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

Abstract

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.