In-situ transient photovoltage study on interface electron transfer regulation of carbon dots/NiCo_(2)O_(4) photocatalyst for the enhanced overall water splitting activity

Photocatalytic hydrogen production by overall water solar-splitting is a prospective strategy to solve energy crisis.However,the rapid recombination of photogenerated electron–hole pairs deeply restricts photocatalytic activity of catalysts.Here,the in-situ transient photovoltage(TPV)technique was developed to investigate the interfacial photogenerated carrier extraction,photogenerated carrier recombination and the interfacial electron delivery kinetics of the photocatalyst.The carbon dots/NiCo_(2)O_(4)(CDs/NiCo_(2)O_(4))composite shows weakened recombination rate of photogenerated carriers due to charge storage of CDs,which enhances the photocatalytic water decomposition activity without any scavenger.CDs can accelerate the interface electron extraction about 0.09 ms,while the maximum electron storage time by CDs is up to 0.7 ms.The optimal CDs/NiCo_(2)O_(4)composite(5 wt.%CDs)displays the hydrogen production of 62µmol·h^(−1)·g^(−1) and oxygen production of 29µmol·h^(−1)·g^(−1) at normal atmosphere,which is about 4 times greater than that of pristine NiCo_(2)O_(4).This work provides sufficient evidence on the charge storage of CDs and the interfacial charge kinetics of photocatalysts on the basis of in-situ TPV tests.

Highly efficient metal-free catalyst from cellulose for hydrogen peroxide photoproduction instructed by machine learning and transient photovoltage technology

Great attention has been paid to green procedures and technologies for the design of environmental catalytic systems.Biomassderived catalysts represent one of the greener alternatives for green catalysis.Photocatalytic production of hydrogen peroxide(H_(2)O_(2))from O_(2) and H_(2)O is an ideal green way and has attracted widespread attention.Here,we show a metal-free photocatalyst from cellulose,which has a high photocatalytic activity for the photoproduction of H_(2)O_(2) with the reaction rate up to 2,093μmol/(h·g)and the apparent quantum efficiency of 2.33%.Importantly,a machine learning model was constructed to guide the synthesis of this metal-free photocatalyst.With the help of transient photovoltage(TPV)tests,we optimized their fabrication and catalytic activity,and clearly showed that the formation of carbon dots(CDs)facilitates the generation,separation,and transfer of photo-induced charges on the catalyst surface.This work provides a green way for the highly efficient metal-free photocatalyst design and study from biomass materials with the machine learning and TPV technology.

Transient photovoltage and photoluminescence study of exciton dissociation at indium tin oxide/pentacene interface

The exciton dissociation at ITO/pentacene interface is studied by means of transient photovoltage measurement.Opposite to ITO/NPB,ITO/CuPc or ITO/C60 interface where polarity change of transient photovoltage is observed,no interfacial dissociation is found at room temperature,which indicates a lack of Frenkel excitons in pentacene.Temperature-dependent photoluminescence (PL) is investigated.More like the behavior of inorganic semiconductors,the integrated PL intensity exhibits monotonic decrease with increasing temperature.A nonradiative path with characteristic activation energy of 8 meV is found to dominate at room temperature.The PL measurement also indicates that like in inorganic semiconductors,other types of excitation,for example,free carriers,could be responsible for the photoelectric processes.

Ag_3PO_4/Ag_2CO_3 p–n heterojunction composites with enhanced photocatalytic activity under visible light

Formation of a p–n heterojunction rather than p-type or n-type semiconductors can enhance the separation of photogenerated electrons and holes and increase the quantum efficiency of photocatalytic reactions owing to the difference of the electric potential in the inner electric field near the junction,pointing from n toward p. n-Ag3PO4/p-Ag2CO3 p–n heterojunction composites are prepared through a facile coprecipitation process. The obtained Ag3PO4/Ag2CO3 p–n heterojunctions exhibit excellent photocatalytic performance in the removal of rhodamine B（RhB） compared with Ag3PO4 and Ag2CO3. The 40%-Ag3PO4/Ag2CO3 composite photocatalyst（40 mol% Ag3PO4 and 60 mol% Ag2CO3） exhibits the best photocatalytic activity under visible light,demonstrating the ability to completely degrade RhB within 15 min. Transient photovoltage characterization and an active species trapping experiment further indicate that the formation of a p–n heterojunction structure can greatly enhance the separation efficiency of photogenerated carriers and produce more free h＋active species,which is the predominant contributor for RhB removal.

Carbon dots/Bi_(2)WO_(6) composite with compensatory photo-electronic effect for overall water photo-splitting at normal pressure

Overall water photo-splitting is a prospective ideal pathway to produce ultra-clean H_(2) energy by semiconductors.However,the band structure of many semiconductors cannot satisfy the requirement of H_(2) and O_(2) production at the same time.Herein,we illustrate that carbon dots(CDs)/Bi_(2)WO_(6) photocatalyst with compensatory photo-electronic effect has enhanced activity for overall water photo-splitting without any sacrificial agent.In this complex photocatalytic system,the photo-potential provided by CDs makes the CDs/Bi2WO6(C-BWO)composite could satisfy the band structure conditions for overall water photo-splitting.The C-BWO composite(3 wt%CDs content)exhibits optimized hydrogen evolution(oxygen evolution)of 0.28μmol/h(0.12μmol/h)with an approximate 2:1(H_(2):O_(2))stoichiometry at normal pressure.We further employed the in-situ transient photovoltage(TPV)technique to study the photoelectron extraction and the interface charge transfer kinetics of this composite catalyst.