Synthesis And Electrocatalytic Properties Of Transition Metal Oxide Catalysts Grown Onto Orderd Mesoporous Carbon

Transition metal oxides are a vital component of the fuel cell cathode catalysts, which have the advangtages of low cost, simple preparation, extensive sources. Moreover, they possess the potential catalytic activities for oxygen reduction and oxygen evolution reactions. In this paper, the ordered mesoporous carbon used as the support was prepared by a conventional nanocasting strategy using a mesoporous silica rod as a hard template. Transition metal oxides nanoparticles (monometal, bimetal, trimetal) were successfully in situ grown onto ordered mesoporous carbon by a facile, scalable hydrothermal method. The catalytic activities for oxygen reduction and oxygen evolution reactions were investigated via conventional three electrode system in basic solutions.CoFe2O4 nanoparticles grown onto ordered mesoporous carbon with the CTAB as surfactant were synthezised by hydrothermal method, followed by annealing at different temperatures. The as-acquired CFO/MC nanohybrid pyrolyzed at 400℃(CFO/RC-400) has a high specific surface area (150.3 m2 g"1) and two sets of uniform mesopore systems (3.38 and 19.1 nm), all of which are favorable for the improvement of the electrocatalytic activity. The hybridization of CFO nanoparticles and the MC matrix results in increased ORR and OER electrocatalytic activity of the CFO/MC nanohybrids. CFO/RC-400 shows better catalytic activity for the ORR with a direct four-electron reaction pathway than those prepared at other temperatures in terms of the onset potential and limiting current density. Furthermore, the CFO/MC-400 nanohybrid exhibits outstanding durability for both the ORR and OER, and can outperform commercial Pt/C. The excellent bifunctional electrocatalytic activities of the CFO/RC nanohybrids are mainly owing to the hierarchical mesoporous structures of the nanohybrids and strong coupling between the CFO nanoparticles and the MC matrix.NixCo1-xFe2O4/MC nanohybrids were prepared via a one-pot hydrothermal method, followed by annealing at 400℃. Along with the gradually decrease of the content of Ni element, the NixCo1-xFe2O4/MC nanohybrid demonstrate increasing better catalytic activity towards oxygen reduction reaction. When Ni elements exist in the nanohybrid, the nanoparticles on the MC reunite together, which could cover some of the active sites, and the ORR activity decreased. Moreover, the nanoparticles could fall off from the MC in the process of the oxygen reduction, which would lower the catalytic stability of the nanohybrid.CoO nanoparticles and ordered mesoporous carbon were combined as nanohybrid (CoO/MC) via a one-pot hydrothermal method to demonstrate excellent catalytic activity towards oxygen reduction reaction (ORR). Different content of polyvinylpyrrolidone (PVP) were added to the precursors as surfactant during the hydrothermal procedure, which could decompose completely during the following pyrolyzation process. Among the as-acquired products, the CoO/MC nanohybrid with 1.5 g PVP (CoO/MC-1.5) exhibits excellent catalytic activity for the ORR with a more positive onset potential and higher current density than the others. Furthermore, the CoO/MC-1.5 nanohybrid demonstrates outstanding durability based on the current-time chronoamperometric test for the ORR, which can outperform the commercial Pt/C. With the PVP as surfactant, the CoO/MC-1.5 nanohybrid possesses higher specific surface area than CoO/MC-0 (free of PVP) which can create more active sites during electrocatalysis.