Fast Proton NMR Detection of Aqueous Ammonia with Relaxation Agent and Nitrogen Decoupling.

The Haber-Bosch process, which synthesizes ammonia (NH) from nitrogen (N) and hydrogen (H), consumes approximately 2% of the global energy supply. A sustainable alternative is the direct electrochemical conversion of N to NH. The selectivity and activity of the electrocatalysts for this process are assessed by quantifying the NH present in the electrolyte. Compared with other analytical methods, H NMR offers a straightforward approach for detecting NH (by analyzing NH ). H NMR method can also definitely confirm that the detected ammonia originates from the electroreduction of N by comparing results obtained from isotopically labeled N and regular N gases. This capability is unique to the H NMR method, as no alternative approaches offer this level of specificity. However, this method suffers from low sensitivity when measuring NH of low concentration of such as at μM or lower. To address this issue, we developed a novel approach that improves sensitivity by ∼3-fold through the introduction of N decoupling during the H NMR data acquisition. Recently [Kolen M.ACS Omega2021, 6, 5698-5704], demonstrated a ∼3.5-fold increase in sensitivity by using a 1 mM concentration of the paramagnetic relaxation agent Gd. By combining our N decoupling technique with the relaxation agent Gd, we achieved a synergistic enhancement in sensitivity, resulting in an overall ∼10.9-fold sensitivity increase for the H NMR detection of NH . This translates to a reduction in NMR detection time by a factor of ∼119 (10.9). This significant advancement enables the fast detection of ammonia at μM concentration or lower. H NMR of NH with N decoupling was also demonstrated.