Fundamental Limits of Dissociative Electrochemical Ammonia Synthesis via Electrodeposited Metals

TL;DR

This paper investigates the fundamental thermodynamic limits of electrochemical ammonia synthesis using metals, identifying energetic constraints and proposing strategies to reduce energy costs while maintaining selectivity.

Contribution

It establishes the thermodynamic limits for dissociative nitrogen reduction with metals and suggests design principles to lower energy input in ammonia synthesis.

Findings

Highly reducing metals incur significant energetic penalties.

Solvent tuning and bimetallic alloys can shift deposition potentials.

Design principles can lower energy input while preserving selectivity.

Abstract

Electrochemical ammonia synthesis via lithium-mediated nitrogen dissociation has demonstrated exceptional Faradaic efficiency at ambient conditions, but its viability is limited by a high energy cost of ~9.12 eV per NH3 via lithium electrodeposition. Here, we establish the thermodynamic limits for dissociative nitrogen reduction using elemental metals by decomposing the process into three steps: metal deposition, nitridation, and protonation. We derive energetic constraints that any viable mediator must satisfy and show that highly reducing metals impose significant energetic penalties. To reduce this cost, we explore solvent tuning and bimetallic alloy strategies that shift deposition potentials without compromising nitridation spontaneity. Our results offer design principles for lowering the energy input of dissociative nitrogen reduction while maintaining its selectivity advantage over associative routes.