions and alkali cations pose challenges. Our pure-water-fed system overcomes these, paving the way for a stable and efficient ECO2R process.
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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

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Materials for Energy and Catalysis
Physical Sciences > Materials Science > Materials for Energy and Catalysis
Electrochemistry
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