Defect engineering in 1D Ti-W oxide nanotube arrays and their correlated photoelectrochemical performance

Pulsed Light Synthesis of High Entropy Nanocatalysts with Enhanced Catalytic Activity and Prolonged Stability for Oxygen Evolution Reaction

The ability to synthesize compositionally complex nanostructures rapidly is a key to high-throughput functional materials discovery. In addition to being time-consuming, a majority of conventional materials synthesis processes closely follow thermodynamics equilibria, which limit the discovery of new classes of metastable phases such as high entropy oxides (HEO). Herein, a photonic flash synthesis of HEO nanoparticles at timescales of milliseconds is demonstrated. By leveraging the abrupt heating and cooling cycles induced by a high-power-density xenon pulsed light, mixed transition metal salt precursors undergo rapid chemical transformations. Hence, nanoparticles form within milliseconds with a strong affinity to bind to the carbon substrate. Oxygen evolution reaction (OER) activity measurements of the synthesized nanoparticles demonstrate two orders of magnitude prolonged stability at high current densities, without noticeable decay in performance, compared to commercial IrO₂ catalyst. This superior catalytic activity originates from the synergistic effect of different alloying elements mixed at a high entropic state. It is found that Cr addition influences surface activity the most by promoting higher oxidation states, favoring optimal interaction with OER intermediates. The proposed high-throughput method opens new pathways toward developing next-generation functional materials for various electronics, sensing, and environmental applications, in addition to renewable energy conversion.

Superior visible light antimicrobial performance of facet engineered cobalt doped TiO2 mesocrystals in pathogenic bacterium and fungi

Pristine and Co-doped TiO2 mesocrystals have been synthesized via a simple sol-gel method and their antimicrobial activity has been investigated. The antimicrobial performance was evaluated in terms of zone of inhibition, minimum inhibitory concentration (MIC), antibiofilm activity, and effect of UV illumination in liquid media. The Co-doped TiO2 mesocrystals showed very promising MIC of 0.390 μg/mL and 0.781 μg/mL for P. mirabilis and P. mirabilis, respectively. Additionally, the material showed an MIC of 12.5 μg/mL against C. albicans, suggesting its use as antifungal agent. Upon the addition of 10.0 µg/mL of Co-doped TiO2 mesocrystals, the biofilm inhibition% reaches 84.43% for P. aeruginosa, 78.58% for P. mirabilis, and 77.81% for S. typhi, which can be ascribed to the created active oxygen species that decompose the tested microbial cells upon illumination. Thus the fabricated Co-doped TiO2 mesocrystals exhibit sufficient antimicrobial features under visible light, qualifying them for use as antimicrobial agents against pathogenic bacteria and fungi and subsequently inhibit their hazardous effects.

Computational Design of Novel Hydrogen-Doped, Oxygen-Deficient Monoclinic Zirconia with Excellent Optical Absorption and Electronic Properties

Monoclinic ZrO2 has recently emerged as a new highly efficient material for the photovoltaic and photocatalytic applications. Herein, first-principles calculations were carried out to understand how Hydrogen doping can affect the electronic structure and optical properties of the material. The effects of Hydrogen interstitial and substitutional doping at different sites and concentrations in m-ZrO2 were examined by an extensive model study to predict the best structure with the optimal properties for use in solar energy conversion devices. Hydrogen interstitials (Hi) in pristine m-ZrO2 were found to lower the formation energy but without useful effects on the electronic or optical properties. Hydrogen mono- and co-occupying oxygen vacancy (Ov) were also investigated. At low concentration of Hydrogen mono-occupying oxygen vacancy (HOv), Hydrogen atoms introduced shallow states below the conduction band minimum (CBM) and increase the dielectric constant, which could be very useful for gate dielectric application. The number and position of such defect states strongly depend on the doping sites and concentration. At high oxygen vacancy concentration, the modeled HOv-Ov structure shows the formation of shallow and localized states that are only 1.1 eV below the CBM with significantly high dielectric constant and extended optical absorption to the infrared region. This strong absorption with the high permittivity and low exciton binding energies make the material an ideal candidate for use in solar energy harvesting devices. Finally, the band edge positions of pristine and doped structures with respect to the redox potentials of water splitting indicated that Hydrogen occupying oxygen vacancies can increase the photocatalytic activity of the material for hydrogen generation due the extremely improved optical absorption and the band gap states.

Sandwiched Graphene Interdiffusion Barrier for Preserving Au@Pt Atomically Thin Core@Shell Structure and the Resulting Oxygen Reduction Reaction Catalytic Activity

The concept of a core-shell metallic structures, with a few atomic layers of the "shell" metal delineated from the "core" metal with atomic sharpness opens the door to a multitude of surface-driven materials properties that can be tuned. However, in practice, such architectures are difficult to retain due to the entropic cost of a segregated near-surface architecture, and the core and surface atoms inevitably mix through interdiffusion over time. We present here a systematic study of interdiffusion in a Pt on Au core-shell architecture and the role of an interrupting single layer of graphene sandwiched between them. The physical and chemical structure of the (near)surface is probed via mean-free-path tuned X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy (HRTEM), and electrochemistry (the oxygen reduction reaction, ORR). We find that at operating temperatures above 100 °C, there is potential for interdiffusion to occur between the primary and support metals of the core-shell catalyst system, which can diminish the catalyst activity toward ORR. The introduction of a single-layer graphene, as an interface between the core and shell metal layers, acts as a barrier that prevents unwanted surface alloying between the layered metals. HRTEM imaging shows that fully wetted Pt monolayers can be grown on a graphene template, allowing a high level of surface utilization of the catalyst material. We present how the use of graphene as a barrier to diffusion mitigates the loss of surface catalytic sites, showing much improved retention of Pt monolayer surface at elevated temperatures.