Structural Modulation Of SnS_x(x=1,2) Photoelectrodes And Its Photoelectrochemical Properties

With the continuous growth of the world’s population and the rapid development of industrialization,energy shortage and ecological environment problems are becoming more and more serious.Therefore,it is important to actively seek and develop low-cost and environmentally friendly renewable energy.Hydrogen is a green energy with high combustion calorific value,which is easy to convert into other energy forms,transportable,storable,and the combustion products are clean.It is considered to be the most ideal future energy.In view of the renewable nature of solar energy and the abundance of water resources on earth,photoelectrochemical water splitting（PEC）hydrogen production technology is considered to be the most promising hydrogen production route,which can realize the perfect conversion of solar energy to hydrogen energy.In recent years,two-dimensional metal sulfide materials have been widely used in the field of photoelectrochemical water splitting due to their unique layered structure,suitable band gap and good photoelectric response properties.Especially SnS and SnS₂ materials are considered as ideal photocathode materials and ideal photoanode materials,respectively.In this paper,based on the research premise of constructing efficient SnS_x（x=1,2）-based photoelectrodes,by optimizing preparation methods,constructing heterojunctions,designing material alloying,modifying co-catalysts and other means to achieve the goal of improve the light absorption capacity of semiconductor photoelectrodes,enhance the carrier separation rate and promote the carrier interface reaction rate,thereby enhancing the photoelectrochemical performance of the samples.The specific research contents and conclusions are as follows:（1）A phase-pure SnS photoelectrode with tunable conductivity was successfully fabricated on Ti substrate by a novel two-step strategy（first,the SnS₂/Ti thin film photoelectrode was prepared by chemical vapor deposition method,and then the SnS₂/Ti thin film photoelectrode was converted into SnS/Ti thin film photoelectrode by high temperature annealing）,avoiding the problem of SnS₂ and Sn₂S₃ impurity phases easily generated in the traditional SnS fabrication method.The tunable conductivity type is determined by the Na₂SO₄ pretreatment before annealing.Na⁺absorbed to the edge of the precursor SnS₂ nanosheet forming a dangling adsorption bond will protect S^2-against interacting with the trace oxygen in the chemical vapor deposition system within a certain temperature range（<525℃）during high temperature annealing,thereby reducing the generation of S vacancies to adjust the S/Snratio and further regulate the conductivity type.（2）A phototrap-like direct Z-scheme SnS@In₂S₃ heterojunction photoelectrode was successfully constructed on a Ti substrate.The construction of the heterojunction can effectively broaden the spectral absorption range,improve the separation efficiency of photogenerated carriers,reduce the charge interface transfer resistance and increase the electroactive area of the In₂S₃ sample,thus greatly improving the photoelectrochemical performance.The photocurrent density of SnS@In₂S₃ heterojunction is 194μA/cm² at 1.23V vs.RHE,which is about 4.85 times that of In₂S₃（40μA/cm²）.（3）The SnSe_xS_2-x alloy photoanode with fully tunable chemical composition was successfully fabricated on the FTO substrate by chemical vapor deposition method.Compared with pure SnS₂ and SnSe₂,SnSe_xS_2-x alloy samples have wider spectral absorption range,faster photogenerated carrier mobility rate,and longer carrier lifetime,thus also exhibiting better photoelectrochemical performance.When the content of Se and S in the samples satisfies Se:S=1:3(SnSe_0.5S_1.5),the photocurrent density of the sample reaches the maximum,about 2.48 m A/cm²（1.23 V vs.RHE）,which is 6.9 times that of pure SnS₂（0.36 m A/cm²）and 6.0 times that of pure SnSe₂（0.41 m A/cm²）,respectively.The photocurrent density of the CQDs/SnSe_0.5S_1.5 composite sample was further increased3.83 m A/cm² by the modification of CQDs.