Operando scanning electrochemical microscopic investigation and visualization of NRR-HER competition in electrochemical NH3 synthesis

Electrochemical dinitrogen reduction (NRR) has emerged as one of the most promising potential alternatives to the energy-intensive Haber-Bosch process for clean and carbon-free ammonia (NH3) production. However, the major setback in this electrochemical synthesis is the selectivity between NRR and the competing hydrogen evolution reaction (HER) that leads to poor faradaic efficiency. The competition between NRR and HER is underexplored, and the existing ex situ NH3 and H-2 detection methods do not provide the real-time detection of products formed near the electrode surface with high spatial resolution. Therefore, the operando investigation of NH4+ production during electrochemical N-2 reduction and its competition with HER was demonstrated using scanning electrochemical microscopy (SECM) via the sample generation-tip collection (SG-TC) mode. A distinct net current density difference was observed at an Au-ultramicroelectrode (UME) during sequential chronoamperometry and the visualization of local catalytic activity over the catalyst in Ar- and N-2-saturated electrolytes. Therefore, this study provides invaluable information on the competition between the NRR and the HER at applied potentials within milliseconds and also visualization with high spatial resolution and accuracy.