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Abstract The most feasible technique for producing green hydrogen is water electrolysis. In recent years, there has been significant study conducted on the use of transition metal compounds as electrocatalysts for both anodes and cathodes. Peoples have attempted several strategies to improve the electrocatalytic activity of their original structure. One such technique involves introducing rare earth metals or creating heterostructures with compounds based on rare earth metals. The incorporation of rare earth metals significantly enhances the activity by many folds, while their compounds offer structural stability and the ability to manipulate the electronic properties of the original system. These factors have led to a recent boom in investigations on rare earth metal‐based electrocatalysts. There is currently a pressing demand for a review article that can provide a comprehensive overview of the scientific advancements and elucidate the mechanistic aspects of the impact of lanthanide doping. This review begins by explaining the electronic structure of the lanthanides. We next examine the mechanistic aspects, followed by recent advancements in lanthanide doping and heterostructure formation for water electrolysis applications. It is expected that this particular effort will benefit a broad audience and stimulate more research in this area of interest.

Abstract Over the past decades, tremendous effort has been made to enhance the water‐splitting via fabricating eco‐friendly electrocatalyst with increased conductivity, and large number of accessible active sites in lab scale. However, the development of earth abundant efficient electrocatalyst with superior activity for ‐seawater‐splitting remains a great challenge for the researchers. In this regard, self‐supported catalysts are found to be the most promising candidates, they have the features of increased loading, superior adhesion, rapid mass and charge transfer, and easy wettability for large scale hydrogen production via electrochemical seawater splitting. This review investigates different fabrication processes for the self‐supported catalyst, emphasizing their distinct characteristics that contribute to improved activity. Furthermore, we provided a detailed elucidation of the procedure and characteristics of seawater splitting, emphasizing the most recent progress in the creation of self‐supportive catalyst for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and bifunctional activity. We have also examined the current barriers and potential prospects for advancing the utilization of self‐supported catalysts in the process of seawater splitting.

Titanium dioxide (TiO₂) is a widely studied material with many attractive properties such as its photocatalytic features. However, its commercial use is limited due to issues such as deactivation in the visible spectrum caused by its wide bandgap and the short lifetime of photo-excited charge carriers. To overcome these challenges, various modifications could be considered. In this study, we investigated copper doping and electron beam treatment. As-spun TiO2 nanofibers were fabricated by electrospinning a TiO2 sol, which obtained viscosity through a polyvinylpyrrolidone (PVP) matrix. Cu-doped TiO2 nanofibers with varying dopant concentrations were synthesized by adding copper salts. Then, the as-spun nanofibers were calcined for crystallization. To evaluate photocatalytic performance, a photodegradation test of methylene blue aqueous solution was performed for 6 h. Methylene blue concentration was measured over time using UV-Vis spectroscopy. The results showed that Cu doping at an appropriate concentration and electron-beam irradiation showed improved photocatalytic efficiency compared to bare TiO2 nanofibers. When the molar ratio of Cu/Ti was 0.05%, photodegradation rate was highest, which was 10.39% higher than that of bare TiO2. As a result of additional electron-beam treatment of this sample, photocatalytic efficiency improved up to 8.93% compared to samples without electron-beam treatment.

Abstract We investigated the effect of specific surface area on the electrochemical properties of NiCo2O4 (NCO) for glucose detection. NCO nanomaterials with controlled specific surface areas were prepared by additive-assisted hydrothermal synthesis, and self-assembled nanostructures with urchin-, pine-needle-, tremella-, and flower-like morphologies were obtained. The novelty of this method is the systematic control of chemical reaction routes assisted by the addition of different additives during synthesis, which results in the spontaneous formation of various morphologies without any difference in the crystal structure and chemical states of the constituent elements. Such morphological control of NCO nanomaterials leads to considerable changes in the electrochemical performance for glucose detection. Combined with materials characterization, the relationship between the specific surface area and the electrochemical performance is discussed for glucose detection. This work can provide scientific insights for tailoring the surface area of nanostructures, which determines their functionality for potential applications in glucose biosensors.

Abstract Oxygen evolution reaction (OER) under acidic conditions becomes of significant importance for the practical use of a proton exchange membrane (PEM) water electrolyzer. In particular, maximizing the mass activity of iridium (Ir) is one of the maiden issues. Herein, the authors discover that the Ir‐doped calcium copper titanate (CaCu₃Ti₄O₁₂, CCTO) perovskite exhibits ultrahigh mass activity up to 1000 A gIr−1 for the acidic OER, which is 66 times higher than that of the benchmark catalyst, IrO2. By substituting Ti with Ir in CCTO, metal‐oxygen (M‐O) covalency can be significantly increased leading to the reduced energy barrier for charge transfer. Further, highly polarizable CCTO perovskite referred to as “colossal dielectric”, possesses low defect formation energy for oxygen vacancy inducing a high number of oxygen vacancies in Ir‐doped CCTO (Ir‐CCTO). Electron transfer occurs from the oxygen vacancies and Ti to the substituted Ir consequentially resulting in the electron‐rich Ir and ‐deficient Ti sites. Thus, favorable adsorptions of oxygen intermediates can take place at Ti sites while the Ir ensures efficient charge supplies during OER, taking a top position of the volcano plot. Simultaneously, the introduced Ir dopants form nanoclusters at the surface of Ir‐CCTO, which can boost catalytic activity for the acidic OER.

Bismuth vanadate (BiVO4) has emerged as one of the most promising materials that can be used for the fabrication of solar-driven water splitting photoanodes. However, its photocatalytic activity is limited by the low charge carriers’ mobility, fast charge carrier recombination, and the slow kinetics of the water oxidation reaction. In this study, silver phosphate nanoparticles (Ag3PO4 NPs) are decorated on the BiVO4 surface via a facile photodeposition of Ag NPs, which are subsequently oxidized into Ag3PO4 NPs by a photoelectrochemical oxidation process. We demonstrate that Ag3PO4 NPs play as a passivator to reduce the charge carrier recombination on the BiVO4 surface and to accelerate the water oxidation reaction at the BiVO4/electrolyte interface. The best BiVO4/Ag3PO4 photoanode generates a photocatalytic current density of ca. 4.1 mA/cm2 when it is operated at 1.23 V vs. RHE in a pH 7 phosphate electrolyte and under 1 sun illumination. This photocatalytic performance is more than twice compared to that obtained for the pristine BiVO4 photoanode.

Abstract Thin film-based optical sensors have been attracting increasing interest for use in developing technologies such as biometrics. Multilayered dielectric thin films with different refractive indices have been utilized to modulate the optical properties in specific wavelength bands for spectral selectivity of Thin Film Narrow Bandpass Filters (TFNBFs). Progress in TFNBF design has been made with the incorporation of metallic thin films. Narrower bandwidths with higher transmittance have been achieved in specific spectral bands. In this work, Ti/TiO2/SiO2 based multilayer thin films were prepared using pulsed-DC reactive sputtering. Computer simulations using the Essential Macleod Program allowed the optimal number of layers and thickness of the multilayer thin films to be determined to efficiently tailor the optical path transmitting specific wavelength bands. The addition of Ti metal layers within dielectric (TiO2/SiO2) multilayer thin films significantly changes the cutoff frequency of transmittance at specific wavelengths. Representative 26 multilayer films consisting of Ti, TiO2, and SiO2 show lower transmittance of 10.29% at 400 nm and 10.48% at 680 nm. High transmittance of 80.42% at 485 nm was observed, which is expected to improve the spectral selectivity of the TFNBF. This work provides a contribution to future simulation based design strategy based on experimental thin film engineering for potential industrial development opportunities such as optical biometrics.

The superior chemical and electrical properties of TiO2 are considered to be suitable material for various applications, such as photoelectrodes, photocatalysts, and semiconductor gas sensors; however, it is difficult to commercialize the applications due to their low photoelectric conversion efficiency. Various solutions have been suggested and among them, the increase of active sites through surface modification is one of the most studied methods. A porous nanostructure with a large specific surface area is an attractive solution to increasing active sites, and in the electrospinning process, mesoporous nanofibers can be obtained by controlling the composition of the precursor solution. This study successfully carried out surface modification of TiO2 nanofibers by mixing polyvinylpyrrolidone with different molecular weights and using diisopropyl azodicarboxylate (DIPA). The morphology and crystallographic properties of the TiO2 samples were analyzed using a field emission electron microscope and X-ray diffraction method. The specific surface area and pore properties of the nanofiber samples were compared using the Brunauer-Emmett-Teller method. The TiO2 nanofibers fabricated by the precursor with K-30 polyvinyl pyrrolidone and diisopropyl azodicarboxylate were more porous than the TiO2 nanofibers without them. The modified nanofibers with K-30 and DIPA had a photocatalytic efficiency of 150% compared to TiO2 nanofibers. Their X-ray diffraction patterns revealed anatase peaks. The average crystallite size of the modified nanofibers was calculated to be 6.27–9.27 nm, and the specific surface area was 23.5–27.4 m2/g, which was more than 150% larger than the 17.2 m2/g of ordinary TiO2 nanofibers.

Exploring bifunctional electrocatalysts to lower the activation energy barriers for sluggish electrochemical reactions for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of great importance in achieving lower energy consumption and higher conversion efficiency for future energy conversion and storage system. Despite the excellent performance of precious metal-based electrocatalysts for OER and ORR, their high cost and scarcity hamper their large-scale industrial application. As alternatives to precious metal-based electrocatalysts, the development of earth-abundant and efficient catalysts with excellent electrocatalytic performance in both the OER and the ORR is urgently required. Herein, we report a core–shell CoFeS2@CoS2 heterostructure entangled with carbon nanotubes as an efficient bifunctional electrocatalyst for both the OER and the ORR. The CoFeS2@CoS2 nanocubes entangled with carbon nanotubes show superior electrochemical performance for both the OER and the ORR: a potential of 1.5 V (vs. RHE) at a current density of 10 mA cm−2 for the OER in alkaline medium and an onset potential of 0.976 V for the ORR. This work suggests a processing methodology for the development of the core–shell heterostructures with enhanced bifunctional performance for both the OER and the ORR.

In this work, we prepared spinel-type NiCo2O4 (NCO) nanopowders as a low-cost and sensitive electrochemical sensor for nonenzymatic glucose detection. A facile and simple chemical bath method to synthesize the NCO nanopowders is demonstrated. The effect of pH and annealing temperature on the formation mechanism of NCO nanoparticles was systematically investigated. Our studies show that different pHs of the precursor solution during synthesis result in different intermediate phases and relating chemical reactions for the formation of NCO nanoparticles. Different morphologies of the NCO depending on pHs are also discussed based on the mechanism of growth. Electrochemical performance of the prepared NCO was characterized towards glucose, which reveals that sensitivity and selectivity of the NCO are significantly related with the final microstructure combined with constituent species with multiple oxidation states in the spinel structure.

Transition metal chalcogenides have been widely studied as a promising electrocatalyst for the hydrogen evolution reaction (HER) in acidic conditions. Among various transition metal chalcogenides, tungsten disulfide (WS2) is a distinguishable candidate due to abundant active sites and good electrical properties. Herein, we report a facile and selective synthetic method to synthesize WS2 with an intriguing two-dimensional nanostructure by using cysteine (C3H7NO2S) as a chemical agent. In addition, nitrogen can be incorporated during chemical synthesis from cysteine, which may be helpful for enhancing the HER. The electrocatalytic activity of N-doped WS2 exhibits a promising HER in acidic conditions, which are not only higher than W18O49 nanowires and hex-WO3 nanowires, but also comparable to the benchmark Pt/C. Moreover, excellent electrocatalytic stability is also demonstrated for acidic HER during long-term tests, thus highlighting its potential use of practical applications as an electrolyzer.

The development of electrochemical devices for renewable energy depends to a large extent on fundamental improvements in catalysts for oxygen evolution reactions (OERs). OER activity of transition metal sulfides (TMSs) can be improved by compositing with highly conductive supports possessing a high surface-to-volume ratio, such as reduced graphene oxide (rGO). Herein we report on the relationship between synthetic conditions and the OER catalytic properties of TMSs and rGO (TMS–rGO) hybrids. Starting materials, reaction temperature and reaction time were controlled to synergistically boost the OER catalytic activity of TMS–rGO hybrids. Our results showed that (i) compared with sulfides, hydroxides are favourable as starting materials to produce the desired TMS–rGO hybrid nanostructure and (ii) high reaction temperatures and longer reaction times can increase physico-chemical interaction between TMSs and rGO supports, resulting in highly efficient OER catalytic activity.

Zinc oxide (ZnO) has attractive photocatalytic properties. However, the high recombination rate of the photo-excited charge carriers on this material often restricts application. Here, we report that hybridization of one dimensional (1D) carbon nanotubes (CNT) on two dimensional (2D) porous ZnO nanosheets (NS) can be a promising strategy to overcome some of the challenges of ZnO. Specifically, a pulsed laser ablation technique was utilized to hybridize 1D CNT with 2D porous ZnO NS in environmentally friendly as well as super-economic (short time, less than 10 min) conditions. The synthesized ZnO NS-CNT hybrids show a significantly enhanced photocatalytic activity for water splitting relative to their counterpart ZnO NS.

High-performance oxygen evolution reaction (OER) electrocatalysts are needed to produce hydrogen for energy generation through a carbon-free route. In this work, the solution combustion synthesis (SCS) method was employed to synthesize mixed phases of Co- and Mn-based oxides, and the relationships between the crystalline structure and the catalytic properties in the mixed phases were established. The mixed phases of Co- and Mn-based oxides shows promising OER properties, such as acceptable overpotential (450 mV for 10 mA∙cm−2) and Tafel slope (35.8 mV∙dec−1), highlighting the use of the mixed phases of Co- and Mn-based oxides as a new efficient catalysts for water splitting. Electronic structure of the mixed phases of Co- and Mn based oxides is studied in detail to give insight for the origin of high catalytic activities. In addition, excellent long-term stability for OER in alkaline media is achieved for the mixed phase of Co- and Mn based oxides.