Single/dual Co-catalyst Regulation Of Surface Polarization-electron Library Coupling For CdS-based Photocatalytic Hydrogen Production Mechanism

In recent decades,the energy shortage caused by population growth and industrialization has become a huge challenge for the environmental protection.The change from fossil fuels to new energy sources is inevitable in the background of carbon peaking and carbon neutrality.Because of its high efficiency and low cost,the clean hydrogen energy has become an important trend for future energy sources.The photocatalytic hydrogen production（PHP）technology is attracting much attention for the mild reaction conditions and the advantage of being able to directly use solar energy to convert into chemical energy.The semiconductor catalytic material is the key to PHP technology.In this paper,CdS as the main catalyst is the foundation for the study.The problems of electron-hole separation,photogenerated electron annihilation due to insufficient active sites and photo-corrosion of CdS are solved through the modification of loaded co-catalysts.The effect of temperature regulation on the matching of organic ligands and metal centers in MOF-derived co-catalysts,the effect of doping regulation on the electron arrangement in co-catalysts and the effect of organic ligand microenvironment on the attraction ability of co-catalysts were also investigated.This research aims to develop new photocatalysts with high activity,stability and applicability,and to understand the mechanism of PHP from CdS under the coupling of surface polarization and electron library.The results of this research are as follows:（1）Temperature modulation engineering and doping engineering explore the effect on PHP performance under surface polarization and electron library boosting in a CdS-based catalytic single co-catalyst system.The temperature regulation strategy is based on the thermal stability of the organic ligands in ZIF-67,and the phosphorylation of the organic ligands at different temperatures leads to different degrees of pyrolysis leading to the formation of different stable CN layers and different sizes of surface-active sites.The best match between the electron library and the surface-active sites is found when the phosphorylation temperature reaches 350°C.In other words,the electron library maintains the original ligand properties and the structure is relatively stable,and the size of the surface-active sites is in the best state.The surface Polarization-Electron library is indirectly regulated by doping engineering with the single co-catalyst.The doping engineering explores the replacement of a small amount of Co in ZIF-67 with Ni as a heteroatom for doping regulation.The introduction of Ni leads to the redistribution of electrons near the Fermi energy level of Co P,which breaks the stability inside the material and causes the surface polarization phenomenon in the Ni-Co P material.The polarization electric field generated by the surface polarization phenomenon will promote the electron-hole separation,while the electron library in the CN layer can store the electrons in the excited state to avoid annihilation due to the lack of surface-active sites,thus greatly promoting high-efficiency separation of electron-hole.The single co-catalyst（Ni-Co P）modified CdS（7%Ni-Co P/CdS）exhibited high PHP activity under surface polarization and electron library,with PHP performance 2.2 times that of 7%Co P/CdS and 15.1 times that of CdS.（2）A ternary hollow shell-core structure and a modulated microelectronic environment in the reduced region is used to explore the effect of surface polarization-electron library on the performance of PHP in a CdS-based catalytic dual co-catalyst system.A ternary hollow shell core structure and a modulated microelectronic environment in the reduced region is used to explore the effect of surface polarization-electron library on the performance of PHP in a CdS-based catalytic dual co-catalyst system.The surface polarization-electron library is directly modulated by the spatial separation property of the dual co-catalysts to separate the oxidation region（Mn Ox）from the reduction region（Co-MOF）,which directly leads to surface polarization by redistribution of electrons in the catalyst system.The microenvironment of the electron library in the CN layer is also modified by modulating the Co-MOF organic ligands in the reduced region:the electron-rich state of methylimidazole,the electron-deficient state of benzimidazole and the carbon-nitrogen-free layer of Co（OH）₂.By the relationship between the surface polarization phenomenon and the electron library is mutually beneficial:the larger the capacity of the electron library,the more photo-generated electrons are stored,leading to a stronger asymmetry in the system and therefore a more severe surface polarization phenomenon leading to the greater the polarization electric field.The better PHP performance of Mn@Cd-Co P QDs/MCN is due to the electron library consisting of methylimidazoles in their electron-rich state,which results in the high electron flux and electron storage during this dynamic process of electron migration.The PHP of Mn@Cd-Co P QDs/MCN reaches 35.31 mmol/h/g,which is superior to that of Mn@Cd-Co P QDs/BCN（PHP:23.69 mmol/h/g）and Mn@Cd-Co P QDs（PHP:11.08 mmol/h/g）.