Research On The Preparation And Hydrogen Evolution Performance Of Halide Perovskites Based Photocatalysts

Developing clean energy has become the inevitable way to solve the current energy shortage and environmental pollution.Semiconductor photocatalysts can convert solar energy into high-energy-density,easy-storage,and environmentally friendly hydrogen energy.Halide perovskite materials are a kind of semiconductors with ABX₃ chemical structure,whose A,B,and X sites can be regulated under the common constraints of tolerance factor and octahedral factor to optimize their intrinsic properties.Halide perovskites derived from MAPb I₃ possess advantages over traditional semiconductors,such as wide light capture range,easily adjustable band gap,long photo-generated carrier transport path and photo-induced carrier lifetime.Therefore,halide perovskites have become a research hotspot in the field of photocatalytic hydrogen evolution reaction（HER）in recent years.This thesis mainly focuses on the design and preparation of a variety of highly active and long-term stable composite photocatalysts based on metal halide perovskites,utilizing the strategies including compositional manipulation,surface modification,and heterojunction sculpture.Then the thesis displays applications of the composites in the photocatalytic hydrohalic acid splitting for hydrogen evolution.The specific research contents are as follows:（1）An efficient and stable mixed-organic-cation perovskite MA_0.6FA_0.4Pb I₃(M_0.6F_0.4PI)integrated with Mo S₂ photocatalyst has been prepared through a simple immersion and blend procedure in saturated HI solution.By partly replacing MA⁺with FA⁺,the lifespan of photo-induced charge carriers inside pristine MAPb I₃ has been prolonged.The charge-carrier transfer&separation capabilities of M_0.6F_0.4PI has been enhanced via the surface modification of Mo S₂ nanosheets.The interaction and the electron transfer path between M_0.6F_0.4PI and Mo S₂ are confirmed by characterizations and density functional theory calculation results.The optimal composite(i.e.20wt%Mo S₂/M_0.6F_0.4PI)exhibits the highest 2131μmol h^-1 g^-1 visible HER rate,increasing by approximate 88-fold in comparison with pure MAPb I₃(24μmol h^-1 g^-1),and significantly higher than the optimized Pt/M_0.6F_0.4PI(1328μmol h^-1 g^-1)as well.Remarkably,the Mo S₂/M_0.6F_0.4PI photocatalyst displays no obvious performance degradation during the 200-hour hydrogen evolution process,ascribed to the inherent high stability of Mo S₂ as well as the dynamic equilibrium of M_0.6F_0.4PI in saturated HI solution during the photoreaction.This work offers a versatile route to fabricate efficient organic-inorganic perovskite photocatalysts by diversifying and/or mixing organic cations internally,along with loading non-precious metal cocatalyst onto perovskite externally.（2）A lead-free halide perovskite CABB decorated with Mo S₂ nanoflowers has been simply synthesized to form a kinetics-facilitated type I Mo S₂/CABB heterojunction via a facile dissolution-recrystallization process of CABB perovskite.The optimized composite,i.e.20%Mo S₂/CABB,demonstrates a visible-light HER rate of 87.5μmol h^-1 g^-1,which is ca.20-fold compared to that of pure CABB(4.3μmol h^-1 g^-1),and likewise superior to the optimum Pt/CABB counterpart(25.5μmol h^-1 g^-1).More meaningfully,the optimal 20%Mo S₂/CABB presents superior photocatalytic HER stability with no evident loss during a discontinuous 500-hour cyclic test punctuated by total 40-day storage.The Mo S₂/CABB type I heterojunction across the Mo S₂-CABB interface boosts the photo-induced charge-carrier separation&transfer process.Meantime,the edges and defects on/in the Mo S₂ nanoflowers leaning on CABB brings enriched reactive centers.Both the two aspects contribute to the improvement in the visible-light HER activity of pristine CABB together.In addition,the synergistic effect of the intrinsic high stability of Mo S₂ in HBr solution and the dissolution-recrystallization dynamic balance of CABB in CABB-saturated HBr solution enables the long-term photocatalytic HER stability of Mo S₂/CABB.This work proposes a facile and versatile dissolution-recrystallization tactic to construct lead-free halide perovskite composites combined with low-cost heterostructured cocatalysts for efficient and long-term photocatalysis.（3）SWCNT/CSI composite photocatalysts with heterogeneous structure have been synthesized by one-pot hydrothermal method.Non-noble metal single-walled carbon nanotubes（SWCNT）were in situ anchored on Cs₂Sn I₆（CSI）during the crystallization of CSI perovskite.After optimizing the usage of SWCNT,the HER rate of the SWCNT/CSI composites reach 324μmol h^-1 g^-1 under visible-light illumination,nearly 10 times equal to that of pure CSI(33.5μmol h^-1 g^-1)under the same conditions.It is worth noting that the most active composite shows excellent photocatalytic HER stability during a discontinuous cycle test for total 60 hours punctuated by 7-day storage,and there is no obvious reduction in the hydrogen evolution rate before and after the standing period.The characterization results verify that SWCNT,as highways connecting CSI,promote the rapid separation and transfer of photo-generated electrons in the CSI perovskite.Furthermore,SWCNT are in full contact with protons in the solution,providing a large-area reaction spot for the subsequent HER,thus wholly improving the kinetics of photocatalytic reaction.The synergistic effect of the inherent high stability of SWCNT in HI solution and the dissolution-recrystallization dynamic equilibrium process of CSI in its saturated HI solution throughout the visible-light catalytic HER process enables the constructed SWCNT/CSI heterostructure to retain stable photocatalytic HER.This work provides a convenient one-pot hydrothermal synthesis method for the preparation of highly efficient and stable photocatalytic heterostructures based on Cs₂Sn I₆.The prepared Cs₂Sn I₆-based heterostructures are not only suitable in the field of photocatalysis,but also expansible to optoelectronic devices and other fields.