Machine learning aided design of perovskite oxide materials for photocatalytic water splitting

Suffering from the inefficient traditional trial-and-error methods and the huge searching space filled by millions of candidates, discovering new perovskite visible photocatalysts with higher hydrogen production rate(RH_(2)) still remains a challenge in the field of photocatalytic water splitting(PWS). Herein, we established structural-property models targeted to RH_(2) and the proper bandgap(Eg) via machine learning(ML) technology to accelerate the discovery of efficient perovskite photocatalysts for PWS. The Pearson correlation coefficients(R) of leave-one-out cross validation(LOOCV) were adopted to compare the performances of different algorithms including gradient boosting regression(GBR), support vector regression(SVR), backpropagation artificial neural network(BPANN), and random forest(RF). It was found that the BPANN model showed the highest R values from LOOCV and testing data of 0.9897 and 0.9740 for RH_(2),while the GBR model had the best values of 0.9290 and 0.9207 for Eg. Furtherly, 14 potential PWS perovskite candidates were screened out from 30,000 ABO3-type perovskite structures under the criteria of structural stability, Eg, conduction band energy, valence band energy and RH_(2). The average RH_(2) of these14 perovskites is 6.4% higher than the highest value in the training data set. Moreover, the online web servers were developed to share our prediction models, which could be accessible in http://materialsdata-mining.com/ocpmdm/material_api/ahfga3d9puqlknig(E_g prediction) and http://materials-datamining.com/ocpmdm/material_api/i0 ucuyn3 wsd14940(RH_(2) prediction).

Engineering the Local Coordination Environment of Single-Atom Catalysts and Their Applications in Photocatalytic Water Splitting:A Review

Single-atom catalysts(SACs),with atomically dispersed metal atoms anchored on a typical support,representing the utmost utilization effi ciency of the atoms,have recently emerged as promising catalysts for a variety of catalytic applications.The electronic properties of the active center of SACs are highly dependent on the local environment constituted by the single metal atom and its surrounding coordination elements.Therefore,engineering the coordination environment near single metal sites,from the fi rst coordination shell to the second shell or higher,would be a rational way to design effi cient SACs with optimized electronic structure for catalytic applications.The wide range of coordination confi gurations,guaranteed by the multiple choices of the type and heterogeneity of the coordination element(N,O,P,S,etc.),further off er a large opportunity to rationally design SACs for satisfactory activities and investigate the structure-performance relationship.In this review,the coordination engineering of SACs by varying the type of coordination element was elaborated and the photocatalytic water splitting of SACs was highlighted.Finally,challenging issues related to the coordination engineering of SACs and their photocatalytic applications were discussed to call for more eff orts devoted to the further development of single-atom catalysis.

Enhanced photocatalytic water splitting with surface defective SrTiO_(3)nanocrystals

Surface reconstructed SrTiO_(3)nanocrystals were synthesized by a thermal treatment process in presence of NaBH_(4)and SrTiO_(3)nanocrystals.The surface reconstruction of SrTiO_(3)nanocrystals is attributed to the introduction of surface oxygen vacancies or Ti sites(such as Ti^(3+)and Ti^(2+))during the hydrogenation treatment process.The light absorption and the charge transfer ability of SrTiO_(3)nanocrystals are simultaneously enhanced due to surface oxygen vacancies or Ti sites(such as Ti^(3+)and Ti^(2+)),which are beneficial to photocatalytic water splitting.Meanwhile,these defects also change the redox potential of the photocatalysts.Since there existed a synergistic effect between the three,the ratio of hydrogen to oxygen production was also regulated.

Blue phosphorene/MoSi2N4 van der Waals type-Ⅱ heterostructure:Highly efficient bifunctional materials for photocatalytics and photovoltaics

Converting solar energy into electric power or hydrogen fuel is a promising means to obtain renewable green energy.Here, we design a two-dimensional blue phosphorene(BlueP)/MoSi2N4van der Waals heterostructure(vdWH) and investigate its potential application in photocatalysis and photovoltaics using first-principles calculations. We find that the BlueP/MoSi2N4vdWH possesses type-Ⅱ band structure with a large build-in electric field, thus endowing it with a potential ability to separate photogenerated electron–hole pairs. The calculated band-edge positions show that the heterostructure is a very promising water-splitting photocatalyst. Its solar-to-hydrogen efficiency(ηSTH) can reach up to 15.8%, which is quite promising for commercial applications. Furthermore, the BlueP/MoSi2N4vdWH shows remarkably light absorption capacity and distinguished maximum power conversion efficiency(ηPCE) up to 10.61%. Remarkably, its ηPCEcan be further enhanced by the external strain: the ηPCEof 21.20% can be obtained under a 4% tensile strain. Finally, we determine that adjusting the number of the BlueP sublayer is another effective method to modulate the band gaps and band alignments of the heterostructures. These theoretical findings indicate that BlueP/MoSi2N4vd WH is a promising candidate for photocatalyst and photovoltaic device.

Regulating photocatalytic overall water splitting of ferroelectric heterostructures by size effect

In the past decade,ferroelectric materials have been intensively explored as promising photocatalysts.An intriguing ability of ferroelectrics is to directly sperate the photogenerated electrons and holes,which is believed to arise from a spontaneous polarization.Understanding how polarization affects the photocatalytic performance is vital to design high-efficiency photocatalysts.In this work,we report a size effect of ferroelectric polarization on regulating the photocatalytic overall water splitting of SrTiO_(3)/PbTiO_(3)nanoplate heterostructures for the first time.This was realized hydrothermally by controlling the thickness and thus spontaneous polarization strength of single-crystal and single-domain PbTiO_(3)nanoplates,which served as the substrate for selective heteroepitaxial growth of SrTiO_(3).An enhancement of 22 times in the photocatalytic overall water splitting performance of the heterostructures has been achieved when the average thickness of the nanoplate increases from 30 to 107 nm.A combined experimental investigation revealed that the incompletely compensated depolarization filed is the dominated driving force for the photogenerated carrier separation within heterostructures,and its increase with the thickness of the nanoplates accounts for the enhancement of photocatalytic activity.Moreover,the concentration of oxygen vacancies for negative polarization compensation has been found to grow as the thickness of the nanoplates increases,which promotes oxygen evolution reaction and reduces the stoichiometric ratio of H_(2)/O_(2).These findings may provide the opportunity to design and develop high-efficiency ferroelectric photocatalysts.

Self-assembled synthesis of oxygen-doped g-C3N4 nanotubes in enhancement of visible-light photocatalytic hydrogen

Currently,photocatalytic water splitting is regarded as promising technology in renewable energy generation.However,the conversion efficiency suffers great restriction due to the rapid recombination of charge carriers.Rational designed the structure and doping elements become important alternative routes to improve the performance of photocatalyst.In this work,we rational designed oxygen-doped graphitic carbon nitride(OCN)nanotubes derived from supermolecular intermediates for photocata lytic water splitting.The as prepared OCN nanotubes exhibit an outstanding hydrogen evolution rate of 73.84μmol h^(-1),outperforming the most of reported one dimensional(1D)g-C_(3)N_(4) previously.Due to the rational oxygen doping,the band structure of g-C_(3)N_(4) is meliorated,which can narrow the band gap and reduce the recombination rate of photogene rated carriers.Furthermore,the hollow nanotube structure of OCN also provide multiple diffuse reflection during photocata lytic reaction,which can significantly promote the utilization capacity of visible light and enhance the photocatalytic water splitting performance.It is believed that our work not only rationally controls the nanostructure,but also introduces useful heteroatom into the matrix of photocatalyst,which provides an effective way to design high-efficiency g-C_(3)N_(4) photocatalyst.

Fluorination over Cr doped layered perovskite Sr_(2)TiO_(4) for efficient photocatalytic hydrogen production under visible light illumination

Cr doped Ruddlesden-Popper compound Sr2 TiO4 has been successfully modified by fluorine to form a new compound Sr2 Ti(0.95) Cr(0.05) O3 F2. Structure analysis suggests two types of fluorine in the structure of this new compound, i.e. intralayer and interlayer F, which induce strong built-in electric field within this layered compound. The electric field stems from uneven distribution of F atoms on the two sides of perovskite layers therefore leads to charge disproportionation. DFT calculations suggest that this unique structural feature is highly beneficial for charge dissociations as it breaks the coplanar settlement of conduction band minimum and valence band maximum whilst maintains the 2 D charge transportation properties. This is clearly demonstrated by the superior photocatalytic activities of Sr2 Ti(0.95) Cr(0.05) O3 F2 for hydrogen production from water. Apparent quantum efficiency(AQE) as high as 1.16% at 420 ± 20 nm has been achieved which stands as the highest AQE reported on Sr2 TiO4 to date. Photoelectrochemical(PEC)analysis confirms improved charge separation conditions and prolonged charge lifetime.

Simultaneously Effi cient Solar Light Harvesting and Charge Transfer of Hollow Octahedral Cu_(2)S/CdS p-n Heterostructures for Remarkable Photocatalytic Hydrogen Generation

Solar-driven water splitting is a promising alternative to industrial hydrogen production.This study reports an elaborate design and synthesis of the integration of cadmium sulfi de(CdS)quantum dots and cuprous sulfi de(Cu_(2)S)nanosheets as three-dimensional(3D)hollow octahedral Cu_(2)S/CdS p-n heterostructured architectures by a versatile template and one-pot sulfi dation strategy.3D hierarchical hollow nanostructures can strengthen multiple refl ections of solar light and provide a large specifi c surface area and abundant reaction sites for photocatalytic water splitting.Owing to the construction of the p-n heterostructure as an ideal catalytic model with highly matched band alignment at Cu_(2)S/CdS interfaces,the emerging internal electric fi eld can facilitate the space separation and transfer of photoexcited charges between CdS and Cu_(2)S and also enhance charge dynamics and prolong charge lifetimes.Notably,the unique hollow Cu_(2)S/CdS architectures deliver a largely enhanced visible-light-driven hydrogen generation rate of 4.76 mmol/(g·h),which is nearly 8.5 and 476 times larger than that of pristine CdS and Cu_(2)S catalysts,respectively.This work not only paves the way for the rational design and fabrication of hollow photocatalysts but also clarifi es the crucial role of unique heterostructure in photocatalysis for solar energy conversion.

Intrinsic Mechanisms of Morphological Engineering and Carbon Doping for Improved Photocatalysis of 2D/2D Carbon Nitride Van Der Waals Heterojunction

Van der Waals(VDW)heterojunctions in a 2D/2D contact provide the highest area for the separation and transfer of charge carriers.In this work,a top-down strategy with a gas erosion process was employed to fabricate a 2D/2D carbon nitride VDW heterojunction in carbon nitride(g-C_(3)N_(4))with carbon-rich carbon nitride.The created 2D semiconducting channel in the VDW structure exhibits enhanced electric field exposure and radiation absorption,which facilitates the separation of the charge carriers and their mobility.Consequently,compared with bulk g-C_(3)N_(4)and its nanosheets,the photocatalytic performance of the fabricated carbon nitride VDW heterojunction in the water splitting reaction to hydrogen is improved by 8.6 and 3.3 times,respectively,while maintaining satisfactory photo-stability.Mechanistically,the finite element method(FEM)was employed to evaluate and clarify the contributions of the formation of VDW heterojunction to enhanced photocatalysis,in agreement quantitatively with experimental ones.This study provides a new and effective strategy for the modification and more insights to performance improvement on polymeric semiconductors in photocatalysis and energy conversion.

Synthesis and application of transition metal phosphides as electrocatalyst for water splitting

With continuous research on photocatalytic water splitting, searching for efficient catalyst for hydrogen evolution reaction(HER) becomes popular topic in addition to main catalyst research. Transition metal phosphides are receiving intense attention due to its abundance in the Earth's crust and comparable catalytic properties to noble metals. In this review, the synthesis approaches, HER reaction mechanism,photocatalytic activity, approaches to improve the activity of transition metal phosphides were reviewed and discussed. It was showed that the transition metal phosphides have great potential to reduce the cost of photocatalyst and promising application on water splitting. The stability problem and participation of poisonous reactant and product in its synthesis reaction limit its application and developing in a certain extent, but with the continuous efforts on the development and improvement of the synthesis methods,transition metal phosphides will find wide application in water splitting.

Facile one-pot hydrothermal method to prepare Sn(Ⅱ) and N co-doped TiO_(2) photocatalyst for water splitting under visible light irradiation

In this paper,a visible light-responsive Sn^(2+)and N co-doped TiO_(2)photocatalyst was prepared by facile one-pot hydrothermal method.All as-prepared samples were characterized in detail by a series of characterization approaches.The results showed that the Sn^(2+)and N elements were co-doped into TiO_(2),while the catalyst still maintains anatase crystal structure and gets irregular little nanocluster in diameter of 9–10 nm with higher specific surface area.The absorption edge of Sn^(2+)and N co-doped TiO_(2)extends to the visible light region.Compared with Sn^(2+)-doped TiO_(2)and N-TiO_(2),the absorption edges have obvious red-shift of about 50 and 70 nm,respectively.The synergistic effect of O 2p-N 2p and O 2p-Sn 5s hybridization to form impurity levels is the main reason for the red-shift.The hydrogen production performance of the Sn^(2+)and N co-doping TiO_(2)(n(N)/n(Ti)=1)catalyst reached the maximum value of 0.37 mmol·h^(-1)·g^(-1)under visible light,which is higher than that of N-doped TiO_(2)and SnTiO_(2)-doped TiO_(2)singly.This result is due to the wider visible light region-responsive ability of Sn^(2+)and N codoped into TiO_(2).Furthermore,mild hydrothermal methods will not make the Sn^(2+)oxidized to Sn^(4+),which make the catalysts still maintain high photocatalytic performance.This work provides a simple and mild method for the preparation of dual-element co-doped TiO_(2)with high crystallinity,excellent performance and broad application prospects.

Halogen modified two-dimensional covalent triazine frameworks as visible-light driven photocatalysts for overall water splitting

The covalent triazine framework CTF-1 as a member of the two-dimensional covalent organic frameworks(COFs)is a category of novel metal-free photocatalysts for water splitting.The large band gap severely restricts its energy conversion efficiency.By means of the first-principles calculations,we proposed the decoration of CTF-1 by anchoring halogen atoms onto benzene moieties for improving the solar-to-hydrogen(STH)efficiency.The electronic structures reveal that the halogen substitution successfully decreases the band gap of CTF-1.Meanwhile,the calculated free energy changes along the reaction pathway indicate that all these COFs can spontaneously drive overall water splitting under light irradiation in a specific acid-base environment.The time-dependent ab initio non-adiabatic molecular dynamics simulations suggest that the electron-hole recombination periods of these COFs fall in a few to tens of nanoseconds.Excitingly,CTF-1 modified by linking six iodine atoms onto the benzene ring in the para-position(CTF-1-6I)shows a quite low band gap of 2.81 eV,indicating that it is a visible-light driven COF for overall photocatalytic water splitting.Correspondingly,CTF-1-6I also exhibits an extraordinarily promising STH efficiency of 3.70%,which is an order magnitude higher than that of the pristine CTF-1.

Nanoplasmonic zirconium nitride photocatalyst for direct overall water splitting

The ability of plasmonic nanostructures to efficiently harvest light energy and generate energetic hot carriers makes them promising materials for utilization in photocatalytic water spitting. Apart from the traditional Au and Ag based plasmonic photocatalysts, more recently the noble-metal-free alternative plasmonic materials have attracted ever-increasing interest. Here we report the first use of plasmonic zirconium nitride (ZrN) nanoparticles as a promising photocatalyst for water splitting. Highly crystalline ZrN nanoparticles with sizes dominating at 30-50 nm were synthesized that exhibit intense visible and near-infrared absorption due to localized surface plasmon resonance (LSPR). Without utilizing any noble metal cocatalysts such as Pt, the plasmonic ZrN nanoparticles alone showed stable photocatalytic activity for H_(2) evolution in aqueous solution with methanol as sacrificial electron donor. The addition of a cobalt oxide (CoO_(x)) cocatalyst can facilitate the separation of photogenerated charge carriers and further improve the photocatalytic activity. The optimized CoO_(x) modified ZrN photocatalyst was observed not only to activate the O_(2) evolution reaction with presence of electron acceptor, but also to drive overall water splitting for the simultaneous H_(2) and O_(2) evolution in the absence of any sacrificial agents.

Tailoring the surface and interface structures of photocatalysts to enhance hydrogen production

Photocatalytic water splitting using semiconductor photocatalysts is a promising approach for the production of carbon-neutral,sustainable and clean hydrogen fuel.However,the separation and transport of photoinduced carriers are generally considered to be rate-limiting steps,and their low efficiency remains a major challenge.Therefore,much effort has been devoted to developing new strategies in surface/interface engineering of photocatalysts to improve the dynamics of charge separation/transport.This feature article briefly summarizes recent advances in photocatalyst surface/interface engineering by our research group,which have been achieved through the design of various novel photocatalysts,including interfacial modulation,heterostructure construction,heteroatom doping,single atom and diatom sites.The article is divided into three parts:first,we briefly introduce the three key processes involved in solar water splitting and reveal relationships between the properties of nanostructural photocatalysts and the fundamentals of water splitting;second,we detail methods and strategies for surface and interfacial structures to improve the efficiency of the fundamental processes,especially charge separation;finally,we explore prospects for photocatalytic water splitting applications.This article provides a valuable resource and strategies for researchers currently working in the field of photocatalytic water splitting.

Multidimensional CdS nanowire/CdIn2S4 nanosheet heterostructure for photocatalytic and photoelectrochemical applications

Nanomaterial shapes can have profound effects on material properties, and therefore offer an efficient way to improve the performances of designed materials and devices. The rational fabrication of multidimensional architectures such as one dimensional （1D）-two dimensional （2D） hybrid nanomaterials can integrate the merits of individual components and provide enhanced functionality. However, it is still very challenging to fabricate 1D/2D architectures because of the different growth mechanisms of the nanostructures. Here, we present a new solvent- mediated, surface reaction-driven growth route for synthesis of CdS nanowire （NW）/CdIn2S4 nanosheet （NS） 1D/2D architectures. The as-obtained CdS NW/ CdIn2S4 NS structures exhibit much higher visible-light-responsive photocatalytic activities for water splitting than the individual components. The CdS NW/CdIn2S4 NS heterostructure was further fabricated into photoelectrodes, which achieved a considerable photocurrent density of 2.85 mA·cm^-2 at 0 V vs. the reversible hydrogen electrode （RHE） without use of any co-catalysts. This represents one of the best results from a CdS-based photoelectrochemical （PEC） cell. Both the multidimensional nature and type II band alignment of the 1D/2D CdS/CdIn2S4 heterostructure contribute to the enhanced photocatalyfic and photoelectrochemical activity. The present work not only provides a new strategy for designing multidimensional 1D/2D heterostructures, but also documents the development of highly efficient energy conversion catalysts.

Constructing CdSe QDs modified porous g-C_(3)N_(4)heterostructures for visible light photocatalytic hydrogen production

Constructing heterostructures with narrow-band-gap semiconductors is a promising strategy to extend light absorption range of graphitic carbon nitride(g-C_(3)N_(4))and simultaneously promote charge separation for its photocatalytic activity improvement.However,its highly localized electronic states of g-C_(3)N_(4)hinder photo-carrier migration through bulk towards heterostructure interfaces,resulting in low charge carrier separation efficiency of solid bulk g-C_(3)N_(4)-based heterostructures.Herein,porous g-C_(3)N_(4)(PCN)material with greatly shortened migration distance of photo-carriers from bulk to surface was used as an effective substrate to host Cd Se quantum dots to construct type II heterostructure of Cd Se/PCN for photocatalytic hydrogen production.The homogeneous modification of the Cd Se quantum dots throughout the whole bulk of PCN together with proper band alignments between Cd Se and PCN enables the effective separation of photo-generated charge carriers in the heterostructure.Consequently,the Cd Se/PCN heterostructure photocatalyst gives the greatly enhanced photocatalytic hydrogen production activity of192.3μmol h^(-1),which is 4.4 and 8.1 times that of Cd Se and PCN,respectively.This work provides a feasible strategy to construct carbon nitride-based heterostructure photocatalysts for boosting visible light driven water splitting performance.

Crystalline covalent triazine frameworks manipulated by aliphatic amine modulator

Crystallization is an unsolved challenge in the chemistry of covalent triazine frameworks(CTFs) due to the poorly controlled simultaneous polymerization and crystallization processes. Herein, the synthesis of crystalline CTFs via the introduction of aliphatic amine as a dynamic modulator is reported. By optimizing the amount of aliphatic amine, the crystallization process can be controlled in an open system, resulting in the synthesis of crystalline CTFs. These crystalline CTFs exhibit much better photocatalytic hydrogen evolution performance, with highly ordered CTF-1-C3 demonstrating superior performance(10 mmol g^(-1)h^(-1)) compared with most reported CTF-1. This approach also allows for the preparation of various crystalline CTFs.

SiP monolayers： New 2D structures of group IV-V compounds for visible-light photohydrolytic catalysts

Because of graphene and phosphorene, two-dimensional （2D） layered materials of group IV and group V elements arouse great interest. However, group IV-V monolayers have not received due attention. In this work, three types of SiP monolayers were computationally designed to explore their electronic structure and optical properties. Computations confirm the stability of these monolayers, which are all indirect-bandgap semiconductors with bandgaps in the range 1.38-2.21 eV. The bandgaps straddle the redox potentials of water at pH = 0, indicating the potential of the monolayers for use as water- splitting photocatalysts. The computed optical properties demonstrate that certain monolayers of SiP 2D materials axe absorbers of visible light and would serve as good candidates for optoelectronic devices.

二维Ⅲ族硫化物Janus多层结构的高效光解水特性:内建电场和空位缺陷效应（英文）

二维范德华材料被广泛用作光分解水催化剂,但其直接的能量转化效率有待提高.因此,寻找具有高效光解水催化特性的二维材料成为理论和实验研究的热点.本文从量子力学第一性原理出发,预言了一类具有高效光解水特性的光催化剂:二维Ⅲ族硫化物Janus多层结构InGaXY,M2XY和InGaX2(M=In/Ga;X,Y=S/Se/Te).理论计算表明,多层材料的内建电场不仅可以促进光生载流子的空间分离,而且可以有效地调控材料能带的位置,提高能量转化效率.Janus多层材料能量转化效率的理论上限可以达到38.5%,接近了理论极限值(47%).更重要的是,在InGaSSe双层引入Ga空位可以有效降低析氢和析氧反应的过电势,仅仅依靠光生载流子提供的电压就可以驱动光解水催化反应.该理论结果不仅预言了二维Ⅲ族硫化物Janus多层材料可以作为高效的光解水催化材料,而且为设计和寻找高效光催化材料提供了新思路.

Recent Progress in π-Conjugated Polymer-Inorganic Heterostructures for Photocatalysis

Polymer-inorganic(P-Ⅰ) soft-hard heterostructures & heterojunction photocatalysts,featured by large interfacial contact, efficient charge separation, broad light absorption and maximized redox capacity, have received great attention for their applications in energy conversion and environmental remediation. In this minireview, the classification and mechanism of P-Ⅰ heterojunctions, i.e., type-Ⅰ/Ⅱ, p-n, Z-scheme and S-scheme heterojunctions, and their preparation methods are firstly introduced. Next, the photocatalytic applications of P-Ⅰ heterojunctions, including water splitting, environmental remediation and carbon dioxide reduction, are extensively reviewed. Lastly,a brief summary and perspectives on ongoing challenges and opportunities to construct high performance P-Ⅰ soft-hard photocatalysts are intensively highlighted. We envision this review will provide a picture of the state-of-the-art achievements and promote the photocatalytic applications of P-Ⅰ heterostructures in energy conversion and environmental remediation.