Component-controlled synthesis and assembly of Cu-Pd nanocrystals on graphene for oxygen reduction reaction

Exploring low-cost, high-activity, and long-durability hybrid electrocatalysts for cathodic oxygen reduction reaction (ORR) is vital to advance fuel cells technologies. In this paper, a series of graphene (G)-Cu_xPd_y (Cu₄Pd, Cu₃Pd, CuPd, CuPd₃, CuPd₄) nanocomposites (G-Cu_xPd_y NCPs) is obtained by assembly of Cu_xPd_y alloy nanocrystals (NCs) with controlled component ratios on G nanosheets using the "dispersing-mixing-vaporizing solvent" strategy and used as electrocatalysts for ORR. Compared with pure Cu_xPd_y NCs, greatly enhanced interfacial electron transfer dynamics are observed in G-Cu_xPd_y NCPs, which show a strong correlation with the alloy compositions of the NCPs. The electrocatalytic experiments in alkaline solution reveal that the ORR activities of those G-Cu_xPd_y NCPs are also strongly dependent on alloy components and exhibit a double-volcano feature with variations of alloy components. Among them, G-Cu₃Pd NCPs possess the highest electrocatalytic activity, which is much better than some reported electrocatalysts and commercial Pd/C catalyst and close to Pt/C catalyst. By correlating the Pd 3d binding energies and the sizes of Cu_xPd_y NCs with the mass-specific activities of G-Cu_xPd_y NCPs and considering the interfacial electron transfer dynamics, the best catalytic activity of G-Cu₃Pd NCPs may result from the unique electronic structure and the smallest size of Cu₃Pd NCs as well as the strong synergistic effect between G and Cu₃Pd NCs. Moreover, the durability of G-Cu₃Pd NCPs is superior to that of Pt/C catalyst, indicating that they are promising cathodic electrocatalysts for using in alkaline fuel cells.