Double laminated reduced graphene/Cu_2S/reduced graphene/graphene oxide nanofilms and their photoelectrochemical properties

In this work, an efficient photocatalytic material was prepared directly on Indium tin oxide (ITO) glass substrates by fabricating Cu2S and graphene oxide onto graphene for photoelectrochemical (PEC) water splitting. The double laminated reduced graphene/Cu2S/reduced graphene/graphene oxide (RG/Cu2S/RG/GO) nanofilms were characterized, and an enhanced photoelectrochemical response in the visible region was discovered. The photocurrent density of the nanofilms for PEC water splitting was measured to be up to 1.98 mA/cm(2), which could be ascribed to the followings: (i) a higher efficiency of light-harvesting because of GO coupling with Cu2S that could broaden the absorbing solar spectrum and enhance the light utilization efficiency; (ii) a stepwise structure of band-edge levels in the Cu2S/GO electrode was constructed; (iii) double laminated electron accelerator (RG) was used in the Cu2S/GO materials to get better electron-injecting efficiency. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Formation and Photoelectrochemical Properties of Charge Transfer Complexes between Fullerene and Metallophthalocyanine

The formation of charge transfer complexes (CTC) between C-60 with metallophthalocyanine (MPc. M=Zn, Co) has been investigated in three mixed organic solvents. The MPc-C-60 CTC were characterized by using UV-Vis and fluorescence spectra. The formation equilibrium constants (K) of CTC and their stoichiometry were determined. The foundation of CTC leads to a remarkable enhancement of the photoelectrochemical property. The CTC will provide a potential opportunity to develop a new applicable photoelectric material.

Fabrication and research of bi-functional CuNi_(2)S_(4) nanosheets decorated TiO_(2)/CuNi_(2)S_(4) heterojunction photoanode for photoelectrochemical water splitting

As a traditional n-type semiconductor, TiO_(2)has good UV absorption ability and stable physical and chemical properties. However, its wide band gap and low oxygen evolution reaction(OER) activity limit its application in the field of photoelectrochemical(PEC) water splitting. In this work, a type-Ⅱ TiO2/CuNi2S4heterojunction photoanode is successfully constructed, which expanded the light absorption range to visible and enhanced the OER activity. Firstly, TiO2nanotubes(NTs) thin films are prepared on Ti substrates by two-step anodization, and then the bi-functional electrocatalytic material CuNi2S4is grown on TiO2NTs in the shape of nanosheets(NSs) in situ by solvothermal method. As a bi-functional electrocatalytic material, CuNi2S4has good visible light absorption property as well as OER catalytic activity. Compared with TiO_(2), the IPCE value of TiO_(2)/CuNi_(2)S_(4)is 2.59% at 635 nm, and that of TiO2is a mere 0.002%.The separation efficiency and injection efficiency increase from 2.49% and 31.52% to 3.61% and 87.77%, respectively. At 1.23 V vs. RHE, the maximum photocurrent density is 0.26 m A/cm^(2), which is 2.6 times than that of TiO2(0.11 m A/cm^(2)),and can be maintained at 0.25 m A/cm^(2)for at least 2 h under light illumination. Moreover, a hydrogen production rate of 4.21 μmol·cm^(-2)·h^(-1)is achieved within 2 h. This work provides a new idea for the application of TiO_(2)in the field of PEC water splitting and the construction of efficient and stable photoelectronic devices.

Preparation and performance of dye-sensitized solar cells based on ZnO-modified TiO_2 electrodes

The ZnO-modified TiO2 electrode was prepared by adding Zn（CH3COO）2·2H2O to the TiO2 colloid during the sol-gel production process, and was used in dye-sensitized solar cells （DSCs）. The open circuit voltage （Voc） and fill factor （if） of the cells were improved sig- nificantly. The performances of the ZnO-modified TiO2 electrode such as dark current, transient photocurrent, impedance, absorption spectra, and fiat band potential （Vfb） were investigated. It is found that the interface charge recombination impedance increases and Vfb shifts about 200 mV toward the cathodic potential. The effect mechanism of ZnO modification on the performance of DSCs may be that ZnO occupies the surface states of the TiO2 film.

The advanced multi-functional carbon dots in photoelectrochemistry based energy conversion

Carbon dots(CDs),as a unique zero-dimensional member of carbon materials,have attracted numerous attentions for their potential applications in optoelectronic,biological,and energy related fields.Recently,CDs as catalysts for energy conversion reactions under multi-physical conditions such as light and/or electricity have grown into a research frontier due to their advantages of high visible light utilization,fast migration of charge carriers,efficient surface redox reactions and good electrical conductivity.In this review,we summarize the fabrication methods of CDs and corresponding CD nanocomposites,including the strategies of surface modification and heteroatom doping.The properties of CDs that concerned to the photo-and electro-catalysis are highlighted and detailed corresponding applications are listed.More importantly,as new non-contact detection technologies,transient photo-induced voltage/current have been developed to detect and study the charge transfer kinetics,which can sensitively reflect the complex electron separation and transfer behavior in photo-/electro-catalysts.The development and application of the techniques are reviewed.Finally,we discuss and outline the major challenges and opportunities for future CD-based catalysts,and the needs and expectations for the development of novel characterization technologies.

The effect of complexing agent on crystal growth, structure and properties of nanostructured Cu_(2-x)S thin films

Thin films of Cu2 x S（x = 0, 1） were deposited on self-assembled, monolayer modified substrates in the copper–thiosulfate system with various concentrations of ethylene diamine tetraacetic acid（EDTA） at a low temperature of 70 8C. The thin films were characterized by means of X-ray diffraction（XRD）, X-ray photoelectron spectroscope（XPS）, field emission scanning electron microscopy（FESEM）, transmission electron microscopy（TEM）. The optical and photoelectrochemical（PEC） properties of the Cu2 x S semiconductor films were investigated by ultraviolet–visible（UV–vis） absorption spectroscopy and a three-electrode system. It is found that EDTA plays a key role in the process of Cu2 x S nanocrystals formation and growth. The compositions of the Cu2 x S nanocrystals varied from Cu2S（chalcocide） to Cu S（covellite） through adjusting the concentration of EDTA, which is used as a complexing agent to yield high-quality Cu2 x S films. The growth mechanisms of Cu2 x S nanocrystals with different EDTA concentrations are proposed and discussed in detail.

Improved growth rate of anodized TiO2 nanotube arrays under reduced pressure field and light illumination

The one-dimensional titanium oxide(TiO_2) nanotubes(TONT) can be rationally fabricated in the fluoridecontaining electrolyte by electrochemical anodization. The high-speed growth of TONT for elongated nanotubes is highly desirable because the undesirable chemical etching will induce ‘‘nanograss" on the top of nanotubes and restrain the continued elongation of nanotubes. Herein, the external fields were employed to accelerate the growth of TONTs and obtain the elongated TONT arrays. A growth rate up to 18 lm/h was achieved under the presence of reduced pressure(0.07 MPa) and UV light(365 nm) stimulation. The generation of longer nanotube arrays could be attributed to the applied fields, which facilitate timely gas pumping out and induce chemical equilibrium shift forward. The TONT films obtained under different parameters were subsequently employed as anodes for photoelectrochemical(PEC) water splitting. The photocurrent(at 0 V vs Ag/Ag Cl) of TONT electrode obtained under external fields represented a 50% enhancement compared with the photoanode produced by the conventional method.

High performance novel flexible perovskite solar cell based on a low-cost-processed ZnO:Co electron transport layer

In this work,high quality uniform and dense nanostructured cobalt-doped zinc oxide(ZnO:Co)films were used as electron-transport layers in CH3NH3Pbl3-based planar heterojunction perovskite solar cells(PSCs)on a flexible conductive substrate.Highly photo catalytically active ZnO:Co films were prepared by a low cost hydrothermal process using the aqueous solution of zinc nitrate hexahydrate,hexamethylenete-tramine and cobalt(II)nitrate hexahydrate.ZnO:Co films were deposited on indium tin oxide(ITO)covered polyethylene terephthalate(PET)flexible substrates.The growth was controlled by maintaining the autoclave temperature at 150℃for 4 h.The CH3NH3Pbl3 layer was deposited on the ZnO:Co films by spin coating.Spiro-OMeTAD was employed as a hole-transporting material.The structural,morphology and optical properties of the grown ZnO nanostructures were characterized by X-ray diffraction(XRD),field-emission scanning electron microcopy(FESEM),energy-dispersive X-ray spectrometry(EDX),ultraviolet-visible(UV-Vis)and photoelectrochemical propriety.XRD spectra showed that both ZnO and ZnO:Co nanorods had a hexagonal wurtzite structure with a strong preferred orientation along the(002)plane.The surface morphology of films was studied by FESEM and showed that both the pure and Co-doped ZnO films had hexagonal shaped nanorods.In the steady state,the ZnO electrode gave a photocurrent density of about 1.5 mA/cm2.However,the Co-doped ZnO electrode showed a photocurrent density of about 6 mA/cm^2,which is 4-fold higher than that of the ZnO electrode.Based on the above synthesized Co-doped ZnO films,the photovoltaic performance of PSCs was studied.The Co-doped ZnO layers had a significant impact on the photovoltaic conversion efficiency(PCE)of the PSCs.The latter was attributed to an efficient charge separation and transport due to the better coverage of perovskite on the nanostructured Co-doped ZnO films.As a result,the measured PCE under standard solar conditions(A M 1.5G,100 mW/cm^2)reached 7%.SCAPS-1D simulation was also performed to analyze the effect of the co-doped ZnO thin film on the corresponding solar cell performances.