The enhancement of the oxygen reduction reaction (ORR) activity of platinum nanoparticles (Pt NPs) using transition metal oxide (MO x , M = Ti, Nb, Ta, W, Y, and Zr) supports has been examined. To enable the use of transition metal oxides having low electric conductivity as supports, Pt NPs were formed on thin transition metal oxides formed on conducting cup-stacked carbon nanotubes (CSCNTs). Metal oxide composites (M1M2O x ) prepared from two types of transition metal (M1M2: TiNb, NbTa, and TaW) precursors were also used as supports. Pt NPs were photodeposited on MO x /CSCNTs and M1M2O x /CSCNT supports, resulting in MO x /CSCNT- and M1M2O x /CSCNT-supported Pt NP catalysts (abbreviated as Pt/MO x /CSCNTs and Pt/M1M2O x /CSCNTs). Their ORR activities in 0.1 M HClO4 aqueous solution were found to significantly depend on the atomic ratio of M1 and M2 in M1M2O x and the type of metal oxide support. A “volcano-type” dependence of the ORR activity (represented as the current density, mass activity, and specific activity at 0.9 V vs reversible hydrogen electrode (RHE)) on the Pt d-band center, relative to the Fermi level, was obtained in a series of the Pt/MO x /CSCNTs and Pt/M1M2O x /CSCNT catalysts. It was found that the d-band center values (ranging from −3.83 to −3.42 eV) of Pt deposited on MO x /CSCNTs and M1M2O x /CSCNT supports were lower than that (−3.39 eV) of the reference Pt/carbon black (CB) and that the Pt/TiNbO x (Ti/Nb = 1:6.6 in atomic ratio)/CSCNTs with a d-band center of −3.59 eV exhibited the maximum ORR activity, in agreement with the theoretical expectation that an ORR catalyst having a d-band center that is ca. 0.2 eV lower than that of Pt would have maximal ORR activity.

Nanosized ordered intermetallic Pd3Pb nanoparticles (NPs)/carbon black (CB) (1–8 nm), Pd3Pb NPs/CB, in which Pd3Pb has a Cu3Au-type structure and its NPs are supported on CB, were prepared by the polyol method under an air atmosphere and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), and X-ray photoelectron spectroscopy (XPS). The XRD and XPS measurements confirmed the formation of ordered intermetallic Pd3Pb NPs with a super lattice phase, and the TEM and STEM images indicated a relatively uniform dispersion of Pd3Pb NPs on the CB surface with an average size of 4.3 nm and an atomic ratio (Pd:Pb) of 75.9:24.1. The surface of the as-prepared Pd3Pb NPs/CB was found to be covered with the Pb (and its oxide) layer and to possess actually no electrocatalysis for the electrooxidation of formic acid (FA). However, this “inactive” as-prepared Pd3Pb NPs/CB could be changed drastically to the “active” one with a high level of electrocatalysis by the electrochemical treatment using cyclic voltammetry, i.e., the pertinent electrooxidation of the Pb surface coating in a 0.1 M HClO4 aqueous solution. The atomic-resolution STEM measurements confirmed that the surface state of the “inactive” as-prepared Pd3Pb NPs/CB can be controlled by changing the number of potential scans employed in the electrochemical treatment. That is, when the potential scan number is suitably chosen, the surface covered with the Pb coating dissolves and becomes an active, ideal structure of Pd3Pb, and further scanning leads to a surface close to that of Pd NPs. The thus electrochemically treated ideal Pd3Pb NPs/CB possessed a largely higher level of electrocatalysis for the FA oxidation than Pd NPs/CB, which could be explained reasonably on the basis of the experimentally measured and/or theoretically calculated d-band center values of both catalysts and CO binding energies on them.

A structurally ordered phase of PdCu3 nanoparticles (NPs)/carbon black (CB), in which PdCu3 has a Cu3Au-type structure, was prepared by co-reduction of Pd and Cu precursors using ethylene glycol as a reducing agent and an annealing procedure.

Current collectors (CCs) are an important and indispensable constituent of lithium-ion batteries (LIBs) and other batteries. CCs serve a vital bridge function in supporting active materials such as cathode and anode materials, binders, and conductive additives, as well as electrochemically connecting the overall structure of anodes and cathodes with an external circuit. Recently, various factors of CCs such as the thickness, hardness, compositions, coating layers, and structures have been modified to improve aspects of battery performance such as the charge/discharge cyclability, energy density, and the rate performance of a cell. In this paper, the details of interesting and useful attempts of preparing CCs for high battery performance in lithium-ion and post-lithium-ion batteries are reviewed. The advantages and disadvantages of these attempts are discussed.

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