Fast and Sensitive Detection of Ammonia from Electrochemical Nitrogen Reduction Reactions by 1 H NMR with Radiation Damping

Abstract

A facile NMR method is reported for analysis of ammonia from the electrochemical reduction of nitrogen, which compares a calibrated colorimetric method, a calibrated ¹ H NMR method and two ¹ H NMR direct measurements using external reference materials. Unlike spectrophotometric methods, ¹ H NMR requires less bench time and does not require separation of ammonia from the electrolyte. A novel approach to the problem of radiation damping in NMR measurements considered the specific role of hardware tuning. Radiation damping is suppressed improving signal-to-noise ratio and detection limit (1.5 µg L^-1 ). The method is demonstrated to be effective for the analysis of ammonia from direct electrochemical nitrogen reduction in KOH, and from lithium-mediated nitrogen reduction in a non-aqueous solution. An uncertainty budget is prepared for the measurement of ammonia.

Keywords: aqueous nitrogen reduction; lithium-mediated nitrogen reduction; qNMR; radiation damping; uncertainty budget.