Enhancing Localized Electron Density over Pd 1.4 Cu Decorated Oxygen Defective TiO 2-x Nanoarray for Electrocatalytic Nitrite Reduction to Ammonia.

Electrocatalytic nitrite (NO 2 - ) reduction to ammonia (NH 3 ) is a promising method for reducing pollution and aiding industrial production. However, progress is limited by the lack of efficient selective catalysts and ambiguous catalytic mechanisms. This study explores the loading of PdCu alloy onto oxygen defective TiO 2-x , resulting in a significant increase in NH 3 yield (from 70.6 to 366.4 µmol cm -2  h -1 at -0.6 V vs reversible hydrogen electrode) by modulating localized electron density. In situ and operando studies illustrate that the reduction of NO 2 - to NH 3 involves gradual deoxygenation and hydrogenation. The process also demonstrated excellent selectivity and stability, with long-term durability in cycling and 50 h stability tests. Density functional theory (DFT) calculations elucidate that the introduction of PdCu alloys further amplified electron density at oxygen vacancies (Ovs). Additionally, the Ti─O bond is strengthened as the d-band center of the Ti 3d rising after PdCu loading, facilitating the adsorption and activation of * NO 2 . Moreover, the presence of Ovs and PdCu alloy lowers the energy barriers for deoxygenation and hydrogenation, leading to high yield and selectivity of NH 3 . This insight of controlling localized electron density offers valuable insights for advancing sustainable NH 3 synthesis methods.