Enabling High Performance in a Positive Potential of Nitrate-to-Ammonia Electrocatalysis Over Mesoporous Core@Shell Cu₂O/Cu@PdCu Nanozyme.

Abstract

Electrocatalytic tandem nitrate reduction to ammonia (NO₃ ^--to-NH₃) offers a promising pathway for energy and environmental sustainability. Although considerable efforts have been presented to modulate the reaction pathways for enhanced NO₃ ^--to-NH₃ electrocatalysis, these advances often require relatively high overpotentials to balance yield rate and selectivity of NH₃, resulting in a remarkable energy inefficiency. Inspired by enzyme catalysis in nature, herein a tandem enzyme-like electrocatalyst is designed consisting of a core of Cu₂O/Cu heterojunction surrounded by mesoporous PdCu shell (Cu₂O/Cu@mesoPdCu) that accelerated NO₃ ^--to-NH₃ electrocatalysis in positive potentials. Impressively, Cu₂O/Cu@mesoPdCu nanozymes hold superior performance for robust NH₃ electrosynthesis in a fairly positive potential of 0.10 V (versus reversible hydrogen electrode), having Faraday efficiency of 96.2%, yield rate of 13.3 mg h^-1 mg^-1, and half-cell energy efficiency of 46.0%. Kinetic studies, in situ spectra and density functional theory calculations revealed that Cu₂O/Cu core preferentially adsorbed NO₃ ^- and further reduced to *NO₂, while active hydrogen radicals enriched on PdCu shell promoted multistep hydrodeoxygenation of *NO₂ to NH₃ within "semi-closed" mesoporous microenvironment, both of which synergistically enabled tandem electrocatalysis in positive potentials. Moreover, this enzyme-like electrocatalyst disclosed better NO₃ ^--to-NH₃ performance in a more energy-efficient manner when coupling with more thermodynamically favorable ethanol oxidation reaction.