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Precious metal-based mixed metal oxides have been widely used as catalysts for the chlorine evolution reaction (CER). However, a concurrent oxygen evolution reaction (OER) leads to insufficient selectivity for CER at circum-neutral pH. Herein, nanoparticulate Pt-RuO 2 (PRO) is synthesized with various Pt/Ru ratios at sub-boiling temperatures, followed by post-annealing. The synthetic conditions significantly influence the physicochemical properties (crystalline structures, morphologies, surface areas, double-layer capacitance, and charge transfer resistance) and the electrocatalytic activities of CER in NaCl solutions (0.137 and 0.5 M) and seawater (with a salinity of 3.6 g L–1). Among PRO- x @ y samples (where x is the mole fraction of Pt in the mixed Pt and Ru precursor solutions, and y is the annealing temperature [°C]), PRO-0.2@800 and PRO-0.8@500 show remarkable faradaic efficiencies (FEs) for CER (CER-FE). Despite their similar FEs (CER-FEs of approximately 95 % and 99 %, and OER-FEs of 4–6 % and <1 %, for PRO-0.2 and PRO-0.8, respectively), the Pt-rich PRO requires less potential for the same current density (J) and exhibits excellent stability at J = 800 mA cm–2 over 250 h in seawater at circum-neutral pH. The optimized PRO electrode is further used for seawater desalination and simultaneous production of HClO, achieving FEs of ∼100 %. Finally, various electrochemical analyses are conducted to elucidate the CER mechanism. [Display omitted] [ABSTRACT FROM AUTHOR]

• Three dimensionally ordered ZnFe 2 O 4 photoanode was fabricated via chemical conversion of β-FeOOH. • SiO 2 passivation layer was anchored on ZnFe 2 O 4 nanorods photoanode. • The existence of the SiO 2 on the ZnFe 2 O 4 nanoords surface improves the photocurrent density from 1.43 to 212 µA/cm2 at 1.23 V RHE. • Almost 99% of photelectrochemical stability was achieved for 0.25 mM Si–ZnFe 2 O photoanodes after 9 h. • The aim for simultaneously improving the photoelectrochemical performance and stability is achieved. ZnFe 2 O 4 nanorods (NR's) were prepared by a chemical conversion method from β-FeOOH NRs grown on FTO substrates. To activate their photoactivity of ZnFe 2 O 4 NRs for solar water splitting, the surface passivation was achieved with SiO 2 layer via facile and effective spray pyrolysis method. The presence of SiO 2 layer enhances the photocurrent density of the Pristine ZnFe 2 O 4 from 143 µA/cm2 to 212 µA/cm2 at 1.23 V RHE for 0.25 mM Si–ZnFe 2 O 4 , representing two time increment in the photocurrent density. The influences of amount of Si precursor (Tetraethyl orthosilicate) solutions on the physical properties and the passivation effect of SiO 2 /ZnFe 2 O 4 interfaces were investigated. This improved photoresponse of the Si-treated ZnFe 2 O 4 NRs was attributed to the excellent charge transfer electrode/electrolyte interface. The effectively improved charge transfer properties of the Si-treated ZnFe 2 O 4 NRs were demonstrated by the electrochemical impedance spectroscopy (EIS), Mott–Schottky (MS) and intensity-modulated photocurrent spectroscopy (IMPS) analyses. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate the enhanced photoelectrochemical (PEC) performance of the titanium foil based TiO2 nanotube (TNT) array through a simple hydrothermal (HT) acid treatment method. The influence of hydrochloric acid (HCl) concentration variation in HT method on morphology and the photoelectrochemical performances of TNTs nanostructures were studied. Field Emission Scanning Electron Microscopy and X‐ray powder diffraction results confirmed the morphology and crystal structure easily restructured during HCl assisted one step in‐situ hydrothermal approach. The photocurrent density of optimized acid treated TiO2 nanotube (TH‐40) electrode was observed to be 2‐times higher than the pristine TNT electrode. Thereafter, TH‐40 sample exhibited noticeably photoelectrochemical solar hydrogen production of 66 μmol and 82 μmol in NaOH and Na2S/Na2SO3 electrolytes respectively than the pristine TNT. The enhancement of photocatalytic activity was ascribed to the restructured morphology, as well as the efficient charge separation at rutile‐anatase interface in the TH‐40 sample as well as at the electrode‐electrolyte interface. A hydrochloric acid assisted one step in‐situ hydrothermal approach tailors the crystal structure and morphological features, which enhanced the photoelectrochemical properties of TiO2 nanotube. [ABSTRACT FROM AUTHOR]

Highlights: [•] Carbon materials successfully catalyzed Eosin Y-sensitized H2 production under solar light. [•] H2 production and photocurrent generations were 9- and 4-fold enhanced by CNT, respectively. [•] Pt-loading onto carbon materials further enhanced the H2 production by 10 times. [•] Eosin Y underwent spectral shifts because of de-bromination. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews recent studies on the semiconductor photocatalysis based on surface-modified TiO2 of which application is mainly focused on environmental remediation. TiO2 photocatalysis that is based on the photoinduced interfacial charge transfer has been extensively studied over the past four decades. A great number of modification methods of semiconductor photocatalysts have been developed and investigated to accelerate the photoconversion, to enable the absorption of visible light, or to alter the reaction mechanism to control the products and intermediates. In this regard, various modification methods of TiO2 are classified according to the kind of surface modifiers (metal-loading, impurity doping, inorganic adsorbates, polymer coating, dye-sensitization, charge transfer complexation) and their effects on photocatalytic reaction mechanism and kinetics are discussed in detail. Modifying TiO2 in various ways not only changes the mechanism and kinetics under UV irradiation but also introduces visible light activity that is absent with pure TiO2. Each modification method influences the photocatalytic activity and mechanism in a way different from others and the observed modification effects are often different depending on the test substrates and conditions even for the same modification method. Better understanding of the modification effects on TiO2 photocatalysis is necessary to obtain reliable results, to assess the photoconversion efficiency more quantitatively, and to further improve the modification methods. [Copyright &y& Elsevier]

To date, the in situ fabrication of the large‐scale van der Waals multi‐heterojunction transition metal dichalcogenides (multi‐TMDs) is significantly challenging using conventional deposition methods. In this study, vertically stacked centimeter‐scale multi‐TMD (MoS2/WS2/WSe2 and MoS2/WSe2) thin films are successfully fabricated via sequential pulsed laser deposition (PLD), which is an in situ growth process. The fabricated MoS2/WS2/WSe2 thin film on p‐type silicon (p‐Si) substrate is designed to form multistaggered gaps (type‐II band structure) with p‐Si, and this film exhibits excellent spatial and thickness uniformity, which is verified by Raman spectroscopy. Among various application fields, MoS2/WS2/WSe2 is applied to the thin‐film catalyst of a p‐Si photocathode, to effectively transfer the photogenerated electrons from p‐Si to the electrolyte in the photo‐electrochemical (PEC) hydrogen evolution. From a comparison between the PEC performances of the homostructure TMDs (homo‐TMDs)/p‐Si and multi‐TMDs/p‐Si, it is demonstrated that the multistaggered gap of multi‐TMDs/p‐Si improves the PEC performance significantly more than the homo‐TMDs/p‐Si and bare p‐Si by effective charge transfer. The new in situ growth process for the fabrication of multi‐TMD thin films offers a novel and innovative method for the application of multi‐TMD thin films to various fields. [ABSTRACT FROM AUTHOR]

• TNA films grown on Ti substrates are transferred onto FTO via a two-step anodization. • TNA films are vertically aligned in normal and reverse ways, and irradiated through FTO (SE) or solution (EE). • The front and back planes of TNA films are the same in XRD, XPS, and UV–vis transmittance. • Irradiation direction is a key factor in photocurrent generation. • In photocatalysis, the effect of alignment direction is comparable to that of irradiation direction. Although one-dimensional TiO 2 nanotube arrays (TNA) grown on Ti substrates via electrochemical anodization are extensively studied in photoelectrochemistry, the photo(electro)catalytic activity of TNA detached from the Ti substrates remains unexplored. Herein, we synthesize TNA samples with various pore sizes (40–100 nm) and tube lengths (4–15 μm) via two-step electrochemical anodization, and transfer them to transparent conducting oxide (i.e. fluorine-doped tin oxide; FTO) substrates in normal (n) alignment (front plane outward) and reverse (r) alignment (backplane outward). The front and back planes of the as-fabricated TNA film are the same based on X-ray diffraction (anatase structure), X-ray photoelectron spectroscopy (Ti and O), and UV–vis transmittance data, though the tubes are open in the front and closed in the back. Regardless of the direction of irradiation (SE : FTO → TNA vs. EE : TNA → FTO), longer tubes generate a higher photocurrent (I ph) due to the large light absorption. However, for the same alignment of TNA (either n- or r -TNA), SE irradiation leads to a very large I ph (e.g., nSE > nEE), whereas n -TNA consistently generates a larger I ph than r -TNA for a given irradiation direction (i.e., n > r). The photocatalytic decomposition of phenol follows the same tendency (n > r); however, the Faraday efficiency (based on the photocharge) is higher with EE (nEE 28%, rEE 20%) than SE (rSE 11%, nSE 7%) irradiation. These photoelectrochemical and photocatalytic behaviors are explained in terms of charge carrier generation (FTO/TNA vs. TNA/solution), dissimilar charge carrier transfer pathways (e − transfer through tube framework vs. h + transfer via radial direction), and charge injection at the tube (open vs. clogged tube mouth)/solution interface. The time-resolved photoluminescence (TRPL) emission and incident photon-to-current efficiency (IPCE) are also studied to gain insight into the charge transfer kinetics. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • White TiO 2 nanotube arrays grown on Ti foils are transplanted onto FTO. • W-TNAs/FTO is electrochemically reduced, forming blackish TNAs (B-TNAs/FTO). • B-TNAs/FTO shows an 8-fold larger photocurrent compared to W-TNAs/FTO. • The OER and urea oxidation reaction using B-TNAs/FTO are enhanced by 3 and 20 times, respectively. • The charge transfer in the B-TNAs/FTO is an order of magnitude-accelerated. Abstract Free-standing, one-dimensional TiO 2 nanotube arrays (TNAs) with a disordered surface structure are synthesized on transparent conducting substrates, and their opto-physicochemical properties and photoelectrocatalytic (PEC) performances are examined in detail. A two-step anodization process is used to transplant TNAs grown on titanium foils onto fluorine-doped SnO 2 substrates (denoted as W-TNAs), after which they are electrochemically reduced for 20 and 90 s (denoted as B-TNAs-20 and 90, respectively). The as-transplanted W-TNAs exhibit low PEC activities in terms of their photocurrent, oxygen evolution reaction (OER), and oxidations of inorganic and organic substrates (iodide and urea, respectively) under simulated sunlight (AM 1.5; 100 mW cm−2), primarily because of the sluggish charge transfer through the poor electrically conductive TNA framework. The quick electrochemical reduction of the W-TNAs leads to an 8-fold larger photocurrent, while significantly accelerating the OER (by three times) and iodide and urea oxidation reactions (by 2 and ∼20 times, respectively). These enhanced PEC activities of the B-TNAs are attributed to the creation of Ti3+ and associated oxygen vacancies which strengthen their n-type characteristics and thereby increase their electrical conductivity. The time-resolved photoluminescence spectra further reveal that the lifetime (τ) of the photogenerated charge carriers in the B-TNAs (τ = 0.33 ns) is an order of magnitude shorter than that of the W-TNAs (τ = 3.63 ns). The disordered surface exhibits a lower Faradaic efficiency for multi-electron transfer oxidation reactions and a higher Faradaic efficiency for single-electron transfer oxidation reactions compared to the W-TNAs. The detailed surface characterization and PEC mechanism are discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-doped TiO 2 /g-C 3 N 4 (In-T/CN) composites are synthesized via a facile and reliable method. • The yield of C 2 H 4 with In-T/CN is ∼ 11-times greater than the sum of In-T and CN. • In-T acts as a CO 2 adsorbent and photocatalyst whereas CN works as a photocatalyst. • In-doping facilitates charge transfer and a strongly coupled CN induces cascaded charge transfer. • A prolonged photocatalysis with In-T/CN results in a photonic efficiency ∼ 40%. Achieving high-efficiency photocatalytic conversion of CO 2 into value-added chemicals remains a challenge. This study synthesizes In-doped TiO 2 and g-C 3 N 4 composites (In-TiO 2 /g-C 3 N 4) via a facile and reliable method. The as-synthesized In-TiO 2 /g-C 3 N 4 produces CO, CH 4 , and C 2 H 4 under UV, and CO and CH 4 under visible light from gaseous CO 2 and H 2 O vapor. A prolonged photocatalysis results in the continuous production of the same set of carbonaceous compounds over 30 h, with a photonic yield of ∼ 40%. The yield of C 2 H 4 with In-TiO 2 /g-C 3 N 4 is ∼ 11-times greater than the sum of In-TiO 2 and g-C 3 N 4. The CO 2 adsorption isotherms show that In-TiO 2 acts as a CO 2 adsorbent and photocatalyst whereas g-C 3 N 4 mainly works as a photocatalyst. In-situ FTIR study reveals the formation of CH 4 and C 2 H 4 on In-TiO 2 /g-C 3 N 4. Time-resolved photoluminescence indicate that In-doping facilitates charge transfer and a strongly coupled g-C 3 N 4 induces cascaded charge transfer. This leads to inhibited charge recombination and long-lived charge carriers. [ABSTRACT FROM AUTHOR]

• α-, β-, and γ-FeOOH polymorphs have some specific complexation with bicarbonate and As(III). • α-FeOOH is active for oxygen evolution reaction. • The activity of β-FeOOH is low for both oxidations of As(III) and water. • γ-FeOOH exhibits a significantly high catalytic activity for As(III) oxidation. • γ-FeOOH is the most active in generating hydroxyl radicals. α-, β-, and γ-FeOOH polymorphs have been synthesized and used for electrocatalytic As(III) oxidation into less toxic As(V) in aqueous bicarbonate solution. As-synthesized FeOOH electrodes exhibit unique crystalline structures and morphologies. All three FeOOH polymorphs have specific complexation with bicarbonate under alkaline conditions, whereas the complexation disappears at pH 6.7. α-FeOOH is active for both As(III) oxidation and competitive water oxidation, and the Faradaic efficiency (FE) of the latter is the greatest among the polymorphs. Despite the highest current density, β-FeOOH shows the lowest FE values for both As(III) and water oxidation. In contrast, γ-FeOOH exhibits a significantly higher catalytic activity for As(III) oxidation, up to two-fold and five-fold greater FE values compared to α- and β-FeOOH, respectively. The superior activity of γ-FeOOH is attributed to the combined effects of large As(III) adsorption, fast charge transfer, and facile generation of hydroxyl radicals. [ABSTRACT FROM AUTHOR]

Resource recovery from natural reserves is appealing and Li extraction from different brines is in the forefront. Li extraction by membranes is reviewed in the literature much more than electrochemical processes. However, a very recent review thoroughly discussed Li recovery by electrochemically switchable ion exchange (ESIX). This paper reviews Li recovery by both charge transfer processes, namely electrodialysis (ED), and electro-sorption processes, namely capacitive deionization (CDI). It also reviews ESIX with a focus on performance matrices and includes comments on the technology readiness of each separation technique. These processes exhibit promising perspectives on the separation and recovery of Li both selectively and non-selectively from simulated brine solutions and Li salt solutions. Readers are provided with guidelines to choose between the processes, depending on the applied voltage, current density, specific energy consumption and purity of recovered Li. Most electrochemical lithium capturing systems (ELiCSs) have been tested at the lab scale. Therefore, future research should be directed toward pilot-scale development and parameter optimization. Furthermore, we urge the ELiCSs research community to report information in a standard form that allows meaningful comparisons and insights into the systems. Unlabelled Image • SED and BMED are the most appropriate methods for high recovery of Li+ at low SEC. • ESIX technology for Li recovery considered extracting Li from other liquid Li resources. • CDI is an advancement of ESIX since it utilizes intercalating electrodes with IEMs. • ELiCSs need to be studied at pilot-scale using continuous processes. • Future ELiCSs research needs to focus on using natural Li liquid resources. [ABSTRACT FROM AUTHOR]