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 ¹⁵NO _<i>x</i> 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).