NixCo3−xO4 nanowire arrays are grown on a Ti foil for efficient oxygen evolution reactions. Ni‐doped nanowire arrays have higher electrocatalytic activity than pure Co3O4. The success of the nanowire electrodes results from their high surface areas and direct electron contact to the conductive substrate.

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We have systematically studied the effects of substitutional doping of p-type nanoparticulate NiO with cobalt ions. Thin films of pure and Co-doped NiO nanoparticles with nominal compositions Co(x)Ni(1-x)O(y) (0 ≤ x ≤ 0.1) were fabricated using sol-gel method. X-ray photoelectron spectroscopy revealed a surface enrichment of divalent cobalt ions in the Co(x)Ni(1-x)O(y) nanoparticles. Mott-Schottky analysis in aqueous solutions was used to determine the space charge capacitance values of the films against aqueous electrolytes, which yielded acceptor state densities (N(A)) and apparent flat-band potentials (E(fb)). Both N(A) and E(fb) values of the doped NiO were found to gradually increase with increasing amount of doping; thus the Fermi energy level of the charge carriers decreased with Co-doping. The photovoltage of p-DSCs constructed using the Co(x)Ni(1-x)O(y) films increased with increasing amount of cobalt, as expected from the trend in the E(fb). Co-doping increased both carrier lifetimes within the p-DSCs and the carrier transport times within the nanoparticulate semiconductor network. The nominal composition of Co₀.₀₆Ni₀.₉₄O(y) was found to be optimal for use in p-DSCs.

Graphene films have been used as transparent conductive electrodes (TCEs) and counter electrodes in dye-sensitized solar cells (DSCs) in order to reduce the cost of fabrication. This work reports the fundamental electrocatalytic properties of graphene films toward I−/I3 − by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The films were prepared from chemical or thermal reduction of graphene oxide. We demonstrate that graphene films obtained under different reduction conditions exhibit different electrocatalytic properties. The mechanism is elucidated by the structural differences as confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. We also show that the electrocatalytic activity of graphene films could be tuned by surface modification with polyelectrolytes.

Mesoporous Nb-doped TiO 2 film was prepared by the sol-gel method on a transparent conducting FTO glass. Pt nanoparticles were impregnated in the mesoporous TiO 2 support substrate and tested for the counter electrode in dye-sensitized solar cells (DSSCs). The mesoporous Pt/Nb-doped TiO 2 was characterized by scanning electron microscopy and high-resolution transmission electron microscopy. The electrocatalytic activity of the Pt nanoparticles on different supports was studied by electrochemical impedance spectroscopy for the tri-iodide (I 3 -)/iodide (I -) redox reaction in acetonitrile, a common electrolyte solution for DSSCs. By fabricating a Pt/Nb-doped TiO 2 electrode, the charge transfer resistance was reduced and the exchange current density was increased as the result of a larger active surface area of Pt in the mesoporous Nb-doped TiO 2 . This electrode could be used in other systems where there is a need to control the amount of Pt surface area and hamper Pt particle aggregation when operating at high temperatures. The impregnation of Pt in the mesoporous TiO 2 can also improve the mechanical rigidity and stability of the electrocatalyst against abrasion or generally mechanical contact, a desired property for practical applications.