Hierarchical Ta-Doped TiO₂ Nanorod Arrays with Improved Charge Separation for Photoelectrochemical Water Oxidation under FTO Side Illumination

TiO2 is one of the most attractive semiconductors for use as a photoanode for photoelectrochemical (PEC) water oxidation. However, the large-scale application of TiO2 photoanodes is restricted due to a short hole diffusion length and low electron mobility, which can be addressed by metal doping and surface decorating. In this paper we report the successful synthesis of hierarchical Ta doped TiO2 nanorod arrays, with nanoparticles on the top (Ta:TiO2), on F-doped tin oxide (FTO) glass by a hydrothermal method, and its application as photoanodes for photoelectrochemical water oxidation. It has been found that the incorporation of Ta5+ in the TiO2 lattice can decrease the diameter of surface TiO2 nanoparticles. Ta:TiO2-140, obtained with a moderate Ta concentration, yields a photocurrent of ∼1.36 mA cm−2 at 1.23 V vs. a reversible hydrogen electrode (RHE) under FTO side illumination. The large photocurrent is attributed to the large interface area of the surface TiO2 nanoparticles and the good electron conductivity due to Ta doping. Besides, the electron trap-free model illustrates that Ta:TiO2 affords higher transport speed and lower electron resistance when under FTO side illumination

Utilizing a Photocatalysis Process to Achieve a Cathode with Low Charging Overpotential and High Cycling Durability for a Li-O2 Battery

The practical applications of non-aqueous lithium-oxygen batteries are impeded by large overpotentials and unsatisfactory cycling durability. Reported here is that commonly encountered fatal problems can be efficiently solved by using a carbon- and binder-free electrode of titanium coated with TiO2 nanotube arrays (TNAs) and gold nanoparticles (AuNPs). Ultraviolet irradiation of the TNAs generates positively charged holes, which efficiently decompose Li2O2 and Li2CO3 during recharging, thereby reducing the overpotential to one that is near the equilibrium potential for Li2O2 formation. The AuNPs promote Li2O2 formation, resulting in a large discharge capacity. The electrode exhibits excellent stability with about 100 % coulombic efficiency during continuous cycling of up to 200 cycles, which is due to the carbon- and binder-free composition. This work reveals a new strategy towards the development of highly efficient oxygen electrode materials for lithium-oxygen batteries.</p

Effect of O2 adsorption on the termination of Li–O2 batteries discharge

Lithium-oxygen (Li–O2) batteries can exhibit high theoretical energy density and be surely suitable for potential energy storage. However, they suffer from early discharge termination and consequently low practical capacity, which has been regarded as the blockage of the diffusion of oxygen and the electron transfer on cathode surface. Herein, based on experimental results and theoretical simulation, it is confirmed that the discharge termination is largely caused by the surface adsorption of oxygen and the corresponding reaction intermediates. A TiO2-coated binder-free carbon paper has been prepared and used as cathode for Li–O2 battery. During the first discharge, the discharge plateau at ca. 2.55 V has not been observed due to the weak adsorption of oxygen on TiO2 surface, indicative of an early discharge termination of Li–O2 battery. It is further identified that the formed vacancies on TiO2 surface during lithiation/delithiation prevents the early discharge termination. Therefore, the interaction between oxygen and electrode surface plays a key role in discharge termination mechanism of Li–O2 batteries.</p

Acid‐activated and WOx‐loaded montmorillonite catalysts and their catalytic behaviors in glycerol dehydration

Acid-activated and WOx-loaded montmorillonite catalysts and their catalytic behaviors in glycerol dehydration The use of H2SO4-, HCl-, H3PO4-, and CH3COOH-activated montmorillonite (Mt) and WOx/H3PO4-activated Mt as catalysts for the gas-phase dehydration of glycerol was investigated. The WOx/H3PO4-activated Mt catalysts were prepared by an impregnation method using H3PO4-activated Mt (Mt-P) as the support. The catalysts were characterized using powder X-ray diffraction, Fourier-transform infrared spectroscopy, N2 adsorption-desorption, diffuse reflectance ultraviolet-visible spectroscopy, temperature-programmed desorption of NH3, and thermogravimetric analysis. The acid activation of Mt and WOx loaded on Mt-P affected the strength and number of acid sites arising from H+ exchange, the leaching of octahedral Al3+ cations from Mt octahedral sheets, and the types of WOx (2.7 ≤ x ≤ 3) species (i.e., isolated WO4/WO6-containing clusters, two-dimensional [WO6] polytungstates, or three-dimensional WO3 crystals). The strong acid sites were weakened, and the weak and medium acid sites were strengthened when the W loading on Mt-P was 12 wt% (12%W/Mt-P). The 12%W/Mt-P catalyst showed the highest catalytic activity. It gave a glycerol conversion of 89.6% and an acrolein selectivity of 81.8% at 320℃. Coke deposition on the surface of the catalyst led to deactivation

Hierarchical yolk-shell layered potassium niobate for tuned pH-dependent photocatalytic H2 evolution

Photocatalysts and the reaction environments in which they act are crucial for improving the photocatalytic efficiency. But the pH-dependent evolution of H2 photocatalysed using nanoscale potassium niobate particles with high surface areas has not received attention. In this study, a straightforward Ostwald ripening method was developed to synthesize KNb3O8 with a thin nanosheet assembled hierarchical yolk–shell structure and large surface area of 60.6 m2 g−1. The H2 evolution from a water–methanol solution in an alkaline to neutral environment was studied. The photocatalytic H2 evolution rates over fabricated hierarchical yolk–shell KNb3O8 increased when OH− concentrations were decreased. Such behaviour implied that the concentration of H+ dominated the H2 evolution over hierarchical yolk–shell KNb3O8 rather than the reduction ability from the conduction band, differing from the corresponding bulk material. This study demonstrated an efficient method to achieve a high H2 evolution rate in a neutral environment through the use of photocatalysts with hierarchical structures and large surface areas

Halogen Hybrid Flow Batteries Advances for Stationary Chemical Power Sources Technologies

This review aims to highlight the current advances in hybrid redox flow battery (HRFB) technology, encompassing one of the best combinations of efficiency, cost and flexibility due to its module construction, which offers independent scaling of power density and energy capacity. This work emphasizes the interest of the scientific community both in (i) studying the properties and principles of HRFB operation in order to improve commonly proposed systems, and in (ii) the development of energy storage devices with new reagent types or RFB concepts. The data provided enhances the reader to conclude whether novel concepts in halogen oxidizers utilization could help to overcome the problem of insufficient power and energy densities of common RFB

Chestnut-Like TiO₂@α-Fe₂O₃ Core–Shell Nanostructures with Abundant Interfaces for Efficient and Ultralong Life Lithium-Ion Storage

Transition metal oxides caused much attention owing to the scientific interests and potential applications in energy storage systems. In this study, a free-standing three-dimensional (3D) chestnut-like TiO₂@α-Fe₂O₃ core–shell nanostructure (TFN) is rationally synthesized and utilized as a carbon-free electrode for lithium-ion batteries (LIBs). Two new interfaces between anatase TiO₂ and α-Fe₂O₃ are observed and supposed to provide synergistic effect. The TiO₂ microsphere framework significantly improves the mechanical stability, while the α-Fe₂O₃ provides large capacity. The abundant boundary structures offer the possibility for interfacial lithium storage and electron transport. The as-prepared TFN delivers a high capacity of 820 mAh g^–1 even after 1000 continuous cycles with a Coulombic efficiency of ca. 99% at a current of 500 mA g^–1, which is better than the works reported previously. A thin gel-like SEI (solid electrolyte interphase) film and Fe⁰ phase yielded during charge/discharge cycling have been confirmed which makes it possible to alleviate the volumetric change and enhance the electronic conductivity. This confirmation is helpful for understanding the mechanism of lithium-ion storage in α-Fe₂O₃-based materials. The as-prepared free-standing TFN with excellent stability and high capacity can be an appropriate candidate for carbon-free anode material in LIBs