Nitrogen Reduction Testing with Real-Time 15NH3 Yield Quantification Using Orbital Multiturn Time-of-Flight Mass Spectrometry

Yield validation of dinitrogen reduction reaction (N2RR) catalysts with 15N isotope labeling experiments is frustrated by the high cost of 15N2 and the frequent occurrence of 15NH3 and 15NOx impurities in commercial 15N2 sources. Also, gas diffusion electrode (GDE) cell architectures are relevant to scaling N2RR but underexplored and limited by ex situ product analysis methods. To overcome these obstacles, we develop and demonstrate a protocol for N2RR catalyst testing using a scalable GDE cell architecture and specialized test station that facilitates in-line product analysis with multiturn time-of-flight mass spectrometry. This approach provides robust yield measurements through real-time monitoring of 15NH3 with ultrahigh mass resolution. The 15N-containing impurities are also monitored, allowing their influence to be mitigated. A minimum detectable yield of 6 pmol cm-2 s-1 (at 2.00 sccm and utilizing a 5 cm2 electrode) for real-time 15NH3 yield rate measurements is achieved while using a cost-effective amount of 15N2 (<100 mL).