Pd Clusters Loaded with Multivalent Cu Foam for Superior Electrochemical Nitrate Reduction and Selective N≡N Bond Formation.

The electrochemical denitrification of nitrate (NO 3 - ) in actual wastewater to nitrogen (N 2 ) is an effective approach to reversing the current imbalance of the nitrogen cycle and the eutrophication of water. However, electrostatic repulsion between NO 3 - and the cathode results in the low efficiency of NO 3 - reduction reaction (NO 3 RR). Here, density functional theory (DFT) calculations are used as a theoretical guide to design a Pd cluster-loaded multivalent Cu foam (Pd/Cu 2 O-CF) electrocatalyst, which achieves a splendid 97.8% NO 3 - removal rate, 97.9% N 2 selectivity, 695.5 mg N g -1 Pd h -1 reduction efficiency, and 60.0% Faradaic efficiency at -1.3 V versus SCE. The projected density of states (pDOS) indicates that NO 3 - and Pd/Cu 2 O-CF are bonded via strong complexation between the O 2p (in NO 3 - ) and Cu 3d (in Cu 2 O) with the input of voltage, which reduces the electrostatic repulsion and enhances the enrichment of NO 3 - on the cathode. In-situ characterizations demonstrate that Pd[H] can reduce Cu 2 O to Cu, and subsequently Cu reduces NO 3 - to nitrite (NO 2 - ) accompanied by in situ reconfiguration of multivalent Cu foam. NO 2 - is then transferred to the surface of Pd clusters by the cascade catalysis and accelerates the breaking of N─O bonds to form Pd─N, and eventually achieves the N≡N bond formation.