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1.
Artigo em Inglês | MEDLINE | ID: mdl-32067299

RESUMO

Atomic co-catalysts offer high potential to improve the photocatalytic performance, of which the preparation with earth-abundant elements is challenging. Here, a new molten salt method (MSM) is designed to prepare atomic Ni co-catalyst on widely studied TiO2 nanoparticles. The liquid environment and space confinement effect of the molten salt leads to atomic dispersion of Ni ions on TiO2 , while the strong polarizing force provided by the molten salt promotes formation of strong Ni-O bonds. Interestingly, Ni atoms are found to facilitate the formation of oxygen vacancies (OV) on TiO2 during the MSM process, which benefits the charge transfer and hydrogen evolution reaction. The synergy of atomic Ni co-catalyst and OV results in 4-time increase in H2 evolution rate compared to that of the Ni co-catalyst on TiO2 prepared by an impregnation method. This work provides a new strategy of controlling atomic co-catalyst together with defects for efficient photocatalytic water splitting.

2.
ACS Appl Mater Interfaces ; 12(5): 6651-6661, 2020 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-31918551

RESUMO

Perovskite solar cells (PSCs) have achieved unprecedented progress in terms of enhancement of power conversion efficiency (PCE). Nevertheless, device stability is still an obstacle to the commercialization of this emerging photovoltaic technology. Though strategies such as compositional management and ligand engineering have been reported to tackle this critical issue, these methods often have drawbacks such as compromised device performance. Herein, we propose an approach combining material dimensionality control and interfacial passivation by a post-device treatment via triethylenetetramine (TETA) vapor to enhance both efficiency and stability of Cs0.05FA0.79MA0.16PbI2.5Br0.5-based PSCs. Results of X-ray diffraction and scanning electron microscopy show the formation of low-dimensional perovskites at the interface between the perovskite film and the hole transporting layer after the TETA vapor treatment. Measurements of the energy level alignment and electrochemical properties by ultraviolet photoelectron spectroscopy and impedance spectra confirm the reduced density of trap states and improved interfacial charge transport. Consequently, TETA-based treatment significantly enhances both efficiency (from 17.07 to 18.03%) and stability (PCE retention from 73.4 to 88.9%) of the PSCs under >65% relative humidity for 1000 h compared to the controlled device without TETA treatment. Furthermore, the TETA vapor also shows an advantageous effect of dramatically improving the performance of PSC devices, which initially had poor performance (from 6.8 to 10.5%) through surface defect passivation.

3.
ChemSusChem ; 13(4): 811-818, 2020 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-31802649

RESUMO

Nickel-iron layered double hydroxide (NiFe LDH) is a promising oxygen evolution reaction (OER) electrocatalyst under alkaline conditions. Much research has been performed to understand the structure-activity relationship of NiFe LDH under OER conditions. However, the specific role of the Fe species remains unclear and under debate. Herein, based on DFT calculations, it was discovered that the edge Fe sites show higher activity towards OER than either the edge Ni sites or lattice sites. Therefore, a facile acid-etching method was proposed to controllably induce the formation of edge Fe sites in NiFe LDH, and the obtained sample exhibited higher OER activity. X-ray absorption near edge structure and extended X-ray absorption fine structure analyses further revealed that the interaction of the edge Fe species with Ni is believed to contribute to the enhancement of the OER performance. This work provides a new understanding of the structure-activity relationship in NiFe LDH and offers a facile method for the design of efficient electrocatalysts in an alkaline environment.

4.
Chem Soc Rev ; 49(2): 354-381, 2020 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-31859320

RESUMO

The power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) are already higher than those of other thin-film photovoltaic technologies, but the high-efficiency cells are based on complicated device architectures with multiple layers of coating. A promising strategy to commercialize this emerging technology is to simplify the device structure while simultaneously maintaining high-efficiency. Charge transport layers (CTLs) are generally indispensable for achieving high-performance PSCs, but the high cost and possibility of instability hinder the mass production of efficient, stable PSCs in a cost-effective manner. The ambipolar carrier transfer characteristic of perovskite materials makes it possible to fabricate efficient PSCs even in the absence of electron and/or hole transport layers. Encouragingly, the reported PCEs of CTL-free PSCs are already over 20%. However, it is still a mystery about why and how CTL-free devices can work efficiently. Here, we summarize the recent strategies developed to improve the performance of CTL-free PSCs, aiming at strengthening the comprehensive understanding of the fundamental carrier dynamics, heterojunction merits and device physics behind these mysteriously simple yet efficient devices. This review sheds light on identifying the limiting and determining factors in achieving high-efficiency CTL-free devices, and proposes some empirical charge transport models (e.g. p-type doping of perovskites for HTL-free PSCs, n-type doping of perovskites for ETL-free PSCs, constructing efficient p-n heterojunctions and/or homojunctions at one side/interface or employing perovskite single crystal-based lateral geometry for both HTL and ETL-free PSCs, etc.) that are useful to further improve device performance. In addition, an insightful perspective for the future design and commercial development of large-scale, efficient and stable optoelectronic devices by employing carbon electrodes is provided.

5.
ChemSusChem ; 2019 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-31793744

RESUMO

Functional separators have attracted much attention owing to their effectiveness in supporting the stable and safe operation of future ultrahigh-capacity electrodes, especially sulfur cathodes and metal anodes in rechargeable batteries. Among the functional materials for separator modification, two-dimensional (2 D) materials offer the unique advantages of intimate coverage, mechanical robustness, and rich surface chemistry. This Minireview summarizes up-to-date achievements in the development of 2 D material-functionalized separators to promote the application of sulfur cathodes and metal anodes. With a deep understanding of the roles of 2 D materials and their precise control in functionalizing separators, 2 D materials will find great opportunities in advancing high-energy-density rechargeable batteries.

6.
Adv Mater ; : e1904717, 2019 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-31814196

RESUMO

Photocatalytic and photoelectrochemical processes are two key systems in harvesting sunlight for energy and environmental applications. As both systems are employing photoactive semiconductors as the major active component, strategies have been formulated to improve the properties of the semiconductors for better performances. However, requirements to yield excellent performances are different in these two distinctive systems. Although there are universal strategies applicable to improve the performance of photoactive semiconductors, similarities and differences exist when the semiconductors are to be used differently. Here, considerations on selected typical factors governing the performances in photocatalytic and photoelectrochemical systems, even though the same type of semiconductor is used, are provided. Understanding of the underlying mechanisms in relation to their photoactivities is of fundamental importance for rational design of high-performing photoactive materials, which may serve as a general guideline for the fabrication of good photocatalysts or photoelectrodes toward sustainable solar fuel generation.

7.
ACS Appl Mater Interfaces ; 11(39): 35641-35652, 2019 Oct 02.
Artigo em Inglês | MEDLINE | ID: mdl-31532199

RESUMO

Triiodide/iodide (I3-/I-) redox couple-mediated solar cells, batteries, and electrochromic devices require highly efficient and stable electrocatalysts for I3- reduction reaction (IRR) to overcome performance limitations, whereas the widely used platinum (Pt) cathode for IRR has limitations of high price and unfavorable durability. In this work, we present a halogen element (chlorine) doping strategy to design low-cost perovskite-type electrocatalysts with enhanced IRR activity and stability. The dye-sensitized solar cell (DSSC) assembled by the LaFeO2.965-δCl0.035 cathode delivers an attractive power conversion efficiency (PCE) of 11.4% with a remarkable PCE enhancement factor of 23% compared with Pt, which is higher than most of the reported non-Pt DSSC cathodes. Attractively, LaFeO2.965-δCl0.035 displays superior IRR activity/stability and structural stability in the I3-/I--based electrolyte compared to pristine LaFeO3 because chlorine doping facilitates the creation of oxygen vacancies (active sites) and enhances surface acidity simultaneously. This study provides a new way for designing outstanding IRR electrocatalysts, which could be applied to many redox couple-mediated photo/electrochemical devices.

8.
Angew Chem Int Ed Engl ; 58(49): 17604-17609, 2019 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-31560406

RESUMO

Metal oxides are an important family of semiconductors for effective photoelectrodes in solar-to-chemical energy conversion. Defect engineering, such as modification of oxygen vacancy density, has been extensively applied in tailoring the optoelectric properties of photoelectrodes. Very limited attention has been paid to the influence of metal vacancies. Herein, we study metal vacancies in a typical CuO photocathode for photoelectrochemical (PEC) water splitting. The Cu vacancies can improve the charge carrier concentration, and facilitate the charge separation and transfer in the CuO photocathode. By changing the O2 partial pressure, the density of Cu vacancies can be tuned, which leads to improved PEC performance. The CuO photocathode prepared in pure O2 exhibits a 100 % photocurrent increase compared to that prepared in air. The promotion effect of Cu vacancies on the PEC is also observed in other Cu based photocathodes, showing the generic role of metal vacancies in efficient photocathodes.

9.
ACS Appl Mater Interfaces ; 11(41): 37850-37858, 2019 Oct 16.
Artigo em Inglês | MEDLINE | ID: mdl-31552729

RESUMO

Herein, a metal-organic framework (MOF)/polythiophene (PTh)-derived S-doped carbon is successfully designed and prepared employing zeolitic imidazolate frameworks (ZIF-8/ZIF-67) and thiophene (Th) as precursors. The S-doped carbon presents a neuronlike three-dimensional network structure (3DSC). The 3DSC delivers extra-high capacities (225 mAh/g at 5000 mA/g after 3000 cycles) and excellent endurance ability of current changes when applied in Na-ion batteries (SIBs). Moreover, when the 3DSC-700 anode is coupled with a sodium vanadium phosphate cathode to construct a Na-ion full cell, after 50 cycles, a high capacity of ∼229.64 mAh/g is obtained at 100 mA/g. Electrochemical impedance spectroscopy analysis, density functional theory calculations, and pseudocapacitance contributions are adopted to investigate the excellent sodium storage mechanism of the 3DSC electrode. A new idea has been provided in this work to open up the possibility of MOF materials and carbon-based materials applications in SIBs in the future.

10.
ACS Appl Mater Interfaces ; 11(32): 29004-29013, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31314495

RESUMO

Crystal facet engineering has been proved as a versatile approach in modulating the photocatalytic activity of semiconductors. However, the facet-dependent properties and underlying mechanisms of spinel ZnFe2O4 in photocatalysis still have rarely been explored. Herein, ZnFe2O4 nanoparticles with different {001} and {111} facets exposed were successfully synthesized via a facile hydrothermal method. Facet-dependent photocatalytic degradation performance toward gaseous toluene under visible light irradiation was observed, where truncated octahedral ZnFe2O4 (ZFO(T)) nanoparticles with both {001} and {111} facets exposed exhibited a superior performance than the others. The formed surface facet junction between {010} and {100} facets was responsible for the improved activity by separating photogenerated e-/h+ pairs efficiently to reduce their recombination rate. Photogenerated electrons and holes were demonstrated to be immigrated onto {001} and {111} facets, separately. Intriguingly, electron paramagnetic resonance trapping results indicated that both •O2- and •OH were abundantly present in the ZFO(T) sample under visible light irradiation as major reactive oxygen species involved in the photocatalytic degradation process. Additionally, further investigation revealed that {001} facets played a predominant role in activating photogenerated transient species H2O2 into •OH, beneficially boosting the intrinsic photocatalytic activity. This work has not only presented a promising strategy in regulating photocatalytic performance through the synergetic effect of facet junction and specific facet activation but also broadened the application of facet engineering with multiple effects simultaneously cooperating.

11.
ACS Appl Mater Interfaces ; 11(21): 19638-19646, 2019 May 29.
Artigo em Inglês | MEDLINE | ID: mdl-31094504

RESUMO

The high-efficiency photocarrier collection at the interfaces plays an important role in improving the performance of perovskite solar cells (PSCs) because the photocarrier effective diffusion lengths in the lead halide perovskite absorbers usually surpass the incident depths of light. Developing the electron selective layer (ESL) that has good interfaces with photoactive perovskite and current collector layer-like fluorine-doped tin oxide (FTO) is actively pursued. Here, an unusual dense film of faceted rutile TiO2 single crystals with a gradient of the Sn4+ dopant grown heteroepitaxially on the FTO layer is obtained by a hydrothermal route and subsequent thermal treatment. Owing to the global features including low concentration of defects, atomically smooth coherent interface with FTO, and gradient doping-induced built-in electric field to promote the collection of photoelectrons in it, an optimal PSC with such a film as the ESL exhibits an efficiency of 17.2% with an open-circuit voltage of 1.1 V and fill factor of 76.1%, which are among the highest values of the PSCs with rutile TiO2 films as ESLs.

12.
Chem Rev ; 119(8): 5192-5247, 2019 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-30875200

RESUMO

Photoelectrochemical (PEC) water splitting is a promising approach for solar-driven hydrogen production with zero emissions, and it has been intensively studied over the past decades. However, the solar-to-hydrogen (STH) efficiencies of the current PEC systems are still far from the 10% target needed for practical application. The development of efficient photoelectrodes in PEC systems holds the key to achieving high STH efficiencies. In recent years, crystal facet engineering has emerged as an important strategy in designing efficient photoelectrodes for PEC water splitting, which has yet to be comprehensively reviewed and is the main focus of this article. After the Introduction, the second section of this review concisely introduces the mechanisms of crystal facet engineering. The subsequent section provides a snapshot of the unique facet-dependent properties of some semiconductor crystals including surface electronic structures, redox reaction sites, surface built-in electric fields, molecular adsorption, photoreaction activity, photocorrosion resistance, and electrical conductivity. Then, the methods for fabricating photoelectrodes with faceted semiconductor crystals are reviewed, with a focus on the preparation processes. In addition, the notable advantages of the crystal facet engineering of photoelectrodes in terms of light harvesting, charge separation and transfer, and surface reactions are critically discussed. This is followed by a systematic overview of the modification strategies of faceted photoelectrodes to further enhance the PEC performance. The last section summarizes the major challenges and some invigorating perspectives for future research on crystal facet engineered photoelectrodes, which are believed to play a vital role in promoting the development of this important research field.

13.
Small ; 15(16): e1900606, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30913374

RESUMO

Ordered 1D metal oxide structure is desirable in thin film solar cells owing to its excellent charge collection capability. However, the electron transfer in 1D electron transporting layer (ETL)-based devices is still limited to a submicrometer-long pathway that is vertical to the substrate. Here, an innovative closely packed rutile TiO2 nanowire (CRTNW) network parallel to the facet of fluorine-doped tin oxide (FTO) substrate is reported, which can serve as a 1D nanoscale electron transport pathway for efficient perovskite solar cells (PSCs). The PSC constructed using newly prepared CRTNW ETL achieves an impressive power conversion efficiency of 21.10%, which can be attributed to the facilitated electron extraction induced by the favorable junctions formed at FTO/ETL and ETL/perovskite interfaces and also the suppressed charge recombination originating from improved perovskite morphology with large grains, flat surface, and good surface coverage. The bifacial contact junctions engineering also enables large-area device fabrication. The PSC with 1 cm2 aperture yields an efficiency of 19.50% under one sun illumination. This work highlights the significance of controlling the orientation and packing density of the ordered 1D oxide nanostructured thin films for highly efficient optoelectronic devices in a large-scale manner.

14.
Angew Chem Int Ed Engl ; 58(14): 4587-4591, 2019 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-30734453

RESUMO

Water adsorption capacity is a key factor to influence the photocatalytic H2 evolution activity of polymeric g-C3 N4 . Herein, we report the synthesis of 3D ordered close-packed g-C3 N4 nanosphere arrays (CNAs) that significantly enhance the water adsorption capacity. Through precisely controlling the average stacking-layer number (ASLN) of the nanospheres in CNAs, we reveal an interesting stacking-layer-number dependence of water adsorption in the newly designed CNAs for accelerating the H2 evolution reaction, which can be attributed to the differences in adsorption surface areas and adsorption sites endowed by the point-defect cavities in sample CNAs.

15.
Small ; 15(29): e1804578, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-30680923

RESUMO

To realize practical lithium-sulfur batteries (LSBs) with long cycling life, designing cathode hosts with a high specific surface area (SSA) is recognized as an efficient way to trap the soluble polysulfides. However, it is also blamed for diminishing the volumetric energy density and being susceptible to side reactions. Herein, polyethylenimine intercalated graphite oxide (PEI-GO) with a low SSA of 4.6 m2 g-1 and enlarged interlayer spacing of 13 Å is proposed as a superior sulfur host, which enables homogeneous distribution of high sulfur content (73%) and facilitates Li+ transfer in thick sulfur electrode. LSBs with a moderate sulfur loading (3.4 mg S cm-2 ) achieve an initial capacity of 1157 and 668 mAh g-1 after 500 cycles at 0.5 C. Even when the sulfur loading is increased to 7.3 mg cm-2 , the electrode still delivers a high areal capacity of 4.7 mAh cm-2 (641 mAh g-1 ) after 200 cycles at 0.2 C. The excellent electrochemical properties of PEI-GO are mainly attributed to the homogeneous distribution of sulfur in PEI-GO and the strong chemical interactions between polysulfides and amine groups, which can mitigate the loss of active phases and contribute to the better cycling stability.

16.
Sci Rep ; 9(1): 718, 2019 Jan 24.
Artigo em Inglês | MEDLINE | ID: mdl-30679678

RESUMO

Developing of lead-free double perovskites have drawn significant interest for photovoltaics and optoelectronics as the materials have the potential to avoid toxicity and instability issues associated with lead-based organometallic perovskites. In this study, we report the optoelectronic properties of a new group of non-toxic lead-free organic-inorganic halide double perovskites composed of caesium (Cs), methylammonium (MA) or formamidinium (FA) with bismuth (Bi) and metal copper (Cu). We perform density functional theory investigations to calculate the structural, electronic and optical properties of 18 Pb-free compounds, ABiCuX6 [A = Cs2, (MA)2, (FA)2, CsMA, CsFA, MAFA; X = I, Br, Cl] to predict their suitability in photovoltaic and optoelectronic applications. We found that the considered compounds are semiconductors with a tunable band gap characteristics that are suitable for some devices like light emitting diodes. In addition to this, the high dielectric constant, high absorption, high optical conductivity and low reflectivity suggest that the materials have the potential in a wide range of optoelectronic applications including solar cells. Furthermore, we predict that the organic-inorganic hybrid double perovskite (FA)2BiCuI6 is the best candidate in photovoltaic and optoelectronic applications as the material has superior optical and electronic properties.

17.
Adv Mater ; 31(13): e1805367, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30648293

RESUMO

The electrocatalytic nitrogen reduction reaction (NRR) is a promising catalytic system for N2 fixation in ambient conditions. Currently, metal-based catalysts are the most widely studied catalysts for electrocatalytic NRR. Unfortunately, the low selectivity and poor resistance to acids and bases, and the low Faradaic efficiency, production rate, and stability of metal-based catalysts for NRR make them uncompetitive for the synthesis of ammonia in comparison to the industrial Haber-Bosch process. Inspired by applications of carbon-based metal-free catalysts (CMFCs) for the oxygen reduction reaction (ORR) and CO2 reduction reaction (CO2 RR), the studies of these CMFCs in electrocatalytic NRR have attracted great attention in the past year. However, due to the differences in electrocatalytic NRR, there are several critical issues that need to be addressed in order to achieve rational design of advanced carbon-based metal-free electrocatalysts to improve activity, selectivity, and stability for NRR. Herein, the recent developments in the field of carbon-based metal-free NRR catalysts are presented, along with critical issues, challenges, and perspectives concerning metal-free catalysts for electrocatalytic reduction of nitrogen for synthesis of ammonia at ambient conditions.


Assuntos
Amônia/síntese química , Carbono/química , Nanoestruturas/química , Nitrogênio/química , Catálise , Técnicas de Química Sintética/métodos , Técnicas Eletroquímicas/métodos , Modelos Moleculares , Oxirredução , Temperatura Ambiente
18.
Adv Mater ; 31(38): e1801369, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-30125390

RESUMO

Photocatalysis for solar-driven reactions promises a bright future in addressing energy and environmental challenges. The performance of photocatalysis is highly dependent on the design of photocatalysts, which can be rationally tailored to achieve efficient light harvesting, promoted charge separation and transport, and accelerated surface reactions. Due to its unique feature, semiconductors with hollow structure offer many advantages in photocatalyst design including improved light scattering and harvesting, reduced distance for charge migration and directed charge separation, and abundant surface reactive sites of the shells. Herein, the relationship between hollow nanostructures and their photocatalytic performance are discussed. The advantages of hollow nanostructures are summarized as: 1) enhancement in the light harvesting through light scattering and slow photon effects; 2) suppression of charge recombination by reducing charge transfer distance and directing separation of charge carriers; and 3) acceleration of the surface reactions by increasing accessible surface areas for separating the redox reactions spatially. Toward the end of the review, some insights into the key challenges and perspectives of hollow structured photocatalysts are also discussed, with a good hope to shed light on further promoting the rapid progress of this dynamic research field.

19.
Chemistry ; 25(7): 1787-1794, 2019 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-30489669

RESUMO

The strong band-to-band absorption of photocatalysts spanning the whole visible-light region (400-700 nm) is critically important for solar-driven photocatalysis. Although it has been actively and widely used as a photocatalyst for various reactions in the past four decades, TiO2 has a very poor ability to capture the whole spectrum of visible light. In this work, by controlling the spatially homogeneous distribution of boron and nitrogen heteroatoms in anatase TiO2 microspheres with a predominance of high-energy {001} facets, a strong visible-light absorption spectrum with a sharp edge beyond 680 nm has been achieved. The red TiO2 obtained with homogeneous doping of boron and nitrogen shows no increase in defects like Ti3+ that are commonly observed in doped TiO2 . More importantly, it has the ability to induce photocatalytic water oxidation to produce oxygen under the irradiation of visible light beyond 550 nm and also the photocatalytic reduction of water to produce hydrogen under visible light. These results demonstrate the great promise of using red TiO2 for visible-light photocatalytic water splitting and also reveal an attractive strategy for realizing the wide-spectrum visible-light absorption of wide-band-gap oxide photocatalysts.

20.
Angew Chem Int Ed Engl ; 58(4): 1030-1034, 2019 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-30417505

RESUMO

Oxygen vacancy (VO ) engineering is an effective method to tune the photoelectrochemical (PEC) performance, but the influence of VO on photoelectrodes is not well understood. Using hematite as a prototype, we herein report that VO functions in a more complicated way in PEC process than previously reported. Through a comprehensive analysis of the key charge transfer and surface reaction steps in PEC processes on a hematite photoanode, we clarify that VO can facilitate surface electrocatalytic processes while leading to severe interfacial recombination at the semiconductor/electrolyte (S-E) interface, in addition to the well-reported improvements in bulk conductivity. The improved bulk conductivity and surface catalysis are beneficial for bulk charge transfer and surface charge consumption while interfacial charge transfer deteriorates because of recombination through VO -induced trap states at the S-E interface.

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