Ti Foil Research Articles

Hydrothermal synthesis of rutile TiO2 nanotubes film on Ti foil for photocatalytic degradation

One-dimensional TiO2 nanotubes film was synthesized on the Ti foil oxidized at 800℃ by hydrothermal method in a highly alkaline solution. The crystal structure, morphology and chemical state of the samples were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy. The result indicates that the TiO2 nanotubes film still remains rutile phase structure after hydrothermal treatment. The growth mechanism of TiO2 nanotubes is also discussed that includes dissolution, nucleation and growing process. The photocatalytic activity of TiO2 film is remarkably improved after hydrothermal reaction. Due to the one-dimensional tubular structure, TiO2 nanotubes film hydrothermally synthesized for 6 hours displays the highest photocatalytic degradation rate of methylene blue

Photoelectrocatalytic degradation of humic acid and disinfection over Ni TiO2-Ni/ AC-PTFE electrode under natural sunlight irradiation: Modeling, optimization and reaction pathway

NiTiO2NT and TiO2 nanotube-based photoelectrodes were prepared by anodic oxidation and employed for the degradation of humic acid (HA) and disinfection simultaneously by the photoelectrocatalytic (PEC) process under natural sunlight irradiation. Scanning electron microscopy coupled with energy-dispersive spectroscopy (EDX) studies confirmed that uniform nanotubes TiO2 covered all surface of Ti foil and Ni doped to TiO2NT. The highest efficiency for HA degradation and disinfection rate by PEC was observed for the NiTiO2NT photoelectrode. The influences of different parameters such as initial HA concentration (2–8 mg/L), voltage (2–20 V), bacterial density (2 × 102,104,107 CFU), time (30–60 min), light source (UV–Vis) and type of electrode (NiTiO2NT/AC-PTFE, TiO2NT/AC-PTFE) on disinfection of water and degradation of the HA were studied using response surface methodology (RSM). The results showed that the maximum degradation rate of HA and Log bacterial removal reached 87.18% and 3.77 after 60 min reaction time at a 20 V voltage with NiTiO2NT/AC-PTFE electrode and UV as a source of irradiation. Also, results showed that doping Ni to TiO2NT electrode increase PEC efficiency under Vis-light source. To determine the HA degradation pathway, the organic byproducts were identified by GC–MS analysis.

Microstructure and superior mechanical property of in situ (TiBw + TiCp)/Ti composites with laminated structure

The strength and ductility of titanium matrix composites (TMCs) hardly co-exist and show a trade-off between each other. In order to balance the strength and ductility of TMCs, in situ TiB whiskers (TiBw) and TiC particles (TiCp) strengthened Ti composites with laminated structure were constructed via electrophoretic depositing (EPD) boron (B) powders + graphene oxides (GOs) on pure Ti foils followed by spark plasma sintering (SPS). The experiment results reveal that increasing EPD duration leads to more synthesized TiBw + TiCp reinforcements accompanied by decreased grain size of Ti matrix in the sintered composites, which favorably results in gradually enhanced strength. A maximum yield strength (YS) of 569 MPa is achieved in the laminated composite, which is 75.6% higher than that of pure Ti sample (YS: 324 MPa). Meanwhile, the composite still owns a relatively higher elongation of 12.0%. The achievement of good ductility should benefit from the laminated architecture which exerts constraint effect on crack propagation. This work provides a short cut to achieve strength-ductility synergy in TMCs.

Electrochemical glucose sensor based on the glucose oxidase entrapped in chitosan immobilized onto laser-processed Au-Ti electrode

Abstract Glucose is essential to keep the human body in well order. Therefore, the control of its level is of key importance. The study on novel electrode material composed of structured titanium foil with embedded Au nanoparticles and modified with chitosan with entrapped glucose oxidase is presented. In the first step, Ti foil undergoes anodization followed by chemical etching resulting in formation of homogenously distributed inverted caps of diameter of 85 nm. After deposition of thin Au layer, the rapid and well optimized laser dewetting is applied to form Au nanoparticles of size limited by the dimensions of cavities. Finally, the surface is modified using enzyme and chitosan mixture. To confirm the successful immobilization of glucose oxidase FT-IR analysis was performed. The response of electrodes were tested towards glucose in 0.1 M PBS containing most different interference compounds and biological fluids. It is proven that prepared material exhibits excellent performance for glucose detection with a wide linear range of 0.04–15.05 and 15.05–40.00 mM, with sensitivity of 23.47 ± 1.36 and 10.63 ± 1.28 μAcm−2 mM-1, respectively, and very low limit of detection 1.75 ± 0.30 μM. The perfect selectivity and stability promotes the material selection as the main biosensor component.

Micro/nano topography with altered nanotube diameter differentially trigger endoplasmic reticulum stress to mediate bone mesenchymal stem cell osteogenic differentiation

Micro/nano-topography (MNT) can promote osteogenic differentiation of stem cells, but the mechanism of topographical signaling transduction remains unclear. We have confirmed MNT, as a stressor, triggers endoplasmic reticulum (ER) stress and activates unfolded protein response in rat bone marrow mesenchymal stem cells, and such topography-induced ER stress promotes osteogenic differentiation. In order to reveal the influence of nanotube dimensions on ER stress, MNTs containing vertically oriented TiO2 nanotubes of diameters ranging from 30 nm to 100 nm were fabricated on pure titanium (Ti) foils, and ER stress and osteogenic differentiation of cells were systematically studied. After 12 h of cultivation, the transmission electron microscopy showed that cells on MNTs presented gross distortions of rough ER morphology containing the electron-dense material, and the expansion of the ER lumen became more pronounced as the dimension of nanotubes increased. Additionally, PCR and western blotting showed that the ER stress-related gene, the ER chaperone 78 kDa glucose-regulated protein, also known as binding-immunoglobulin protein (GRP78/BiP), was up-regulated, which was consistent with the osteogenesis-inducing ability of MNTs. Based on our previous studies, the findings in this article further revealed the mechanism for topographical cues modulating osteogenic differentiation of cells, which may provide an innovative approach for the optimal design of implant surface topography.

Polyaniline/reduced graphene oxide nanosheets on TiO2 nanotube arrays as a high-performance supercapacitor electrode: Understanding the origin of high rate capability

As charge storage occurs both on the surface and in the bulk of material, the dynamics of charge storage is a key issue in the practice of energy storage. Although the energy storage can be increased in the bulk of the material, it often suffers from a quite slow kinetics, which seriously hinders the rate capability. Keeping high surface-induced capacitive contribution is proposed to address this issue. Herein, a porous scaffold, TiO2 nanotube arrays grown in a Ti foil (TiO2 NTs/Ti) is selected as the current collector for electrodeposition of porous polyaniline/reduced graphene oxide (PANI/rGO) hybrid film. The capacitive contribution of PANI/rGO@TiO2/Ti is quantitatively evaluated, showing a high surface-induced capacitive contribution up to 58% at high rates (>25 mV s−1) and large electron transfer coefficient of 2. As a result, the electrode not only shows an ultrahigh specific capacity of 908 C g−1 at 1 mV s−1, but also delivers an outstanding rate capacity of 310 C g−1 at 500 mV s−1. PANI/rGO@TiO2/Ti also shows excellent cycling stability with 80% capacity retention after 10,000 cycles at a high current density of 25 A g−1.

TiO2 Nanotube Arrays on Flexible Kapton Substrates for Photo-Electrochemical Solar Energy Conversion

This work reports the growth of stable TiO2 nanotube arrays on flexible Kapton substrates by electrochemical anodization of a sputtered Ti (titanium) film. Although such nanotubes are conventionally fabricated on Ti foils, obtaining these on polymer-based flexible substrates remained a challenge because of higher annealing temperature not compatible with thermal stability of the substrates. Here, we demonstrate the fabrication of TiO2 nanotubes (1.5 μm long and 80 nm diameter) by anodization of the Ti film deposited using the RF sputtering technique at two different substrate temperatures (room temperature and 300 °C). Nanoindentation and nanoscratch techniques reveal better adhesion of the Ti film with an underlying Kapton substrate for 300 °C deposition temperature. Such investigations reveal a more than twofold enhancement of the “rear pileup” for the Ti film deposited at elevated temperature compared to that at room temperature. The amorphous TiO2 nanotubes are crystallized at 220 °C for 3 h using a solvothermal technique that allows crystallization at temperatures much lower than the annealing temperature. Application of these nanotubes for photo-electrochemical water splitting reveals a photocurrent density of 18 μA/cm2 under AM 1.5 G conditions. Furthermore, the charge density and flat band potential (VFB) are calculated from Mott–Schottky analysis, showing features comparable to the TiO2 nanotubes on the Ti foil crystallized through thermal annealing. The present work establishes a scalable approach for developing TiO2 nanotube arrays on the flexible substrate and its use for photo-electrochemical solar energy conversion.

Bi2S3/rGO co-modified TiO2 nanotube photoanode for enhanced photoelectrochemical cathodic protection of stainless steel

A novel Bi2S3/reduced graphene oxide (rGO) co-modified TiO2 nanotube photoanode was fabricated on a Ti foil by anodization combined with cyclic voltammetric electrodeposition, and successive ionic layer adsorption and reaction. After modifying the TiO2 nanotube film with rGO sheets and Bi2S3 nanoparticles, the band gap of the Bi2S3/rGO/TiO2 composite film decreased, and its photoresponse was extended to the visible region. Under white light irradiation, the composite film in a 0.1 M Na2SO3 and 0.1 M Na2S solution exhibited 62.5 times higher photocurrent density than the TiO2 film. The composite film photoanode could make the potential of the coupled 403 stainless steel in a 0.5 M NaCl solution negatively shift by 490 mV, showing enhanced photoelectrochemical cathodic protection.

Study of the structure of exploding flat foils at superhigh current density

We have investigated the features produced in flat metal foils as a result of nanosecond explosions and phase transitions at current densities of (0.1–2) ⋅ 109 A/cm2. Thin foils made of aluminum, copper, nickel, and titanium, with thicknesses of 1–15 μm, were tested. The exploded foil structure was studied using X-pinch radiography and laser shadow imaging. Al, Ti, and Cu (5 and 7 μm thick) foils had an initial two-dimensional structure. At the same time, no apparent structure was registered in 1 μm Cu and 5 μm Ni foils. Experiments on generators with different output parameters have shown that the dominant structures that developed in the explosion are either cracks or bubbles and may depend on the orientation of the initial structure in the thin foil with respect to the current direction. In addition, the energy deposited in the foil differs by a factor of about 1.5 for the orthogonal vs parallel current and initial foil structure directions.

Fabrication and Electrochemical Performance of TiO2-TiN/Sn-SnO2 Composite Films for High Capacity and High Conductivity Lib Anodes

Recently, anodic nanoporous TiO2 films have gained widespread attention as promising anode candidates for Li ion batteries to replace traditional C-based anodes. TiO2 delivers very small volume expansion (<4%) and works at a relatively high working voltage (1.7 V vs. Li/Li+) during Li+ insertion/extraction. This eliminates the influence from the solid electrolyte interface (SEI) layer and avoid the risk of lithium electrodeposition during charge/discharge process, thus further ensuring the cycling stability and safety of batteries. However, the development of TiO2 materials as LIB anodes is limited by its poor electric conductivity and low theoretical capacity. Therefore, we propose a new approach to fill Sn-based materials, which possess around 3 times theoretic capacity higher that the C-based anode, into the nanoporous anodic TiO2 films. Since the TiO2 nanostructure can alleviate the volume expansion of Sn-based materials, the synergistic effect of Sn with high capacity and TiO2 with large surface area is expected.In this study, we first formed nanoporous TiO2-TiN composite films on Ti foils by a smart anodization in NO3 –-based solutions. The inclusion of conductive TiN component in TiO2 matrix film improves the electronic conductivity effectively, which enables the successive electrodeposition on anodic TiO2 film. Then, the nanoporous TiO2-TiN composite films were used as matrix films to deposit Sn and/or SnO2 nanoparticles by a cathodic electrodeposition in acidic baths containing different Sn ions. The electric conductivity and nanostructures were tailored through anodizing process to perform successive electrodeposition. The microstructures, chemical composition, and crystalline structure of the anodized specimens before and after annealed were investigated FE-SEM (EDS), TEM (FIB), and XPS. Moreover, the cyclic voltammetric behaviors, impedance spectra, and charge-discharge performances of various composite films on Ti foils were investigated as binder-free anode materials for Li ion secondary batteries.Fig.1a-b shows the FE-SEM images of surface and cross section of TiO2-TiN composite films. An ordered nanoporous structure is obtained, with parallel pores of 50-100 nm in diameter and around 3-μm thickness after anodization for 90 min. Fig.1c shows the surface morphology of a TiO2-TiN/Sn composite film by electrodeposition in a Sn2+-based solution for 25 min. A granular Sn-based film with particle size of 100-300 nm in diameter formed on the anodic TiO2-TiN film. This indicates that the prolonged electrodeposition led to the filling of Sn not only inside but also on the anodic TiO2-TiN film. XPS analysis revealed that Sn deposits existed in metallic Sn and Sn oxides as SnO and/or SnO2. Moreover, it is confirmed by TEM observation that the nanocrystalline Sn-SnO2 deposits filled in the porous TiO2-TiN film. It is normally that the particles emerging on the film surface are larger than the pores of TiO2-TiN film.Fig.1d demonstrates the cycling performance and coulombic efficiency of TiO2-TiN/Sn-SnO2 and TiO2-TiN composite films on Ti sheets at 30 mA cm-2 for the first cycle and then 80 mA cm-2. The initial capacity of TiO2-TiN/Sn-SnO2 is 2100 μA h cm-2, which is around 5 times larger than the TiO2-TiN matrix film of 396 μA h cm-2. After 40 cycles, the capacity of the composite film remains 1153 μA h cm-2 and 4.6 times higher than the film without Sn electrodeposition. Since the nanoporous structure of TiO2-TiN can alleviate the volume expansion of Sn-based particles inside, the capacity deterioration can be mainly ascribed to the Sn-based particles overflowed on the surface, which may fall off or crush during charge/discharge process by the large volume expansion. Moreover, it was found from the EIS measurement that the internal electrical resistance of the TiO2-TiN composite film decreased considerably after the electrodeposition of the Sn-based materials, in proportional to the deposition time. Therefore, electrodeposition of Sn-based material in porous TiO2-TiN films is an effective approach to enhance the capacity and to improve the conductivity of the electrode material. Nevertheless, optimizing the conditions of anodization Ti base materials and Sn-based electrodeposition are necessary and will be an issue in the future study. Figure 1

(Keynote) Facile Fabrication of High-Performance Lib Anode and Cathode Materials on Al and Ti By Smart Anodization and Hybrid Electrodeposition

Aluminum and titanium materials are well known as typical light metals which are widely applied to versatile products for their high corrosion resistance, conductive and decorative properties, etc. Recently, aluminum and titanium materials are paid extensive attention to battery industry, using as current collectors or electrode materials. Lithium-ion batteries (LIBs) are known as important power sources in many electric/electronic products such as cellular phones, digital cameras, portable computers, as well as electric vehicles (EVs) and hybrid electric vehicles (HEVs). To meet the ever-expanding needs for lithium-ion battery industry, it is an urgent task to develop new technologies for producing LIB materials with optimal performance-safety balance, and to substituting conventional sintering-casting process by cost-effective process in manufacture of LIBs. In this study, we report three new processes to fabricate cathode and anode materials for LIBs as below. Fabrication of Li-V-Mn-Ni-O composite films on Al by a hybrid electrodeposition for LIB Cathodes Fig.1a shows a cross-sectional scheme of Li-V-Mn-Ni-O composite films on Al foils. Different from the conventional sintering methods for producing LiCoO2-based LIB cathodes, we proposed a novel hybrid electrodeposition to fabricate Li-V-Mn-Ni-O composite films directly on Al, which is expected to increase the working potential with Li ions above 4 V vs. Li+/Li and to decrease the cost of active materials. The composite films were obtained by a cathodic electrodeposition in ethanol-water bath containing V5+、Ni2+, Mn2+, and Li+ ions. Before electrodeposition, an electro-etching pretreatment was adopted to enhance the adhesion between the Al substrate and the electrodeposits. It is found that the resultant composite films after annealing consists of V2O5, Li2MnO4, NiOOH, and metallic Li components. The cyclic voltammetric measurements detected three peaks at 3.2, 4.01, and 4.33 V vs. Li+/Li, which can be ascribed to the Li extraction reactions from the substance mentioned above, indicating the composite films worked as active materials as LIB cathodes. Formation of nanoporous TiO2-TiO-TiN composite films on Ti by a smart anodization for LIB anodes Nanoporous anodic TiO2 films are considered as promising LIB anode materials to solve the safe issue caused by lithium electrodeposition during charge/discharge process as use C-base anodes conventionally. However, the poor conductivity and low theoretic capacity of TiO2 materials are big concerns for practical uses for high density LIBs. Here, we formed successfully nanoporous TiO2-TiO-TiN composite films on Ti foils by a smart anodization in aqueous NO3 –-based solutions and found that the inclusion of conductive TiN component in TiO2 matrix film improved the electronic conductivity effectively (Fig.1.b). The TiO2-TiO-TiN composite films after being heated at 150–500 ºC can be used as binder-conductive reagent free LIB anodes and exhibited higher capacity than ordinary TiO2 films. Fabrication of TiO2-TiN/M-MOx (M = Sn, Mo) composite films on Ti by Hybrid electrolytic process In order to increase the capacity of anodic TiO2-TiN films, we conducted various electrodeposition of Sn-based and Mo-based materials with high theoretic capacities into the anodic TiO2-TiN matrix films, as shown in Fig.1c. The inclusion of highly conductive TiN component in TiO2 matrix film during anodization endows the necessary electronic conductivity for the successive cathodic hybrid electrodeposition of various active materials with high theoretic capacities. The one approach is to fill Sn and SnO2 nanoparticles into TiO2-TiN matrix films by using an acidic plating bath containing different Sn ions. This not only increased the areal specific capacity in 4–9 times compared to the anodic TiO2-TiN films, but also improved the conductivity of the composite films. Another approach is to fill Mo-based materials from a molybdate solution. It is found by XPS analysis that the resultant Mo-based deposits composed of molybdate oxides (MoO2-MoO3) and molybdate nitrides (Mo2N-MoN). The electrodeposition of Mo-based materials into TiO2-TiN films improved the conductivity of the composite films significantly due to the high conductive components of molybdate nitrides. As a result, TiO2-TiN/MoOx-MoyN composite films exhibited around 5 times higher discharge capacity than the TiO2-TiN films and excellent cycling performance with a retention of 97%, indicating a promising anode material with high power density and high safety for LIBs. Figure 1

Fabrication of Iron Phosphide Nanoparticle/Carbon Paper Electrodes Via Electrophoretic Deposition for HER Catalysis

As a renewable energy source to replace traditional fossil fuels, hydrogen is a promising sustainable energy carrier due to its eco-friendly nature and high energy density. Although Pt-based materials are widely used as catalysts for generating hydrogen through water electrolysis because of their high catalytic activity, Pt is expensive, and its scarcity hinders the commercialization of large-scale hydrogen production. The development of alternative low-cost materials with low hydrogen evolution reaction (HER) overpotential is the key to achieve low price and highly efficient hydrogen generators such as proton-exchange membrane water electrolysis (PEMWE). Among the numerous candidates of earth-abundant materials, transition metal-based phosphides (TMPs) are suitable for HER applications due to their low toxicity, high electrical conductivity, and catalytic activity. Especially, FeP is in the spotlight as a HER catalyst due to its high catalytic activity in solutions with a wide pH range, and this is a competitive material for large-scale commercial production of hydrogen, since Fe is one of the most abundant elements on earth.In this study, we synthesized the colloidal FeP nanoparticles (NPs) via a hot injection process, so that the pre-synthesized Fe NPs can be converted to FeP NPs through the phosphorization reactions by various phosphorus sources (trioctylphosphine, triphenylphosphite (TPP), tris(diethylamino)phosphine, and tri-n-butylphosphine). Different HER activities were induced by the phase transformation of NPs over the controlled reaction time for the NP samples synthesized with each phosphorus precursor. The FeP synthesized using TPP achieved excellent HER activity with an overpotential of 76 mV at 10 mA cm-2 in 0.5 M H2SO4 as measured by drop casting the catalyst on Ti foil. In terms of the fabrication for the efficient HER electrode, the prepared FeP NPs were deposited on the carbon paper (CP) via electrophoretic deposition (EPD), which is a suitable method for the fabrication of NP films that can be used for various electronic applications. Different morphologies and catalytic activities of the FeP/CP samples were derived by controlling EPD parameters such as mixing ratio of solvents, NP concentration, and deposition voltage. The optimized EPD process lead to excellent HER activity of the FeP/CP with an overpotential of 38 mV and 91 mV at 10 mA cm-2 in 0.5 M H2SO4 and 1 M KOH, respectively. The maximum activity of the catalyst was mainly attributed to the large active surface area and low charge transfer resistance due to the strong contact between the NPs and CP. A PEMWE single cell with the FeP/CP cathode achieved 1.2 A cm-2 at cell voltage of 2.0 V. This study of the EPD procedure for fabricating the NP film from the colloidal NP catalysts contributes to advance manufacturing of HER electrodes for efficient hydrogen generation through water electrolysis.

Film Fabrication and Composition Control of Transition Metal Oxide Nanoparticles for Oxygen Evolution Catalysts

Development of highly efficient oxygen evolution reaction (OER) catalysts is necessary for commercial implementation of water electrolysis due to overcome slow kinetics of OER. Noble metal based electrocatalysts such as Ir and Ru demonstrate high performance for OER in acidic media. In contrast, the first-row transition metal oxides such as Ni, Co, and Fe oxides show the high catalytic activity and stability in alkaline media. In this work, the composition of bimetallic metal oxide NPs was tuned and their electrochemical performance was analyzed. Furthermore, the electrophoretic deposition (EPD) technique was utilized for the efficient fabrication of NP thin film electrode. The bimetallic transition metal oxide NPs were synthesized by using Ni(acac)2 as Ni precursor and Fe(acac)3 as Fe precursor, leading to the phase control of bimetallic Ni-Fe oxide NPs. As Fe precursor amount was gradually increased compared to that of Ni, the particle size of Ni-Fe oxide NPs was increased, and the shape of NPs was transformed from spherical to irregular shape. The magnetic property of Ni-Fe oxide NPs was also analyzed by vibrating sample magnetometer. The saturation magnetization (Ms) of bimetallic metal oxide was increased and the magnetic coercivity was decreased when the Fe composition was increased. For the electrochemical analysis for OER, the overpotential of bimetallic metal oxide NPs catalysts was highly influenced by the composition of bimetallic metal oxide NPs. Higher Fe contents than Ni in the NPs led to high performance as OER catalysts. The EPD technique was introduced to manufacture the uniform NP films with improved catalytic activity. The catalyst film formed through EPD technique was prepared under the applied voltage of 500 V for 10 minutes. The film of Ni-Fe oxide NPs was well covered on the substrate of the Ti foil. The overpotential of the bimetallic metal oxide NP film fabricated by EPD was decreased from 510 mV to 400 mV at 10 mA/cm2 compared to the films fabricated by drop casting. These results provide useful insights not only for understanding the catalytic activity of bimetallic metal oxide NPs in OER but also for suggesting the film fabrication method for enhancing the catalytic activity.

Electrochemical Properties of AuNP-Tind Nanostructures As Glucose Sensing Materials and Thorough Interference Study

Non-enzymatic glucose sensors are prominent alternatives to the commercially available glucometers. Their main advantages over enzyme–based devices are higher stability to changes of the environment such as pH and temperature and lack of complicated immobilization procedure [1]. However non-enzymatic glucose sensitive materials are typically less selective, so there is a strong requirement for the development of proper coatings or membranes in order to minimize the negative influence of interferences. Therefore we present Au-Ti heterostructure covered with various coatings (e.g. Nafion, poly(sulfobetaine methacrylate)) and novel approach for analysis of interfering species influence onto electrode performance in neutral solution.Fabrication procedure of material consists of the following steps: preparing structured titanium template (TiND) by anodization and etching of nanotubes, gold sputtering and subsequent dewetting. After those steps electrode morphology is investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM) [2] revealing the presence of gold nanoparticles (AuNPs) in every dimple of Ti foil. Lastly, as formed material is covered by protective coating. Electrochemical properties and catalytic activity towards glucose oxidation are determined by standard techniques - cyclic voltammetry (CV) and impedance spectroscopy (EIS). Examining interference phenomena of various compounds (such as ascorbic acid (AA), acetaminophen (AAp), urea and glycine) is realized by both CV and EIS techniques in certain configuration. Moreover influence of those species on the catalytic activity of the material is established. Obtained results confirm the possibility of using prepared electrodes in sensors applied for noninvasive glucose detection in human body fluids. Acknowledgements This work has been financed by National Center for Research and Development under the LIDER program (LIDER/2/0003/L-8/16/NCBR/2017).

Electrodialysis and Nitrate Reduction to Synthesize and Recover Ammonia from Wastewaters

Humans have drastically altered the global nitrogen cycle, asymmetrically doubling its throughput due to industrial Haber-Bosch fertilizer production.1,2 Fertilizer runoff and inadequate wastewater removal cause waterborne emissions of reactive nitrogen (e.g., NH4 +, NO3 -) that induce harmful algal blooms.3,4 Meanwhile, both water purification and ammonia synthesis are conducted separately in centralized facilities with severe limitations: only 20% of wastewater is collected at treatment plants,5 and ammonia synthesis requires high temperature (400 °C), pressure (200 atm), energy input (1.2% of global energy), and greenhouse gas emissions (5% of industrial CO2).6,7 To couple water purification and ammonia production more efficiently, the following two reactions can be leveraged to synthesize and recover ammonia from nitrogen-polluted wastewater. Ammonia synthesis via electrochemical nitrate reduction: NO3 - + 9H++ 8e- → NH3 + 3H2OAmmonia recovery via electrodialysis and electrochemical pH control: NH4 + + OH- ↔ NH3 + H2O In our previous work, we have successfully demonstrated electrochemical stripping (ECS), a novel process combining electrodialysis and membrane stripping that selectively extracts (NH4)2SO4 from wastewater with > 93% recovery efficiency.8 We have also constructed a nitrogen mass transfer model for this process to inform rational decision of operating parameters.9 Building on these results, we reimagine nitrogen pollutants as products and propose electrodialysis and nitrate Reduction (EDNR). This novel unit process consists of three stages: (1) electrodialysis to separate influent NO3 - and NH4 +; (2) electrocatalytic reduction of NO3 - to NH3 (NO3RR), along with migration of undesired anions; and (3) product purification via migration of undesired cations (see Figure 1). We have built a proof-of-concept EDNR reactor using Ti/IrO2-Ta2O5 mesh (left and middle chambers) and stainless steel electrodes (right chamber). With recirculating batches of synthetic ion exchange brine (NaNO3/NH4Cl solution) and LiCl supporting electrolyte, we demonstrated that (1) over 99% of influent NH4 + is recovered to the right chamber; (2) 12% of initial NO3 - reacts, reaching 32% peak Faradaic efficiency towards NH3; (3) Cl- migrates out of the left chamber during NO3RR as desired and Cl2 gas evolution is minimal; and (4) ideal pH values are sustained in all three chambers to maximize NH3 synthesis and recovery.Aiming at selective NO3RR to NH3, we have also explored the effect of varying electrochemical conditions (e.g., pH, NO3 - concentration, applied potential) at a titanium foil cathode, which has shown high NH3 selectivity and corrosion resistance. Moving forward, we plan to use Ti foil electrode in the left chamber of EDNR, in which it will perform the oxygen evolution reaction (OER) in stage 1 and NO3RR in stage 2. To better understand the evolution of the catalyst during reactions and rationally identify EDNR operating potentials and cycle durations that maximize active catalyst stability, we perform characterizations of the Ti surface.By enabling automated, distributed ammonia manufacturing with minimal environmental impacts from prevalent wastewater contaminants, EDNR furthers our endeavor to re-engineer the nitrogen cycle. References (1) Galloway, J. N.; Townsend, A. R.; Erisman, J. W.; Bekunda, M.; Cai, Z.; Freney, J. R.; Martinelli, L. A.; Seitzinger, S. P.; Sutton, M. A. Transformation of the Nitrogen Cycle: Recent Trends, Questions, and Potential Solutions. Science 2008, 320 (5878), 889–892.(2) Fields, S. Global Nitrogen: Cycling out of Control. Environ Health Perspect 2004, 112 (10), A556–A563.(3) Dodds, W. K.; Bouska, W. W.; Eitzmann, J. L.; Pilger, T. J.; Pitts, K. L.; Riley, A. J.; Schloesser, J. T.; Thornbrugh, D. J. Eutrophication of U.S. Freshwaters: Analysis of Potential Economic Damages. Environ. Sci. Technol. 2009, 43 (1), 12–19.(4) Nyenje, P. M.; Foppen, J. W.; Uhlenbrook, S.; Kulabako, R.; Muwanga, A. Eutrophication and Nutrient Release in Urban Areas of Sub-Saharan Africa — A Review. Science of The Total Environment 2010, 408 (3), 447–455.(5) Larsen, T. A.; Hoffmann, S.; Lüthi, C.; Truffer, B.; Maurer, M. Emerging Solutions to the Water Challenges of an Urbanizing World. Science 2016, 352 (6288), 928–933.(6) Singh, A. R.; Rohr, B. A.; Schwalbe, J. A.; Cargnello, M.; Chan, K.; Jaramillo, T. F.; Chorkendorff, I.; Nørskov, J. K. Electrochemical Ammonia Synthesis—The Selectivity Challenge. ACS Catal. 2017, 7 (1), 706–709.(7) Norskov, J.; Chen, J. Sustainable Ammonia Synthesis; Department of Energy, 2016.(8) Tarpeh, W. A.; Barazesh, J. M.; Cath, T. Y.; Nelson, K. L. Electrochemical Stripping to Recover Nitrogen from Source-Separated Urine. Environ. Sci. Technol. 2018, 52 (3), 1453–1460.(9) Liu, M. J.; Neo, B. S.; Tarpeh, W. A. Building an Operational Framework for Selective Nitrogen Recovery via Electrochemical Stripping. Water Research 2020, 169, 115226. Figure 1

On the Stability of Co3O4 Oxygen Evolution Electrocatalysts in Acid

AbstractOxygen evolution reaction (OER) electrocatalysts suitable to work in acid are typically restricted to platinum group noble metal oxides because of their high activity and, especially, stability. Co3O4 is currently explored as an alternative OER catalyst. Herein we prepared Co3O4 films on fluorine‐doped Sn oxide (FTO) glass and Ti foil via thermal decomposition of nitrate salts and evaluated their activity and stability in 0.05 M H2SO4. Crystalline Co3O4 films deposited on FTO were stable during chronopotentiometry at 10 mA cm−2 for over 16 hours. The dissolution rate was 61 ngCo cm−2 min−1. The choice of a stable support such as FTO is essential to ensure the stability of the catalyst‐substrate interface and to prevent substrate passivation under OER conditions. Doping Co3O4 with Li resulted in a higher OER activity under acidic conditions to be attributed to the larger electrochemical surface area, although the stability was impeded compared to undoped Co3O4.

Improving energy density of crystalline–amorphous multilayer films deposited on Ti foils by structural modulation

AbstractDielectric capacitors are one of the most important energy‐storage components specifically used for various high‐power pulse applications. However, the low energy‐storage density (Ue) of dielectrics used today limits their application. In this study, crystalline–amorphous multilayer films of crystalline Sr0.85Bi0.1TiO3 (SBT)/amorphous SBT/amorphous Al2O3 (Sc–(8−n)Sa–nAa) were fabricated on flexible Ti foils using the sol–gel method. An enhancement in energy density was achieved by adjusting the thicknesses of the amorphous SBT and Al2O3 (AO) layers. The crystalline SBT layer contributes to an increase in the dielectric constant and the amorphous AO layer to an increase in the breakdown strength. Moreover, the AO layers that are inserted are capable of suppressing the leakage current by eliminating the space charge limited conductance mechanism and thereby effectively decreasing the probability of breakdown of the SBT layers. A lower leakage current and higher breakdown strength can be further achieved using an Al electrode instead of the Au electrode. A large energy density of 27.2 J cm−3 can be realized via the crystalline–amorphous multilayer films with the Al electrode, which represents an enhancement of ~234% over that of the amorphous SBT film (8.14 J cm−3). In addition to the high energy‐storage enhancement, this study also presents a promising method that can be used to fabricate flexible multilayer films for lightweight and high energy density applications and for devices used to service high‐temperature conditions.

Growth of dimensionally favoured TiO2 morphologies by AACVD and their recognized performance as LIB anode

The current effort aims at the morphological displays of TiO2 materials grown on Ti foil substrates using aerosol assisted chemical vapour deposition. Optimization of temperature, surfactant concentrations and substrate orientation has been found to play a vital role in the smart designing of micro/nanostructures, ranging from microspheres, nanopetals, nanospikes to the nanorods. Interestingly, when tested as LIB anode these various morphologies showed a much distinct performance and stability during charge/discharge cycles. The nanorod structures with smooth carbon covering have shown excellent reversibility followed by the nano-petals that showed an impressively stable capacity.

Pd quantum dots loading Ti3+,N co-doped TiO2 nanotube arrays with enhanced photocatalytic hydrogen production and the salt ions effects

Pd quantum dots (QDs) loading Ti3+,N co-doped TiO2 nanotube array (NTA) films were prepared by anodic oxidation of Ti foils, followed by calcination at 400 °C and Pd photo-depositions using a PdCl2 solution. The photocatalytic hydrogen production activity of the Pd QDs loading Ti3+,N co-doped TiO2 NTA was tested under UV–vis light irradiation in a methanol aqueous solution and compared with those of Ag and Au loaded Ti3+,N co-doped TiO2 NTAs. The effects of Pd content, salt ions and catalytic reaction temperature on the photocatalytic activities of the Pd QDs loading Ti3+,N co-doped TiO2 NTA catalysts were explored systematically. The photocatalytic reaction mechanism was proposed based on the experimental results. The results show that the hydrogen evolution reaction (HER) rate (17.6 µmol cm−2h−1) over the Pd QDs loading TiO2NTA/Pd10 (10 cycles of Pd photo-depositions) was increased to 16 times higher than that of the unloaded TiO2NTA (1.1 µmol cm−2h−1). Interestingly, adding small amount of alkali salt (0.5 g L−1) in the preparation process of the TiO2 NTAs or in the photocatalytic reaction medium (1 g L−1) can further increase the HER rates distinctly (2.7–3.4 times).

Synthesis of Ni- and N-Doped Titania Nanotube Arrays for Photocatalytic Hydrogen Production from Glycerol–Water Solutions

Synthesis of Ni- and N-doped Titania Nanotube Arrays (Ni-N-TiNTAs) was conducted to produce photocatalysts for hydrogen production from a glycerol–water mixture. Ni-N-TiNTAs were synthesized in two steps, namely anodization and chemical reduction. Ti foil was anodized at 50 V for two h in an electrolyte solution containing 0.2% urea as a source of N atoms. Ni doping (at various content of 5%, 10%, 15%, and 20% wt) was performed by one-hour chemical reduction with sodium borohydride as a reducing agent. The photocatalyst was annealed at different temperatures, i.e., 500 °C, 550 °C, and 600 °C under 60 mL/min N2 gas for two h. On the basis of X-ray Diffraction (XRD) patterns, Ni-N-TiNTAs are mostly of anatase crystallite phase when annealed at 500 °C and 550 °C, while that of rutile was observable when calcination was done at 600 °C. The morphology of the photocatalysts was scrutinized by means of Field Emission Scanning Electron Microscopy (FESEM) imaging, which reveals nanotubular structures, with elemental composition measured by Energy Dispersive X-ray (EDX). The bandgap of the photocatalysts was analyzed using Ultraviolet Diffuse Reflectance Spectroscopy (UV DRS), which showed a lower value for the case of Ni-N-TiNTAs as compared to those of TiNTAs and N-TiNTAs. Photocatalytic tests showed that the highest amount of hydrogen produced (ca. 30973 μmol/m2) was obtained in the case of Ni-N-TiNTAs with a Ni content of 10wt%.