Membranes Matter: Preventing Ammonia Crossover during Electrochemical Ammonia Synthesis

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Abstract

The electrochemical nitrogen and nitrate reduction reactions (E-NRR and E-NO3RR) promise to provide decentralized and fossil-fuel-free ammonia synthesis, and as a result, E-NRR and E-NO3RR research has surged in recent years. Membrane NH3/NH4+ crossover during E-NRR and E-NO3RR 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. NH3/NH4+ 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 NH4+ crossover, addressing the problem of measurement error due to NH4+ crossover. Further investigation of select membranes in a zero-gap gas diffusion electrode (GDE)-cell determines that most membranes show significant NH3 crossover when the cell is in an open circuit. However, uptake and crossover of NH3 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-NO3RR electrolyzer studies and present critical insight into membrane crossover in zero-gap GDE-cell E-NRR and E-NO3RR electrolyzers.
Original languageAmerican English
Pages (from-to)536-545
Number of pages10
JournalACS Applied Energy Materials
Volume7
Issue number2
DOIs
StatePublished - 2024

NREL Publication Number

  • NREL/JA-5900-86236

Keywords

  • ammonia
  • crossover
  • electrochemical nitrate reduction
  • electrochemical nitrogen reduction
  • gas diffusion electrode
  • H-cell
  • membrane
  • Nafion
  • solar-photochemistry

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