Tandem electroreduction of nitrate to green ammonia on recycled copper sheets from spent batteries: splicing surface roughness achieves high yield rate

Abstract

Electrochemical conversion of nitrate to ammonia (eNitRR) offers a sustainable alternative to ammonia production. However, the lack of efficient and high turnover electrocatalysts is hindering the eventual commercialization of eNitRR. Moreover, in order to improve the viability of eNitRR commercialization further, electrocatalysts should also be sourced from recycled or waste materials. Battery waste, in particular spent lithium-ion batteries, is a massive and versatile resource for valuable metals. Herein, we extracted Cu foil from spent Li-ion batteries and modified it via various treatments to control the surface roughness factor (RF). The electrocatalytic performance increased as the RF increases, resulting in a maximum NH₃ faradaic efficiency (FE) of ∼97.6% and a yield rate (YR) of ∼2.162 mmol h⁻¹ cm⁻². As surface morphology and roughness can play an integrative role in the catalytic activity, different roughened surfaces were built using Python code. Molecular dynamics (MD) studies revealed that the Cu roughened surfaces have square sites and close-packed sites with Cu (100) and Cu (111) facets, respectively. Ab initio calculations illustrate that NO₃⁻ adsorption likely takes place on the Cu (100) facets and transforms into NO₂⁻, at which point the reactant species transfer to a Cu (111) facet, where further protonation occurs until ammonia is produced. This tandem interaction was theorized to be the underlying mechanism behind the obtained superior catalytic performance.