Quantitative Operando Detection of Electro Synthesized Ammonia Using Mass Spectrometry

In this work the successful operando detection of synthesized ammonia from nitrogen reduction in non-aqueous electrolytes with an electron-ionization mass spectrometer was reported. Using selective ionization at 22 eV together with a highly sensitive micro-chip-based electrochemistry mass spectrometry set-up, quantitative detection of produced ammonia down to few pmol s(-1) in non-aqueous as well as aqueous electrolytes was demonstrated. The well-defined electrochemical and mass transport environment of the thin-layer electrochemical cell allowed for fundamental studies of the nitrogen reduction process, which was shown to produce ammonia at faradaic efficiencies of 49 +/- 3 % at ambient pressure. Moreover, through the operando capabilities of the developed method, it was shown that ammonia production proceeded even after lithium electroplating had been terminated This potentially explained why higher faradaic efficiencies of lithium mediated ammonia synthesis were observed under dynamic cycling conditions. Two possible mechanisms for this behavior were proposed and an outlook towards future research in operando studies of lithium mediated ammonia synthesis was given.