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Deciphering Competitive Kinetics in Nitrate Reduction via Mechanistic Modeling: Impact of Ru and Pd Dopants on
Bo Li1,2, Cheng Chen1, Ouwen Peng1,3
1Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518000, China.
None:
The electrochemical nitrate reduction reaction (NO3RR) presents a sustainable route to ammonia (NH3), but its practical application is hindered by competition from the parasitic hydrogen evolution reaction (HER) and the accumulation of undesired nitrite (NO2-) intermediates. A quantitative understanding of these competing pathways is essential for rational catalyst design, yet a comprehensive framework is currently lacking. To address this, we introduce a competitive kinetic model that explicitly couples the reaction networks of the NO3RR and HER. Applied to Ru- and Pd-doped Fe3C catalysts, this model is rigorously constrained by data from operando infrared spectroscopy (ATR-SEIRAS) and in situ impedance spectroscopy with distribution of relaxation times (EIS-DRT) analysis. The model successfully deconvolutes the reaction network, revealing that Ru promotes matched, high-rate kinetics for sequential deoxygenation steps, leading to high selectivity and achieving an NH3 Faradaic efficiency of 96.3% at - 0.5 V vs RHE. Conversely, Pd induces a kinetic mismatch between sequential deoxygenation steps: upstream formation of *NO2-related intermediates is relatively efficient, whereas their subsequent hydrogen-assisted deoxygenation/consumption is comparatively sluggish, leading to the substantial accumulation and release of the NO2-. By seamlessly bridging advanced operando characterization with rigorous quantitative modeling, this work provides a predictive blueprint for diagnosing kinetic bottlenecks and accelerating the rational design of highly selective electrocatalysts.
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