Crystalline films of Co3O4 are deposited by electrochemically oxidizing a tartrate complex of Co2+ in an aqueous, alkaline solution at elevated temperatures. The crystallinity and stability of the films are a strong function of the deposition temperature. Films deposited at temperatures from 50 to 90 °C are amorphous, but films deposited from refluxing solution at 103 °C are crystalline. The crystalline films adhere strongly to the substrate, whereas the amorphous films peel off of the substrate when dried due to drying stresses. The crystalline films deposit with the normal spinel structure, with a lattice parameter of 0.8097 nm and crystallite size of 26 nm. The catalytic activity of Co3O4 for the oxygen evolution reaction (OER) of the crystalline and amorphous films is compared by Tafel analysis in alkaline solution at pH 14. The crystalline Co3O4 film has a Tafel slope of 49 mV/decade and an exchange current density of 2.0 × 10–10 A cm–2, whereas an amorphous film deposited at 50 °C has a Tafel slope of 36 mV/decade and an exchange current density of 5.4 × 10–12 A cm–2. Because the films deposited from refluxing electrolyte deposit directly as crystalline films, it is possible to deposit them epitaxially on single-crystal Au(100). This opens up the possibility to study the catalytic activity of different Co3O4 planes exposed to the electrolyte.

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Films of β-Co(OH)2 with a dense microcone morphology are electrodeposited at room temperature by reducing tris(ethylenediamine)cobalt(III) in alkaline solution. The synthesis exploits the fact that the kinetically inert Co(III) complex of ethylenediamine (en) is 35 orders of magnitude more stable than the kinetically labile Co(II) complex. [Co(en)3]3+ is therefore stable in alkaline solution, but [Co(en)3]2+ reacts with excess hydroxide ion to produce β-Co(OH)2. The electrodeposited β-Co(OH)2 is an active catalyst for the oxygen evolution reaction. Raman spectroscopy suggests that the surface of β-Co(OH)2 is converted to CoOOH at the potentials at which oxygen evolution occurs.

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An electrochemical/chemical route is introduced to deposit both textured and epitaxial films of methylammonium lead iodide (MAPbI3) perovskites. The perovskite films are produced by chemical conversion of lead dioxide films that have been electrodeposited as either textured or epitaxial films onto [111]-textured Au and [100] and [111] single-crystal Au substrates. The epitaxial relationships for the MAPbI3 films are MAPbI3(001)­[010]∥PbO2(100)⟨001⟩ and MAPbI3(110)­[111]∥PbO2(100)⟨001⟩ regardless of the Au substrate orientation, because the in-plane order of the converted film is controlled by the epitaxial PbO2 precursor film. The textured and epitaxial MAPbI3 films both have trap densities lower than and photoluminescence intensities higher than those of polycrystalline films produced by spin coating.

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Germanium (Ge) is a group IV semiconductor with superior electronic properties compared with silicon, such as larger carrier mobilities and smaller effective masses. It is also a candidate anode material for lithium-ion batteries. Here, a simple, one-step method is introduced to electrodeposit dense arrays of Ge nanowires onto indium tin oxide (ITO) substrates from aqueous solution. The electrochemical reduction of ITO produces In nanoparticles that act as a reduction site for aqueous Ge(IV) species, and as a solvent for the crystallization of Ge nanowires. Nanowires deposited at 95 °C have an average diameter of 100 nm, whereas those deposited at room temperature have an average diameter of 35 nm. Both optical absorption and Raman spectroscopy suggest that the electrodeposited Ge is degenerate. The material has an indirect bandgap of 0.90-0.92 eV, compared with a value of 0.67 eV for bulk, intrinsic Ge. The blue shift is attributed to the Moss-Burstein effect, because the material is a p-type degenerate semiconductor. On the basis of the magnitude of the blue shift, the hole concentration is estimated to be 8 × 10(19) cm(-3). This corresponds to an In impurity concentration of about 0.2 atom %. The resistivity of the wires is estimated to be 4 × 10(-5) Ω·cm. The high conductivity of the wires should make them ideal for lithium-ion battery applications.