Unassisted overall water splitting with a solar-to-hydrogen efficiency of over 10% by coupled lead halide perovskite photoelectrodes

Hydrogen is a promising future sustainable fuel candidate with boundless opportunities.Research into photoelectrochemical(PEC)water splitting based on a lead halide perovskite(LHP)has progressed significantly with the aim of more efficient solar hydrogen production.Herein,we unite a well-known photo-absorbing LHP with cost-effective water-splitting catalysts,and we introduce two types of monolithic LHP-based PEC devices that act as a photocathode and a photoanode for the hydrogen evolution reaction and oxygen evolution reaction,leading to efficient unbiased overall water splitting.Through the integration of these two monolithic LHP-based photoelectrodes,an unbiased solar-to-hydrogen conversion efficiency of 10.64%and a photocurrent density of 8.65 mA cm^(−2) are achieved.

Nanocarbon-Enhanced 2D Photoelectrodes:A New Paradigm in Photoelectrochemical Water Splitting

Solar-driven photoelectrochemical(PEC)water splitting systems are highly promising for converting solar energy into clean and sustainable chemical energy.In such PEC systems,an integrated photoelectrode incorporates a light harvester for absorbing solar energy,an interlayer for transporting photogenerated charge carriers,and a co-catalyst for triggering redox reactions.Thus,understanding the correlations between the intrinsic structural properties and functions of the photoelectrodes is crucial.Here we critically examine various 2D layered photoanodes/photocathodes,including graphitic carbon nitrides,transition metal dichalcogenides,layered double hydroxides,layered bismuth oxyhalide nanosheets,and MXenes,combined with advanced nanocarbons(carbon dots,carbon nanotubes,graphene,and graphdiyne)as co-catalysts to assemble integrated photoelectrodes for oxygen evolution/hydrogen evolution reactions.The fundamental principles of PEC water splitting and physicochemical properties of photoelectrodes and the associated catalytic reactions are analyzed.Elaborate strategies for the assembly of 2D photoelectrodes with nanocarbons to enhance the PEC performances are introduced.The mechanisms of interplay of 2D photoelectrodes and nanocarbon co-catalysts are further discussed.The challenges and opportunities in the field are identified to guide future research for maximizing the conversion efficiency of PEC water splitting.

Kinetics of photoelectrocatalytic degradation of endocrine disrupting chemicals using sulfur-doped TiO_2 /Ti photoelectrodes

In this study,sulfur-doped TiO2 /Ti photoelectrodes were prepared by anodization. The morphology, crystalline structure,composition of sulfur-doped TiO2 /Ti film and light absorption property were examined by SEM,XRD,XRF,XPS and UV/VIS respectively. Dimethyl phthalate( DMP) ,one kind of environmental disrupting chemicals( EDCs) ,was degraded by the optimized photoelectrodes. Power of xenon light,initial concentration of DMP,photoelectrocatalytic( PEC) area of photoelectrode and bias were investigated in the study on kinetics of PEC degradation of DMP. Hence,this study concluded that the optimum conditions were power of xenon light 150 W,initial concentration of DMP 1 mg/L,PEC area of sulfur-doped TiO2 /Ti photoelectrode 10 cm2,bias 1. 3 V in the PEC reaction system.

Physicochemical Characterization of Photoelectrodes of Ti/TiO₂Prepared by Thermal Oxidation of Titanium

The preparation and study of supported TiO2 for photocatalytic application in solar cell devices is a relevant research field. Thin films of TiO2 prepared on Ti by thermal oxidation in a wide range of temperatures (450°C - 900°C) were characterized by electrochemical impedance spectroscopy, potentiometry and amperometry. This material presents photoelectrochemical activity, which depends dramatically of the oxidation temperature and the exposition time at the studied temperatures. The flatband potential as well as the donor density and the resistance to the charge transfer were measured. All these parameters are temperature dependent, and the optimal values are observed on the photoelectrodes prepared at 750°C. This result is consistent with the photochemical response reported in the literature for thin films of Ti/TiO2 prepared under similar conditions.

Progress in designing effective photoelectrodes for solar water splitting

Photoelectrochemical(PEC)water splitting process is regarded as a promising route to generate hydrogen by solar energy and at the heart of PEC is efficient electrode design.Great progress has been achieved in the aspects of material design,cocatalyst study,and electrode fabrication over the past decades.However,some key challenges remain unsolved,including the most demanded conversion efficiency issue.As three critical steps,i.e.light harvesting,charge transfer and surface reaction of the PEC process,occur in a huge range of time scale(from10-12s to100s),how to manage these subsequent steps to facilitate the seamless cooperation between each step to realize efficient PEC process is essentially important.This review focuses on an integral consideration of the three key criteria based on the recent progress on high efficient and stable photoelectrode design in PEC.The basic principles and potential strategies are summarized.Moreover,the challenge and perspective are also discussed.

Enhanced photocatalytic degradation of methyl orange by CdS quantum dots sensitized platelike WO_3 photoelectrodes

CdS quantum dots sensitized platelike WO_3 photoelectrodes were successfully synthesized by a facile hydrothermal method and a modified chemical bath deposition(CBD) technique.To further improve the stability of the photoelectrodes in alkaline environment,the platelike WO_3 films were treated with TiCl_4 to form a nano-TiO_2 buffer layer on the WO_3 plate surface before loading CdSQDs.The resulting electrodes were characterized by using XRD,SEM,HR-TEM and UV-vis spectrum.The photocatalytic activity of the resulting electrodes was investigated by degradation of methyl orange(MO) in aqueous solution.The photoelectrochemical(PEC) property of the resulting electrodes was also characterized by the linear sweep voltammetry.The results of both the degradation of MO and photocurrent tests indicated that the as-prepared CdSQDs sensitized WO_3 platelike photoelectrodes exhibit a significant improvement in photocatalytic degradation and PEC activity under visible light irradiation,compared with unsupported CdSQDs electrodes.Significantly,coating the WO_3 plates with nano-TiO_2 obviously facilitate the charge separation and retards the charge-pair recombination,and results in a highest activity for QDsCdS/TiO_2/WO_3 photoelectrodes.

Metal chalcogenide-based photoelectrodes for photoelectrochemical water splitting

Photoelectrochemical water splitting(PEC-WS)is a promising technique for transforming solar energy into storable and environmentally friendly chemical energy.Designing semiconductor photoelectrodes with high light absorption capability,rapid e-/h+separation and transfer,and sufficient chemical stability is vital for developing an efficient PEC-WS system.Metal chalcogenides(MCs)have emerged as promising candidates for light absorbers because of their unique electrical and optical characteristics.In this review,we present recent developments in hydrogen generation via PEC-WS using MC-based photoelectrodes.First,we present a simple illustration of PEC-WS fundamentals.Second,the current performance of various metal(mono-,di-,and tri-)chalcogenide/semiconductor photoelectrodes in PEC-WS is summarized.Then,the charge transfer mechanism at the MC/semiconductor interface and the PEC-WS mechanism is thoroughly explained.Finally,we discuss future research perspectives toward developing efficient and stable MC/semiconductor photoelectrodes.

Controllable synthesis of CdS nanospheres photoelectrode for photoelectrochemical water splitting

CdS nanospheres were grown on indium tin oxide(ITO)substrate using a hydrothermal method.The crystal structure,morphology and electronic structure of the samples synthesized were characterized in detail.The results confirm that the crystallinity,size,crystal defects of the CdS nanospheres and the film thickness of CdS photoelectrodes can be tuned by varying the precursor Cd2+concentration.Combined with charge transfer dynamics analysis,it can be found that proper particle size and film thickness,as well as fewer defects,will result in better charge separation efficiency of the prepared CdS/ITO photoelectrodes,thereby exhibiting better photoelectrochemical performance for water splitting.The optimized CdS/ITO photoelectrode synthesized with a Cd2+concentration of 0.14 mol⋅L1 gave a photocurrent density of 5.10 mA⋅cm^(-2)at potential of 1.23 V versus the reversible hydrogen electrode(RHE),under a simulated solar illumination of 100 mW⋅cm^(-2).

Rational design on photoelectrodes and devices to boost photoelectrochemical performance of solar-driven water splitting: a mini review

As an eco-friendly,efficient,and low-cost technique,photoelectrochemical water splitting has attracted growing interest in the production of clean and sustainable hydrogen by the conversion of abundant solar energy.In the photoelectrochemical system,the photoelectrode plays a vital role in absorbing the energy of sunlight to trigger the water splitting process and the overall efficiency depends largely on the integration and design of photoelectrochemical devices.In recent years,the optimization of photoelectrodes and photoelectrochemical devices to achieve highly efficient hydrogen production has been extensively investigated.In this paper,a concise review of recent advances in the modification of nanostructured photoelectrodes and the design of photoelectrochemical devices is presented.Meanwhile,the general principles of structural and morphological factors in altering the photoelectrochemical performance of photoelectrodes are discussed.Furthermore,the performance indicators and first principles to describe the behaviors of charge carriers are analyzed,which will be of profound guiding significance to increasing the overall efficiency of the photoelectrochemical water splitting system.Finally,current challenges and prospects for an in-depth understanding of reaction mechanisms using advanced characterization technologies and potential strategies for developing novel photoelectrodes and advanced photoelectrochemical water splitting devices are demonstrated.

Efficient photoelectrodes based on two-dimensional transition metal dichalcogenides heterostructures:from design to construction

Hydrogen production by photoelectrochemical(PEC) water splitting converts the inexhaustible supply of solar radiation to storable H2 as clean energy and thus has received widespread attention.The efficiency of PEC water splitting is largely determined by the properties of the photoelectrodes.Two-dimensional(2 D) layered transition metal dichalcogenides(TMDs) are promising candidates for photoelectrodes due to their atomic layer thickness,tunable bandgap,large specific surface area,and high carrier mobility.Moreover,the construction of 2 D TMDs heterostructures provides freedom in material design,which facilitates the further improvement of PEC water splitting.This review begins by describing the mechanism of PEC water splitting and the advantages of 2 D TMDbased heterostructures for photo electrodes.Then,the design considerations of the heterostructures for enhanced PEC efficiency are comprehensively reviewed with a focus on material selection,band engineering,surface modification,and long-term durability.Finally,current challenges and future perspectives for the development of photoelectrodes based on 2 D TMDs heterostructures are addressed.

Graded bandgap semiconductor thin film photoelectrodes

<Abstract>A graded bandgap oxide semiconductor thin film electrode was designed in order to obtain a photoelec-trochemically stable photoelectrode, with wide absorption range. The graded bandgap Ti1-xVxO2 film electrode was prepared by heating the stacked layers of V/Ti in varying ratios, which were coated on the substrate by the sol-gel method using the starting solution with various V/Ti ratios. XPS result showed that the composition gradient was achieved for the film. The Ti1-xVxO2 film electrode was found to be photoelectrochemically stable. Its photovoltage was about 360 mV. Obvious visible light photoresponse was observed for the Ti1-xVxO2 film electrode. Compared with the pure TiO2 electrode, the photocurrent onset potential of the Ti1-xVxO2 film electrode was shifted positively, probably because the accumulation of vanadium at the electrode surface causes the recombination of the electrons and holes, and the lowest level of the conduction band of Ti1-xVxO2 is lower than that of TiO2. Impedance

Anodized metal oxide nanostructures for photoelectrochemical water splitting

Photoelectrochemical(PEC) water splitting offers the capability of harvesting, storing, and converting solar energy into clean and sustainable hydrogen energy. Metal oxides are appealing photoelectrode materials because of their easy manufacturing and relatively high stability. In particular, metal oxides prepared by electrochemical anodization are typical of ordered nanostructures, which are beneficial for light harvesting, charge transfer and transport, and the adsorption and desorption of reactive species due to their high specific surface area and rich channels. However, bare anodic oxides still suffer from low charge separation and sunlight absorption efficiencies. Accordingly, many strategies of modifying anodic oxides have been explored and investigated. In this review, we attempt to summarize the recent advances in the rational design and modifications of these oxides from processes before, during, and after anodization. Rational design strategies are thoroughly addressed for each part with an aim to boost overall PEC performance. The ongoing efforts and challenges for future development of practical PEC electrodes are also presented.

Preparation of TiO_2/Ti mesh photoelectrode and properties

An innovative photoelectrode, TiO_2/Ti mesh electrode, was prepared by anodisation. In anodisation, 0.5 mol/L H_2SO_4 was used as electrolytic solution, the current had been constantly 1A from the beginning of the oxidation until reaching a designed voltage. Results showed that the photocatalytic activity of electrode was better when the designed voltage was 160 V. The morphology and the crystalline texture of the TiO_2 film on mesh electrode were examined by scanning electronic microscopy and Raman spectroscopy respectively. The examination results indicated that the structure and properties of the film depended on anodisation rate, and the anatase was the dominant component under the controlled experimental conditions. Degradation of Rhodamine B in photocatalytic (PC) and photoelectrocatalytic (PEC) reaction was investigated.

TiO2 Nanoparticles Produced by Electric-Discharge-Nanofluid-Process as Photoelectrode of DSSC

Self-made TiO2 nanoparticles were used as photoelectrode material of dye sensitized solar cell. The TiO2 thin film coats through spreading nanoparticles evenly onto the ITO glass via self-made spin-heat platform, and then TiO2 thin film is soaked in the dye N-719 more than 12 h to prepare the photoelectrode device. The TiO2 nanoparticles produced by electric-discharge-nanofluid-process have premium anatase crystal property, and its diameter can be controlled within a range of 20-50 nm. The surface energy zeta potential of nanofluid is from -22 mV to -28.8 mV, it is a stable particle suspension in the deionized water. A trace of surfactant Triton X-100 put upon the surface of ITO glass can produce a uniform and dense TiO2 thin film and heating up the spin platform to 200 oC is able to eliminate mixed surfac-tant. Self-made TiO2 film presents excellent dye absorption performance and even doesn＇t need heat treatment procedure to enhance essential property. Results of energy analysis show the thicker film structure will increase the short-circuit current density that causes higher conversion efficiency. But, as the film structure is large and thick, both the open-circuit voltage and fill factor will decline gradually to lead bad efficiency of dye-sensitized solar cell.

Photoelectrocatalysis for high‐value‐added chemicals production

Photoelectrocatalysis(PEC)is a promising approach that can convert renewable solar energy into chemical energy,while most concern is concentrated on PEC water splitting to obtain high‐value‐added fuel—hydrogen.In practice,more economic benefits can be produced based on PEC technique,such as H_(2)O oxidative H_(2)O_(2) synthesis,organic selective oxidation,organic pollutants degradation and CO_(2) reduction.Although there are plenty of excellent reviews focusing on the PEC water splitting system,the production of various high‐value‐added chemicals in PEC systems has not been discussed synthetically.This Account will focus on the production process of various high‐value‐added chemicals through PEC technology.The photoelectrode design,reaction environment and working mechanisms of PEC systems are also discussed in detail.We believe that this comprehensive Account of the expanded application of photoelectrocatalysis can add an inestimable impetus to the follow‐up development of this technology.

Current trending and beyond for solar-driven water splitting reaction on WO_(3)photoanodes

This review shows the importance of WO_(3)photoanode as a potentially low-cost,efficient,stable,and photoactive material for light-driven water splitting.For such,this manuscript aims to review the most recent publications regarding the strategies to improve the phoelectroactivity of WO_(3)films for water oxidation.In addition,this review aims to graphically highlight and discuss the general trendings of the photocurrent density response and stability test of the recent outstanding studies in the literature for photoelectrochemical water splitting application.The strategies covered in this review will not only concern the WO_(3)morphology and crystal plane growth,but also the many arrangements possibilities to improve the WO_(3)efficiency for water photoelectrooxidation,such as defect engineering based on oxygen vacancies,doping,decorations,and homo and heterojunctions.All these strategies are compared by the photocurrent density results and by the stability of these photocatalysts.The best results in this sense were observed in cases where the use of heterojunction was applied together with a desired morphology and crystal plane of the WO_(3)photoanode.However,the modifications that caused a decrease in the photocurrent density reaching values that are even lower than the pure WO_(3)were also discussed.In this way,this review intends to improve the knowledge about the synthesis and design of WO_(3)photoanodes to further obtain an efficient photocatalyst to minimize the recombination losses or losses across the interfaces and improve the photoelectroactivity for water splitting in the large-scale application.

Enhancement in solar hydrogen generation efficiency using InGaN photoelectrode after surface roughening treatment with nano-sized Ni mask

A significant enhancement in solar hydrogen generation efficiency has been achieved by inductive coupled etching （ICP） surface roughening treatment using nano-sized nickel mask. As much as 7 times improvement of photocurrent is demonstrated in comparison with a planar one fabricated from the same parent wafer. Under identical illumination conditions in HBr solution, the incident photon conversion efficiency （IPCE） shows an enhancement with a factor of 3, which even exceed 54% at 400 nm wavelength. We believe the enhancement is attributed to several facts including improvement in absorption, reacting area, carder localization and carrier lifetime.

Visible Light Photoelectrocatalytic Degradation of Rhodamine B Using Ti/TiO2-NiO Photoanode

The method of Ti/TiO2-NiO photoelectrode prepared by using sol-gel method continued by calcination process was introduced. The prepared TiO2-NiO film was observed with XRD and TEM. The anatase-rutile TiO2 was mainly on the prepared TiO2-NiO composite surface electrode. In addition to NiO, the composite also formed NiTiO3 that increased with increasing calcination temperature. Photoelectrocatalytic degradation of Rhodamine B (RB) using this electrode was investigated, and anodic potential and pH were optimized. RB degradation was investigated under different conditions, and it showed that photoelectrocatalytic degradation could achieve efficient and complete mineralization of organic pollutant. Through comparison of the photoelectrocatalytic oxidation using the Ti/TiO2-NiO electrode operated by single photoanode with the Ti/TiO2-NiO electrode operated by several photoanode, it was found that the photoelectrocatalytic efficiency of that by series photoanodes was higher. Additionally, photoelectrocatalytic system was performed at the several different photoelectrodes, which verified the higher photocatalytic activity compared with the single photoelectrode.

Effect of Tantalum Doping on TiO₂Nanotube Arrays for Water-Splitting

This work is intended to define a new possible methodology for TiO2 doping through the use of electrochemical deposition of tantalum directly on the titanium nanotubes obtained by a previous galvanostatic anodization treatment in an ethylene glycol solution. This method does not seem to cause any influence on the nanotube structure, showing final products with news and interesting features with respect to the unmodified sample. Together with a decrease in the band gap and flat band potential of the TiO2 nanotubes, the tantalum doped specimen reports an increase of the photo conversion efficiency under UV light.