Steering Reaction Coordinates on Laser-Programmed Fe/FeO/Ag Electrodes for Nitrate-to-Ammonia Electrosynthesis

Abstract

Electrocatalytic nitrate reduction to ammonia (NO3RR) offers a dual-benefit strategy for pollution remediation and sustainable NH3 synthesis, but steering the complex eight-electron/proton reaction coordinate on earth-abundant iron catalysts remains challenging due to sluggish hydrogenation kinetics and competing hydrogen evolution. Herein, we report a laser-programmed Fe/FeO/Ag electrode that cooperatively engineers three synergistic modalities: an in situ-generated FeO layer, a hydrophobic honeycomb microstructure for enhanced mass transport, and abundant Ag–Fe interfacial sites. Using in situ spectroscopy and density functional theory (DFT) calculations, we reveal that the Ag–Fe heterointerface is accompanied by pronounced electron redistribution from Fe to Ag, creating electron-deficient Fe sites that strengthen NO3 adsorption and electron-enriched Ag sites that weaken H binding. This bifunctional electronic modulation lowers the energy barriers for the rate-determining hydrogenation steps while effectively suppressing the hydrogen evolution reaction (HER). Consequently, the electrode achieves a Faradaic efficiency of 94.7% and an NH3 yield of 14.6 mg h–1 cm–2 in an H-cell, and sustains ∼500 mA cm–2 for over 30 h in a membrane electrode assembly (MEA) flow reactor. This work demonstrates that precise interfacial engineering can steer the reaction coordinate of a multi-electron catalytic process, and establishes laser programming as a versatile platform for designing monolithic electrocatalysts.