Beyond Interfacial Structure: Ion Transport Mediates Cation Effects in Electrochemical Nitrate Reduction

Area of Science:

• Electrochemistry
• Materials Science
• Computational Chemistry

Background:

• Electrochemical reduction of nitrate to ammonia offers dual benefits for wastewater treatment and sustainable ammonia synthesis.
• Observed cation-specific effects on nitrate reduction rates (Li+ < Na+ < K+ < Cs+) lack atomistic understanding.
• Previous studies focused on interfacial structure, neglecting mass transport contributions.

Purpose of the Study:

• To elucidate the atomistic origins of cation-specific rate enhancements in electrochemical nitrate reduction.
• To investigate the roles of interfacial structure and mass transport in nitrate reduction kinetics.
• To provide insights for rational electrolyte design in electrochemical nitrate remediation and ammonia production.

Main Methods:

• Classical molecular dynamics simulations in the constant potential ensemble.
• Modeling of the electric double layer in nitrate-based electrolytes.
• Analysis of interfacial structure, nitrate adsorption thermodynamics, and bulk ion transport properties.

Main Results:

• Interfacial structure is cation-dependent, but nitrate physisorption is weakly influenced by cations due to dominant water polarization.
• Larger cations decrease the nitrate transference number, lowering migration energy barriers.
• Increased electrolyte diffusivity and enhanced nitrate flux to the cathode correlate with experimental rate trends.

Conclusions:

• Ion transport, specifically nitrate migration and diffusion, is a critical factor in electrochemical nitrate reduction rate enhancement.
• Electrolyte cation choice significantly influences reactant transport dynamics at the electrode interface.
• Strategic electrolyte design can be employed to optimize reactant transport for efficient electrochemical nitrate reduction.