Our current time is strongly influenced by climate change and the energy crisis, which lead to a need for greener chemical industry processes. One of the biggest chemistry branches in industry is the ammonia production based on the large-scale Haber-Bosch process. A possible greener alternative to this process is small-scale distributed production such as the electrocatalytic reduction of molecular nitrogen (eN2RR). However, the field of the eN2RR suffers from the lack of a suitable catalyst that offers relevant, stable and reproducible activities. The joint goal of our group is to tackle the problem of the inefficient eN2RR by using boron doped diamond (BDD) as a catalytic material. Therefore, we are investigating different cell designs including aqueous and aprotic electrolytes and improving the catalysts itself by varying the B/C ratio and nano-structuring [1].

The electrochemical experiments are conducted in a flow cell with a gas diffusion electrode as a working electrode. The main ammonia quantification method is the indophenol method. Furthermore, false positives caused by nitrogen containing compounds are identified by control measurements with ¹⁵N₂ and determination of background impurities such as NO_X. The effect of possible nitrogen containing impurities is minimised by applying our own established cleaning protocol, which also includes the purification of the gas stream. The performance of the boron doped diamond catalyst will be compared with two suitable reference catalysts from literature, the LiMn₂O₄ and Au flower catalyst, which were already tested in our setup in aqueous electrolyte and feature a yield of 183 and 420 nmol h^-1 cm^-2 respectively which is consistent with literature [2], [3].

Our group also studied an alternative quantification method via an Ammonia-Gas Selective Electrode (NH₃-GSE). The actual work shows the unprecedented deployment of an Ammonia-Gas Selective Electrode as an online potentiometric quantification method for NH₃ in aqueous-alkaline environments, with main focus to its application to electrocatalytic NO₃^- reduction reaction (NO₃RR) experiments. Hence, the accumulation of NH₃ in traditional three-electrodes electrochemical cells does not usually exceed concentrations in order of magnitude of µM in the case of N₂ Reduction Reaction (N₂RR) and NO_xRR. This aspect poses a significant challenge to apply a precise and accurate way to readily quantify the product in such low-yielding reaction experiments [4], [5]. To this matter, the NH₃-GSE is capable to achieve meaningful low detection and quantification levels suitable for those electrocatalytic reaction studies (LOD = 0.38 µM, LOQ = 0.84 µM). Moreover, we proved that this device is able to track instantaneously the NH₃ concentration produced during an electrolysis running in a three-electrodes cell. The concentration profile obtained can be fitted to retrieve fundamental electrocatalytic activity descriptors such as the Yield of ammonia production and the related Faradaic Efficiency.