The continuing development of Magnéli phase titanium sub-oxides and Ebonex® electrodes

Robust titanium suboxide anodes doped by sintering enhance PFOS degradation in water

Per- and Polyfluoroalkyl Substances (PFAS) are a class of persistent organic pollutants that are ubiquitous in the environment, while PFOS is one most representative PFAS of extraordinary persistence. Electrochemical oxidation (EO) is promising for destructive treatment of PFAS in water, and Magnéli phase titanium suboxide (TSO) is regarded as one of only few suitable anode materials for this application. We herein conducted an in-silico survey with Density Functional Theory (DFT) simulations to identify possible beneficial dopant elements, and then prepared TSO anodes doped with Niobium (Nb-TSO) or Cerium (Ce-TSO) by sintering. The doped TSO thus prepared exhibited great robustness, having service lifetimes longer than the pristine Ti4O7 anode, making them useful for EO applications in PFAS treatment. PFOS degradation by EO using Nb-TSO anode was faster than that on the pristine Ti4O7 anode, with energy consumption approximately 1.8 times lower. Further characterizations and DFT simulations reveal that the enhanced efficiency of Nb-TSO anode is attributed to its reduced charge transfer resistance and increased effective electroactive surface area (EESA). The EESA of the Ce-TSO anode was reduced in comparison to the pristine Ti4O7, but PFOS degradation rates normalized by EESA were increased significantly for EO with Ce-TSO anode, due to its increased oxygen evolution potential (OEP) and hydroxyl radical production. The doped TSO anodes prepared in this study by sintering will be useful in EO treatment of PFAS-contaminated waters, with improved service life and performance, and the study provides understandings to guide further improvements of the TSO anodes via doping.

Oxygen Vacancy in Magnéli Phases and Its Effect on Thermoelectric Performances

Magnéli phases exhibit significant potential for applications in electronic materials in energy conversion due to their high electrical conductivity and excellent thermal stability. In this study, single-phase TinO2n-1 (n = 4, 5, 6) bulk materials were successfully prepared by a combination of the carbothermal reduction of nano-sized rutile TiO2 and hot-press sintering methods. The relationships between the phase evolution, microstructural features, and thermoelectric performance were investigated systematically. Synchrotron X-ray diffraction (SXRD) and scanning electron microscopy (SEM) analyses revealed that the Ti4O7 and Ti5O9 materials had single-phase structures with high densities (relative density > 97%) and no obvious grain boundary holes or microcracks. We tested the thermoelectric properties of the Magnéli phases in the temperature range of 300-1100 K. The Magnéli phases exhibited a significant temperature dependence, with peak zT values of 0.17, 0.18, and 0.14 for Ti4O7, Ti5O9, and Ti6O11, respectively, at 1100 K. This variation in thermoelectric performance was mainly attributed to the synergistic effect of the oxygen vacancy concentration and the shear surface density on the carrier concentration and lattice thermal conductivity. Furthermore, the Fermi energy levels and electronic thermal conductivity of the Magnéli phases were calculated using the single parabolic band (SPB) model.

Matrix Effects on Electrochemical Oxidation of Per- and Polyfluoroalkyl Substances in Sludge Centrate

This study investigated the electrochemical oxidation of per- and polyfluoroalkyl substances (PFAS) using a Ti4O7 anode in centrate from sludge dewatering. Synthetic solutions containing perfluorooctanoic acid (PFOA), other PFAS, and inorganic constituents (phosphate, ammonium, chloride, carbonate, and acetate salts) found in centrate were studied to assess their impact on the oxidation process. PFOA removal decreased from 95% in a stable electrolyte (NaClO4) to 81% in a Na2HPO4 electrolyte and 30% in a solution mimicking concentrated centrate. X-ray photoelectron spectroscopy detected phosphate and nitrogen species on the electrode surface. At potentials required to oxidize PFAS (>3.0 V/SHE), phosphate and ammonium were oxidized to radicals that blocked electrode sites, inhibiting PFAS removal and shifting PFOA oxidation from first-order kinetics. The kinetics were accurately modeled using a Langmuir-Hinshelwood approach with a transient inhibition term. Results suggested that phosphate, ammonium, and bicarbonate ions reduced hydroxyl radical availability, thereby limiting PFOA defluorination. In concentrated centrate, 95% of the chemical oxygen demand and 93% of total PFAS were removed after 233 s of electrolysis at 30 mA cm-2. However, partial degradation of perfluorohexanoic acid and accumulation of perfluoroheptanoic acid, attributed to inorganic electrode fouling, suggested the need for a multistage reactor system for more complete PFAS mineralization.

Recent advances in synthesis and application of Magnéli phase titanium oxides for energy storage and environmental remediation

High-temperature reduction of TiO2 causes the gradual formation of structural defects, leading to oxygen vacancy planar defects and giving rise to Magnéli phases, which are substoichiometric titanium oxides that follow the formula Ti n O2n-1, with 4 ≤ n ≤ 9. A high concentration of defects provides several possible configurations for Ti4+ and Ti3+ within the crystal, with the variation in charge ordered states changing the electronic structure of the material. The changes in crystal and electronic structures of Magnéli phases introduce unique properties absent in TiO2, facilitating their diverse applications. Their exceptional electrical conductivity, stability in harsh chemical environments and capability to generate hydroxyl radicals make them highly valuable in electrochemical applications. Additionally, their high specific capacity and corrosion resistance make them ideal for energy storage facilities. These properties, combined with excellent solar light absorption, have led to their widespread use in electrochemical, photochemical, photothermal, catalytic and energy storage applications. To provide a complete overview of the formation, properties, and environmental- and energy-related applications of Magnéli phase titanium suboxides, this review initially highlights the crystal structure and the physical, thermoelectrical and optical properties of these materials. The conventional and novel strategies developed to synthesise these materials are then discussed, along with potential approaches to overcome challenges associated with current issues and future low-energy fabrication methods. Finally, we provide a comprehensive overview of their applications across various fields, including environmental remediation, energy storage, and thermoelectric and optoelectronic technologies. We also discuss promising new directions for the use of Magnéli phase titanium suboxides and solutions to challenges in energy and environment-related applications, and provide guidance on how these materials can be developed and utilised to meet diverse research application needs. By making use of control measures to mitigate the potential hazards associated with their nanoparticles, Magnéli phases can be considered as versatile materials with potential for next generation energy needs.

The impact of anions on electrooxidation of perfluoroalkyl acids by porous Magnéli phase titanium suboxide anodes

Previous studies have indicated the great performance of electrooxidation (EO) to mineralize per- and polyfluoroalkyl substances (PFASs) in water, but different anions presented in wastewater may affect the implementation of EO treatment in field applications. This study invetigated EO treatment of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), two representative perfluoroalkyl acids (PFAAs), using porous Magnéli phase titanium suboxide anodes in electrolyte solutions with different anions present, including NO3-, SO42-, CO32- and PO43-. The experiment results indicate that CO32- enhanced PFAS degradation, while NO3- suppressed the degradation reactions with its concentration higher than 10 mM. SO42- and PO43- exhibited less impact. Further studies with electrochemical characterizations and radical quenching experiments illustrate the mechanisms of how the anions may impact EO performance.

Establishing Non-Stoichiometric Ti4O7 Assisted Asymmetrical C-C Coupling for Highly Energy-Efficient Electroreduction of Carbon Monoxide

Exploring an appropriate support material for Cu-based electrocatalyst is conducive for stably producing multi-carbon chemicals from electroreduction of carbon monoxide. However, the insufficient metal-support adaptability and low conductivity of the support would hinder the C-C coupling capacity and energy efficiency. Herein, non-stoichiometric Ti4O7 was incorporated into Cu electrocatalysts (Cu-Ti4O7), and served as a highly conductive and stable support for highly energy-efficient electrochemical conversion of CO. The abundant oxygen vacancies originated from ordered lattice defects in Ti4O7 facilitate the water dissociation and the CO adsorption to accelerate the hydrogenation to *COH. The highly adaptable metal-support interface of Cu-Ti4O7 enables a direct asymmetrical C-C coupling between *CO on Cu and *COH on Ti4O7, which significantly lowers the reaction energy barrier for C2+ products formation. Additionally, the excellent electroconductivity of Ti4O7 benefits the reaction charge transfer through robust Cu/Ti4O7 interface for minimizing the energy loss. Thus, the optimized 20Cu-Ti4O7 catalyst exhibits an impressive selectivity of 96.4 % and ultrahigh energy efficiency of 45.1 % for multi-carbon products, along with a remarkable partial current density of 432.6 mA cm-2. Our study underscores a novel C-C coupling strategy between Cu and the support material, advancing the development of Cu-supported catalysts for highly efficient electroreduction of carbon monoxide.

High photothermal conversion efficiency of RF sputtered Ti4O7 Magneli phase thin films and its linear correlation with light absorption capacity

RF-sputtering is used to deposit Ti4O7-Magneli-phase films onto various substrates at deposition temperatures (Ts) ranging from 25 to 650 °C. Not only the structural, but also electrical conductivity, optical absorbance and photothermal properties of the Ti4O7 films are shown to change significantly with Ts. A Ts of 500 °C is pointed out as the optimal temperature that yields highly-crystalized pure-Ti4O7-Magneli phase with a densely-packed morphology and a conductivity as high as 740 S/cm. The Ti4O7 films deposited at Ts = 450-500 °C also exhibited the highest optical absorption over all the broad (200-1500) nm range. The absorbed sunlight (AM1.5) was efficiently converted into heat by raising the temperature of the Ti4O7 films up to ~ 54 °C. Thus, the external photothermal efficiency (ηext) of the Ti4O7 films, was found to be as high as ~ 74%. This is the highest ηext reported so far for sputtered-Ti4O7 coatings (just ~ 450 nm-thick), highlighting their significant potential for photothermal applications such as desalination, deicing and/or smart windows. Finally, the ηext of the Ti4O7 coatings is demonstrated, for the first time, to be linearly correlated to their integrated light absorption coefficient. This fundamental relationship paves the way towards the design and optimization of highly efficient solar-thermal conversion devices.

Electrochemical advanced oxidation combined to electro-Fenton for effective treatment of perfluoroalkyl substances "PFAS" in water using a Magnéli phase-based anode

Per-and polyfluoroalkyl substances (PFAS), known as "forever chemicals", are posing a considerable threat to human health and the environment, that conventional treatment methods are unable to treat. In recent years, electrochemical advanced oxidation emerged as a promising technology for the degradation of recalcitrant pollutants such as PFAS. This work reports the degradation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), using a Magnéli phase-based anode type Ti4O7 by electro-oxidation and electro-oxidation combined with electro-Fenton. First the Ti4O7 anode was prepared from Rutile TiO2 powder and characterized, the results showed that the Ti n O2n-1 phase is the dominant phase. Afterward, the degradation of PFOA and PFOS was evaluated on the developed anode. After 5 hours of treatment, 52% and 82% of PFOA and PFOS were removed respectively. To improve this results electro-oxidation was combined with electro-Fenton, the degradation of both pollutants increased, 92% of PFOA was degraded and PFOS was totally removed after 5 hours of treatment. The energy consumption was also evaluated at t 1/2 which is defined as the time when half of the initial concentration of PFOA and PFOS was degraded. Combining the two degradation approaches showed promising results that need to be further optimized for potential application at large volumes.

Efficient electro-oxidation-based degradation of per- and polyfluoroalkyl (PFAS) persistent pollutants by using plasma torch synthesized pure-Magnéli phase-Ti4O7 anodes

Pure Magnéli-phase Ti4O7 were prepared by means of a Plasma Torch (PT) coating method and integrated into an advanced electro-catalytic oxidation (AEO) process in order to degrade perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) persistent pollutants present in waters. The X-ray diffraction analysis confirmed the polycrystalline nature of the pure Magnéli phase PT-Ti4O7 coatings (∼100 μm thick)). The Raman spectra of the PT-Ti4O7 coatings also exhibited the two characteristic peaks (at 138 and 183 cm-1) of the PT-Ti4O7 Magnéli phase. Scanning electron microscopy revealed the nanostructured hierarchical morphology of the PT-Ti4O7 thus conferring them high surface area. The PT-Ti4O7 anodes are shown to achieve higher degradation efficiencies towards PFOA and PFOS in comparison with the conventional boron-doped diamond anodes. By investigating several AEO parameters (including current density, treatment time, nature of the anode material), we were able to optimise the AEO process. Thus, for both PFOA and PFOS (at an initial concentration of 500 ppb in synthetic wastewaters), degradation efficiencies as high as 96.6% and 99.7% were achieved, respectively, with a current density of 20 mA/cm2, a treatment time of 120 min and PT-Ti4O7 mesh-type anodes. PFOA and PFOS can be degraded by both direct anodic electrochemical oxidation (•OH radicals) and indirect electrochemical oxidation via mediators, such as persulphate acid (H2S2O8) generated by sulphate anodic oxidation. The degradation of both compounds followed pseudo-first-order kinetics. The reaction rate constant (k) for PFOS removal was 4.63 × 10-2 min-1, whereas 2.76 × 10-2 min-1 was recorded for PFOA removal. Subsequently, we have used the above optimal AEO operating conditions to treat real wastewater effluents (containing 17 types of PFAS molecules with a total content of 8500 ppb) and achieved a degradation rate of 39.1%-87.4% for eight of the 17 PFAS compounds. The degradation rate was found to be dependent on the chemical structure and chain length of each PFOA/PFOS component.

Preparation and Electrochemical Applications of Magnéli Phase Titanium Suboxides: A Review

Magnéli phase titanium suboxides (M-TSOs) belong to a type of sub-stoichiometric titanium oxides based on the crystal structure of rutile TiO2. They possess a unique shear structure, granting them exceptional electrical conductivity and corrosion resistance. These two advantages are crucial for electrode materials in electrochemistry, hence the significant interest from numerous researchers. However, the preparation of M-TSOs is uneconomic due to high temperature reduction and other complex synthesis process, thus limiting their practical application in electrochemical fields. This review delves into the crystal structure, properties, and synthesis methods of M-TSOs, and touches on their applications as electrocatalysts in wastewater treatment and electrochemical water splitting. Furthermore, it highlights the research challenges and potential future research directions in M-TSOs.

A critical review of persulfate-based electrochemical advanced oxidation processes for the degradation of emerging contaminants: From mechanisms and electrode materials to applications

The persulfate-based electrochemical advanced oxidation processes (PS-EAOPs) exhibit distinctive advantages in the degradation of emerging contaminants (ECs) and have garnered significant attention among researchers, leading to a consistent surge in related research publications over the past decade. Regrettably, there is still a lack of a critical review gaining deep into understanding of ECs degradation by PS-EAOPs. To address the knowledge gaps, in this review, the mechanism of electro-activated PS at the interface of the electrodes (anode, cathode and particle electrodes) is elaborated. The correlation between these electrode materials and the activation mechanism of PS is systematically discussed. The strategies for improving the performance of electrode material that determining the efficiency of PS-EAOPs are also summarized. Then, the applications of PS-EAOPs for the degradation of ECs are described. Finally, the challenges and outlook of PS-EAOPs are discussed. In summary, this review offers valuable guidance for the degradation of ECs by PS-EAOPs.

Active and highly durable supported catalysts for proton exchange membrane electrolysers

The design and development of supported catalysts for the oxygen evolution reaction (OER) is a promising pathway to reducing iridium loading in proton exchange membrane water electrolysers. However, supported catalysts often suffer from poor activity and durability, particularly when deployed in membrane electrode assemblies. In this work, we deploy iridium coated hollow titanium dioxide particles as OER catalysts to achieve higher Ir mass activities than the leading commercial catalysts. Critically, we demonstrate state-of-the-art durabilities for supported iridium catalysts when compared against the previously reported values for analogous device architectures, operating conditions and accelerated stress test profiles. Through extensive materials characterisations alongside rotating disk electrode measurements, we investigate the role of conductivity, morphology, oxidation state and crystallinity on the OER electrochemical performance. Our work highlights a new supported catalyst design that unlocks high-performance OER activity and durability in commercially relevant testing configurations.

Electrochemical filtration for drinking water purification: A review on membrane materials, mechanisms and roles

Electrochemical filtration can not only enrich low concentrations of pollutants but also produce reactive oxygen species to interact with toxic pollutants with the assistance of a power supply, making it an effective strategy for drinking water purification. In addition, the application of electrochemical filtration facilitates the reduction of pretreatment procedures and the use of chemicals, which has outstanding potential for maximizing process simplicity and reducing operating costs, enabling the production of safe drinking water in smaller installations. In recent years, the research on electrochemical filtration has gradually increased, but there has been a lack of attention on its application in the removal of low concentrations of pollutants from low conductivity water. In this review, membrane substrates and electrocatalysts used to improve the performance of electrochemical membranes are briefly summarized. Meanwhile, the application prospects of emerging single-atom catalysts in electrochemical filtration are also presented. Thereafter, several electrochemical advanced oxidation processes coupled with membrane filtration are described, and the related working mechanisms and their advantages and shortcomings used in drinking water purification are illustrated. Finally, the roles of electrochemical filtration in drinking water purification are presented, and the main problems and future perspectives of electrochemical filtration in the removal of low concentration pollutants are discussed.

Research on carbon black and cerium co-doped Ti4O7-CB-Ce electrocatalytic oxidation of tetracycline-based antibiotics

Elemental doping is a promising way for enhancing the electrocatalytic activity of metal oxides. Herein, we fabricate Ti/ Ti4O7-CB-Ce anode materials by the modification means of carbon black and cerium co-doped Ti4O7, and this shift effectively improves the interfacial charge transfer rate of Ti4O7 and •OH yield in the electrocatalytic process. Remarkably, the Ti4O7-CB-Ce anode exhibits excellent efficiency of minocycline (MNC) wastewater treatment (100% removal within 20 min), and the removal rate reduces from 100 to 98.5% after five cycles, which is comparable to BDD electrode. •OH and 1O2 are identified as the active species in the reaction. Meanwhile, it is discovered that Ti/ Ti4O7-CB-Ce anodes can effectively improve the biochemical properties of the non-biodegradable pharmaceutical wastewater (B/C values from 0.25 to 0.44) and significantly reduce the toxicity of the wastewater (luminescent bacteria inhibition rate from 100 to 26.6%). This work paves an effective strategy for designing superior metal oxides electrocatalysts.

Sn Bulk Phase Doping and Surface Modification on Ti4 O7 for Oxygen Reduction to Hydrogen Peroxide

Developing stable and highly selective two-electron oxygen reduction reaction (2e- ORR) electrocatalysts for producing hydrogen peroxide (H2 O2 ) is considered a major challenge to replace the anthraquinone process and achieve a sustainable green economy. Here, we doped Sn into Ti4 O7 (D-Sn-Ti4 O7 ) by simple polymerization post-calcination method as a high-efficiency 2e- ORR electrocatalyst. In addition, we also applied plain calcination after the grinding method to load Sn on Ti4 O7 (L-Sn-Ti4 O7 ) as a comparison. However, the performance of L-Sn-Ti4 O7 is far inferior to that of the D-Sn-Ti4 O7 . D-Sn-Ti4 O7 exhibits a starting potential of 0.769 V (versus the reversible hydrogen electrode, RHE) and a high H2 O2 selectivity of 95.7 %. Excitingly, the catalyst can maintain a stable current density of 2.43 mA ⋅ cm-2 for 3600 s in our self-made H-type cell, and the cumulative H2 O2 production reaches 359.2 mg ⋅ L-1 within 50,000 s at 0.3 V. The performance of D-Sn-Ti4 O7 is better than that of the non-noble metal 2e- ORR catalysts reported so far. The doping of Sn not only improves the conductivity but also leads to the lattice distortion of Ti4 O7 , further forming more oxygen vacancies and Ti3+ , which greatly improves its 2e- ORR performance compared with the original Ti4 O7 . In contrast, since the Sn on the surface of L-Sn-Ti4 O7 displays a synergistic effect with Tin+ (3≤n≤4) of Ti4 O7 , the active center Tin+ dissociates the O=O bond, making it more inclined to 4e- ORR.

In Situ Lubrication in Forging of Pure Titanium Using Carbon Supersaturated Die Materials

A new solid lubrication method was proposed for dry forging of pure titanium with high reduction in thickness. A free-carbon tribofilm was formed in situ at the hot spots on the contact interface to protect the die surfaces from severe adhesion of work materials. This film consisted of the free carbon, which isolated from the carbon supersaturated die substrate materials, diffused to the contact interface and agglomerated to a thin film. Two different routes of carbon supersaturation process were developed to prepare carbon supersaturated ceramic and metal dies for the dry forging of pure titanium wires. A pure titanium bar was utilized as an easy-to-adherent work material for upsetting in dry and cold. The round bar was upset up to 70% in reduction in thickness with a low friction coefficient from 0.05 to 0.1 in a single stroke. Work hardening was suppressed by this low friction. SEM-EDX, EBSD and Raman spectroscopy were utilized to analyze the contact interface and to understand the role of in situ formed free-carbon films on the low friction and low work hardening during forging. Precise nanostructure analyses were utilized to describe low friction forging behavior commonly observed in these two processes. The in situ solid lubrication mechanism is discussed based on the equivalence between the nitrogen and carbon supersaturation processes.

Effects of anode materials on nitrate reduction and microbial community in a three-dimensional electrode biofilm reactor with sulfate

Graphite rod corrosion and peeling are serious problems in three-dimensional electrode biofilm reactors (3D-BERs). In this study, titanium rods, titanium suboxide-coated titanium rods and graphite rods were used as anodes to investigate the effect of anodic materials on the electrochemical and bioelectrochemical reduction of nitrate and sulfate. The results showed that the reactor with the titanium suboxide-coated titanium rod anode (3D-ER-T) exhibited a stable NO3--N removal efficiency (46%-95%) with a current range of 160-320 mA in the electrochemical reduction process. In the bioelectrochemical reduction, the removal efficiencies of NO3--N and SO42- and nitrogen selectivity in the 3D-BER with titanium suboxide-coated titanium rod anode (3D-BER-T) were higher than those in the 3D-BER with titanium suboxide-coated graphite rod anode (3D-BER-G). The removal efficiencies of NO3--N and SO42- and nitrogen selectivity were 92%, 43% and 86%, respectively, in 3D-BER-T under 320 mA and HRT 12 h. Anode materials affected the microbial community. Hydrogenophaga and Dethiobacter were the dominant bacteria in 3D-BER-T, while OPB41 and Sulfurospirillum were dominant in 3D-BER-G. Nitrate and sulfate were effectively removed in 3D-BER-T by the synergistic work of electrochemical reduction, bioelectrochemical reduction and indirect electrochemical reduction. The resupply/reserve mode of the electron donor promoted the load of shock resistance of 3D-BER-T via the sulfur cycle. Titanium suboxide coating could significantly enhance the anti-corrosion ability of matrix anodes.

A Review: Synthesis and Applications of Titanium Sub-Oxides

Magnéli phase titanium oxides, also called titanium sub-oxides (TinO2n-1, 4 < n < 9), are a series of electrically conducting ceramic materials. The synthesis and applications of these materials have recently attracted tremendous attention because of their applications in a number of existing and emerging areas. Titanium sub-oxides are generally synthesized through the reduction of titanium dioxide using hydrogen, carbon, metals or metal hydrides as reduction agents. More recently, the synthesis of nanostructured titanium sub-oxides has been making progress through optimizing thermal reduction processes or using new titanium-containing precursors. Titanium sub-oxides have attractive properties such as electrical conductivity, corrosion resistance and optical properties. Titanium sub-oxides have played important roles in a number of areas such as conducting materials, fuel cells and organic degradation. Titanium sub-oxides also show promising applications in batteries, solar energy, coatings and electronic and optoelectronic devices. Titanium sub-oxides are expected to become more important materials in the future. In this review, the recent progress in the synthesis methods and applications of titanium sub-oxides in the existing and emerging areas are reviewed.

Ti/Ti4O7 Anodes for Efficient Electrodeposition of Manganese Metal and Anode Slime Generation Reduction

Preventing lead-based anodes from causing high-energy consumption, lead pollution, and harmful anode slime emission is a major challenge for the current electrolytic manganese metal industry. In this work, a Ti4O7-coated titanium electrode was used as anode material (Ti/Ti4O7 anode) in manganese electrowinning process for the first time and compared with a lead-based anode (Pb anode). The Ti/Ti4O7 anode was used for galvanostatic electrolysis; the cathodic current efficiency improved by 3.22% and energy consumption decreased by 7.82%. During 8 h of electrolysis, it reduced 90.42% solution anode slime and 72.80% plate anode slime formation. Anode product characterization and electrochemical tests indicated that the Ti/Ti4O7 anode possesses good oxygen evolution activity, and γ-MnO2 has a positive catalytic effect on oxygen evolution reaction (OER), which inhibited anode Mn2+ oxidation reaction and reduced the formation of anode slime. In addition, the low charge-transfer resistance, high diffusion resistance, and dense MnO2 layer of the anode blocked the diffusion path of Mn3+ in the system and inhibited the formation of anode slime. The Ti/Ti4O7 anode exhibits excellent electrochemical performance, which provides a new idea for the selection of novel anodes, energy savings and emission reduction, and the establishment of a new mode of clean production in the electrolytic manganese metal industry.

Positive Charge Holes Revealed by Energy Band Theory in Multiphase Tix O2x-1 and Exploration of its Microscopic Electromagnetic Loss Mechanism

Although numerous experimental investigations have been carried out on the problem of defect engineering in semiconductor absorbers, the relationship among charge carrier, defects, heterointerfaces, and electromagnetic (EM) wave absorption has not been established systematically. Herein, the new thermodynamic and kinetic control strategy is proposed to establish multiphase Tix O2 x -1 (1 ≤ x ≤ 6) through a hydrogenation calcination. The TiOC-900 composite shows the efficient EM wave absorption capability with a minimum reflection loss (RLmin ) of -69.6 dB at a thickness of 2.04 mm corresponding to an effective absorption bandwidth (EAB) of 4.0 GHz due to the holes induced conductance loss and heterointerfaces induced interfacial polarization. Benefiting from the controllable preparation of multiphase Tix O2 x -1 , a new pathway is proposed for designing high-efficiency EM wave absorbing semiconducting oxides. The validity of the method for adopting energy band theory to explore the underlying relations among charge carriers, defects, heterointerfaces, and EM properties in multiphase Tix O2 x -1 is demonstrated for the first time, which is of great importance in optimizing the EM wave absorption performance by electronic structure tailoring.

Construction of Built-In Electric Field in TiO2@Ti2O3 Core-Shell Heterojunctions toward Optimized Photocatalytic Performance

A series of Ti₂O₃@TiO₂ core-shell heterojunction composite photocatalysts with different internal electric fields were synthesized using simple heat treatment methods. The synthesized Ti₂O₃@TiO₂ core-shell heterojunction composites were characterized by means of SEM, XRD, PL, UV-Vis, BET, SPV, TEM and other related analytical techniques. Tetracycline (TC) was used as the degradation target to evaluate the photocatalytic performance of the synthesized Ti₂O₃@TiO₂ core-shell heterojunction composites. The relevant test results show that the photocatalytic performance of the optimized materials has been significantly enhanced compared to Ti₂O₃, while the photocatalytic degradation rate has increased from 28% to 70.1%. After verification via several different testing and characterization techniques, the excellent catalytic performance is attributed to the efficient separation efficiency of the photogenerated charge carriers derived from the built-in electric field formed between Ti₂O₃ and TiO₂. When the recombination of electrons and holes is occupied, more charges are generated to reach the surface of the photocatalyst, thereby improving the photocatalytic degradation efficiency. Thus, this work provides a universal strategy to enhance the photocatalytic performance of Ti₂O₃ by coupling it with TiO₂ to build an internal electric field.

In-situ fabrication of titanium suboxide-laser induced graphene composites: Removal of organic pollutants and MS2 Bacteriophage

Titanium suboxides (TSO) are identified as a series of compounds showing excellent electro- and photochemical properties. TSO composites with carbon-based materials such as graphene have further improved water splitting and pollutant removal performance. However, their expensive and multi-step synthesis limits their wide-scale use. Furthermore, recently discovered laser-induced graphene (LIG) is a single-step and low-cost fabrication of graphene-based composites. Moreover, LIG's highly electrically conductive surface aids in tremendous environmental applications, including bacterial inactivation, anti-biofouling, and pollutant sensing. Here, we demonstrate the single-step in-situ fabrication of TSO-LIG composite by directly scribing the TiO₂ mixed poly(ether) sulfone sheets using a CO₂ infrared laser. In contrast, earlier composites were derived from either commercial-grade TSO or synthesized TSO with graphene. The characteristic Ti³⁺ peaks in XPS confirmed the conversion of TiO₂ into its sub-stoichiometric form, enhancing the electro-catalytical properties of the LIG-TiO_x composite surface. Electrochemical characterization, including impedance spectroscopy, validated the surface's enhanced electrochemical activity and electrode stability. Furthermore, the LIG-TiO_x composite surfaces were tested for anti-biofouling action and electrochemical application as electrodes and filters. The composite electrodes exhibit enhanced degradation performance for removing emerging pollutant antibiotics ciprofloxacin and methylene blue due to the in-situ hydroxyl radical generation. Additionally, the LIG-TiO_x conductive filters showed the complete 6-log killing of mixed bacterial culture and MS2 phage virus in flow-through filtration mode at 2.5 V, which is ∼2.5-log more killing compared to non-composited LIG filers at 500 Lm^-2h^-1. Nevertheless, these cost-effective LIG-TiO_x composites have excellent electrical properties and can be effectively utilized for energy and environmental applications.

Ultrasound-enhanced Magnéli phase Ti4O7 anodic oxidation of per- and polyfluoroalkyl substances (PFAS) towards remediation of aqueous film forming foams (AFFF)

Per-and polyfluoroalkyl substances (PFAS) remediation is still a challenge. In this study, we propose a hybrid system that combines electrochemical treatment with ultrasound irradiation, aiming for an enhanced degradation of PFAS. Equipped with a titanium suboxide (Ti₄O₇) anode, the electrochemical cell is able to remove perfluorooctanoic acid (PFOA) effectively. Under the optimal conditions (50 mA/cm² current density, 0.15 M Na₂SO₄ supporting electrolyte, and stainless steel/Ti₄O₇/stainless steel electrode configuration with a gap of ∼10 mm), the electrochemical process achieves ∼100 % PFOA removal and 43 % defluorination after 6 h. Applying ultrasound irradiation (130 kHz) alone offers a limited PFOA removal, with 33 % PFOA removal and 5.5 % defluorination. When the electrochemical process is combined with ultrasound irradiation, we observe a significant improvement in the remediation performance, with ∼100 % PFOA removal and 63.5 % defluorination, higher than the sum of 48.5 % (43 % achieved by the electrochemical process, plus 5.5 % by the ultrasound irradiation), implying synergistic removal/oxidation effects. The hybrid system also consistently shows the synergistic defluorination during degradation of other PFAS and the PFAS constituents in aqueous film forming foam (AFFF). We attribute the synergistic effect to an activated/cleaned electrode surface, improved mass transfer, and enhanced production of radicals.

Magnéli-Phase Ti4O7-Doped Laser-Induced Graphene Surfaces and Filters for Pollutant Degradation and Microorganism Removal

Laser-induced graphene (LIG) has recently become a point of attraction globally as an environmentally friendly method to fabricate graphene foam in a single step using a CO₂ laser. The electrical properties of LIG are studied in different environmental applications, such as bacterial inactivation, antibiofouling, and pollutant sensing. Furthermore, metal or nonmetal doping of graphene enhances its catalytical performance in pollutant degradation and decontamination. Magnéli phase (Ti_nO_2n-1) is a substoichiometric titanium oxide known for its high electrocatalytic behavior and chemical inertness and is being explored as a membrane or electrode material for environmental decontamination. Here, we show the fabrication and characterization of LIG-Magnéli-phase (Ti₄O₇) titanium suboxide composites as electrodes and filters on poly(ether sulfone). Unlike undoped LIG electrodes, the doped Ti₄O₇-LIG electrodes exhibit enhanced electrochemical activity, as demonstrated in electrochemical characterization using cyclic voltammetry and electrochemical impedance spectroscopy. Due to the in situ generation of hydroxyl radicals on the surface, the doped electrodes exhibit increase in methylene blue degradation and microorganism removal. Effects of voltage and doping were examined, resulting in a clear trend of degradation and decontamination performance proportional to the doping concentration and applied voltage giving the best result at 2.5 V for 10% Ti₄O₇ doping. The LIG-Ti₄O₇ surfaces also showed biofilm inhibition against mixed bacterial culture. The flow-through filtration using a LIG-Ti₄O₇ conductive filter showed complete bacterial killing with 6 log removal in the permeate at 2.5 V, an enhancement of ∼2.5 log compared to undoped LIG filters at a flow rate of ∼500 L m^-2 h^-1. The facile fabrication of Ti₄O₇-doped LIG with enhanced electrochemical properties can be effectively used for energy and environmental applications.

Magnéli phase titanium sub-oxides synthesis, fabrication and its application for environmental remediation: Current status and prospect

Sub-stoichiometric titanium oxide, also called titanium suboxides (TSO), had been a focus of research for many decades with a chemical composition of Ti_nO_2n-1 (n ≥ 1). It has a unique oxygen-deficient crystal structure which provides it an outstanding electrical conductivity and high corrosion resistance similar to ceramic materials. High electrical conductivity and ability to sustain in adverse media make these phases a point of attention for researchers in energy storage and environmental remediation applications. The Magnéli phase-based reactive electroconductive membranes (REM) and electrodes have demonstrated the electrochemical oxidation of pollutants in the water in flow-through and flow by configuration. Additionally, it has also shown its potential for visible light photochemical degradation as well. This review attempts to summarize state of the art in various Magnéli phases materials synthesis routes and their electrochemical and photochemical ability for environmental application. The manuscript introduces the Magnéli phase, its crystal structure, and catalytic properties, followed by the recent development in synthesis methods from diverse titanium sources, notably TiO₂ through thermal reduction. The various fabrication methods for Magnéli phase-base REMs and electrodes have also been summarized. Furthermore, the article discussed the environmental remediations via electrochemical and photochemical advanced oxidation processes. Additionally, the hybrid technology with REMs and electrodes is used to counter membrane biofouling and develop electrochemical sensing devices for the pollutants. The Magnéli phase materials have a bright future for both electrochemical and photochemical advanced oxidation of emerging contaminants in water and wastewater treatment.

Electrooxidation of per- and polyfluoroalkyl substances in chloride-containing water on surface-fluorinated Ti4O7 anodes: Mitigation and elimination of chlorate and perchlorate formation

Electrooxidation (EO) has been shown effective in degrading per- and polyfluoroalkyl substances (PFASs) in water, but concurrent formation of chlorate and perchlorate in the presence of chloride is of concern due to their toxicity. This study examined EO treatment of three representative PFASs, perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and 6:2 fluorotelomer sulfonate (6:2 FTS), in chloride-containing solutions on pristine and surface-fluorinated Ti₄O₇ anodes having different percentage of surface fluorination. The experiment results indicate that surface fluorination of Ti₄O₇ anodes slightly inhibited PFAS degradation, while significantly decreased the formation of chlorate and perchlorate. Further studies with spectroscopic and electrochemical characterizations and density functional theory (DFT) computation reveal the mechanisms of the impact on EO performance by anode fluorination. In particular, chlorate and perchlorate formation were fully inhibited when fluorinated Ti₄O₇ anode was used in reactive electrochemical membrane (REM) under a proper anodic potential range (<3.0 V vs Standard Hydrogen Electrode), resulting from slower intermediate reaction steps and short residence time of the REM system. The results of this study provide a basis for design and optimization of modified Ti₄O₇ anodes for efficient EO treatment of PFAS while limiting chlorate and perchlorate formation.

Nanostructured IrO x supported on N-doped TiO2 as an efficient electrocatalyst towards acidic oxygen evolution reaction

Reducing the Ir consumption without compromising the catalytic performance for the oxygen evolution reaction (OER) is highly paramount to promote the extensive development of the environmentally-friendly solid polymer electrolyte water electrolysis (SPEWE) system. Herein, TiO2 is doped with N through facile NH3 gas treatment and innovatively employed to support IrO x nanoparticles towards acidic OER. N-doping action not only dramatically boosts the electrical conductivity and dispersing/anchoring effects of TiO2, but also effectively improves the electron-transfer procedure. As a result, the IrO x /N-TiO2 electrocatalyst exhibits prominent catalyst utilization, catalytic activity and stability. Specifically, the overpotential required to deliver 10 mA cm-2 is only 270 mV, and the mass activity climbs to 278.7 A gIr -1 @ 1.55 VRHE. Moreover, the single cell voltage is only 1.761 V @ 2.0 A cm-2 when adopting IrO x /N-TiO2 as the anode catalyst, which is 44 mV lower than that of the commercial IrO2 counterpart.

Cost and efficiency perspectives of ceramic membranes for water treatment

More robust ceramic membranes with tailorable structures and functions are increasingly employed for water treatment, particularly in some harsh applications for their ultra-long service lifespan due to their high mechanical, structural, chemical and thermal stability and anti-fouling properties. Decreasing cost and enhancing efficiency are two key but quite challenging application-oriented issues for broader and larger-scale engineering application of current ceramic membranes, and are required to make ceramic membranes a highly efficient and economic water treatment technique. In this review, we critically discuss these two significant concerns of both cost and efficiency for water treatment ceramic membranes, focusing on an overview of various advanced strategies and mechanism insights. A brief up-to-date discussion is first introduced about recent developments of ceramic membranes covering the major advances of novel membranes and applications. Then some promising strategies for decreasing the cost of ceramic membranes are discussed, including membrane material cost and processing cost. To fully address the issue of moderate efficiency with single separation function, valuable and considerable insights are provided into recent major progress and mechanism understandings in application with other unit processes, such as advanced oxidation and electrochemistry techniques, to significantly enhance treatment efficiency. Subsequently, a review of recent ceramic membrane applications emphasizing harsh operating environments is presented, such as oil-water separation, saline water, refractory organic and emerging contaminant wastewater treatment. Finally, engineering application, conclusions, and future perspectives of ceramic membrane for water treatment applications are critically discussed offering new insight based on understanding the issues of cost and efficiency.

Flow-through electrochemical removal of benzotriazole by electroactive ceramic membrane

Benzotriazole (BTA) is a widely used anticorrosive additive that is of endurance, bioaccumulation and toxicity, and BTA industrial wastewater treatment remains a challenge. This study reports efficient electrochemical removal of BTA by titanium oxide (TiSO) electroactive ceramic membrane (ECM), indicated by 98.1% removal at current density of 20 mA∙cm-2 and permeate flux of 692 LHM under cathode-to-anode flow pattern (1 h). Electrochemical analysis demonstrated the pH-dependent formation of anti-corrosive BTA film on the TiSO anode, which was responsible for improved BTA removal for cathode-to-anode (CA) flow pattern compared with that for anode-to-cathode (AC). The modelling results showed the CA flow pattern to be more favourable for BTA oxidation mediated by electro-generated •OH by preventing the formation of deactivation film via creating an alkaline boundary layer at the anode/electrolyte interface. Intermediates and essential active sites were identified by using experimental analysis and theoretical density functional theory (DFT) calculations, thereby the most likely degradation pathways were underlined. Toxicity analysis revealed remarkable decrease in oral rat LD50 values and bioaccumulation factor during electrochemical degradation of BTA. This study provides a proof-in-concept demonstration of effective removal for anti-corrosive emerging pollutants by TiSO-ECM under flow-through pattern.

Progress in Preparation and Application of Titanium Sub-Oxides Electrode in Electrocatalytic Degradation for Wastewater Treatment

To achieve low-carbon and sustainable development it is imperative to explore water treatment technologies in a carbon-neutral model. Because of its advantages of high efficiency, low consumption, and no secondary pollution, electrocatalytic oxidation technology has attracted increasing attention in tackling the challenges of organic wastewater treatment. The performance of an electrocatalytic oxidation system depends mainly on the properties of electrodes materials. Compared with the instability of graphite electrodes, the high expenditure of noble metal electrodes and boron-doped diamond electrodes, and the hidden dangers of titanium-based metal oxide electrodes, a titanium sub-oxide material has been characterized as an ideal choice of anode material due to its unique crystal and electronic structure, including high conductivity, decent catalytic activity, intense physical and chemical stability, corrosion resistance, low cost, and long service life, etc. This paper systematically reviews the electrode preparation technology of Magnéli phase titanium sub-oxide and its research progress in the electrochemical advanced oxidation treatment of organic wastewater in recent years, with technical difficulties highlighted. Future research directions are further proposed in process optimization, material modification, and application expansion. It is worth noting that Magnéli phase titanium sub-oxides have played very important roles in organic degradation. There is no doubt that titanium sub-oxides will become indispensable materials in the future.

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Gas Sensors Based on Titanium Oxides (Review)

Nanostructured titanium compounds have recently been applied in the design of gas sensors. Among titanium compounds, titanium oxides (TiO2) are the most frequently used in gas sensing devices. Therefore, in this review, we are paying significant attention to the variety of allotropic modifications of titanium oxides, which include anatase, rutile, brukite. Very recently, the applicability of non-stoichiometric titanium oxide (TiO2−x)-based layers for the design of gas sensors was demonstrated. For this reason, in this review, we are addressing some research related to the formation of non-stoichiometric titanium oxide (TiO2−x) and Magnéli phase (TinO2n−1)-based layers suitable for sensor design. The most promising titanium compounds and hetero- and nano-structures based on these compounds are discussed. It is also outlined that during the past decade, many new strategies for the synthesis of TiO2 and conducting polymer-based composite materials were developed, which have found some specific application areas. Therefore, in this review, we are highlighting how specific formation methods, which can be used for the formation of TiO2 and conducting polymer composites, can be applied to tune composite characteristics that are leading towards advanced applications in these specific technological fields. The possibility to tune the sensitivity and selectivity of titanium compound-based sensing layers is addressed. In this review, some other recent reviews related to the development of sensors based on titanium oxides are overviewed. Some designs of titanium-based nanomaterials used for the development of sensors are outlined.

Electrocatalytic Water Oxidation: An Overview With an Example of Translation From Lab to Market

Water oxidation has become very popular due to its prime role in water splitting and metal–air batteries. Thus, the development of efficient, abundant, and economical catalysts, as well as electrode design, is very demanding today. In this review, we have discussed the principles of electrocatalytic water oxidation reaction (WOR), the electrocatalyst and electrode design strategies for the most efficient results, and recent advancement in the oxygen evolution reaction (OER) catalyst design. Finally, we have discussed the use of OER in the Oxygen Maker (OM) design with the example of OM REDOX by Solaire Initiative Private Ltd. The review clearly summarizes the future directions and applications for sustainable energy utilization with the help of water splitting and the way forward to develop better cell designs with electrodes and catalysts for practical applications. We hope this review will offer a basic understanding of the OER process and WOR in general along with the standard parameters to evaluate the performance and encourage more WOR-based profound innovations to make their way from the lab to the market following the example of OM REDOX.

Gradient Titanium Oxide Nanowire Film: a Multifunctional Solar Energy Utilization Platform for High-Salinity Organic Sewage Treatment

The treatment of high salt organic sewage is considered to be a high energy consumption process, and it is difficult to degrade organic matter and separate salt and water simultaneously. In this study, a gradient structure titanium oxide nanowire film is developed, which can realize the thorough treatment of sewage under sunlight. Among the film, part TiO_2-x has enhanced photocatalytic properties and can completely degrade 0.02 g·L^-1 methylene blue in 90 min under 2 sun. Part Ti_nO_2n-1 has excellent photothermal conversion efficiency and can achieve 1.833 kg·m^-2·h^-1 water evaporation rate at 1 sun. Through the special structure design, salt positioning crystallization can be realized to ensure the film's stable operation for a long time. The gradient hydrophilicity of the film ensures adequate and rapid water transfer, while the water flow can induce a significant hydrovoltaic effect. The measured V_OC is positively correlated with light intensity and photothermal area and corresponds to the water evaporation rate.

Study of the Relationship between Metal–Support Interactions and the Electrocatalytic Performance of Pt/Ti4O7 with Different Loadings

The application potential of Pt/Ti4O7 has been reported, but the lack of research on the relationship between Pt loading, MSI, and catalytic activity hinders further development. Micron-sized Ti4O7 powders synthesized by a thermal reduction method under an H2 atmosphere were used as a support material for Pt-based catalysts. Using a modified polyol method, Pt/Ti4O7-5, Pt/Ti4O7-10, and Pt/Ti4O7-20 with different mass ratios (Pt to Pt/Ti4O7 is 0.05, 0.1, 0.2) were successfully synthesized. Uniformly dispersed platinum nanoparticles exhibit disparate morphologies, rod-like for Pt/Ti4O7-5 and approximately spherical for Pt/Ti4O7-10 and Pt/Ti4O7-20. Small-angle deflections and lattice reconstruction induced by strong metal–support interactions were observed in Pt/Ti4O7-5, which indicated the formation of a new phase at the interface. However, lattice distortions and dislocations for higher loading samples imply the existence of weak metal–support interactions. A possible mechanism is proposed to explain the different morphologies and varying metal–support interactions (MSI). With X-ray photoelectron spectroscopy, spectrums of Pt and Ti display apparent shifts in binding energy compared with commercial Pt-C and non-platinized Ti4O7, which can properly explain the changes in absorption ability and oxygen reduction reaction activity, as described in the electrochemical results. The synthetic method, Pt loading, and surface coverage of the support play an important role in the adjustment of MSI, which gives significant guidance for better utilizing MSI to prepare the target catalyst.

The effects of dietary exposure to Magnéli phase titanium suboxide and titanium dioxide on rainbow trout (Oncorhynchus mykiss)

Magnéli phase titanium suboxides (Magnéli TiO_x) are promising, novel materials with superior properties compared to TiO₂, they are substoichiometric titanium oxides with the chemical formula Ti_nO_2n-1 (where n ≥ 1). In this study, for the first time, subchronic effects of dietary intake of Magnéli TiO_x were evaluated and compared with TiO₂ particles of similar size, in concentrations 0.1% and 0.01% of feed. The experiment consisted of 38 d of an exposition period and 14 d of a depuration period. Minor effects on plasma biochemical profile and morphological parameters were recorded. A reduced count of leukocytes was found in the blood of both Magnéli TiO_x and TiO₂ exposed fish, suggesting immunotoxic effects. Erythrocytosis was specific for Magnéli TiO_x. Indices of oxidative stress, namely increased lipid peroxidation in liver, increased activity of superoxide dismutase in liver, kidney and gills and glutathione S-transferase (GST) in gills, as well as decreased activity of ceruloplasmin and GST in liver were found predominantly in fish exposed to TiO₂. Histopathological examination revealed increased lipid-like vacuolation in the liver, the presence of hyaline droplets in renal tubules and multiplication of mucous glands in the epidermis in both tested substances and intestine damage in TiO₂ groups. Overall, in Magnéli TiO_x exposed groups, fewer adverse effects compared to TiO₂ expositions were recorded. Their wider practical implementation in place of TiO₂ is therefore beneficial.

Au(111)@Ti6O11 heterostructure composites with enhanced synergistic effects as efficient electrocatalysts for the hydrogen evolution reaction

Developing cost-effective electrocatalysts for the hydrogen evolution reaction (HER) is of great significance for the renewable energy field. The Magnéli phase Ti_nO_2n-1 (4 ≤ n ≤ 10) has attracted much attention as a promising carbon-free support for electrocatalysts due to its high electrical conductivity and favorable electrochemical stability. Herein, we report the synthesis of a specific crystal-plane coupling heterostructure between Au(111) nanoparticles (NPs) and Ti₆O₁₁ by photoreduction. Benefitting from the modification of the electronic structure and synergistic effects of the heterostructure, the electron density around Au atoms is enhanced, and the Gibbs free energy of hydrogen absorption (ΔG_H*) was dramatically optimized to facilitate the HER process. The best electrocatalyst Au(111)@Ti₆O₁₁-50 exhibits a lower overpotential of 49 mV at a current density of -10 mA cm^-2 and a Tafel slope of 39 mV dec^-1 in 0.5 M H₂SO₄, and shows long-term electrochemical stability over 30 h. Au(111)@Ti₆O₁₁-50 shows a mass activity of 9.25 A mg_Au^-1, which is about 18 times higher than that of commercial Pt/C (0.51 A mg_Pt^-1). Meanwhile, the density functional theory (DFT) calculations suggest that the ΔG_H* of Au(111)@Ti₆O₁₁ is -0.098 eV, which is comparable to that of Pt (-0.09 eV). This work would be a powerful guide for the realization of efficient utilization of noble metals in catalysis.

Is HFPO-DA (GenX) a suitable substitute for PFOA? A comprehensive degradation comparison of PFOA and GenX via electrooxidation

Due to the potential hazard of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimer acid (HFPO-DA, GenX) has become a typical alternative since 2009. However, GenX has recently been reported to have equal or even greater toxicity and bioaccumulation than PFOA. Considering the suitability of alternatives, it is quite essential to study and compare the degradation degree between PFOA and GenX in water. Therefore, in the present study, a comprehensive degradation comparison between them via electrooxidation with a titanium suboxide membrane anode was conducted. The degradation rate decreased throughout for PFOA, while it first increased and then decreased for GenX when the permeate flux increased from 17.3 L to 100.3 L m^-2·h^-1. The different responses of PFOA and GenX to flux might be attributed to their different solubilities. In addition, the higher k_obs of PFOA demonstrated that it had a better degradability than GenX by 2.4-fold in a mixed solution. The fluorinated byproduct perfluoropropanoic acid (PFPrA) was detected as a GenX intermediate, suggesting that ether bridge splitting was needed for GenX electrooxidation. This study provides a reference for assessing the degradability of GenX and PFOA and indicates that it is worth reconsidering whether GenX is a suitable alternative for PFOA from the point of view of environmental protection.

Fabrication and Characterization of the Porous Ti4O7 Reactive Electrochemical Membrane

Preparation of the Magnéli Ti₄O₇ reactive electrochemical membrane (REM) with high purity is of great significance for its application in electrochemical advanced oxidation processes (EAOPs) for wastewater treatment. In this study, the Ti₄O₇ REM with high purity was synthesized by mechanical pressing of TiO₂ powders followed by thermal reduction to Ti₄O₇ using the Ti powder as the reducing reagent, where the TiO₂ monolith and Ti powder were separated from each other with the distance of about 5 cm in the vacuum furnace. When the temperature was elevated to 1333 K, the Magnéli phase Ti₄O₇ REM with the Ti₄O₇ content of 98.5% was obtained after thermal reduction for 4 h. Noticeably, the surface and interior of the obtained REM bulk sample has a homogeneous Ti₄O₇ content. Doping carbon black (0wt%-15wt%) could increase the porosity of the Ti₄O₇ REM (38–59%). Accordingly, the internal resistance of the electrode and electrolyte and the charge-transfer impedance increased slightly with the increasing carbon black content. The optimum electroactive surface area (1.1 m²) was obtained at a carbon black content of 5wt%, which increased by 1.3-fold in comparison with that without carbon black. The as-prepared Ti₄O₇ REMs show high oxygen evolution potential, approximately 2.7 V/SHE, indicating their appreciable electrocatalytic activity toward the production of •OH.