Preparation And Photoelectrochemical Performance Of Copper-based Sulfide Nanoarrays

Due to their higher light absorption coefficients,good carrier transport properties and tunable bandgap,copper-based chalcogenides as high-efficient photocathode materials for H₂ production through a photoelectrochemical?PEC?water splitting process have attracted significant attention.However,the thin film photoelectrodes have shown unsatisfying conversion efficiency and relatively higher fabrication cost.Therefore,proposing a low-cost method for the preparation of high-performance copper-based chalcogenide photocathodes has very important practical significance.This thesis focuses on the fabrication of copper-based sulfide nanoarrays by combining gas-solid reaction method and solvothermal reaction approach,emphasizes the preparation of ternary CuInS₂ nanoarrays using binary Cu₂S and In₂S₃ as the self-sacrificial templates,and inverstigates their PEC performance and the corresponding improvement approaches.The main results are as follows:?1?Investigate the light absorption and PEC properties of the Cu₂S nanowire arrays?NWAs?grown on copper substrates by gas-solid reaction method.This method can realize the controllable and large-area growth of Cu₂S NWAs on various copper substrates at room temperature.With the increase of reaction temperature,the nanowire diameter increases but its length decreases.Both nanowire diameter and length can be increased by prolonging the reaction time.The Cu₂S NWAs with higher aspect ratios exhibit superior light trapping ability as well as PEC performance.The optimized sample has demonstrated light absorptance as high as 93.1-99.7%over the wavelength range of 250-850 nm,and its photocurrent density at bias voltage of 0.2 V_RHE is 8.5times larger than that of the Cu₂S film phothocathode fabricated by the gas-solid reaction method.?2?It is found that carbon quantum dots?CQDs?can be used as modifiers to enhance the PEC performance of Cu₂S NWAs photocathodes due to the energy-down-shift effect and the catalytic function promoting the photogenerated electron transfer.The CQDs are decorated on the surfaces of Cu₂S nanowires by a self-assembly approach,and the Cu₂S/CQDs composite NWAs show the optimal photocurrent density of 1.05 mA/cm² at 0 V_RHE,which is 4 times higher than that of the pristine Cu₂S NWAs.Additionally,CQDs can partly protect Cu₂S NWAs from photocorrosion.?3?Utilize binary Cu₂S NWAs as self-sacrificial templates to fabricate ternary CuInS₂ NWAs with different morphologies through a solvothermal reaction process,and propose a novel“exchange-corrosion-peeling”growth mechanism to illustrate their formation process.The experimental results indicate that the cation exchange between In³⁺in the precursor solution and Cu⁺in Cu₂S nanowire,the H⁺corrosion for Cu₂S nanowire and the self-peeling resulted from lattice mismatch between the Cu₂S self-sacrificial template and the in-situ formed CuInS₂ are the three main reasons for the formation of CuInS₂ NWAs with different morphologies.When the precursor concentration is low,relatively slower reaction process will result in the formation of1D CuInS₂ NWAs.The increase of precursor concentration can enhance the reaction rate and then realize the fabrication of 3D hierarchically CuInS₂ nanosheet-constructed NWAs?NCNAs?.?4?Study the PEC properties of CuInS₂ NWAs with different morphologies fabricated by self-sacrificial template method,and the results of the first-principles density functional theory calculations incicate that the ultrathin CuInS₂ nanosheets favor for higher carrier mobility compared to bulk material and then ensure promoted PEC efficiency.Compared to the Cu₂S self-sacrificial templates,p-type CuInS₂ NWAs photocathodes show enhanced PEC performance due to their optimized energy band structure,improved light absorption and increased specific surface area,and the performance can be further elevated by decorating n-type CdS quantum dots.The 1D CuInS₂ NWAs have demonstrated the optimal photocurrent density and IPCE efficiency of 0.71 mA/cm²(-0.1 V_RHE)and 9.0%(0 V_RHE,450 nm),respectively.The corresponding values for 3D hierarchically CuInS₂ NCNAs are 1.14 mA/cm² and11.0%.Their photocurrent is 2-3 orders higher than that of the CuInS₂ NWAs photocathodes fabricated by the traditional AAO template method.?5?Report the controllable growth of In₂S₃ nanosheet arrays?NSAs?on FTO substrates by a solvothermal method,find that ZnO can be used as modifier to greatly enhance the PEC properties of the photoanodes,and realize the fabrication of ultrathin CuInS₂ NSAs photocathodes using the In₂S₃ NSAs as the self-sacrificial templates.The solvothermal reaction conditions such as time and precursor concentration can be used to control the growth of In₂S₃ NWAs,which show optical bandgap in the range of 2.32-2.58 eV.It is found that the In₂S₃/ZnO heterojunction plays an important role in the improved PEC performance and the enhancement is more obvious with the increase of positive bias voltage.Compared to sputtering method,atomic layer deposition technology can realize the uniform growth of In₂S₃/ZnO heterojunction,which then results in relatively better light absorption ability,photocurrent response and stability.The In₂S₃/ZnO NSAs have demonstrated the maximum photocurrent density and IPCE efficicency of 1.64 mA/cm²(1.5 V_RHE)and 27.64%(380 nm,1.23 V_RHE),which are 60and 103 times larger than that of the bare In₂S₃ NSAs counterparts.