Toward reliable and accessible ammonia quantification in the electrocatalytic reduction of nitrogen

Abstract

Nitrogen electroreduction may alleviate fossil energy requirements to produce fertilizers, but efficient catalysts must still be developed. The development of accurate and accessible ammonia quantification tools is key to accelerate this process. This article provides guidelines to optimize sensitivity of UV-vis spectroscopy and the ion-selective electrode for initial catalyst screening. However, confirmation of the catalytic origin of ammonia is only feasible through 1 H-NMR, which is much less frequently applied largely due to the high expertise and expensive apparatuses needed. We introduce a protocol accessible to catalyst practitioners applicable to widely available 300 MHz NMR spectrometers. To this end, we adapted the WATERGATE suppression method to accomplish high signal-to-noise ratios even in non-deuterated samples. It was demonstrated for a relevant concentration of 1 ppm, enabling qualitative and quantitative analysis in 2 and 15 min, respectively. By making 1 H-NMR quantification more accessible, this study facilitates the application of state-of-the-art catalytic assessments. • Guidelines to maximize sensitivity of UV-vis and ion-sensing electrode are provided • We offer a sensitive 1 H-NMR protocol allowing quantification of unmodified samples • The protocol was demonstrated in low-grade spectrometers (300 MHz) • Ammonia quantification through 1 H-NMR is now widely accessible The distributed production of ammonia may complement the current model based on large Haber-Bosch plants, thus contributing to the UN Sustainable Development Goal of Good Health and Well-Being . One of the more appealing candidates is the electrocatalytic transformation of nitrogen into ammonia using renewable electricity. An intense race has developed to find suitable electrocatalysts but uncertainty on the performance of benchmark catalysts has recently led to rigorous testing protocols based on 1 H-NMR. Currently, these protocols lack accessibility due to the need for expensive apparatuses and high skills. We firstly provide guidelines for commonly reported quantification techniques, although our focus is the development of a 1 H-NMR protocol with outstanding sensitivity and spectrum quality while only requiring a user-level understanding. We demonstrate its application in widely available low-grade spectrometers, making 1 H-NMR as accessible as the most commonly reported UV-vis spectroscopy. One of the obstacles hindering the discovery of effective electrocatalysts to produce ammonia is the costly equipment and high skills required to quantify ammonia following state-of-the-art 1 H-NMR protocols. We develop a protocol implementable in widely available low-grade spectrometers offering exceptional spectrum quality and amenable to all catalyst practitioners. This contribution thus lowers entry barriers and may accelerate the progress toward the sustainable production of fertilizers.