Synergy of Pd 2+ /S 2- -Doped TiO 2 Supported on 2-Methylimidazolium-Functionalized Polypyrrole/Graphene Oxide for Enhanced Nitrogen Electrooxidation.

The electrosynthesis of nitrate catalyzed by electrochemical nitrogen oxidation reaction (NOR) is considered as an alternative and sustainable approach to the conventional industrial manufacture, but optimizing the electrocatalytic NOR performance and fabricating the efficient NOR electrocatalysts at the design level still encounter great challenges. Herein, unique Pd 2+ - and S 2- -doped TiO 2 (Pb/S-TiO 2 ) nanoparticles are successfully in situ grown on the surface of 2-methylimidazolium-functionalized polypyrrole/graphene oxide (2-MeIm/PPy/GO), which present the typical hierarchical micro-nanostructures, resulting in the excellent electrocatalytic NOR performance with the highest NO 3 - yield of 72.69 µg h -1 mg -1 act. and the maximum Faraday efficiency of 8.92% at 2.04 V (vs reversible hydrogen electrode) due to the synergistic effect of each component. Due to the doping effect, the appropriate oxygen evolution reaction (OER) activity is achieved by Ti-site, where OER principally occurs, providing *O during the non-electrochemical step of NOR, while the electrocatalytic NOR process as the electrochemical conversion of inert N 2 to active *NO intermediates mainly occurs at the Pd-site. Especially, the sulfate radicals in situ formed on Pb/S-TiO 2 @2-MeIm/PPy/GO further promote nitrogen adsorption and decrease the reaction energy barrier, resulting in the acceleration of NOR. It provides theoretical and practical experience for the design and preparation of NOR electrocatalysts.