Accurate Online Quantification of Electrocatalytic Ammonia Production Using a Gas-Selective Electrode

Abstract Ammonia is a key intermediate for the catalytic production of fertilizers, important industrial feedstocks, and the basis of the ammonia economy as an alternative hydrogen carrier. Therefore, there is much interest in its quantification, especially by online methods. For basic research on electrocatalytic materials for ammonia production, typically low concentrations need to be quantified, and fast measurements are highly desirable for screening and rejecting environmental influences. In this paper, we evaluate a potentiometric method based on a gas-selective electrode (GSE) for online quantification of ammonia in an alkaline electrolyte, which closes a methodical gap in the field as it allows additive-free online measurements with T90 response times shorter than 1 min for NH3 concentrations above 15 µM using a simple setup. Boron-doped nanodiamond (B-ND) is used as a test case for electrocatalytic ammonia production from nitrate (NO3RR) using a RDE setup and for ammonia production from nitric oxide (NORR) in a gas diffusion electrode (GDE) setup. The parameters of the calibration curve are predictable using the Nernst equation and agree well with the measurements, that is, the measurements are accurate. The lower limit of detection (LOD) and limit of quantification (LOQ) are determined as 0.57 and 1.36 µM. The yield rate and Faradaic efficiency of the test cases are 2.18 ± 0.01 nmol s–1 cm–2 and 42.45 ± 0.07% for NO3RR using the RDE as well as 0.48 ± 0.01 nmol s–1 cm–2 and 9.32 ± 0.34% for NORR using the GDE, respectively. These findings are of interest to researchers in the field of electrocatalysis of nitrogen and nitrogen oxides to ammonia who study catalyst materials and devices for ammonia synthesis, unveiling the potential to be extended to other reactor types.