类石墨烯MoS2 复合催化剂结构优化及其异质结结构在光/电催化析氢反应中光电催化作用机制的研究

Photoelectrocatalytic production of H2 from water splitting has received considerable attention as a solar energy driven pathway to hydrogen. Studies on semiconductor-type photoelectrocatalysts have indicated that CdS, ZnO, TiO2 and ZnS are promising as catalysts for photoelectrocatalytic water reduction due to their unique properties, such as high extinction coefficient of light absorption, tunable bandgap, and carrier multiplication effect, etc. However, these semiconductors alone exhibit very low photocatalytic activities under visible light due to high recombination rate of photogenerated electron_hole pairs. To achieve high photocatalytic activity, co-catalysts are loaded on the surface of semiconductor to suppress charge recombination and provide designated redox reaction sites to avoid back reactions. From the view point of photocatalytic water splitting, numerous studies had focused on water splitting using semiconductor photoanodes where the photogenerated electrons reduce water to form H2 on a Pt counter electrode while holes oxidize water to form O2 on the photoanode with some external bias (reverse bias) by a power supply..Layered MoS2 has been rigorously characterized by experimental and computational means as an alternative electrocatalyst to Pt-group metals towards the HER. MoS2 reduces protons at low overpotentials via under co-ordinated sulphur edge sites of MoS2 plates. As p type MoS2 and n type semiconductor can form a high-quality, intimate heterojunction, the cocatalyst of p-MoS2/n-semicondutor is not only an efficient photocatalyst, in which the p-n junction formed between the MoS2 and n type semiconductors could promote the separation of photoexcited electrons and holes, and decrease the activation potentials for H2 evolution, thus greatly enhancing the photocatalytic activity for H2 evolution, also a more effective electrochemical catalyst for HER in comparison with that of the solitary MoS2. However, our previous studies indicated that achieving high energetic photocatalysis for the cathode catalyst is probably correlated with the morphologies of the catalyst hybrid. .Here we demonstrate a morphology-dependent photo-and electrocatalysis of p-MoS2 /n-semiconductor hybrid for the HER by comparing a nanorod array of CdS @MoS2 layer, vertical arrays of elemental doping MoS2 nanosheet and CdS nanorod @ vertical arrays of elemental doping MoS2 nanosheet with a bilayer of CdS/MoS2 heterostructure for use as a photocathode in solar cells. The well-defined physical features make the as prepared heterostructure an ideal platform for studies of the structure−catalysis correlation. In this investigation, a regular array structure of p-MoS2 / n-semiconductor was fabricated not only to create a large percentage of edge sites, but also to increase the contact area with the surface of CdS nanorod, which will facilitate charge separation at the CdS/MoS2 interface and electron transportation. The photoelectronic activity dependence on heterostructure design is found by conducting the electrochemical experiments for various structures of p-MoS2/n-semiconductor respectively, while the bias potential is applied. This structure-dependent photoelectrocatalysis can be correlated to the hopping of photogenerated electrons in the vertical direction of regular arrays of p-MoS2/n-semiconductor in which p-n junction is probably reverse biased the P region, leading to the depletion region enhanced, and thus, suppresses charge recombination. Here we also demonstrate the high HER electrocatalytic activity of the resulting regular array hybrid. This work indicates that effectively integrated regular array structure and the suitable band position of p-MoS2 /n-semiconductor nanohybrid lead to a highly photo-and electrochemical activity even though at the cathodic polarization. This achievement can be regarded as a valuable result in designing the nanostructure of cathode with enhanced electrocatalytic activity by photo-assistance.

要制备具有良好光电催化性能的MoS2基阴极催化剂，设计制备具有可控形貌的MoS2基催化剂体系是解决问题的关键。首先，在 n型半导体改性的ITO基材上直接制备垂直阵列的的MoS2 纳米片材。通过调整影响微观结构形貌的关键因素，调控MoS2的畴区尺寸、活性位点，电子结构及导电性；最后将该复合材料作为光阴极和金属导电电极组装成为析氢电解池，测试其光电析氢效率。通过对复合体系的组分设计使其不仅具有低能带隙且与太阳光谱相匹配，而且其能带位置利于电子-空穴的分离。利用其p-n异质结构的整流性，使得优化的催化剂体系的异质结构同时受到正、反偏压的影响。正偏压导通p-n结，利于电催化；反偏压增强势垒，利于光催化；进一步研究形貌结构与其光电催化性能的构效关系，探讨杂化界面设计、能带结构以及偏压的作用对于光电催化机理的影响，建立一套在光和电场的共同作用下，MoS2基光电催化剂p-n杂化结对材料光电物理性能影响规

采用原位生长法在不同的导电基底（金属钛片、钼片、泡沫铜, Co 片）上结合助催化剂得到了三种高效稳定的光电阴极材料。对电极的催化剂进行晶体结构、微观形貌、光学性能以及光电化学性能的测试与表征，构建适宜的能带模型，分别阐述了复合光电阴极催化体系的光电性能来源和提升机制。实验结果表明：（1）金属钛片经阳极氧化法随后电泳沉积法制备了原位生长的包覆了硫化钼的二氧化钛复合光电阴极（v-TiO2@MoS2/Ti foil）。该结构通过提升暴露MoS2催化活性位点，提高光生载流子的定向迁移，降低了光生电子-空穴对的复合几率，提高光电催化性能。（2）金属泡沫铜基底经湿化学法和电泳沉积法制备了原位生长的包覆了二硫化钼的铜纳米线光电阴极（Cu NWs@MoS2/Cu foam）。该光电阴极通过Cu NWs等离激元效应产生的热电子并通过MoS2有效的捕获热电子进而快速的发生析氢反应。同时电极多孔结构赋予超亲水疏气性质，更多的析氢活性位点并降低了析氢阻力。Cu NWs与MoS2界面处中间相的生成使电极表现优异的结构和电化学稳定性。（3）以金属钼片为导电基底，在不同气氛下煅烧处理制备了原位生长的氮化钼电极（Mo3N2/Mo foil）。实验测试和密度泛函理论计算证明了Mo3N2的金属性及对可见光的光吸收性。通过低温表面硫化法制备了Mo3N2-MoS2/Mo foil复合电极。Mo3N2受可见光激发产生热电子，MoS2与Mo3N2形成了适宜的能带结构，加强电子-空穴对的分离，提升了光生电子的利用效率，提升了光电阴极的光电催化析氢效率。（4）Co片为基材采用阳极氧化技术制备出Co3O4/Co复合物(ACO)，并负载钼酸盐以提升其性能。结果表明钼酸盐和ACO之间的协同作用利于催化剂的HER。所得到的CoMoO4/ACO驱动10 mA/cm2的HER和全水解反应仅需78 mV和1.64 V。