Semiconductor nanostructure-based photoelectrochemical water splitting: A brief review

Red and near-infrared light-activated photoelectrochemical nanobiosensors for biomedical target detection

Photoelectrochemical (PEC) nanobiosensors integrate molecular (bio)recognition elements with semiconductor/plasmonic photoactive nanomaterials to produce measurable signals after light-induced reactions. Recent advancements in PEC nanobiosensors, using light-matter interactions, have significantly improved sensitivity, specificity, and signal-to-noise ratio in detecting (bio)analytes. Tunable nanomaterials activated by a wide spectral radiation window coupled to electrochemical transduction platforms have further improved detection by stabilizing and amplifying electrical signals. This work reviews PEC biosensors based on nanomaterials like metal oxides, carbon nitrides, quantum dots, and transition metal chalcogenides (TMCs), showing their superior optoelectronic properties and analytical performance for the detection of clinically relevant biomarkers. Furthermore, it highlights the innovative role of red light and NIR-activated PEC nanobiosensors in enhancing charge transfer processes, protecting them from biomolecule photodamage in vitro and in vivo applications. Overall, advances in PEC detection systems have the potential to revolutionize rapid and accurate measurements in clinical diagnostic applications. Their integration into miniaturized devices also supports the development of portable, easy-to-use diagnostic tools, facilitating point-of-care (POC) testing solutions and real-time monitoring.

Photoassisted Water Purification through an Electrochemically Artificially Adjusted p-Cu2O Light Absorption Layer

The implementation of photoelectrochemical water purification technology can address prevailing environmental challenges that impede the advancement and prosperity of human society. In this study, Cu, which is abundant on Earth, was fabricated using an electrochemical deposition process, in which the preferential orientation direction and carrier concentration of the Cu-based oxide semiconductor were artificially adjusted by carefully controlling the OH- and applied voltage. In particular, Cu2O grown with a sufficient supply of OH- ions exhibited the (111) preferred orientation, and the (200) surface facet was exposed, independently achieving 90% decomposition efficiency in a methyl orange (MO) solution for 100 min. This specialized method minimizes the recombination loss of electron-hole pairs by increasing the charge separation and transport efficiency of the bulk and surface of the Cu2O multifunctional absorption layer. These discoveries and comprehension not only offer valuable perspectives on mitigating self-photocorrosion in Cu2O absorbing layers but also provide a convenient and expeditious method for the mass production of water purification systems that harness unlimited solar energy. These properties enable significant energy saving and promote high-speed independent removal of organic pollutants (i.e., MO reduction) during the water purification process.

Enhancing the Photoelectrochemical Performance of a Nanoporous Silicon Photocathode through Electroless Nickel Deposition

Renewable energy sources, particularly solar energy, are key to our efforts to decarbonize. This study investigates the photoelectrochemical (PEC) behavior of nanoporous silicon (NPSi) and its Ni-coated hybrid system. The methods involve the application of a Ni coating to NPSi, a process aimed at augmenting catalytic activity, light absorption, and carrier transport. Scanning electron microscopy was used to analyze the morphological changes on NPSi surfaces due to the Ni coating. Results demonstrate that the Ni coating creates unique structures on NPSi surfaces, with peak PEC performance observed at 15 min of coating time and 60 °C. These conditions were found to promote electron-hole pair separation and uniform Ni coverage. A continuous 50-min white light illumination experiment confirmed stable PEC fluctuations, showing the interplay of NPSi's characteristics and Ni's catalytic effect. This study provides practical guidance for the design of efficient water-splitting catalysts, contributing to the broader field of renewable energy conversion.

Unravelling Dynamics Involving Multiple Charge Carriers in Semiconductor Nanocrystals

The use of colloidal nanocrystals as part of artificial photosynthetic systems has recently gained significant attention, owing to their strong light absorption and highly reproducible, tunable electronic and optical properties. The complete photocatalytic conversion of water to its components is yet to be achieved in a practically suitable and commercially viable manner. To complete this challenging task, we are required to fully understand the mechanistic aspects of the underlying light-driven processes involving not just single charge carriers but also multiple charge carriers in detail. This review focuses on recent progress in understanding charge carrier dynamics in semiconductor nanocrystals and the influence of various parameters such as dimension, composition, and cocatalysts. Transient absorption spectroscopic studies involving single and multiple charge carriers, and the challenges associated with the need for accumulation of multiple charge carriers to drive the targeted chemical reactions, are discussed.

Menezes L, Tittl A, Ren H, Maier SA. Optical Metasurfaces for Energy Conversion

Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light-matter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.

Facile Zn and Ni Co-Doped Hematite Nanorods for Efficient Photocatalytic Water Oxidation

In this work, we report the effect of zinc (Zn) and nickel (Ni) co-doping of hydrothermally synthesized hematite nanorods prepared on fluorine-doped tin oxide (FTO) substrates for enhanced photoelectrochemical (PEC) water splitting. Seeded hematite nanorods (NRs) were facilely doped with a fixed concentration of 3 mM Zn and varied concentrations of 0, 3, 5, 7, and 9 mM Ni. The samples were observed to have a largely uniform morphology of vertically aligned NRs with slight inclinations. The samples showed high photon absorption within the visible spectrum due to their bandgaps, which ranged between 1.9-2.2 eV. The highest photocurrent density of 0.072 mA/cm2 at 1.5 V vs. a reversible hydrogen electrode (RHE) was realized for the 3 mM Zn/7 mM Ni NRs sample. This photocurrent was 279% higher compared to the value observed for pristine hematite NRs. The Mott-Schottky results reveal an increase in donor density values with increasing Ni dopant concentration. The 3 mM Zn/7 mM Ni NRs sample produced the highest donor concentration of 2.89 × 1019 (cm-3), which was 2.1 times higher than that of pristine hematite. This work demonstrates the role of Zn and Ni co-dopants in enhancing the photocatalytic water oxidation of hematite nanorods for the generation of hydrogen.

Remediation of pesticides using TiO2 based photocatalytic strategies: A review

Nowadays, pesticides are regarded as the most dangerous of the various organic pollutants, posing substantial environmental and human threats worldwide. Pesticide contamination has become one of the most crucial environmental issues due to its bio-persistence and bioaccumulation. Different conventional methods are being utilized for pesticide removal, yet pesticides are thought to be significantly present in the environment. The development and application of sophisticated wastewater treatment methods are being pursued to remove contaminants effectively, particularly pesticides. In the past several decades, nanoscience and nanotechnology have emerged as essential tools for the identification, removal, and mineralization of persistent pesticides by employing advanced nanomaterials such as pristine titanium dioxide (TiO₂), doped TiO₂, nanocomposites (NCs) TiO₂, and ternary nanocomposites (TNCs) TiO₂ by advanced oxidation processes (AOPs). Advancement in the characteristics of TiO₂ by doping, co-doping, construction of NCs and TNCs has contributed to the dramatic efficiency up-gradation by reducing band gap, solar active photocatalyst, enhancing PCA, high photostability, chemically inertness and multiple time reusability. Based on previous literature, utilizing La-TiO₂ NCs photocatalyst, the mineralization of pesticide (imidacloprid) attained up to 98.17% that is almost 40-53% greater than pristine TiO₂. The present review attempt to discuss the recent research performed on TiO₂ based nanoparticles (NPs) and NCs for photocatalytic mineralization of various pesticides. The basic mechanism of TiO₂ photocatalysis, types of reactors used for photocatalysis, and optimized experimental conditions of TiO₂ for pesticides mineralization are discussed.

Electron Transfer at Quantum Dot–Metal Oxide Interfaces for Solar Energy Conversion

Electron transfer at a donor–acceptor quantum dot–metal oxide interface is a process fundamentally relevant to solar energy conversion architectures as, e.g., sensitized solar cells and solar fuels schemes. As kinetic competition at these technologically relevant interfaces largely determines device performance, this Review surveys several aspects linking electron transfer dynamics and device efficiency; this correlation is done for systems aiming for efficiencies up to and above the ∼33% efficiency limit set by Shockley and Queisser for single gap devices. Furthermore, we critically comment on common pitfalls associated with the interpretation of kinetic data obtained from current methodologies and experimental approaches, and finally, we highlight works that, to our judgment, have contributed to a better understanding of the fundamentals governing electron transfer at quantum dot–metal oxide interfaces.

Review on optofluidic microreactors for photocatalysis

Four interrelated issues have been arising with the development of modern industry, namely environmental pollution, the energy crisis, the greenhouse effect and the global food crisis. Photocatalysis is one of the most promising methods to solve them in the future. To promote high photocatalytic reaction efficiency and utilize solar energy to its fullest, a well-designed photoreactor is vital. Photocatalytic optofluidic microreactors, a promising technology that brings the merits of microfluidics to photocatalysis, offer the advantages of a large surface-to-volume ratio, a short molecular diffusion length and high reaction efficiency, providing a potential method for mitigating the aforementioned crises in the future. Although various photocatalytic optofluidic microreactors have been reported, a comprehensive review of microreactors applied to these four fields is still lacking. In this paper, we review the typical design and development of photocatalytic microreactors in the fields of water purification, water splitting, CO2 fixation and coenzyme regeneration in the past few years. As the most promising tool for solar energy utilization, we believe that the increasing innovation of photocatalytic optofluidic microreactors will drive rapid development of related fields in the future.

Occurrence, toxic effects, and mitigation of pesticides as emerging environmental pollutants using robust nanomaterials - A review

Increasing demand of food and agriculture is leading us towards the increasing use and introduction of pesticides to the environment. The upright increase of pesticides in water and associated adverse effects have become a great point of concern to develop proficient methods for their mitigation from water. Various different methods have been traditionally employed for this purpose. Recently, nanotechnology has turned out to be the field of prodigious interest for this purpose, and various specific methods were developed and employed to remove pesticides from water. In this study, nanotechnological methods such as adsorption and degradation have been thoroughly discussed along with their applications and limitations where different types of nanoparticles, nanocomposites, nanotubes, and nanomembranes have played a vital role. However, in this study the most commonly adopted method of adsorption is considered to be the better technique due to its low cost, efficiency, and ease of operation. The adsorption kinetic models were described to explain the efficiency of the nano-adrsorbants in order to evaluate the mass transfer processes. However, various degradation methodologies including photocatalysis and catalytic reduction have also been elaborated. Numerous robust metal, metal oxide and functionalized magnetic nanomaterials have been emphasized, categorized, and compared for the removal of pesticides from water. Additionally, current challenges faced by researchers and future directions have also been provided.

Enhancing photoelectrochemical water splitting with plasmonic Au nanoparticles

The water-based renewable chemical energy cycle has attracted interest due to its role in replacing existing non-renewable resources and alleviating environmental issues. Utilizing the semi-infinite solar energy source is the most appropriate way to sustain such a water-based energy cycle by producing and feeding hydrogen and oxygen. For production, an efficient photoelectrode is required to effectively perform the photoelectrochemical water splitting reaction. For this purpose, appropriately engineered nanostructures can be introduced into the photoelectrode to enhance light-matter interactions for efficient generation and transport of charges and activation of surface chemical reactions. Plasmon enhanced photoelectrochemical water splitting, whose performance can potentially exceed classical efficiency limits, is of great importance in this respect. Plasmonic gold nanoparticles are widely accepted nanomaterials for such applications because they possess high chemical stability, efficiently absorb visible light unlike many inorganic oxides, and enhance light-matter interactions with localized plasmon relaxation processes. However, our understanding of the physical phenomena behind these particles is still not complete. This review paper focuses on understanding the interfacial phenomena between gold nanoparticles and semiconductors and provides a summary and perspective of recent studies on plasmon enhanced photoelectrochemical water splitting using gold nanoparticles.

Nanoarray Structures for Artificial Photosynthesis

Conversion and storage of solar energy into fuels and chemicals by artificial photosynthesis has been considered as one of the promising methods to address the global energy crisis. However, it is still far from the practical applications on a large scale. Nanoarray structures that combine the advantages of nanosize and array alignment have demonstrated great potential to improve solar energy conversion efficiency, stability, and selectivity. This article provides a comprehensive review on the utilization of nanoarray structures in artificial photosynthesis of renewable fuels and high value-added chemicals. First, basic principles of solar energy conversion and superiorities of using nanoarray structures in this field are described. Recent research progress on nanoarray structures in both abiotic and abiotic-biotic hybrid systems is then outlined, highlighting contributions to light absorption, charge transport and transfer, and catalytic reactions (including kinetics and selectivity). Finally, conclusions and outlooks on future research directions of nanoarray structures for artificial photosynthesis are presented.

Transition metal-based layered double hydroxides for photo(electro)chemical water splitting: a mini review

The conversion of solar energy into usable chemical fuels, such as hydrogen gas, via photo(electro)chemical water splitting is a promising approach for creating a carbon neutral energy ecosystem. The deployment of this technology industrially and at scale requires photoelectrodes that are highly active, cost-effective, and stable. To create these new photoelectrodes, transition metal-based electrocatalysts have been proposed as potential cocatalysts for improving the performance of water splitting catalysts. Layered double hydroxides (LDHs) are a class of clays with brucite like layers and intercalated anions. Transition metal-based LDHs are increasingly popular in the field of photo(electro)chemical water splitting due to their unique physicochemical properties. This article aims to review recent advances in transition metal-based LDHs for photo(electro)chemical water splitting. This article provides a brief overview of the research in a format approachable for the general scientific audience. Specifically, this review examines the following areas: (i) routes for synthesis of transition metal-based LDHs, (ii) recent developments in transition metal-based LDHs for photo(electro)chemical water splitting, and (iii) an overview of the structure-property relationships therein.

Nanostructure-based photoelectrochemical sensing platforms for biomedical applications

As a newly developed and powerful analytical method, the use of photoelectrochemical (PEC) biosensors opens up new opportunities to provide wide applications in the early diagnosis of diseases, environmental monitoring and food safety detection. The properties of diverse photoactive materials are one of the essential factors, which can greatly impact the PEC performance. The continuous development of nanotechnology has injected new vitality into the field of PEC biosensors. In many studies, much effort on PEC sensing with semiconductor materials is highlighted. Thus, we propose a systematic introduction to the recent progress in nanostructure-based PEC biosensors to exploit more promising materials and advanced PEC technologies. This review briefly evaluates the several advanced photoactive nanomaterials in the PEC field with an emphasis on the charge separation and transfer mechanism over the past few years. In addition, we introduce the application and research progress of PEC sensors from the perspective of basic principles, and give a brief overview of the main advances in the versatile sensing pattern of nanostructure-based PEC platforms. This last section covers the aspects of future prospects and challenges in the nanostructure-based PEC analysis field.

3D/2D Bi2S3/SnS2 heterostructures: superior charge separation and enhanced solar light-driven photocatalytic performance

A type-II band alignment between Bi₂S₃ and SnS₂ was established by theoretical investigation which accelerates photoinduced charge separation and improved the photocatalytic activity of the Bi₂S₃/SnS₂ heterostructure.

Tuning Light-Driven Water Oxidation Efficiency of Molybdenum-Doped BiVO4 by Means of Multicomposite Catalysts Containing Nickel, Iron, and Chromium Oxides

Mo-doped BiVO₄ has emerged as a promising material for photoelectrodes for photoelectrochemical water splitting, however, still shows a limited efficiency for light-driven water oxidation. We present the influence of an oxygen-evolution catalyst composed of Ni, Fe, and Cr oxides on the activity of Mo:BiVO₄ photoanodes. The photoanodes are prepared by spray-coating, enabling compositional and thickness gradients of the incorporated catalyst. Two different configurations are evaluated, namely with the catalyst embedded into the Mo:BiVO₄ film or deposited on top of it. Both configurations provide a significantly different impact on the photoelectrocatalytic efficiency. Structural characterisation of the materials by means of SEM, TEM and XRD as well as the photoelectrocatalytic activity investigated by means of an optical scanning droplet cell and in situ detection of oxygen using scanning photoelectrochemical microscopy are presented.

Atomic Layer Deposition of Inorganic Films for the Synthesis of Vertically Aligned Carbon Nanotube Arrays and Their Hybrids

Vertically aligned carbon nanotube arrays (VACNTs) have many excellent properties and show great potential for various applications. Recently, there has been a desire to grow VACNTs on nonplanar surfaces and synthesize core-sheath-structured VACNT–inorganic hybrids. To achieve this aim, atomic layer deposition (ALD) has been extensively applied, especially due to its atomic-scale thickness controllability and excellent conformality of films on three-dimensional (3D) structures with high aspect ratios. In this paper, the ALD of catalyst thin films for the growth of VACNTs, such as Co3O4, Al2O3, and Fe2O3, was first mentioned. After that, the ALD of thin films for the synthesis of VACNT–inorganic hybrids was also discussed. To highlight the importance of these hybrids, their potential applications in supercapacitors, solar cells, fuel cells, and sensors have also been reviewed.

Transition metal silicides: fundamentals, preparation and catalytic applications

Transition metal silicides as low-cost and earth-abundant inorganic materials are becoming indispensable constituents in catalytic systems for a variety of applications and exhibit excellent properties for sustainable industrial process.

The production of an efficient visible light photocatalyst for CO oxidation through the surface plasmonic effect of Ag nanoparticles on SiO2@α-Fe2O3 nanocomposites

A process for the photo deposition of noble Ag nanoparticles on a core-shell structure of SiO2@α-Fe2O3 nanocomposite spheres was performed to produce a CO photo oxidation catalyst. The structural analyses were carried out for samples produced using different Ag metal nanoparticle weight percentages on SiO2@α-Fe2O3 nanocomposite spheres by X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), UV-vis spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). A computational study was also performed to confirm the existence of the synergic effect of surface plasmon resonance (SPR) for different weight percentages of Ag on the SiO2@α-Fe2O3 nanocomposites. The mechanism for CO oxidation on the catalyst was explored using diffuse reflectance infrared Fourier transform spectroscopy (DRFIT). The CO oxidation results for the Ag (2 wt%)-SiO2@α-Fe2O3 nanocomposite spheres showed 48% higher photocatalytic activity than α-Fe2O3 and SiO2@α-Fe2O3 at stable temperature.

Preparation of polyaniline/PbS core-shell nano/microcomposite and its application for photocatalytic H2 electrogeneration from H2O

Lead sulfide (PbS) and polyaniline (PANI) nano/microparticles were prepared. Then, PANI/PbS core-shell nano/microcomposites (I, II, and III) were prepared by oxidative polymerization of different aniline concentrations (0.01, 0.03, and 0.05 M), respectively, in the presence of 0.05 M PbS. FT-IR, XRD, SEM, HR-TEM, and UV-Vis analyses were carried out to characterize the samples. From the FT-IR data, there are redshifts in PbS and PANI nano/microparticles bands in comparison with PANI/PbS nano/microcomposites. The average crystallite sizes of PANI/PbS core-shell nano/microcomposites (I, II, and III) from XRD analyses were 46.5, 55, and 42.16 nm, respectively. From the optical analyses, nano/microcomposite (II) has the optimum optical properties with two band gaps values of 1.41 and 2.79 eV. Then, the nano/microcomposite (II) membrane electrode supported on ITO glass was prepared and applied on the photoelectrochemical (PEC) H₂ generation from H₂O. The characteristics current-voltage and current-time behaviors were measured at different wavelengths from 390 to 636 nm. Also, the incident photon-to-current conversion efficiency (IPCE) under monochromatic illumination condition was calculated. The optimum values for IPCE were 36.5 and 35.2% at 390 and 405 nm, respectively. Finally, a simple mechanism for PEC H₂ generation from H₂O using the nano/microcomposite (II) membrane electrode was mentioned.

Review on optofluidic microreactors for artificial photosynthesis

Artificial photosynthesis (APS) mimics natural photosynthesis (NPS) to store solar energy in chemical compounds for applications such as water splitting, CO2 fixation and coenzyme regeneration. NPS is naturally an optofluidic system since the cells (typical size 10 to 100 µm) of green plants, algae, and cyanobacteria enable light capture, biochemical and enzymatic reactions and the related material transport in a microscale, aqueous environment. The long history of evolution has equipped NPS with the remarkable merits of a large surface-area-to-volume ratio, fast small molecule diffusion and precise control of mass transfer. APS is expected to share many of the same advantages of NPS and could even provide more functionality if optofluidic technology is introduced. Recently, many studies have reported on optofluidic APS systems, but there is still a lack of an in-depth review. This article will start with a brief introduction of the physical mechanisms and will then review recent progresses in water splitting, CO2 fixation and coenzyme regeneration in optofluidic APS systems, followed by discussions on pending problems for real applications.

Facile Surfactant-Free Synthesis of Composition-Tunable Bimetallic PtCu Alloy Nanosponges for Direct Methanol Fuel Cell Applications

Sponge-like metal nanomaterials have been paid great attention due to their unique structure for wide applications in hydrogen storage, filtration, sensors, heterogeneous catalysis, and fuel cells. Here, we first use a facile, bottom-up method to successfully prepare composition-tunable PtCu alloy nanosponges constructed with sub-4.5 nm particle building blocks. Due to the porous structure, structure defects, and synergetic effect of Pt and Cu, the PtCu alloy nanosponges exhibit good electrocatalytic performances towards methanol oxidation. Compared with pure Pt nanosponges, the specific/mass activity on PtCu2 alloy nanosponges is 5.84/2.93 times that on pure Pt nanosponges. Furthermore, the stability and reactivation ability of PtCu alloy nanosponges are also superior to pure Pt nanosponges.

Revealing the Influence of Doping and Surface Treatment on the Surface Carrier Dynamics in Hematite Nanorod Photoanodes

Photoelectrochemical (PEC) water oxidation is considered to be the rate-limiting step of the two half-reactions in light-driven water splitting. Consequently, considerable effort has focused on improving the performance of photoanodes for water oxidation. While these efforts have met with some success, the mechanisms responsible for improvements resulting from photoanode modifications are often difficult to determine. This is mainly caused by the entanglement of numerous properties that influence the PEC performance, particularly processes that occur at the photoanode/electrolyte interface. In this study, we set out to elucidate the effects on the surface carrier dynamics of hematite photoanodes of introducing manganese (Mn) into hematite nanorods and of creating a core-shell structure. Intensity-modulated photocurrent spectroscopy (IMPS) measurements reveal that the introduction of Mn into hematite not only increases the rate constant for hole transfer but also reduces the rate constant for surface recombination. In contrast, the core-shell architecture evidently passivates the surface states where recombination occurs; no change is observed for the charge transfer rate constant, whereas the surface recombination rate constant is suppressed by ∼1 order of magnitude.

Visualizing the Nano Cocatalyst Aligned Electric Fields on Single Photocatalyst Particles

The cocatalysts or dual cocatalysts of photocatalysts are indispensable for high efficiency in artificial photosynthesis for solar fuel production. However, the reaction activity increased by cocatalysts cannot be directly ascribed to the accelerated catalytic kinetics, since photogenerated charges are involved in the elementary steps of photocatalytic reactions. To date, diverging views about cocatalysts show that their exact role for photocatalysis is not well understood yet. Herein, we image directly the local separation of photogenerated charge carriers across single crystals of the BiVO₄ photocatalyst which loaded locally with nanoparticles of a MnO_x single cocatalyst or with nanoparticles of a spatially separated MnO_x and Pt dual cocatalyst. The deposition of the single cocatalyst resulted not only in a strong increase of the interfacial charge transfer but also, surprisingly, in a change of the direction of built-in electric fields beneath the uncovered surface of the photocatalyst. The additive electric fields caused a strong increase of local surface photovoltage signals (up to 80 times) and correlated with the increase of the photocatalytic performance. The local electric fields were further increased (up to 2.5 kV·cm^-1) by a synergetic effect of the spatially separated dual cocatalysts. The results reveal that cocatalyst has a conclusive effect on charge separation in photocatalyst particle by aligning the vectors of built-in electric fields in the photocatalyst particle. This effect is beyond its catalytic function in thermal catalysis.

Highly (001)-Textured Tetragonal BiFeO3 Film and Its Photoelectrochemical Behaviors Tuned by Magnetic Field

Highly (001)-textured BiFeO₃ film in tetragonal phase (T-BFO) with a giant c/a ratio was first obtained on quartz/polycrystalline ITO substrate. Our results indicate that the polycrystalline ITO layer with small surface roughness is a critical point to control the growth of T-BFO structure. It should be ascribed to the fact that a Bi-rich phase interlayer (∼5 nm) could be formed on ITO, which acted as a crystal seed layer and thus induced the growth of (001)-textured T-BFO structure. The observed weak room temperature ferromagnetism should be attributed to Fe valence change. Open circuit potential measurements under 360 μW/cm² full spectra irradiation show that the open circuit potential and the lifetime of photo-induced carriers increased under applied magnetic field, which reveals that the applied magnetic field can manipulate the photo electrochemical behaviors of BFO film. Our findings offer a simple way to fabricate highly (001)-textured T-BFO film, which make it desirable to obtain extensive applications for these oriented BFO films.

Visible-Light-Induced Water Splitting Based on a Novel α-Fe2O3/CdS Heterostructure

In this work, CdS nanoparticles were grown on top of a hematite (α-Fe₂O₃) film as photoanodes for the photoelectrochemical water splitting. Such type of composition was chosen to enhance the electrical conductivity and photoactivity of traditionally used bare hematite nanostructures. The fabricated thin film was probed by various physicochemical, electrochemical, and optical techniques, revealing high crystallinity of the prepared nanocomposite and the presence of two distinct phases with different band gaps. Furthermore, photoassisted water splitting tests exhibit a noteworthy photocurrent of 0.6 mA/cm² and a relatively low onset potential of 0.4 V (vs reversible hydrogen electrode) for the composite electrode. The high photocurrent generation ability was attributed to the synergistic interplay between conduction and valence band (VB) levels of CdS and α-Fe₂O₃, which was further interpreted by J-V curves. Finally, electrochemical impedance spectroscopy investigation of the obtained films suggests that the photogenerated holes could be transferred from the VB of α-Fe₂O₃ to the electrolyte more efficiently in the hybrid nanostructure.

Nanomaterials for photocatalytic hydrogen production: from theoretical perspectives

To overcome the increasing demand of energy worldwide and global warming due to CO₂emissions from the use of traditional fuel sources, renewable and clean energy sources are in high demand.

Sequentially surface modified hematite enables lower applied bias photoelectrochemical water splitting

We achieve a low onset potential of 0.49 V using heavily doped Fe_2−xSn_xO₃surface passivation layer and NiOOH dual surface treatments.

Sum Frequency Generation of Acetonitrile on a Rutile (110) Surface from Density Functional Theory-Based Molecular Dynamics

We present the calculation of vibrational sum frequency generation for molecules adsorbed on a semiconductor surface via density functional theory-based molecular dynamics. Using an efficient approach relying on the Gaussian and plane waves method and density functional perturbation theory, acetonitrile adsorbed on a rutile (110) surface has been studied, the vapor-solid interface of which has recently been investigated experimentally. Further analysis of the orientation of the acetonitrile molecules directly adsorbed on the rutile (110) surface agrees well with parameters derived from experiment. This opens a promising way for detailed study of semiconductor interfaces, which is of particular importance with respect to numerous applications such as, for instance, in materials design.

Gap-plasmon based broadband absorbers for enhanced hot-electron and photocurrent generation

Plasmonic hot-electron generation has recently come into focus as a new scheme for solar energy conversion. So far, however, due to the relatively narrow bandwidth of the surface plasmon resonances and the insufficient resonant light absorption, most of plasmonic photocatalysts show narrow-band spectral responsivities and small solar energy conversion efficiencies. Here we experimentally demonstrate that a three-layered nanostructure, consisting of a monolayer gold-nanoparticles and a gold film separated by a TiO2 gap layer (Au-NPs/TiO2/Au-film), is capable of near-completely absorbing light within the whole visible region. We show that the Au-NPs/TiO2/Au-film device can take advantage of such strong and broadband light absorption to enhance the generation of hot electrons and thus the photocurrent under visible irradiation. As compared to conventional plasmonic photocatalysts such as Au-NPs/TiO2 nanostructures, a 5-fold-enhanced incident photon-to-current conversion efficiency is achieved within the entire wavelength range 450-850 nm in the Au-NPs/TiO2/Au-film device. Simulations show good agreements with the experimental results, demonstrating that only the plasmon-induced losses contribute to the enhanced photocurrent generation of the Au-NPs/TiO2/Au-film device.

Study of Copper Ferrite as a Novel Photocathode for Water Reduction: Improving Its Photoactivity by Electrochemical Pretreatment

Studies on water-splitting p-type oxide electrodes based on nontoxic earth-abundant elements are scarce. Herein, the behavior of electrodes composed of CuFe2 O4 nanoparticles 30 nm in size is presented. The as-prepared CuFe2 O4 nanoporous electrodes exhibit small anodic photocurrents in 0.1 m NaOH. However, an electrochemical pretreatment consisting in the application of sufficiently positive potentials leads to p-type behavior with a photocurrent onset as high as 1.1 V versus the reversible hydrogen electrode, which is among the most positive values reported for an oxide absorbing visible light (band gap of 2.1 eV). This photocurrent is partly due to H2 evolution, but there are also signs of photoreduction of the material. Although the photocurrents are modest, these results point to the possibility of using CuFe2 O4 as a photocathode material in water-splitting devices. Furthermore, the strategy employed for the enhancement in the CuFe2 O4 photoactivity could be extended to other photocathode materials.

Photoelectrochemical water splitting enhanced by self-assembled metal nanopillars embedded in an oxide semiconductor photoelectrode

Production of chemical fuels by direct solar energy conversion in a photoelectrochemical cell is of great practical interest for developing a sustainable energy system. Various nanoscale designs such as nanowires, nanotubes, heterostructures and nanocomposites have been explored to increase the energy conversion efficiency of photoelectrochemical water splitting. Here we demonstrate a self-organized nanocomposite material concept for enhancing the efficiency of photocarrier separation and electrochemical energy conversion. Mechanically robust photoelectrodes are formed by embedding self-assembled metal nanopillars in a semiconductor thin film, forming tubular Schottky junctions around each pillar. The photocarrier transport efficiency is strongly enhanced in the Schottky space charge regions while the pillars provide an efficient charge extraction path. Ir-doped SrTiO₃ with embedded iridium metal nanopillars shows good operational stability in a water oxidation reaction and achieves over 80% utilization of photogenerated carriers under visible light in the 400- to 600-nm wavelength range.

Nanoscale designs are known to increase the energy conversion efficiency of photoelectrochemical water splitting. Here, the authors report a self-organized nanocomposite formed by embedding self-assembled metal nanopillars in a semiconductor thin film, for enhanced photocarrier separation efficiency.

Ion dynamics in a supersonic jet: Experiments and simulations

The authors suggest a model to simulate the dynamics of ions in a supersonic plasma jet. The model relies on experimental argon ion, Ar(+), energy distribution functions measured by a quadrupole mass spectrometer at different positions along the central axis of a supersonic argon plasma jet. The latter is generated by the pressure difference between two vacuum chambers connected through a converging nozzle: a high-pressure chamber (P ≃ 3.20 Pa), where an inductively coupled argon plasma discharge is maintained, and a lower-pressure one (P ≃ 0.11 Pa), where the plasma jet expands. The model is based on the integration of the equations of motion of a single Ar(+), moving along the supersonic jet in a reference system in which neutral species are at rest. Ar(+)-Ar induced dipole interactions are treated using a 12-4 Lennard-Jones potential. The resulting collisions are considered to be purely elastic, and in addition to them, we allow for charge transfer processes. The energy and position of 1000 Ar(+) were calculated, using an integration time step of 10 ps for ion trajectories ranging from 5 mm to 20 mm from the nozzle, well inside the spatial extension of the supersonic jet. The numerically obtained ion energy distribution functions agree remarkably well with the experimental measurements. From our calculations we can draw conclusions about the energy loss and the mean free paths along the jet. In particular, we can distinguish between processes with and without charge transfer, allowing us to determine the effect of charge exchange phenomena in which the ion changes its nature. The calculated mean free paths were used to evaluate the effective cross sections for momentum transfer and charge transfer collisions, valid for ion energies in the range (0.5-10) eV, in very good agreement with those reported in the literature.

Cu2O Nanowire Photocathodes for Efficient and Durable Solar Water Splitting

Due to its abundance, scalability, and nontoxicity, Cu2O has attracted extensive attention toward solar energy conversion, and it is the best performing metal oxide material. Until now, the high efficiency devices are all planar in structure, and their photocurrent densities still fall well below the theoretical value of 14.5 mA cm(-2) due to the incompatible light absorption and charge carrier diffusion lengths. Nanowire structures have been considered as a rational and promising approach to solve this issue, but due to various challenges, performance improvements through the use of nanowires have rarely been achieved. In this work, we develop a new synthetic method to grow Cu2O nanowire arrays on conductive fluorine-doped tin oxide substrates with well-controlled phase and excellent electronic and photonic properties. Also, we introduce an innovative blocking layer strategy to enable high performance. Further, through material engineering by combining a conformal nanoscale p-n junction, durable protective overlayer, and uniform catalyst decoration, we have successfully fabricated Cu2O nanowire array photocathodes for hydrogen generation from solar water splitting delivering unprecedentedly high photocurrent densities of 10 mA cm(-2) and stable operation beyond 50 h, establishing a new benchmark for metal oxide based photoelectrodes.

One-pot synthesis of lotus-shaped Pd–Cu hierarchical superstructure crystals for formic acid oxidation

Lotus-shaped Pd–Cu hierarchical superstructure crystals with enhanced electrocatalytic properties toward HCOOH oxidation were successfully synthesized through an aqueous solution method.

Photocatalytic and photoelectrocatalytic reduction of CO2 using heterogeneous catalysts with controlled nanostructures

Recent advances in photocatalytic and photoelectrocatalytic reduction of CO₂ with H₂O using semiconductor-based catalysts have been highlighted.