Fast Proton NMR Detection of Aqueous Ammonia with Relaxation Agent and Nitrogen Decoupling
Year: 2025
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide The Haber–Bosch process, which synthesizes ammonia (NH 3 ) from nitrogen (N 2 ) and hydrogen (H 2 ), consumes approximately 2% of the global energy supply. A sustainable alternative is the direct electrochemical conversion of N 2 to NH 3 . The selectivity and activity of the electrocatalysts for this process are assessed by quantifying the NH 3 present in the electrolyte. Compared with other analytical methods, 1 H NMR offers a straightforward approach for detecting NH 3 (by analyzing NH 4 + ). 1 H NMR method can also definitely confirm that the detected ammonia originates from the electroreduction of N 2 by comparing results obtained from isotopically labeled 15 N 2 and regular 14 N 2 gases. This capability is unique to the 1 H NMR method, as no alternative approaches offer this level of specificity. However, this method suffers from low sensitivity when measuring NH 4 + 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 14 N decoupling during the 1 H NMR data acquisition. Recently [ Kolen, M. ACS Omega 2021, 6, 5698–5704], demonstrated a ∼3.5-fold increase in sensitivity by using a 1 mM concentration of the paramagnetic relaxation agent Gd 3+ . By combining our 14 N decoupling technique with the relaxation agent Gd 3+, we achieved a synergistic enhancement in sensitivity, resulting in an overall ∼10.9-fold sensitivity increase for the 1 H NMR detection of 14 NH 4 + . This translates to a reduction in NMR detection time by a factor of ∼119 (10.9 2 ). This significant advancement enables the fast detection of ammonia at μM concentration or lower. 1 H NMR of 15 NH 4 + with 15 N decoupling was also demonstrated.
Source: ACS Omega
Language: English
Subfield: Spectroscopy
Field: Chemistry
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,935
OpenAlex ID: W4407761414