Membranes Matter: Preventing Ammonia Crossover during Electrochemical Ammonia Synthesis.

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.

On the Temperature Sensitivity of Electrochemical Reaction Thermodynamics.

Herein, we report a method to estimate the thermodynamic potentials of electrochemical reactions at different temperatures. We use a two-term Taylor series approximation of thermodynamic potential as a function of temperature, and we calculate the temperature sensitivity for a family of twenty seven known half reactions. We further analyze pairs of cathode and anode half-cells to pinpoint optimal voltage matches and discuss implications of changes in temperature on overall cell voltages. Using these observations, we look forward to increased interest in temperature and idealized half-reaction pairing as experimental choices for the optimization of electrochemical processes.

Recent synthetic methods involving carbon radicals generated by electrochemical catalysis.

Driven by a resurgence of interest in electrode-driven synthetic methods, this paper covers recent activity in the field of mediated electrochemical and photoelectrochemical bond activation, inclusive of C-H, C-C, C-N, and other C-heteroatom bonds.