Pd-Cu modified cerium oxide catalysts for selectively electrocatalytic denitrification: Significant roles of oxygen vacancies and activated hydrogen

•Pd-Cu loaded CeO2 with oxygen vacancies (Pd-Cu/CeO2-OVs) was synthesized.•Efficient electrocatalytic reduction of nitrate was realized by Pd-Cu/CeO2-OVs.•Oxygen vacancies thermodynamically favored the adsorption of nitrate.•Pd-Cu bimetallic structure facilitated the generation of activated hydrogen (H*).•H* efficiently boosted the reduction of nitrate to dinitrogen. Developing efficient electrocatalysts for selectively denitrification is particularly critical in the face of the increasing environmental nitrate pollution. Herein, we design and synthesize a Pd-Cu modified cerium oxide (CeO2) catalysts (Pd-Cu/CeO2-OVs) with abundant oxygen vacancies (OVs) within the substrate by a sequential calcination-chemical impregnation strategy. The optimal Pd-Cu/CeO2-OVs (Pd/Cu at 3/1) exhibited a superior electrocatalytic denitrification performance with the NO3--N removal efficiency of 98 % at 25 mA within 2.5 h, compared with 24 % for Pd/CeO2-OVs and 49 % for Cu/CeO2-OVs. And the total nitrogen (TN) removal efficiency reached 47 %. Mechanistic study results obtained from experiment and density functional theory calculation demonstrate that the in-situ formed H2 on cathode can be readily activated by Pd-Cu to form activated hydrogen (H*) with a powerful reducing capacity. Moreover, the oxygen vacancies in CeO2-OVs are able to effectively capture NO3-, thus allowing the efficient conversion of NO3- to N2. Significantly, the Pd-Cu/CeO2-OVs also shows an excellent durability and stability. Electrocatalytic reaction in real wastewater further demonstrates the superiority of Pd-Cu/CeO2-OVs catalyst towards nitrate elimination for sewage effluent.