Well-Coupled Nanohybrids Obtained by Component-Controlled Synthesis and in Situ Integration of Mn Pd Nanocrystals on Vulcan Carbon for Electrocatalytic Oxygen Reduction.

Development of cheap, highly active, and robust bimetallic nanocrystal (NC)-based nanohybrid (NH) electrocatalysts for oxygen reduction reaction (ORR) is helpful for advancing fuel cells or other renewable energy technologies. Here, four kinds of well-coupled Mn Pd (MnPd, MnPd-Pd, MnPd, MnPd-MnPd)/C NHs have been synthesized by in situ integration of Mn Pd NCs with variable component ratios on pretreated Vulcan XC-72 C using the solvothermal method accompanied with annealing under Ar/H atmosphere and used as electrocatalysts for ORR. Among them, the MnPd/C NHs possess the unique "half-embedded and half-encapsulated" interfaces and exhibit the highest catalytic activity, which can compete with some currently reported non-Pt catalysts (e.g., Ag-Co nanoalloys, PdNiAg NCs, PdCo/N-doped porous C, G-CuPd nanocomposites, etc.), and close to commercial Pt/C. Electrocatalytic dynamic measurements disclose that their ORR mechanism abides by the direct 4e pathway. Moreover, their durability and methanol-tolerant capability are much higher than that of Pt/C. As revealed by spectroscopic and electrochemical analyses, the excellent catalytic performance of MnPd/C NHs results from the proper component ratio of Mn and Pd and the strong interplay of their constituents, which not only facilitate to optimize the d-band center or the electronic structure of Pd but also induce the phase transformation of MnPd active components and enhance their conductivity or interfacial electron transfer dynamics. This work demonstrates that MnPd/C NHs are promising methanol-tolerant cathode electrocatalysts that may be employed in fuel cells or other renewable energy option.