Membranes Matter: Preventing Ammonia Crossover during Electrochemical Ammonia Synthesis
Logan M. Wilder, Keenan Wyatt, Christopher A. Skangos, Walter Klein, Makenzie Parimuha, Jaclyn L. Katsirubas, James L. Young, Elisa M. Miller
Abstract
High Resolution Image Download MS PowerPoint Slide The electrochemical nitrogen and nitrate reduction reactions (E-NRR and E-NO 3 RR) promise to provide decentralized and fossil-fuel-free ammonia synthesis, and as a result, E-NRR and E-NO 3 RR research has surged in recent years. Membrane NH 3 /NH 4 + crossover during E-NRR and E-NO 3 RR decreases Faradaic efficiency and thus the overall yield. During catalyst evaluation, such unaccounted-for crossover results in measurement error. Herein, several commercially available membranes were screened and evaluated for use in ammonia-generating electrolyzers. NH 3 /NH 4 + crossover of the commonly used cation-exchange membrane (CEM) Nafion 212 was measured in an H-cell architecture and found to be significant. Interestingly, some anion exchange membranes (AEMs) show negligible NH 4 + crossover, addressing the problem of measurement error due to NH 4 + crossover. Further investigation of select membranes in a zero-gap gas diffusion electrode (GDE)-cell determines that most membranes show significant NH 3 crossover when the cell is in an open circuit. However, uptake and crossover of NH 3 are mitigated when −1.6 V is applied across the GDE-cell. The results of this study present AEMs as a useful alternative to CEMs for H-cell E-NRR and E-NO 3 RR electrolyzer studies and present critical insight into membrane crossover in zero-gap GDE-cell E-NRR and E-NO 3 RR electrolyzers.