Modeling of Electrocatalytic Dinitrogen Reduction on Microstructured Electrodes

One major challenge of electrocatalytic dinitrogen (N₂) reduction is the competition between nitrogen reduction reaction (NRR) and hydrogen evolution reaction (HER). While experimental development of selective NRR catalysts is indispensable, the aim is to derive insights of catalyst design by developing a model that includes both the kinetics of competing reactions on the electrode and the mass transport of reactants in solution. The developed microkinetic model is reported here and it is applied to evaluate NRR selectivity on planar and microstructured electrodes. As a proof-of-principle, the model is numerically simulated under an aqueous electrolyte of 0.1 m nonoxidizing strong acid. The analysis indicates that while the first electron transfer to N₂ is rate-limiting in most cases, under certain scenarios the impact of subsequent proton transfer on the reaction rate can be prominent. The microstructure of electrodes can pose a limit of N₂ mass transport and intriguingly cast a negative impact on the selectivity of N₂ fixation. Overall, the developed model interfaces the kinetics on electrode surfaces with the mass transport in the solution, and will serve as a general platform for the design and optimization of electrochemical N₂-fixing process.