Novel Semiconductor Heterojunction Photoelectrodes:Design And Photoelectrochemical Performances

With the prosperity of industrial society,our demand for power and other energy sources is increasing,and the depletion of fossil fuels makes the world face an urgent energy crisis.Besides,the energy systems based on oil,natural gas,and coal have caused environmental pollution.Therefore,there is an urgent need to use sustainable energy as a substitute for fossil fuels.Currently,hydrogen is considered an ideal alternative to fossil fuels due to its cleanliness and sustainability.The photoelectrochemical(PEC)water splitting is one of the effective methods for solar hydrogen production.However,due to the limited spectral absorption range,low charge separation efficiency,and poor stability of the photoelectrode,the current energy conversion efficiency of the PEC system is difficult to improve,which affects its practical application.Multi-component or multi-phase heterojunctions have become one of the strategies for constructing efficient and stable PEC systems due to their adjustable energy band structure and efficient electron-hole separation and transport process.However,the design of novel heterojunctions and the precise adjustment of their energy band structure to achieve an efficient and stable PEC system are still key scientific issues yet to be solved.This dissertation focuses on the design and adjustment of novel heterojunctions and their PEC hydrogen production performance.Given the current low energy conversion efficiency and poor stability of PEC hydrogen production,we designed and prepared a series of photoelectrodes based on heterojunctions to achieve efficient and stable PEC hydrogen production.At the same time,we combined time-resolved spectroscopy techniques to explain the working mechanism of heterogeneous nanostructures for further optimization.The main findings are summarized as follows:1.Narrow bandgap semiconductors with lattice-matched morphological heterojunctions(LMHs)were designed and fabricated as near-infrared active photoanodes,which improved the energy conversion efficiency of PEC hydrogen production.The LMHs reduce the interfacial defects due to the avoidance of lattice mismatch,thereby reducing the recombination rate of photogenerated carriers,and achieving high-efficiency PEC hydrogen production.We prepared the LMHs composed of BiSeTe ternary alloy nanotubes and ultrathin nanosheets by an epitaxial growth strategy.The spectral absorption range of the photoelectrocatalyst can be extended to near-infrared light,and thus it enables effective separation of photogenerated carriers.The analysis of the transient absorption spectrum shows that the type-? heterojunctions formed by nanotubes and nanosheets drive the rapid transfer of photogenerated electrons from nanotubes to nanosheets,thereby increasing the lifetime of photogenerated electrons.Finally,the spectral absorption range and energy conversion efficiency of the photoanodes composed of these heterojunctions can be greatly improved.This LMHs strategy based on narrow bandgap semiconductors provides new possibilities for designing efficient PEC devices.2.The photoelectrode based on plasmonic metal/semiconductor heterojunctions was designed and prepared,which improved the utilization of near-infrared light in the PEC hydrogen production system.The surface plasmon resonance(SPR)effect of plasmonic metals can greatly improve the absorption ability of heterojunctions to sunlight.The Schottky junction formed by metal and semiconductors can effectively prevent the hot electrons from drifting back to the metal from the semiconductor,thereby effectively extending the life of the hot carrier.We synthesized the Bi/Bi3(SeTe)2 dot-line nanostructures in one step by the chemical transformation process.Due to that the excitation of plasmonic metal Bi belongs to inter-band excitation,by adjusting its size and morphology,its resonance peak can be changed from the ultraviolet region to the near-infrared region,which enhances its ability to absorb near-infrared light.The photoelectrode based on the Bix/Bi3(SeTe)2 nanostructure enhances its light absorption range and photogenerated carriers separation ability and further improves its energy conversion efficiency.This strategy of utilizing near-infrared active plasmonic metals to enhance the spectral absorption capacity of photoelectrodes provides more ideas for the design of new photoelectrodes.3.A hole extraction layer based on hole conductors and oxidation cocatalysts was designed and prepared,which accelerated the transfer and consumption of photogenerated holes,and achieved high stability of the photoanode in the PEC hydrogen production system.As an excellent hole transport layer,RGO can improve the transport kinetics of charge carriers,further combine with the ability of PdS nanoparticles(NPs)to accelerate hole consumption,and effectively reduce the photocorrosion effect of photogenerated holes on photoelectrodes.Finally,the hole extraction layer based on RGO/PdS NPs achieves the rapid transfer and accelerated consumption of photogenerated holes,effectively inhibiting the photocorrosion phenomenon of CdSeTe photoanode,thereby enhancing the stability of the photoanode.The design of this hole extraction layer provides a new way for the development of new high-stability photoanodes.