Characterizing the Influence of Water on Charging and Layering at Electrified Ionic‐Liquid/Solid Interfaces

The importance of water on molecular ion structuring and charging mechanism of solid interfaces in room temperature ionic liquid (RTIL) is unclear and has been largely ignored. Water may alter structures, charging characteristics, and hence performance at electrified solid/RTIL interfaces and is utilized in various fields including energy storage, conversion, or catalysis. Here, atomic force microscopy and surface forces apparatus experiments are utilized to directly measure how water alters the interfacial structuring and charging characteristics of [C₂mim][Tf₂N] on mica and electrified gold surfaces. On hydrophilic and ionophobic mica surfaces, water‐saturated [C₂mim][Tf₂N] dissolves surface‐bound cations, which leads to high surface charging and strong layering. In contrast, layering of dry RTIL at weakly charged mica surfaces is weakly structured. At electrified, hydrophobic, and ionophilic gold electrodes, significant water effects are found only at positive applied electrochemical potentials. Here, the influence of water is limited to interactions within the RTIL layers, and is not related to a direct electrosorption of water on the polarized electrode. More generally, the results suggest that effects of water on interfacial structuring of RTIL strongly depend on both (1) surface charging mechanism and (2) interfacial wetting properties. This may greatly impact utilization/design of RTILs and surfaces for interface‐dominated processes.     

面向基因测序芯片应用的TiN电极薄膜制备及性能研究

基因测序技术正处于快速发展阶段,作为灵敏度极高的测序技术——纳米孔测序,对薄膜电极的电阻率和储能特性提出了更高的要求。为了降低薄膜的电阻率并提高储能特性,本文利用反应磁控溅射方法,基于原位生长原理,分别制备了TiO_xN_y和Ti/TiN/TiO_xN_y电极薄膜。采用扫描电子显微镜、X射线衍射仪和电化学工作站对薄膜的微观结构、化学成分及其电化学性能进行研究。结果表明,在TiN高导电性和TiO_xN_y高比表面积的协同作用下,Ti/TiN/TiO_xN_y电极薄膜表现出优异的电化学性能。当电流密度为0.15 mA/cm²时获得7.01 mF/cm²的比电容,是TiO_xN_y电极薄膜比电容值的1.3倍。同时,与TiO_xN_y单电极相比,Ti/TiN/TiO_xN_y...     

Improved Hybrid Solar Cells via in situ UV Polymerization

One approach for making inexpensive inorganic–organic hybrid photovoltaic (PV) cells is to fill highly ordered TiO₂ nanotube (NT) arrays with solid organic hole conductors such as conjugated polymers. Here, a new in situ UV polymerization method for growing polythiophene (UV‐PT) inside TiO₂ NTs is presented and compared to the conventional approach of infiltrating NTs with pre‐synthesized polymer. A nanotubular TiO₂ substrate is immersed in a 2,5‐diiodothiophene (DIT) monomer precursor solution and then irradiated with UV light. The selective UV photodissociation of the C? I bond produces monomer radicals with intact π‐ring structure that further produce longer oligothiophene/PT molecules. Complete photoluminescence quenching upon UV irradiation suggests coupling between radicals created from DIT and at the TiO₂ surface via a charge transfer complex. Coupling with the TiO₂ surface improves UV‐PT crystallinity and π–π stacking; flat photocurrent values show that charge recombination during hole transport through the polymer is negligible. A non‐ideal, backside‐illuminated setup under illumination of 620‐nm light yields a photocurrent density of ≈5 µA cm²—surprisingly much stronger than with comparable devices fabricated with polymer synthesized ex situ. Since in this backside architecture setup we illuminate the cell through the Ag top electrode, there is a possibility for Ag plasmon‐enhanced solar energy conversion. By using this simple in situ UV polymerization method that couples the conjugated polymer to the TiO₂ surface, the absorption of sunlight can be improved and the charge carrier mobility of the photoactive layer can be enhanced.     

Boosting Sodium Storage in TiO2 Nanotube Arrays through Surface Phosphorylation

Sodium‐ion batteries (SIBs) offer a promise of a scalable, low‐cost, and environmentally benign means of renewable energy storage. However, the low capacity and poor rate capability of anode materials present an unavoidable challenge. In this work, it is demonstrated that surface phosphorylated TiO₂ nanotube arrays grown on Ti substrate can be efficient anode materials for SIBs. Fabrication of the phosphorylated nanoarray film is based on the electrochemical anodization of Ti metal in NH₄F solution and subsequent phosphorylation using sodium hypophosphite. The phosphorylated TiO₂ nanotube arrays afford a reversible capacity of 334 mA h g^?1 at 67 mA g^?1, a superior rate capability of 147 mA h g^?1 at 3350 mA g^?1, and a stable cycle performance up to 1000 cycles. In situ X‐ray diffraction and transmission electron microscopy reveal the near‐zero strain response and robust mechanical behavior of the TiO₂ host upon (de)sodiation, suggesting its excellent structural stability in the Na⁺ storage application.     

Photo-Rechargeable Li-Ion Batteries using TiS2 Cathode

Photo-rechargeable (solar) battery can be considered as an energy harvesting cum storage system, where it can charge the conventional metal-ion battery using light instead of electricity, without having other parasitic reactions. Here a two-electrode lithium-ion solar battery with multifaceted TiS₂–TiO₂ hybrid sheets as cathode. The choice of TiS₂–TiO₂ electrode ensures the formation of a type II semiconductor heterostructure while the lateral heterostructure geometry ensures high mass/charge transfer and light interactions with the electrode. TiS₂ has a higher lithium binding energy (1.6 eV) than TiO₂ (1.03 eV), ensuring the possibilities of higher amount of Li-ion insertion to TiS₂ and hence the maximum recovery with the photocharging, as further confirmed by the experiments. Apart from the demonstration of solar solid-state batteries, the charging of lithium-ion full cell with light indicates the formation of lithium intercalated graphite compounds, ensuring the charging of the battery without any other parasitic reactions at the electrolyte or electrode-electrolyte interfaces. Possible mechanisms proposed here for the charging and discharging processes of solar batteries, based on the experimental and theoretical results, indicate the potential of such systems in the forthcoming era of renewable energies.     

Potential‐Dependent Surface‐Enhanced Resonance Raman Spectroscopy at Nanostructured TiO2: A Case Study on Cytochrome b5

Nanostructured titanium dioxide (TiO₂) electrodes, prepared by anodization of titanium, are employed to probe the electron‐transfer process of cytochrome b₅ (cyt b₅) by surface‐enhanced resonance Raman (SERR) spectroscopy. Concomitant with the increased nanoscopic surface roughness of TiO₂, achieved by raising the anodization voltage from 10 to 20 V, the enhancement factor increases from 2.4 to 8.6, which is rationalized by calculations of the electric field enhancement. Cyt b₅ is immobilized on TiO₂ under preservation of its native structure but it displays a non‐ideal redox behavior due to the limited conductivity of the electrode material. The electron‐transfer efficiency which depends on the crystalline phase of TiO₂ has to be improved by appropriate doping for applications in bioelectrochemistry.     

In Situ Formation of a Cathode–Electrolyte Interface with Enhanced Stability by Titanium Substitution for High Voltage Spinel Lithium‐Ion Batteries

Although LiNi_0.5Mn_1.5O₄ (LNMO) high‐voltage spinel is a promising candidate for a next generation cathode material, LNMO/graphite full cells experience severe capacity fading caused by degradation reactions at electrode/electrolyte interfaces and consequent active Li⁺ loss in the cells. In this study, it is first reported that in situ formation of a Ti–O enriched cathode/electrolyte interfacial (CEI) layer on a Ti‐substituted LiNi_0.5Mn_1.2Ti_0.3O₄ (LNMTO) spinel cathode effectively mitigates electrolyte oxidation and transition metal dissolution, which improves the Coulombic efficiency and cycle life of LNMTO/graphite full cells. The Ti–O enriched CEI layer is produced in situ during an initial cycling of LNMTO as a result of selective Mn and Ni dissolution at its surface, as evidenced by various surface characterizations using X‐ray photoelectron spectroscopy, transmission electron microscopy, time‐of‐flight secondary ion mass spectrometry, Raman spectroscopy, and synchrotron‐based soft X‐ray absorption spectroscopy. The Ti–O enriched CEI has an advantage over traditional LNMO powder coatings, namely the formation of conformal CEI without compromising electronic conduction pathways between cathode particles.     

Rational Design of Three‐Layered TiO2@Carbon@MoS2 Hierarchical Nanotubes for Enhanced Lithium Storage

Here we demonstrate the rational design and synthesis of three‐layered TiO₂@carbon@MoS₂ hierarchical nanotubes for anode applications in lithium‐ion batteries (LIBs). Through an efficient step‐by‐step strategy, ultrathin MoS₂ nanosheets are grown on nitrogen‐doped carbon (NC) coated TiO₂ nanotubes to achieve the TiO₂@NC@MoS₂ tubular nanostructures. This smart design can effectively shorten the diffusion length of Li⁺ ions, increase electric conductivity of the electrode, relax volume variation of electrode materials upon cycling, and provide more active sites for electrochemical reactions. Owing to these structural and compositional features, the hierarchical TiO₂@NC@MoS₂ nanotubes manifest remarkable lithium storage performance with good rate capability and long cycle life.     

Vertically Aligned Graphene–Carbon Fiber Hybrid Electrodes with Superlong Cycling Stability for Flexible Supercapacitors

Graphene electrode–based supercapacitors are in high demand due to their superior electrochemical characteristics. A major bottleneck of using the supercapacitors for commercial applications lies in their inferior electrode cycle life. Herein, a simple and facile method to fabricate highly efficient supercapacitor electrodes using pristine graphene sheets vertically stacked and electrically connected to the carbon fibers which can result in vertically aligned graphene–carbon fiber nanostructure is developed. The vertically aligned graphene–carbon fiber electrode prepared by electrophoretic deposition possesses a mesoporous 3D architecture which enabled faster and efficient electrolyte‐ion diffusion with a gravimetric capacitance of 333.3 F g^?1 and an areal capacitance of 166 mF cm^?2. The electrodes displayed superlong electrochemical cycling stability of more than 100 000 cycles with 100% capacitance retention hence promising for long‐lasting supercapacitors. Apart from the electrochemical double layer charge storage, the oxygen‐containing surface moieties and α‐Ni(OH)₂ present on the graphene sheets enhance the charge storage by faradaic reactions. This enables the assembled device to provide an excellent gravimetric energy density of 76 W h kg^?1 with a 100% capacitance retention even after 1000 bending cycles. This study opens the door for developing high‐performing flexible graphene electrodes for wearable energy storage applications.     

Amorphous Mixed‐Valence Vanadium Oxide/Exfoliated Carbon Cloth Structure Shows a Record High Cycling Stability

Previous studies show that vanadium oxides suffer from severe capacity loss during cycling in the liquid electrolyte, which has hindered their applications in electrochemical energy storage. The electrochemical instability is mainly due to chemical dissolution and structural pulverization of vanadium oxides during charge/discharge cyclings. In this study the authors demonstrate that amorphous mixed‐valence vanadium oxide deposited on exfoliated carbon cloth (CC) can address these two limitations simultaneously. The results suggest that tuning the V⁴⁺/V⁵⁺ ratio of vanadium oxide can efficiently suppress the dissolution of the active materials. The oxygen‐functionalized carbon shell on exfoliated CC can bind strongly with VO _x via the formation of C? O? V bonding, which retains the electrode integrity and suppresses the structural degradation of the oxide during charging/discharging. The uptake of structural water during charging and discharging processes also plays an important role in activating the electrode material. The amorphous mixed‐valence vanadium oxide without any protective coating exhibits record‐high cycling stability in the aqueous electrolyte with no capacitive decay in 100 000 cycles. This work provides new insights on stabilizing vanadium oxide, which is critical for the development of vanadium oxide based energy storage devices.     

Enhanced photoelectrochemical current response of titania nanotube array

Self-organized and highly-ordered TiO₂ nanotube array with disjunctive wall-hole structure has been synthesized from titanium foil by potentiostatic–galvanostatic anodization process. The morphology and microstructure of the TiO₂ layer depend greatly on the electrolyzing parameters and electrolyte components. TiO₂ formation mechanism by anodization oxidation is discussed. The crystallized TiO₂/Ti nanotube electrode exhibited a significant enhancement of photoelectrochemical current response in comparison with micrometer-sized TiO₂/Ti multiporous electrode. Such kind of TiO₂ nanotube will have many potential applications in various areas as an outstanding photoelectrochemical material.     

Additional Lithium Storage on Dynamic Electrode Surface by Charge Redistribution in Inactive Ru Metal

Beyond a traditional view that metal nanoparticles formed upon electrochemical reaction are inactive against lithium, recently their electrochemical participations are manifested and elucidated as catalytic and interfacial effects. Here, ruthenium metal composed of ≈5 nm nanoparticles is prepared and the pure ruthenium as a lithium‐ion battery anode for complete understanding on anomalous lithium storage reaction mechanism is designed. In particular, the pure metal electrode is intended for eliminating the electrochemical reaction‐derived Li₂O phase accompanied by catalytic Li₂O decomposition and the interfacial lithium storage at Ru/Li₂O phase boundary, and thereby focusing on the ruthenium itself in exploring its electrochemical reactivity. Intriguingly, unusual lithium storage not involving redox reactions with electron transfer but leading to lattice expansion is identified in the ruthenium electrode. Size‐dependent charge redistribution at surface enables additional lithium adsorption to occur on the inactive but more environmentally sensitive nanoparticles, providing innovative insight into dynamic electrode environments in rechargeable lithium chemistry.     

A transient molecular probe for characterizing the surface properties of TiO2 nanoparticle in colloidal solution

A transient molecular probe for characterization of the surface properties of TiO₂ nanoparticles in colloidal solution developed recently in our laboratory is briefly reviewed. The probe molecule is all-trans-retinoic acid (ATRA) adsorbed at the TiO₂ nanoparticle surface. After photoexcitation, the photoinduced interfacial charge recombination would generate ATRA triplet state (ATRA^T) with a substantial quantum yield. It is found that the triplet–triplet absorption spectrum of ATRA adsorbed molecule is sensitive to its binding form with the surface Ti atom through the carboxylic group, as well as to the polarity of the medium. Especially the apparent lifetime of ATRA^T at the TiO₂ surface changes substantially when the local polarity around the TiO₂ nanoparticle changes. Therefore the ATRA^T monolayer adsorbed at the surface can be used as a transient molecular probe for the surface binding forms, coordination state of the surface Ti atoms and the light-induced wettability change of the TiO₂ nanoparticle.     

Fabrication of TiO<Subscript>x</Subscript>–Si photoanode and its energetic photoelectrochemical performance

Pristine Si is oxidized to insulative SiO₂ when it comes in contact with air and water. Covering it with a protection layer inhibits passivation of Si and significantly improves its photoelectrochemical performance. In this study, TiO_x with gradient change of oxygen stoichiometry ratio (TiO_x) was designed as a protection layer and fabricated via a chemical vapour deposition process in Ar flow under 400 °C for 1 min. The anaerobic atmosphere and short heating duration synergistically produced the ratio of O and Ti lower than two in the prepared film. XPS analysis suggested the existance of TiO₂ only at the surface of TiO_x film and Ti³⁺ and Ti²⁺ appeared successively with the increase of distance to the surface. The first advantage of lower-valence-state Ti and oxygen deficiency was to inhibit the oxidation of Si and to reduce electric resistance of the interface and the protection layer. The second advantage was to create a defect energy level under the conduction band of TiO₂ which provided the possibility for holes in the valence band of Si to be transferred to this defect level. This tunnel like transfer enhanced the photogenerated charge separation and redox ability of TiO_x–Si which brought a 3.25 folds enhancements in photocurrent density compared to that of stoichiometric TiO₂–Si at 0 V (SCE) under simulated sunlight. This study highly motivates further research on transparent and conductive protection layer of Si photoelectrode.     

Application of titanium oxide nanotube films containing gold nanoparticles for the electroanalytical determination of ascorbic acid

Au/TiO₂/Ti electrodes have been prepared by galvanic deposition of gold particles on TiO₂ nanotube substrates. Titanium oxide nanotubes are fabricated by anodizing titanium foil in a Dimethyl Sulfoxide electrolyte containing fluoride. The scanning electron microscopy results indicated that gold particles are homogeneously deposited on the surface of TiO₂ nanotubes. The TiO₂ layers consist of individual tubes of about 40-80 nm diameters. The electro-catalytic behavior of Au/TiO₂/Ti and flat gold electrodes for the ascorbic acid electro-oxidation was studied by cyclic voltammetry. The results showed that the flat gold electrode is not suitable for the oxidation of ascorbic acid. However, the Au/TiO₂/Ti electrodes are shown to possess catalytic activity toward the oxidation reaction. Catalytic oxidation peak current showed a linear dependence on the ascorbic acid concentration and a linear calibration curve is obtained in the concentration range of 1-5 mM of ascorbic acid. Also, determination of ascorbic acid in real samples was evaluated. The obtained results were found to be satisfactory. Finally the effects of interference on the detection of ascorbic acid were investigated.     

Lithium Silicide Surface Enrichment: A Solution to Lithium Metal Battery

The propensity of lithium dendrite formation during the charging process of lithium metal batteries is linked to inhomogeneity on the lithium surface layer. The high reactivity of lithium and the complex surface structure of the native layer create “hot spots” for fast dendritic growth. Here, it is demonstrated that a fundamental restructuring of the lithium surface in the form of lithium silicide (Li_xSi) can effectively eliminate the surface inhomogeneity on the lithium surface. In situ optical microscopic study is carried out to monitor the electrochemical deposition of lithium on the Li_xSi‐modified lithium electrodes and the bare lithium electrode. It is observed that a much more uniform lithium dissolution/deposition on the Li_xSi‐modified lithium anode can be achieved as compared to the bare lithium electrode. Full cells paring the modified lithium anode with sulfur and LiFePO₄ cathodes show excellent electrochemical performances in terms of rate capability and cycle stability. Compatibility of the anode enrichment method with mass production process also offers a practical way for enabling lithium metal anode for next‐generation lithium batteries.     

A new coral structure TiO2/Ti film electrode applied to photoelectrocatalytic degradation of Reactive Brilliant Red

A novel structure TiO₂/Ti film was prepared on a titanium matrix using anodic oxidation technique and applied to degrade Reactive Brilliant Red (RBR) dye in simulative textile effluents. The film was characterized by Field-Emission Scanning Electron Microscope (FE-SEM), Laser Micro-Raman Spectrometer (LMRS), UV–vis spectrophotometer (UVS) and Photoelectrocatalytic (PEC) experiment. The results show that the surface morphology of the film is coral structure, and the crystal structure of the film is anatase. The absorbency of the coral structure TiO₂/Ti film is 87–93% in the UV light region, and 77–87% in the visible light region. PEC experiment indicates that the photocurrent density of the coral structure TiO₂/Ti film electrode achieves 160 μA/cm². The color and Chemical Oxygen Demand (COD) removal efficiencies of RBR achieve 73% and 60% in 1 h, respectively. These are 16% and 58% higher than those of nanotube TiO₂/Ti film electrode. These were attributed to that these electrodes with different surface morphologies exhibit distinct surface areas and light absorption rate.     

Fast Capacitive Energy Storage and Long Cycle Life in a Deintercalation–Intercalation Cathode Material

Ni‐rich Li‐ion cathode materials promise high energy density, but are limited in power density and cycle life, resulting from their poor dynamic characteristics and quick degradation. On the other hand, capacitor electrode materials promise high power density and long cycle life but limited capacities. A joint energy storage mechanism of these two kinds is performed in the material‐compositional level in this paper. A valence coupling between carbon π‐electrons and O^2? is identified in the as‐prepared composite material, using a tracking X‐ray photoelectron spectroscopy strategy. Besides delivering capacity simultaneously from its LiNi_0.8Co_0.1Mn_0.1O₂ and capacitive carbon components with impressive amount and speed, this material shows robust cycling stability by preventing oxygen emission and phase transformation via the discovered valence coupling effect. Structural evolution of the composite shows a more flattened path compared to that of the pure LiNi_0.8Co_0.1Mn_0.1O₂, revealed by the in situ X‐ray diffraction strategy. Without obvious phase transformation and losing active contents in this composite material, long cycling can be achieved.     

Heterostructured TiO2 Spheres with Tunable Interiors and Shells toward Improved Packing Density and Pseudocapacitive Sodium Storage

Insertion‐type anode materials with beneficial micro‐ and nanostructures are proved to be promising for high‐performance electrochemical metal ion storage. In this work, heterostructured TiO₂ shperes with tunable interiors and shells are controllably fabricated through newly proposed programs, resulting in enhanced pseudocapacitive response as well as favorable Na⁺ storage kinetics and performances. In addition, reasonably designed nanosheets in the extrinsic shells are also able to reduce the excess space generated by hierarchical structure, thus improving the packing density of TiO₂ shperes. Lastly, detailed density functional theory calculations with regard to sodium intercalation and diffusion in TiO₂ crystal units are also employed, further proving the significance of the surface‐controlled pseudocapacitive Na⁺ storage mechanism. The structure design strategies and experimental results demonstrated in this work are meaningful for electrode material preparation with high rate performance and volume energy density.     

Exploration of Advanced Electrode Materials for Approaching High‐Performance Nickel‐Based Superbatteries

The surging interest in high performance, low‐cost, and safe energy storage devices has spurred tremendous research efforts in the development of advanced electrode active materials. Herein, the in situ growth of zinc–iron layered double hydroxide (Zn–Fe LDH) on graphene aerogel (GA) substrates through a facile, one‐pot hydrothermal method is reported. The strong interaction and efficient electronic coupling between LDH and graphene substantially improve interfacial charge transport properties of the resulting nanocomposite and provide more available redox active sites for faradaic reactions. An LDH–GA||Ni(OH)₂ device is also fabricated that results in greatly enhanced specific capacity (187 mAh g^?1 at 0.1 A g^?1), outstanding specific energy (147 Wh kg^?1), excellent specific power (16.7 kW kg^?1), along with 88% capacity retention after >10 000 cycles. This approach is further extended to Ni–MH and Ni–Cd batteries to demonstrate the feasibility of compositing with graphene for boosting the energy storage performance of other well‐known Ni‐based batteries. In contrast to conventional Ni‐based batteries, the nearly flat voltage plateau followed by a sloping potential profile of the integrated supercapacitor–battery enables it to be discharged down to 0 V without being damaged. These findings provide new prospects for the design of high‐performance and affordable superbatteries based on earth‐abundant elements.