Cd-base And Co-base Nanocrystals Located On Two-dimensional Layered Materials As Composite Catalysts Towards Water-splitting Through Photocatalysis Or Electrocatalysis

Two-dimensional?2D?layered materials?g-C₃N₄ and LDH?have shown many unprecedented properties,which offered new opportunities for constructing low-cost and high efficient photocatalysts and electrocatalysts.In the past decades,g-C₃N₄ and LDH-based semiconductor hybrid have been widely used in photocatalysis and electrocatalysis for producing clean energy and solving pollution environment.g-C₃N₄ and LDH can greatly promote the photocatalytic active of hybrid photocatalysts due to the species physical,chemical and structural properties.In the research of g-C₃N₄ and LDH-based composites,promoting visible-light absorption,increasing reactive sites and enhancing photo-induce charge separation and migration make key roles to improve catalytic active.However,noble-mental used as co-catalyst and poor efficient catalysis limited the development of g-C₃N₄ and LDH-based composites.In the field of water electrolysis device,Co-based phosphide have already received considerable attention from the research community because of its high-performance and inexpensive.In this paper,green synthesis and characterization techniques have been combined to design g-C₃N₄ and LDH-based composites as photocatalysts for hydrogen evolution by water splitting,and three-dimensional crystalline Co₂P nanoparticals/amorphous Co₃O₄microsheet as bifunctional electrocatalysts for over water splitting.In the meantime,relationship between morphology and catalytic active offer a platform to understand the catalytic mechanism.The content and type of semiconductors in composites have been tailored toward larger surface area to increase catalytic active;Meanwhile,the interference between two semiconductor has been adjusted to favor the photoinduced charge-hole separate and transport;Synergistic effect of Co₂P and Co₃O₄ and increasing of effective electrode surface area significantly enhanced its catalytic performance.The main research results can be summarized as follows:?1?2D g-C₃N₄ ultrathin microribbons were prepared by a thermal exfoliation and liquid exfoliation process,and a new type Cd_0.5Zn_0.5S QDs sensitized g-C₃N₄ microribbons photocatalysts can be further obtained via an in-situ hydrothermal method.The Cd_0.5Zn_0.5S QDs@C₃N₄ micro/nanostructures present a high-efficiency photocatalytic H₂-generation rate during water splitting process under visible-light irradiation.The optimal weight percentage of Cd_0.5Zn_0.5S QDs was found to be 32 wt%,which resulted in a high visible-light photocatalytic H₂-generation rate of 33.41 mmol h^-1 g^-1 without noble-metal as a cocatalyst.The Cd_0.5Zn_0.5S QDs in the hybrids have largely enhanced visible-light absorption;the electronic coupling between Cd_0.5Zn_0.5S QDs and g-C₃N₄ microribbons has achieved a high-efficiency separation of photo-induced electron-hole pairs,and inhibited their recombination.In addition,the high dispersion of Cd_0.5Zn_0.5S QDs on the g-C₃N₄microribbons made an important contribution to increasing photocatalytic activities due to the full exposure of active sites of QDs.?2?ZnCr-LDH,ZnAl-LDH and MgAl-LDH nanosheets assisted formation of hierarchical flower-like CdZnS@LDH microstructures.Compared with pure Cd_0.5Zn_0.5S,CdZnS@LDH hybrid has shown higher efficient visible-light-driven hydrogen evolution by water splitting.The rate of hydrogen-evolution of was enhanced with the increase of the content of Cd_0.5Zn_0.5S in CdZnS@LDH hybrid.While,the ratio of Cd_0.5Zn_0.5S and LDH is6,the Cd_0.5Zn_0.5S 6@ZnCr-LDH exhibited highest hydrogen evolution rate of 95.99mmol h^-11 g^-1.Extended hierarchical flower-like microstructure,match of the band structure and increasing reactive sites make important role in enhance visible-light-driven hydrogen evolution.In addition,the photocatalytic stability of Cd_0.5Zn_0.5S 6@ZnCr-LDH has been improved.?3?A cost-effective,easy to make and readily scalable method has been developed to fabricated three-Dimensional crystalline Co₂P nanoparticals/amorphous Co₃O₄ microsheet as bifunctional electrocatalysts for over water splitting.The resultant materials can act as self-supported bifounctional electrocatalytic electrodes for direct water splitting with excellent activity toward oxygen evolution reaction and hydrogen evolution reaction in alkaline media.When fabricated as an alkaline water electrolyzer,the bifunctional Co₂P/Co₃O₄ affords 10mA cm^-2 at a cell voltage of 1.57V.Stable performance can be mantained for at least 10h,illustrating their versatile and practival nature for clean energy generation.Increasing active sites is attributed to the small size of Co₂P crystalline nanoparticles?about 5nm?anchourd on the amorphous Co₃O₄ microsheets and synergistic effect of Co₂P and Co₃O₄ enhanced its catalytic performance significantly;simultaneously,it micro-and nanostructures facilitate the release of hydrogen gas bubles from the electrode surface,promoting mechanical stability of the catalyst.We demonstrated low-temperature phosphating treamet in Ar atmosphe induces the structural evolution from single-crystal?-Co?OH?₂ with perfect hexagonal platelets,lead to well-tuned to crystalline Co₂P and amorphous Co₃O₄ hybrids.This work will help pave the way for range of self-supported bifunctional electrocatalysts compose of nanoparticals/microsheet without noble-metal elements,and hold a promising futures as practical catalyst candidates for overall water splitting.In addition,this work provided a new strategy for the design of new earth-abundant,low-cost catalysts toward clean energy.