金属-有机骨架衍生的Ni-CNT/ZnIn_(2)S_(4)异质结用于光催化产氢及其电荷转移途径的确定

Identification of Charge Transfer Pathways in Metal-Organic FrameworkDerived Ni-CNT/ZnIn_(2)S_(4) Heterojunctions for Photocatalytic Hydrogen Evolution

氢气是缓解环境污染和能源短缺的零污染绿色能源,利用太阳能诱导半导体裂解水制氢是最环保的方法之一。本文以MOFs衍生的Ni-CNT(Ni修饰的碳纳米管)作为非贵金属助催化剂,通过简单的油浴法原位生长ZnIn_(2)S_(4)纳米片合成了Ni-CNT/ZnIn_(2)S_(4)。在Ni-CNT/ZnIn_(2)S_(4)中,Ni纳米颗粒包裹在CNT的顶部和横截面上,有效地阻止了Ni纳米颗粒的团聚。Ni-CNT/ZnIn_(2)S_(4)异质结构具有紧密的接触界面,有利于电荷转移,可作为高效的析氢光催化剂。38Ni-CNT/ZnIn_(2)S_(4)样品具有最佳的产氢性能(12267μmol·h^(−1)·g^(−1)),约为纯ZnIn_(2)S_(4)的6.4倍,且在420 nm单色光下其表观量子效率达到11.3%。X射线衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)结果证实了Ni-CNT/ZnIn_(2)S_(4)异质结构的存在。电化学测试表明,Ni-CNT与ZnIn_(2)S_(4)的结合促进了光生电荷的转移,有效地阻止了光生载流子的快速复合,从而增强了ZnIn_(2)S_(4)的析氢性能。电子自旋共振(ESR)结果进一步证明了Ni-CNT助催化剂的存在延长了ZnIn_(2)S_(4)光生电荷的寿命,促进了光生电荷和空穴的分离效率。通过密度泛函理论计算探索并确定了异质结界面中的电荷转移途径。Ni、CNT和ZnIn_(2)S_(4)费米能级的差异导致界面处电荷发生迁移从而形成内嵌电场,ZnIn_(2)S_(4)的能带向下弯曲,促进光生电子从ZnIn_(2)S_(4)流向NiCNT电子受体。平面平均电子密度差结果证实了热电子从Ni转移至CNT再转移至ZnIn_(2)S_(4),表明光生电子转移途径为ZnIn_(2)S_(4)→CNT→Ni。此外,吸附H*吉布斯自由能(ΔGH*)和晶体轨道哈密顿布居(COHP)结果表明Ni纳米颗粒可作为析氢反应的活性位点,促进了产氢效率。本工作将为开发低成本、高效的非贵金属光催化制氢催化剂提供新的策略。

Hydrogen is an important zero-pollution green energy source with potential for alleviating environmental contamination and energy shortages.Hydrogen evolution via solar-energy-induced semiconducting water splitting is among the most environmentally friendly methods available to date.In this study,a metal–organic-framework-derived,Ni-decorated carbon nanotube(Ni-CNT)is used as a non-noble co-catalyst.This Ni-CNT is grown in situ on ZnIn_(2)S_(4) nanosheets using a simple one-step oil bath strategy,wherein Ni nanoparticles are wrapped around the top and cross sections of the nanotubes,preventing their agglomeration.Notably,Ni-CNT/ZnIn_(2)S_(4) heterostructures feature intimate contact interfaces that promote charge transfer,facilitating their use as efficient photocatalysts for hydrogen evolution.The 38Ni-CNT/ZnIn_(2)S_(4) sample exhibits a high H2 production rate(12267μmol·h^(−1)·g^(−1)),with an apparent quantum efficiency(AQE)of 11.3%under 420 nm monochromatic light irradiation,which is nearly 6.4 times that of pure ZnIn_(2)S_(4).The results of X-ray diffraction(XRD),transmission electron microscopy(TEM),and X-ray photoelectron spectroscopy(XPS)corroborate the observations on Ni-CNT/ZnIn_(2)S_(4) heterostructures.Electrochemical measurements reveal that the combination of the Ni-CNT and ZnIn_(2)S_(4) facilitates the transfer of photogenerated electrons and effectively prevents rapid recombination of photocarriers,thus improving the hydrogen evolution performance of ZnIn_(2)S_(4).Electron spin resonance(ESR)results further prove that cocatalyst Ni-CNTs are beneficial for prolonging the lifetimes of ZnIn_(2)S_(4) photogenerated electrons,thereby achieving effective charge separation.A charge transfer pathway in the heterojunction interfaces is further explored and confirmed by density functional theory(DFT)calculations.The difference in the Fermi level energy(Ef)contributes to both charge migration and the generation of a built-in electronic field(BEF),indicating that the energy band of ZnIn_(2)S_(4) bends downward,which is favorable for photogenerated electron flow from ZnIn_(2)S_(4) to the Ni-CNT electron acceptor.The results of planaraveraged electron density difference analysis confirm that the hot electrons are transferred from Ni nanoparticles to the CNT and then to the ZnIn_(2)S_(4) nanosheets,indicating the formation of a photogenerated electron transfer pathway of ZnIn_(2)S_(4)→CNT→Ni.Furthermore,Gibbs free energy of H*adsorption(ΔGH*)and crystal orbital Hamilton population(COHP)analysis indicate that Ni nanoparticles can serve as active sites,promoting H2 evolution.Thus,the present study formulates a new strategy for developing low-cost,high-efficiency,non-noble-metal co-catalysts for photocatalytic hydrogen production.