Design Of Defect-induced Metal-based Photocatalytic Materials And Their Efficient Catalytic Small Molecules For Hydrogen Production

Ammonia borane（NH₃BH₃）and formic acid（HCOOH）have attracted extensive attention because of their high hydrogen content（19.6 wt%and 4.4 wt%,respectively）,good stability and non-toxic by-products.Currently,catalysts for catalytic hydrogen production from NH₃BH₃ and HCOOH are mainly based on noble metals,but their poor reserves and high prices limit the practical applications.Therefore,it is imperative to build catalytic hydrogen production systems based on/containing cheap transition metal catalysts.However,how to improve its catalytic hydrogen production activity is an urgent problem.Based on this,a series of defective mono/polymetallic photocatalysts were designed and synthesized based on the semiconductor Ce O₂,which was abundant in Inner Mongolia,and their relationships with the catalytic hydrogen production performance of NH₃BH₃ and HCOOH were investigated by modulating the composition,structure and electronic properties of the catalysts.The main results were as follows.（1）Taking Ce O₂ as the carrier,a series of visible-light-responsive Schottky photocatalysts were constructed for the room-temperature photocatalytic hydrogen production from NH₃BH₃by using Ce O₂ with different oxygen vacancy contents by different calcination temperatures and loaded with non-plasmonic metal Co nanoparticles.The results showed that improving the oxygen vacancy concentration of Ce O₂ by regulating the calcination temperature could effectively modulate its own response to visible light,the photogenerated carrier separation efficiency,and the adsorption and activation processes of the reactant NH₃BH₃ and H₂O molecules.In addition,the change of its band gap would regulate the strength of the Schottky barrier at the metal/Ce O₂ interface and improve the electron density on the active metal Co surface,which in turn significantly improved the performance of hydrogen production from NH₃BH₃.Among them,the TOF value of catalyst Co/Ce O₂-500 was as high as 301.0 min^-1,which was the highest activity value of the same type of catalyst so far.（2）Semiconductor Ce O₂ has limited visible light absorption.Polydopamine（abbreviated as PDA）was used to coat Ce O₂ with different defect contents,and 3-aminopropyl triethoxysilane（abbreviated as APTS）was added to functionalize the carrier surface with-NH₂ during the preparation of the catalyst.Trimetallic Au Pd Ni nanoparticles were loaded for high-efficiency photocatalytic hydrogen production of HCOOH at room temperature.The results showed that Ce O₂ with different oxygen vacancy contents responded differently to visible light and had different adsorption effects on reactant molecules.By regulating the thickness and cladding integrity of the PDA cladding layer and the functionalized modification to-NH₂,the modulation of the electrons in the active sites on the metal surface could be achieved,then the relationship between different catalyst structures and catalytic activity could be explored.Among all catalysts,Au Pd Ni/Ce O₂-500@PDA-APTS showed the highest photocatalytic HCOOH hydrogen production activity with a TOF value of 971.4 h^-1.The continuous innovation of defective metal-based catalysts and the full application of visible light may provide a viable pathway for the widespread use of hydrogen energy,reducing economic costs and significantly increasing hydrogen production,thus promoting the development of the"hydrogen economy".