Well-Coupled Nanohybrids Obtained by Component-Controlled Synthesis and in Situ Integration of Mn_xPd_y 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_xPd_y(MnPd₃, MnPd-Pd, Mn₂Pd₃, Mn₂Pd₃-Mn₁₁Pd₂₁)/C NHs have been synthesized by in situ integration of Mn_xPd_y NCs with variable component ratios on pretreated Vulcan XC-72 C using the solvothermal method accompanied with annealing under Ar/H₂ atmosphere and used as electrocatalysts for ORR. Among them, the MnPd₃/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, Pd₂NiAg NCs, PdCo/N-doped porous C, G-Cu₃Pd 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 MnPd₃/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 MnPd₃ active components and enhance their conductivity or interfacial electron transfer dynamics. This work demonstrates that MnPd₃/C NHs are promising methanol-tolerant cathode electrocatalysts that may be employed in fuel cells or other renewable energy option.