(653d) Advanced Analytical Chemistry Allows Robust Catalyst Verification for Electrochemical N2 Reduction

Electrochemical reduction of N₂(g) to ammonia (NRR) is a sustainable alternative to the conventional Harber-Borsch process that accounts for > 1 % of global energy consumption. However, developing efficient NRR catalyst is hindered by both low activity and selectivity, due to the sluggish NRR kinetics relative to the competing hydrogen-evolution reaction (HER) in aqueous electrolyte. Recently, the research field has paid more attention to (1) identifying and eliminating possible ammonia impurities during experiment and (2) rigorously verifying the NRR catalyst activity by using isotope-labelled ¹⁵N₂(g). Nuclear magnetic resonance (NMR) spectroscopy has served as the only available technique to distinguish between N14/N15-labbelled ammonia products, which nevertheless suffers from high limit-of-detection (LOD) and long data collection time.

Herein, we will introduce a new analytical method to isotopically quantify N14/N15-labbled ammonia based on mass spectrometry (MS) via chemical derivatization with dansyl chloride. This derivatization reaction can be easily carried out at room temperature and optimal pH, while the derivatized products can be loaded into UPLC-MS for high-throughput quantification. Compared with NMR, this method has achieved much shorter analysis times (< 6 min), lower limit-of-quantification (LOQ) of < 1 uM as well as much higher sensitivity and reproducibility. Further, we leveraged this method to quantify the impact of ammonia contamination in different indoor environments, and rigorously identify a false-positive metallic CoMo NRR electrode. The advanced analytical chemistry will benefit the research community of EC-NRR to further develop electrocatalyst with more robust evidences of their activity and stability.