Boosting oxygen reduction electrocatalytic performance of Cu-N_x by modulating electron structure via construction of Cu-N_x and Cu nanocluster coupling catalyst

The utilization of atom-dispersed Cu-N_x site catalysts holds significant promise as a replacement for commercial Pt/C catalyst in the context of oxygen reduction catalysts. However, practical application of these catalysts has been hindered by their insufficient catalytic activity. It is imperative to enhance the oxygen reduction reaction (ORR) catalytic activity of the Cu-N_x catalysts by manipulating electronic structure of the Cu-N_x site. This study presents the synthesis of a composite catalyst, formed by coupling Cu nanoclusters and Cu-N_x catalysts through pyrolysis of protein-Cu²⁺ gel followed by acid-leaching treatment. The resultant composite catalyst demonstrates superior ORR activity as compared to isolated Cu-N_x catalysts under alkaline conditions. Through density functional theory (DFT) calculations, the synergistic mechanism of the coupled Cu nanoclusters and Cu-N_x for ORR catalytic activity is elucidated. The proximity of the Cu nanoclusters (Cu₄) to the central Cu atom of Cu-N_x (CuN₄) in the composite catalyst causes a shift in the d-band center of the active Cu site towards the Fermi level. This shift strengthens the binding energy of O₂ adsorption, reduces ORR overpotential, and combines with favorable electron transfer from Cu nanoclusters to Cu-N_x sites, thereby enhancing ORR activity. These findings contribute novel insights into the enhancement of ORR catalysis performance through the manipulation of electron structures via nano-sized metal clusters.