Mass Transport Modifies the Interfacial Electrolyte to Influence Electrochemical Nitrate Reduction

Abstract

The electrochemical nitrate reduction reaction (NO3RR) can facilitate remediation of nitrate-polluted wastewater and sustainable production of ammonia. As an important component of the reaction microenvironment, the interfacial electrolyte substantially influences NO3RR but remains underexplored. Mass transport modifies the interfacial electrolyte properties (e.g., pH, solute concentrations) and thus regulates NO3RR activity and selectivity. In a representative flow-cell configuration with a titanium NO3RR electrode, we systematically controlled mass transport conditions and demonstrated their impacts on NO3RR performance. With continuum model simulation and in situ infrared absorption spectroscopy, we characterized the interfacial electrolyte environment under varied mass transport conditions. Furthermore, we strategically tuned the interfacial electrolyte properties and experimentally deconvoluted their impacts on NO3RR activity and selectivity. We found that diffusion layer thickness and background electrolyte concentration govern NO3RR activity, while interfacial pH steers NO3RR selectivity. Inspired by these findings, we applied pulsed potential to periodically refresh the interfacial electrolyte environment and lower the local pH, successfully tripling the relative ammonia-to-nitrite selectivity. Distinct from NO3RR studies that focus on reaction kinetics, this study was conducted under commonly observed mass transport limitations to advance mechanistic understanding behind mass transport effects and to help identify engineering opportunities that optimize ammonia production.

Linking Electric Double Layer Formation to Electrocatalytic Activity

“…Yet, the electrocatalysis literature contains numerous examples of co-ion effects. − ,, For example, the size of solvated anions was found to significantly influence their near-surface concentration and consequently the rate of electrochemical CO 2 reduction (Figure ), indicating the necessity of considering co-ions in cathodic reactions. Growing interest in electrocatalytic reduction of anionic species such as nitrate, − further highlights the importance of studying the behavior of anions in electric double layers on cathodes. A more detailed discussion of co-ion effects is presented in Section .…”

Reports from the Frontier: Electrifying Chemical Transformations and Separations to Valorize Wastewater Nitrogen

“…In a follow-up study, we found that mass transport effects on interfacial electrolyte pH and solute concentrations played a more impactful role than near-surface structure in regulating NO 3 RR activity and selectivity. 35 The influence of electrolyte properties on NO 3 RR was especially salient to the context of water treatment, which involves the need to accommodate various wastewater compositions.…”

Electrochemical Reduction of Flue Gas Denitrification Wastewater to Ammonia Using a Dual-Defective Cu2O@Cu Heterojunction Electrode

“…Low-cost and scalable cathode material is the key to real application of electrochemical treatment of wet denitrification nitrate wastewater. Various metallic electrodes, including Cu, Fe, Ni, Co, Ti, Zr, Nb, and Hf, have been studied, − among which Cu features highly occupied d-orbitals and an energy level comparable to NO 3 – , possesses a strong NO 3 – adsorption capacity, and can rapidly convert NO 3 – to NO 2 – with a low onset potential . The nitrate reduction reaction (NITRR) is a tandem reaction involving two steps of NO 3 -to-NO 2 and NO 2 -to-NH 3 , thus effectively modulating and matching the tandem kinetics, which is the key to accelerating transformation and reducing the accumulation of N-containing species. , …”