Electrocatalytic Nitrate and Nitrite Reduction toward Ammonia Using Cu<sub>2</sub>O Nanocubes: Active Species and Reaction Mechanisms
Lichen Bai, Federico Franco, Janis Timoshenko, Clara Rettenmaier, Fabian Scholten, Hyo Sang Jeon, Aram Yoon, Martina Rüscher, Antonia Herzog, Felix T. Haase, Stefanie Kühl, See Wee Chee, Arno Bergmann, Beatriz Roldán Cuenya
Abstract
High Resolution Image Download MS PowerPoint Slide The electrochemical reduction of nitrate (NO 3 – ) and nitrite (NO 2 – ) enables sustainable, carbon-neutral, and decentralized routes to produce ammonia (NH 3 ). Copper-based materials are promising electrocatalysts for NO x – conversion to NH 3 . However, the underlying reaction mechanisms and the role of different Cu species during the catalytic process are still poorly understood. Herein, by combining quasi in situ X-ray photoelectron spectroscopy (XPS) and operando X-ray absorption spectroscopy (XAS), we unveiled that Cu is mostly in metallic form during the highly selective reduction of NO 3 – /NO 2 – to NH 3 . On the contrary, Cu(I) species are predominant in a potential region where the two-electron reduction of NO 3 – to NO 2 – is the major reaction. Electrokinetic analysis and in situ Raman spectroscopy was also used to propose possible steps and intermediates leading to NO 2 – and NH 3, respectively. This work establishes a correlation between the catalytic performance and the dynamic changes of the chemical state of Cu, and provides crucial mechanistic insights into the pathways for NO 3 – /NO 2 – electrocatalytic reduction.