Query: Atomic-Level Charge Separation Strategies in Semiconductor-Based Photocatalysts

Candidate papers:

abstract: Semiconductor based photocatalysis as a productive technology furnishes a prospective solution to environmental and renewable energy issues, but its efficiency greatly relies on the effective bulk and surface separation of photoexcited charge carriers. Exploitation of atomic level strategies allows in depth understanding on the related mechanisms and enables bottom up precise design of photocatalysts, significantly enhancing photocatalytic activity. Herein, the advances on atomic level charge separation strategies toward developing robust photocatalysts are highlighted, elucidating the fundamentals of charge separation and transfer processes and advanced probing techniques. The atomic level bulk charge separation strategies, embodied by regulation of charge movement pathway and migration dynamic, boil down to shortening the charge diffusion distance to the atomic scale, establishing atomic level charge transfer channels, and enhancing the charge separation driving force. Meanwhile, regulating the in plane surface structure and spatial surface structure are summarized as atomic level surface charge separation strategies. Moreover, collaborative strategies for simultaneous manipulation of bulk and surface photocharges are also introduced. Finally, the existing challenges and future prospects for fabrication of state of the art photocatalysts are discussed on the basis of a thorough comprehension of atomic level charge separation strategies.
author_names: Fei Chen

Tianyi Ma

Tierui Zhang

Yihe Zhang

Hong-wei Huang
title: Atomic Level Charge Separation Strategies in Semiconductor Based Photocatalysts.
venue: Advanced materials
year: 2021

abstract: The status of photocatalytic (PC)/photoelectrochemical (PEC) water splitting as a promising approach to solar to chemical energy conversion has increased significantly over the past several decades for addressing the energy shortage. However, the overall energy conversion efficiency is still relatively poor due to the severe photocorrosion in photosensitive semiconductors. Herein, the review begins with the discussion of the photocorrosion mechanism with several typical semiconductors as examples. Then the feasible characterization methods used to evaluate the stability of semiconductors are summarized. Notably, most studies regarding water splitting focus on achieving high efficiency by improving the charge separation and transfer efficiency within the semiconductors. This review focuses on the recent advances in effective strategies for photocorrosion inhibition of semiconductor based composites with respect to their intrinsic properties and interface charge transfer kinetics, including morphology/size control, heteroatom doping, heterojunction construction, surface modification, and reaction environment regulation. Furthermore, an in depth investigation of photocorrosion pathways and mechanisms is critical to accurately and effectively address the photocorrosion of semiconductor based composites to improve PC/PEC water splitting performance in the future.
author_names: Shan Chen

Danlian Huang

Piao Xu

Wen-jing Xue

Lei Lei

Min Cheng

Rongzhong Wang

Xigui Liu

Rui Deng
title: Semiconductor based photocatalysts for photocatalytic and photoelectrochemical water splitting: will we stop with photocorrosion?
year: 2020

abstract: The efficiencies of photocatalytic solar energy conversion systems are significantly limited by the challenging charge separation process, which can be improved via some commonly used interfacial modulating strategies, e.g. introducing heterojunctions at the interfaces of different semiconductors. However, in many cases, the constructed heterojunctions not always work well mainly due to the serious mismatching of surface and energy structures between different components. In this study, inspired by the similarities in crystalline structures and elemental compositions, a novel heterojunction photocatalyst with hierarchical structure was first fabricated between bismuth based semiconductors (Bi2Ti2O2 and gamma Bi2O3) possessing identical cubic phase via a simple insitu transformation method. The resulted Bi2Ti2O7/gamma Bi2O3 heterojunction photocatalyst (denoted as BT/gamma Bi2O3) shows extremely high photocatalytic activities in photocatalytic removal of various high concentration environmental pollutants, e.g. phenol, dyes and sulfur containing compounds. An enhancement of more than two orders of magnitude in photocatalytic performances can be achieved for the BT/gamma Bi2O3 photocatalyst than the single composite, which is possibly attributable to the co sharing of Bi O tetrahedra units for the composites in heterojunction structures to provide an atomic charge transferring pathway for facilitating the spatial charge separation. This work provides an effective strategy for rationally constructing charge separation and transfer pathway in semiconductor based photocatalysts for solar energy conversion.
title: In situ fabrication of atomic charge transferring path for constructing heterojunction photocatalysts with hierarchical structure
venue: Applied Catalysis B: Environmental
year: 2019

abstract: Spatial separation of photogenerated charges is one of the most critical factors in photocatalysis. Recently, we reported that the spatial charge separation can take place between different facets of semiconductor based photocatalysts (BiVO4, Cu2O, SrTiO3 etc. which is a unique strategy for charge separation differing from the "junction" strategy. Following these findings, we rationally constructed the reduction and oxidation cocatalysts on the different facets of photocatalysts and the photocatalytic activity was found to be greatly enhanced. Spatial charge separation between different facets has been demonstrating to be a general strategy for constructing efficient photocatalyst systems for solar energy conversion.
author_names: Rengui Li

Can Li
title: Spatial Charge Separation on Semiconductor based Photocatalysts for Photocatalytic Water Splitting
year: 2017

abstract: Abstract Metal sulfide based photocatalysts have been investigated intensively over the past two decades. This class of materials offers tunable composition and morphological diversity, which lead to adjustable band structure for visible light absorption, heterostructure for enhanced charge separation and transportation, and active site for surface reactions. In this chapter, the progress made in our laboratory on developing metal sulfide based photocatalysts for H2 evolution under visible light irradiation is reviewed. Our work has been focused on the development of CdS and ZnxCd1 xS systems as the base semiconductor, and NiS and MoS3 as the cocatalysts. Various strategies including doping, forming composites, surface engineering, and support effect have been adopted to achieve high photocatalytic efficiency.
author_names: Wen-xin Zhang

Yabo Wang

Rong Xu
title: Development of metal sulfide based photocatalysts for hydrogen evolution under visible light
year: 2020

abstract: It is well known that photogenerated charge separation is the key and bottleneck step to determine the solar energy efficiency in photocatalysis. Although strategies for facilitating spatial charge separation of semiconductor based photocatalysts like heterojunctions, especially for heterophase junctions have been recognized as useful and adequate approaches, the original morphology tailored structures are always challenging to be maintained during the thermal induced phase transformation process. Herein, using a facile self templated method, we successfully fabricate heterophase junction into the well defined hierarchical porous structure of visible light responsive semiconductor, bismuth oxide (Bi2O3) without destroying the its unique hierarchical porous morphology. Such organic integration of heterophase junction and hierarchical porous structure are demonstrated to enable highly efficient separation of photogenerated electrons and holes, resulting in a remarkable enhancement in photocatalytic activities. Our work showcases a general concept for developing artificial photocatalyst systems via integrating efficient charge separation path into the unique morphology tailoring of semiconductors for highly efficient solar energy conversion.
author_names: Xun Zhang

Chun Ping Li

Junmei Liang

Jiangfei Wang

Jing Zhang

Xuebing Chen

Fangfang Wang

Rengui Li
title: Self templated Constructing of Heterophase Junction into Hierarchical Porous Structure of Semiconductors for Promoting Photogenerated Charge Separation
year: 2020

abstract: Abstract The families of MAX phases and their derivatives MXenes are constantly increasing in terms of both composition and crystalline mixtures. In the last three years, numerous advances were accomplished that improved the preparation of new MAX phases with prearranged double transition metals and, as a result, the production of novel MXenes with a high structural complexity and chemical multiplicity, infrequently observed in other families of two dimensional samples. In this evaluation, hybrids of MXenes and semiconductors are efficient photocatalysts, because of their specific interface characteristics and Schottky heterojunction is capable of giving accelerated charge separation and a lower Schottky barrier for photocatalytic applications. The latest advances were proved that the MXenes supported semiconductors based photocatalysts can be expected as the most advantaged and encouraged novel photocatalysts in the photocatalytic and photoelectrochemical applications. Besides, we have explained significant developments in efficient MXenes supported semiconductors based nanocomposites, including the frequent synthesis strategies and progress mechanisms, in addition to their new applications including, photodegradation of dyes, CO2 conversion, photocatalytic and photoelectrochemical water splitting reaction applications. The review was completed with a short presentation of future challenges and prospects in the progress of MXenes supported semiconductors based photocatalysts. It is also believed that this review will encourage further exploration and will inaugurate new promising to increase new MXenes supported semiconductors based photocatalysts with new and inspiring applications.
author_names: Ch Prasad

Xiaofei Yang

Qinqin Liu

Hua Tang

Aluru Rammohan

Syed Zulfiqar

Grigory V Zyryanov

Sufaid Shah
title: Recent advances in MXenes supported semiconductors based photocatalysts: Properties, synthesis and photocatalytic applications
venue: Journal of Industrial and Engineering Chemistry
year: 2020

abstract: Abstract Heterojunction photocatalysts at present are still suffering from the low charge separation/transfer efficiency due to the poor charge mobility of semiconductor based photocatalysts. Atomic scale heterojunction type photocatalysts are regarded as a promising and effective strategy to overcome the drawbacks of traditional photocatalysts for higher photoenergy conversion efficiencies. Herein, an atomic scale heterojunction composed of a boron nitride monolayer and graphene (h BN C/G) is constructed to significantly shorten the charge transfer path to promote the activation of molecular oxygen for artificial photosynthesis (exemplified with oxidative coupling of amines to imines) As the thinnest heterojunction, h BN C/G gives the highest conversion, which is eightfold higher than that of the mechanical mixture of graphene and boron nitride monolayers. h BN C/G exhibits a high turnover frequency value (4.0 mmol benzylamine g 1 h 1) which is 2.5 fold higher than that of the benchmark metal free photocatalyst in the literature under even critical conditions.
author_names: Ke Zhang

Huilan Su

Hong-Hui Wang

Jun-Jun Zhang

Shu-Yu Zhao

Wei-Wei Lei

Xiao Wei

Xin-Hao Li

Jiesheng Chen
title: Atomic Scale Mott Schottky Heterojunctions of Boron Nitride Monolayer and Graphene as Metal Free Photocatalysts for Artificial Photosynthesis
venue: Advanced science
year: 2018

abstract: Despite the existence of numerous photocatalyst heterostructures, their separation efficiency and charge flow precision remain low due to the poor study on interfacial properties. The photocatalysts with confined defects can effectively control the photogenerated carrier migration, but the metastability of such defects considerably decreases the photocatalyst stability. Meanwhile, the introduction of defective region can increase the coordinative unsaturation and delocalize local electrons to promote their interactions with the molecules/ions in that region. The selective growth of modulated heterogeneous interface by defect induced strategy may not only increase the stability of defective structures, but also enhance the migration of interfacial charges. Using this method, photocatalytic heterostructures with low contact resistances and intimate interfaces are constructed to achieve the optimal charge migration in terms of efficiency and accuracy. In this work, the point, linear, and planar heterogeneous interfaces and related defect engineering techniques are discussed. Particularly, it is focused on the external, defect induced interfacial heterogeneities with various spatial and dimensional configurations, which exhibit modulated and controllable interfacial properties. Furthermore, the main aspects of fabricating photocatalyst heterostructures by the defect induced strategy, including the i) controllable generation of defects, ii) advanced characterization methods, and iii) elaborate construction of the minimal interface, are described.
author_names: Shuqu Zhang

Yanmei Si

Bing Li

Lixia Yang

Weili Dai

Shenglian Luo
title: Atomic Level and Modulated Interfaces of Photocatalyst Heterostructure Constructed by External Defect Induced Strategy: A Critical Review.
venue: Small
year: 2020

abstract: Ever increasing fossil fuel combustion along with massive CO2 emissions has aroused a global energy crisis and climate change. Photocatalytic CO2 reduction represents a promising strategy for clean, cost effective, and environmentally friendly conversion of CO2 into hydrocarbon fuels by utilizing solar energy. This strategy combines the reductive half reaction of CO2 conversion with an oxidative half reaction, e.g. H2 O oxidation, to create a carbon neutral cycle, presenting a viable solution to global energy and environmental problems. There are three pivotal processes in photocatalytic CO2 conversion: (i) solar light absorption, (ii) charge separation/migration, and (iii) catalytic CO2 reduction and H2 O oxidation. While significant progress is made in optimizing the first two processes, much less research is conducted toward enhancing the efficiency of the third step, which requires the presence of cocatalysts. In general, cocatalysts play four important roles: (i) boosting charge separation/transfer, (ii) improving the activity and selectivity of CO2 reduction, (iii) enhancing the stability of photocatalysts, and (iv) suppressing side or back reactions. Herein, for the first time, all the developed CO2 reduction cocatalysts for semiconductor based photocatalytic CO2 conversion are summarized, and their functions and mechanisms are discussed. Finally, perspectives in this emerging area are provided.
author_names: Jingrun Ran

Mietek Jaroniec

Shizhang Qiao
title: Cocatalysts in Semiconductor based Photocatalytic CO2 Reduction: Achievements, Challenges, and Opportunities.
venue: Advanced materials
year: 2018