Films of copper(I) oxide can be electrodeposited by reduction of copper(II) lactate in alkaline solution. Rietveld analysis of electrochemically grown films reveals pure copper(I) oxide with no copper(II) oxide or copper metal present in the films and a lattice parameter of a ) 0.4266 nm. The cathodic deposition current is limited by a Schottky-like barrier that forms between the Cu 2 O and the deposition solution. A barrier height of 0.6 eV was determined from the exponential dependence of the deposition current on the solution temperature. At a solution pH of 9 the orientation of the film is [100], while at a solution pH of 12 the orientation changes to [111]. Atomic force images of the [100] oriented films have crystals shaped as four-sided pyramids, while the [111] films have triangular crystals. The grain size for films grown at 65 °C ranges from 2 to 5 µm. A refractive index of 2.6 was measured from the transmission spectrum for wavelengths between 1350 and 2800 nm. The p-type semiconductor has a direct bandgap of 2.1 eV.

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.

Many biomolecules are chiral--they can exist in one of two enantiomeric forms that only differ in that their structures are mirror images of each other. Because only one enantiomer tends to be physiologically active while the other is inactive or even toxic, drug compounds are increasingly produced in an enantiomerically pure form using solution-phase homogeneous catalysts and enzymes. Chiral surfaces offer the possibility of developing heterogeneous enantioselective catalysts that can more readily be separated from the products and reused. In addition, such surfaces might serve as electrochemical sensors for chiral molecules. To date, chiral surfaces have been obtained by adsorbing chiral molecules or slicing single crystals so that they exhibit high-index faces, and some of these surfaces act as enantioselective heterogeneous catalysts. Here we show that chiral surfaces can also be produced through electrodeposition, a relatively simple solution-based process that resembles biomineralization in that organic molecules adsorbed on surfaces have profound effects on the morphology of the inorganic deposits. When electrodepositing a copper oxide film on an achiral gold surface in the presence of tartrate ion in the deposition solution, the chirality of the ion determines the chirality of the deposited film, which in turn determines the film's enantiospecificity during subsequent electrochemical oxidation reactions.

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The photoelectrochemical splitting of water into hydrogen and oxygen requires a semiconductor to absorb light and generate electron-hole pairs, and a catalyst to enhance the kinetics of electron transfer between the semiconductor and solution. A crucial question is how this catalyst affects the band bending in the semiconductor, and, therefore, the photovoltage of the cell. We introduce a simple and inexpensive electrodeposition method to produce an efficient n-Si/SiOx/Co/CoOOH photoanode for the photoelectrochemical oxidation of water to oxygen. The photoanode functions as a solid-state, metal-insulator-semiconductor photovoltaic cell with spatially non-uniform barrier heights in series with a low overpotential water-splitting electrochemical cell. The barrier height is a function of the Co coverage; it increases from 0.74 eV for a thick, continuous film to 0.91 eV for a thin, inhomogeneous film that has not reached coalescence. The larger barrier height leads to a 360 mV photovoltage enhancement relative to a solid-state Schottky barrier.