Exposure of WO₃ Photoanodes to Ultraviolet Light Enhances Photoelectrochemical Water Oxidation

Exposure of WO₃ photoanodes to sustained irradiation by ultraviolet (UV) light induces a morphology change that enhances the photoelectrochemical (PEC) activity towards the oxygen evolution reaction (OER). A 30% enhancement in photocurrent density at 1.23 V vs RHE was measured despite a nominal change in onset potential. A structural and electrochemical analysis of the films before and after exposure to UV irradiation indicates that a higher film porosity and correspondingly higher specific surface area is responsible for the enhancement in PEC activity. The effect of prolonged UV irradiation on the WO₃ films is fundamentally different to that which was previously observed for BiVO₄ films

Electrolytic CO₂ Reduction in Tandem with Oxidative Organic Chemistry

Electrochemical reduction of CO₂ into carbon-based products using excess clean electricity is a compelling method for producing sustainable fuels while lowering CO₂ emissions. Previous electrolytic CO₂ reduction studies all involve dioxygen production at the anode, yet this anodic reaction requires a large overpotential and yields a product bearing no economic value. We report here that the cathodic reduction of CO₂ to CO can occur in tandem with the anodic oxidation of organic substrates that bear higher economic value than dioxygen. This claim is demonstrated by 3 h of sustained electrolytic conversion of CO₂ into CO at a copper–indium cathode with a current density of 3.7 mA cm^–2 and Faradaic efficiency of >70%, and the concomitant oxidation of an alcohol at a platinum anode with >75% yield. These results were tested for four alcohols representing different classes of alcohols and demonstrate electrolytic reduction and oxidative chemistry that form higher-valued carbon-based products at both electrodes

Rapid Quantification of Film Thickness and Metal Loading for Electrocatalytic Metal Oxide Films

The thicknesses and metal loadings of amorphous nickel, iron, and iridium oxide films widely used for solar fuel electrocatalysis were determined by cross-sectional scanning electron microscopy (SEM) and X-ray fluorescence (XRF) spectroscopy measurements. The thicknesses for a series of films, which were systematically varied from 10 to 400 nm using photodeposition techniques, were accurately measured by cross-sectional SEM using a protocol that successfully resolves the relevant catalyst layers. XRF measurements recorded on each of the films provided a strong linear correlation (<i>R</i>² > 0.97) with the thicknesses determined by cross-sectional SEM. The electrochemical surface areas (ECSAs) determined by double-layer capacitance measurements, a technique widely used in the electrocatalysis community, showed a linear relationship for iridium oxide film thicknesses but not with those consisting of nickel and iron. These results highlight the limitations of using ECSA to determine catalyst film thicknesses and metal loadings. The noninvasive XRF technique is demonstrated to be a far superior method for reporting on the thickness and loadings of thin metal oxide films

Photodecomposition of Metal Nitrate and Chloride Compounds Yields Amorphous Metal Oxide Films

UV light is found to trigger the decomposition of MCl_<i>x</i> or M­(NO₃)_<i>x</i> (where M = Fe, Co, Ni, Cu, or Zn) to form uniform, amorphous films of metal oxides. This process does not elevate the temperature of the substrate and thus conformal films can be coated on a range of substrates, including rigid glass and flexible plastic. The formation of the oxide films were confirmed by a combination of powder X-ray diffraction, X-ray photoelectron spectroscopy, X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Amorphous oxide films of iron, nickel and a combination of iron and nickel demonstrated oxygen evolution reaction electrocatalytic activities commensurate with films of the same compositions prepared by widely used electrodeposition and sputtering methods. These results illuminate a potential route to amorphous oxides at scale using simple metal precursors without vacuum or heat

Coupling CO₂-to-Ethylene Reduction with the Chlor-Alkaline Process in Seawater through In Situ-Formed Cu Catalysts

The overall commercial value of a CO2 electroreduction system is hindered by the valueless product and high energy consumption of the oxygen evolution reaction (OER) at the anode. Herein, with an in situ-formed copper catalyst, we employed the alternative chlorine evolution reaction for OER, and high-speed formation of both C2 products and hypochlorite in seawater can be realized. The EDTA in the sea salt electrolyte can trigger an intense dissolution and deposition of Cu on the surface of the electrode, resulting in the in situ formation of dendrites of Cu with high chemical activity. In this system, a faradaic efficiency of 47% can be realized for C2H4 production at the cathode and a faradaic efficiency of 85% can be realized for hypochlorite production at the anode with an operation current of 100 mA/cm2. This work presents a system for designing a highly efficient coupling system for the CO2 reduction reaction and alternative anodic reactions toward value-added products in a seawater environment

Electrolysis of Gaseous CO₂ to CO in a Flow Cell with a Bipolar Membrane

The conversion of CO₂ to CO is demonstrated in an electrolyzer flow cell containing a bipolar membrane at current densities of 200 mA/cm² with a Faradaic efficiency of 50%. Electrolysis was carried out by delivering gaseous CO₂ at the cathode with a silver catalyst integrated in a carbon-based gas diffusion layer. Nonprecious nickel foam in a strongly alkaline electrolyte (1 M NaOH) was used to mediate the anode reaction. While a configuration where the anode and cathode were separated by only a bipolar membrane was found to be unfavorable for robust CO₂ reduction, a modified configuration with a solid-supported aqueous layer inserted between the silver-based catalyst layer and the bipolar membrane enhanced the cathode selectivity for CO₂ reduction to CO. We report higher current densities (200 mA/cm²) than previously reported for gas-phase CO₂ to CO electrolysis and demonstrate the dependence of long-term stability on adequate hydration of the CO₂ inlet stream

Half-Unit-Cell α‑Fe₂O₃ Semiconductor Nanosheets with Intrinsic and Robust Ferromagnetism

The synthesis of atomically thin transition-metal oxide nanosheets as a conceptually new class of materials is significant for the development of next-generation electronic and magnetic nanodevices but remains a fundamental chemical and physical challenge. Here, based on a “template-assisted oriented growth” strategy, we successfully synthesized half-unit-cell nanosheets of a typical transition-metal oxide α-Fe₂O₃ that show robust intrinsic ferro­magnetism of 0.6 μ_B/atom at 100 K and remain ferromagnetic at room temperature. A unique surface structure distortion, as revealed by X-ray absorption spectroscopy, produces nonidentical Fe ion environments and induces distance fluctuation of Fe ion chains. First-principles calculations reveal that the efficient breaking of the quantum degeneracy of Fe 3d energy states activates ferro­magnetic exchange interaction in these Fe_5‑co–O–Fe_6‑co ion chains. These results provide a solid design principle for tailoring the spin-exchange interactions and offer promise for future semi­conductor spin­tronics

Graphene Activating Room-Temperature Ferromagnetic Exchange in Cobalt-Doped ZnO Dilute Magnetic Semiconductor Quantum Dots

Control over the magnetic interactions in dilute magnetic semiconductor quantum dots (DMSQDs) is a key issue to future development of nanometer-sized integrated “spintronic” devices. However, manipulating the magnetic coupling between impurity ions in DMSQDs remains a great challenge because of the intrinsic quantum confinement effects and self-purification of the quantum dots. Here, we propose a hybrid structure to achieve room-temperature ferromagnetic interactions in DMSQDs, <i>via</i> engineering the density and nature of the energy states at the Fermi level. This idea has been applied to Co-doped ZnO DMSQDs where the growth of a reduced graphene oxide shell around the Zn_0.98Co_0.02O core turns the magnetic interactions from paramagnetic to ferromagnetic at room temperature, due to the hybridization of 2p_<i>z</i> orbitals of graphene and 3d obitals of Co²⁺–oxygen-vacancy complexes. This design may open up a kind of possibility for manipulating the magnetism of doped oxide nanostructures

Vacancy-Induced Ferromagnetism of MoS₂ Nanosheets

Outstanding magnetic properties are highly desired for two-dimensional ultrathin semiconductor nanosheets. Here, we propose a phase incorporation strategy to induce robust room-temperature ferromagnetism in a nonmagnetic MoS₂ semiconductor. A two-step hydrothermal method was used to intentionally introduce sulfur vacancies in a 2H-MoS₂ ultrathin nanosheet host, which prompts the transformation of the surrounding 2H-MoS₂ local lattice into a trigonal (1T-MoS₂) phase. 25% 1T-MoS₂ phase incorporation in 2H-MoS₂ nanosheets can enhance the electron carrier concentration by an order, introduce a Mo⁴⁺ 4d energy state within the bandgap, and create a robust intrinsic ferromagnetic response of 0.25 μ_B/Mo by the exchange interactions between sulfur vacancy and the Mo⁴⁺ 4d bandgap state at room temperature. This design opens up new possibility for effective manipulation of exchange interactions in two-dimensional nanostructures