Hematite has been considered as one of the most promising materials for solar water splitting, although its photoelectrochemical performance is still not very high and limited by its intrinsic ...properties. In the past few years, sizable advances in the development of hematite photoelectrodes for enhanced water splitting activities have been achieved by a variety of rational modification strategies, including nanostructure design for efficient charge collection, metal ion doping for promoted charge carrier transfer, heterojunctions for efficient charge separation, and surface and/or interface modification for retarded charge recombination and enhanced light absorption. In this article, research work and milestone achievement actually focused on hematite photoelectrodes for water splitting is reviewed in detail. A review on this topic by answering the key question, “how to modify or design hematite photoelectrode to improve its conductivity, enhance charge separation as well as catalyze surface water oxidation,” in authors' view, can be potentially helpful to enable hematite for further efficient solar energy conversion, which will be very inspiring and important to this field.
Hematite (α-Fe
2
O
3
), with a bandgap suitable for absorption of the solar spectrum, is ideally suited for use as a photoanode material in photoelectrochemical (PEC) conversion of solar light into ...hydrogen fuel
via
water splitting. However, low hole mobility, short hole lifetime, high density of surface states, and slow kinetics for oxygen evolution at the α-Fe
2
O
3
/electrolyte interface have limited the PEC performance of α-Fe
2
O
3
photoanodes to date. Along with numerous reports on doping and nanostructuring of α-Fe
2
O
3
, increased attention has been paid to α-Fe
2
O
3
heterostructure design for improved PEC performance. This review article provides an overview of four main approaches to rational heterostructure design: coupling α-Fe
2
O
3
with (1) an n- or p-type semiconductor for promoting charge separation; (2) a nanotextured conductive substrate for efficient charge collection; (3) a surface/interface passivation layer for reduced surface/interface charge recombination; (4) a catalyst for accelerated water oxidation kinetics. The achievements to date demonstrate that high PEC performance may be accessed with these designs. In addition, we review time-resolved laser techniques used to probe the charge carrier dynamics of these heterostructures. Dynamic studies have provided insight into the mechanisms responsible for the improved PEC performance in these materials and helped to guide continued design of α-Fe
2
O
3
heterostructures for further enhancement of PEC water splitting. As summarized in this review article, rational heterostructure design is a promising strategy to push forward the application of α-Fe
2
O
3
for potential low cost and high efficiency solar hydrogen conversion. A better fundamental understanding of the charge carrier dynamics in these structures in turn helps to guide and improve the heterostructure design.
Different approaches to improving photoelectrochemical performance through α-Fe
2
O
3
heterostructure design.
A look at the use of semiconductor-based photocatalytic hydrogen generation as an alternative energy source is presented. Issues that still need to be examined include chemical composition and ...electronic properties.
Single Metal Atom Photocatalysis Wang, Bin; Cai, Hairui; Shen, Shaohua
Small methods,
09/2019, Letnik:
3, Številka:
9
Journal Article
Recenzirano
Photocatalysis suffers from rapid recombination of photoexcited charge carriers and limited active sites for the catalytic reactions, resulting in unsatisfactory performances that are far from ...practical application. Single metal atom catalysts not only increase the number of active sites due to the maximum atom‐utilization efficiency, but also enhance the intrinsic activity of each active site because of their unique geometric and electronic features. Furthermore, single metal atom catalysts provide a platform for photocatalysis research on the atomic level. This review discusses the unique characteristics, including geometric and electronic properties, of single metal atom catalysts, summarizes their synthesis strategies, and reviews their most recent development in photocatalysis. Finally, the challenges of single metal catalysts for both fundamental research and practical application are highlighted.
Single metal atom catalysts bridge the gap between heterocatalysis and homocatalysis, and provide a platform for photocatalysis research on the atomic level. Their geometric and electronic properties, synthesis strategies, and the most recent developments in photocatalysis are reviewed. The challenges of single metal atom catalysts for both fundamental research and practical application are also discussed for future investigations.
With the intense interest in inorganic cesium lead halide perovskites and their nanostructures for optoelectronic applications, high-quality crystalline nanomaterials with controllable morphologies ...and growth directions are desirable. Here, we report a vapor-phase epitaxial growth of horizontal single-crystal CsPbX3 (X = Cl, Br, I) nanowires (NWs) and microwires (MWs) with controlled crystallographic orientations on the (001) plane of phlogopite and muscovite mica. Moreover, single NWs, Y-shaped branches, interconnected NW or MW networks with 6-fold symmetry, and, eventually, highly dense epitaxial network of CsPbBr3 with nearly continuous coverage were controllably obtained by varying the growth time. Detailed structural study revealed that the CsPbBr3 wires grow along the 001 directions and have the (100) facets exposed. The incommensurate heteroepitaxial lattice match between the CsPbBr3 and mica crystal structures and the growth mechanism of these horizontal wires due to asymmetric lattice mismatch were proposed. Furthermore, the photoluminescence waveguiding and good performance from the photodetector device fabricated with these CsPbBr3 networks demonstrated that these well-connected CsPbBr3 NWs could serve as straightforward platforms for fundamental studies and optoelectronic applications.
Developing high-efficiency and stable photocatalysts able to accomplish spontaneous overall water splitting, without using sacrificial agents, is the ultimate goal of photocatalytic solar–hydrogen ...production. Metal-free polymeric carbon nitride (CN) has emerged as a promising alternative for photocatalytic water splitting, owing to its excellent physicochemical properties. In the past decade, various strategies, including thermodynamic and kinetic modifications, have been employed to improve the photocatalytic activity of CN. Among these modification strategies, constructing heterojunctions has stimulated intensive research interest due to the enhanced efficiency of carrier separation, and hence the photocatalytic performance. This article reviews the recent progress of CN-based heterojunction photocatalysts for overall water splitting, highlighting the characteristics and fundamental design principles of different heterojunctions from the viewpoint of interfacial charge properties and energy band offsets. Finally, perspectives on the challenges and opportunities for developing advanced CN-based heterojunction photocatalysts are provided.
A series of Cu-doped ZnIn2S4 photocatalysts has been synthesized by a facile hydrothermal method, with the copper concentration varying from 0 wt% to 2.0 wt%. The physical and photophysical ...properties of these Cu-doped ZnIn2S4 photocatalysts were characterized by X-ray diffraction (XRD), photoluminescence spectroscopy (PL), scanning electron microscopy (SEM), and UV−visible diffuse reflectance spectroscopy (UV−vis). The diffuse reflectance and photoluminescence spectra of Cu-doped ZnIn2S4 shifted monotonically to longer wavelengths as the copper concentration increased from 0 wt% to 2.0 wt%, indicating that the optical properties of these photocatalysts greatly depended on the amount of Cu doped. Meanwhile, the layered structure of ZnIn2S4 would be destructed gradually by Cu doping. The photoactivity of ZnIn2S4 was enhanced when Cu2+ was doped into the crystal structure. The highest photocatalytic activity was observed on Cu (0.5 wt%)–doped ZnIn2S4, with the rate of hydrogen evolution to be 151.5 μmol/h under visible light irradiation (λ > 430 nm). On the basis of the calculated energy band positions and optical properties, the effect of copper as a dopant on the photocatalytic activity of Cu-ZnIn2S4 was studied.
Precursor types play crucial factors for synthesizing high-efficiency graphitic carbon nitrides (GCNs). Herein, biuret was employed as a new precursor to prepare a disordered nitrogen-defect-rich ...porous GCN (BCN). The crystallinity, structure and performance properties for BCN were explored by making systematic comparisons with other commonly available GCNs which were derived from conventional precursors under the identical conditions. Biuret could be the optimal choice for the preparation of high-performance GCN according to the reports so far. BCN not only possessed long-range atomic disordered structure, but also contained numerous nitrogen defects embedded into the in-planes of the disordered GCN networks, leading to extended visible-light absorption (absorption edge at 525 nm), improved separation of photoexcited charge carriers, and rich available reactive sites. The large surface area and high porosity of BCN also provided plenty of reactive sites. Consequently, ultrahigh photocatalytic H2 production and excellent O2 production performance were achieved for BCN, the AQY for H2 production achieved 45.5% at 420 nm, which was one of the highest values for GCN-based photocatalysts.
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•Graphitic carbon nitride was prepared by direct thermal polymerization of a kind of new precursor–biuret.•Biuret-derived graphitic carbon nitride (BCN) possessed disordered structure with nitrogen vacancies and cyano groups.•BCN behaved favorable visible-light absorption ability with the absorption edge at about 525 nm, the bandgap was 2.45 eV.•BCN behaved ultrahigh photocatalytic H2 production performance, and the AQY achieved 45.5% at 420 nm.
Solution-based ZnO nanorod arrays (NRAs) were modified with controlled N doping by an advanced ion implantation method, and were subsequently utilized as photoanodes for photoelectrochemical (PEC) ...water splitting under visible light irradiation. A gradient distribution of N dopants along the vertical direction of ZnO nanorods was realized. N doped ZnO NRAs displayed a markedly enhanced visible-light-driven PEC photocurrent density of ~160 μA/cm(2) at 1.1 V vs. saturated calomel electrode (SCE), which was about 2 orders of magnitude higher than pristine ZnO NRAs. The gradiently distributed N dopants not only extended the optical absorption edges to visible light region, but also introduced terraced band structure. As a consequence, N gradient-doped ZnO NRAs can not only utilize the visible light irradiation but also efficiently drive photo-induced electron and hole transfer via the terraced band structure. The superior potential of ion implantation technique for creating gradient dopants distribution in host semiconductors will provide novel insights into doped photoelectrode materials for solar water splitting.
Hydrogen storage is now the “bottle neck” to realize application of hydrogen as the renewable energy. The breakthrough in hydrogen storage is quite urgent. Magnesium is a promising candidate for ...hydrogen storage that attracts tremendous interest in last a few decades and significant progress has been made in recent years. Accordingly, in this article, we comprehensively reviewed different strategies to overcome the key barriers of high desorption temperature and low kinetics, especially on the recent approaches of nanosizing and interfacial confinement. We also try to give our own point of view on the future perspectives of research in Mg for hydrogen storage.
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