| Nowadays,the reported catalysts of photoelectrochemical water splitting can only exhibit low photocurrent density(less than 10 m A cm-2 in most conditions),which limits the practical application of semiconductors in water splitting.In order to solve this problem,highly efficient electrocatalysts of photo-assisted electrocatalytic oxygen evolution reaction?OER?are designed and obtained,which can maintain the high current density and effectively use solar energy.The slow kinetics of OER is the bottleneck of highly efficient water splitting,and improving kinetics is of great significance for clean energy generation.The photo-assisted electrocatalysts can promote OER kinetics by electrocatalysis and assisted light.Semiconductors of WO3,C3N4 and MoS2 have band gaps of 2.60 e V,2.67 e V and 1.85 e V,which can absorb photons and convert them into photo-generated charges?electrons and holes?.This process can accelerate the reaction kinetic,photo-generated holes also improve OER activity because of their oxidizability.However,Semiconductors of WO3,C3N4 and MoS2 show low charge separation efficiency and lower solar energy utilization efficiency.Therefore,some methods are developed to improve the efficiency of photo-generated charge separation by building heterojunction and cocatalysts.Finally,the high-performance catalysts have been obtained using these methods.The details are as follows:?1?Water splitting is very important for the conversion and storage of renewable energy,but the slow OER kinetics greatly limits its development.The n-p heterojunction WO3 and Sn Se2?WS?structure was fabricated by hydrothermal to greatly enhance the electrocatalytic OER performance of Co Fe-LDH/CNTs?CF/CNTs?composites.The CF/WS/CNTs achieve the overpotential of 224 m V at a current density of 10 m A cm-2 and a small Tafel slope(47 m V dec-1)with illumination,apparently better than that of commercial Ru O2 catalyst.The results of electron structure analysis show that the n-p WS heterojunction is equivalent to an“electron pump”,which can transfer electrons of CF to CNTs and CF becomes the active center of OER.And the CF and CNTs can also effectively separate photo-generated electrons and holes of WS,and enhance the efficient utilization and absorption of light and promote the dynamics of OER.The design of the catalyst opens up new avenues for the application of heterojunction structures in the energy field.?2?C3N4 as a potential candidate of electrocatalyst for photo-assisted electrocatalytic OER has attracted great interests due to resources shortage and energy crisis.However,the intrinsically a fast recombination rate of the photo-generated charges for C3N4 limited the further application in generation of clean energy.Therefore,the design of cost-efficient catalysts with improving the photo-generated charges separation of C3N4 still remains a great challenge.A novel C3N4/Se/CNTs catalyst was designed and synthesized by one-step reflux,in which Selenium?Se?and Carbon Nanotubes?CNTs?act as holes storage agent and electrons acceptor respectively to effectively promote the photo-generated charge separation and achieve excellent performance in photo-assisted electrocatalytic OER.As excepted,the C3N4/Se/CNTs shows overpotential of 231 m V to at current density of 10 m A cm-2 with illumination,and a small Tafel slope of 52 m V dec-1 in OER,which represent the best OER performance for metal-free electrocatalysts,even better than that of Ru O2,as far as we are aware.This design highlights the possibility of promoting photo-generated charge separation of C3N4 by incorporating holes and electrons storage agents to obtain excellent photo-assisted electrocatalytic OER activity.This strategy opens a new avenue toward the design of highly efficient OER photoelectrocatalysts boosting water splitting,Zn-air cells and fuel cells.?3?It is of great significance to promote the activity of MoS2,as a candidatematerial,in photo-assisted electrocatalytic OER for the production of clean energy.A simple method was used to improve the photo-assisted electrocatalytic OER performance of MoS2.The MoS2/NiO catalyst was self-assembled by electrostatic interaction of n-type MoS2 and p-type NiO.The catalyst exhibits excellent photo-assisted electrocatalytic OER performance with the overpotential of 255 m V to reach the current density of 10 m A cm-2 with illumination,which is decreased by94 m V compared to without illumination.The type II heterojunction of MoS2/NiO makes photo-generated electrons can be transferred from NiO to MoS2,and photo-generated holes can be transferred from MoS2 to NiO.Therefore,the photo-generated charges can be effectively separated,and the NiO become the active site for improving OER performance of MoS2/NiO.Research on MoS2/NiO provides a simple design method for efficient utilization of light energy and production of clean energy. |
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