Exploring Band Structure Effects in Transition Metal Oxides for Electrocatalytic Nitrite Reduction*

The electrocatalytic reduction of nitrite (NO₂^–) to nitrogen gas (N₂) is of significant environmental and industrial importance. This study investigates the catalytic effectiveness of transition metal oxides, particularly spinels with diverse band structures in their oxygen 2p orbitals, as potential catalysts for nitrite reduction. Our research aims to establishing correlations between band center positions, thermodynamics, and kinetics in the nitrite reduction reaction by manipulating band structure of the oxygen 2p orbitals. Inspired by linear free energy scaling relationships, we explore how changes in the band center position of the oxygen 2p orbitals influence the strength of the nitrite-catalyst bond, thereby impacting thermodynamics and activation energy. Such insights have implications for the development of cost-effective and efficient electrocatalysts for denitrification. Guided by the affinity of transition metal centers for oxygen bonding and inspired by copper nitrite reductases, we investigate transition metal oxides as catalysts, providing a novel perspective on catalysis relevant to various element-oxygen bond reactions. In our investigation, we employ Density Functional Theory (DFT) calculations to establish the relationship between the binding energy and the band center positions in the oxygen 2p orbitals. This computational approach sheds light on how variations in the band structure of oxygen 2p orbitals can impact the catalytic performance of transition metal oxide catalysts. A comprehensive experimental approach involves synthesizing specific spinel catalysts (CoFe₂O₄, NiCo₂O₄, Mn₃O₄, LiMn₂O₄, and Co₃O₄) through advanced nanoparticle techniques, followed by rigorous characterization. Subsequent electrochemical testing assesses their efficiency in nitrite electroreduction. This research strives to unveil the intricate relationship between the properties of these spinel catalysts, particularly the band center position of the oxygen 2p orbitals, and their catalytic performance in nitrite reduction. This has implications for developing more cost-effective and efficient electrocatalysts for denitrification, supported by DFT calculations that highlight the connection between binding energy and the oxygen 2p band structure.