Synthesis Of Organic Polymer Containing Salen Structural Units And Their Electrocatalytic Performance In Hydrogen Evolution By Water Splitting

Developing green hydrogen production technology through water electrolysis is important to achieve sustainable development.The kinetics of hydrogen evolution reaction（HER）in water electrolysis is slow,requiring catalyst to decrease overpotential to reduce power consumption and improve energy conversion efficiency.Therefore,designing and developing efficient and stable catalysts is the key to improving the efficiency of water electrolysis.Covalent organic polymers（COPs）formed by covalent bonding of organic ligands due to their adjustable structure,large specific surface area,and good stability have received widespread attention in the field of electrocatalysis.In this paper,author synthesized one-dimensional metal covalent organic polymers（M-COPs）using Salen（N,N’-ethylidene bis（salicylidene））as the construction unit for electrocatalytic HER research.Experiments combined with density functional theory（DFT）calculation,author studied the electrocatalytic HER performance and activity enhancement mechanism of different materials,and revealed the structure-activity relationship of M-COPs based electrocatalysts.The specific research content is as follows:（1）Preparation of one-dimensional binuclear cobalt（Ⅱ）polymer and study on their synergistic electrocatalytic performance for hydrogen evolution:In this chapter,one-dimensional binuclear cobalt polymer（Co₂ polymer,Co₂-P）and mononuclear cobalt polymer（Co polymer,Co-P）containing Salen structure were synthesized by using 2,2-dimethyl-1,3-propanediamine and linear biphenyldialdehyde as building units.In 1 M KOH alkaline solution,binuclear Co₂-P exhibited superior electrocatalytic HER performance compared to mononuclear Co-P.At an overpotential of 540 m V,the mass activity of Co₂-P was 1233.7 m A/Co_mg,which was 36 times that of Co-P.DFT calculations result indicate that Co₂-P has a more favorable water adsorption energy(ΔG_*H2O)and hydrogen adsorption energy(ΔG_*H)than Co-P,so that Co₂-P has better water dissociation ability.Author also explored the mechanism of binuclear synergistic catalysis of HER through a series of experiments.The experimental results indicate that the electrocatalytic HER activity order of Co₂-P in different alkali metal cations is K⁺>Cs⁺>Na⁺>Li⁺,and does not follow the hydration ability order of cations（Li⁺>Na⁺>K⁺>Cs⁺）.The infrared experiment further indicates that alkali metal cations are more inclined to adsorb on the active surface of Co₂-P,and the adsorption order is consistent with the active order,indicating that alkali metal ions affect HER kinetics under alkaline conditions（2）Mononuclear cobalt（Ⅱ）modulates the electronic structure of Pt nanoparticles to accelerate hydrogen evolution reaction kinetics:Author synthesized bimetallic catalysts Pt-NPs@NPCNs-Co by loading the previous chapter’s Co-P and Pt NPs on heteroatom doped carbon nanotubes（NPCNs）.In 1 M KOH solution,Pt-NPs@NPCNs-Co showed higher activity than single metal Pt-NPs@NPCNs and NPCNs-Co with overpotential of 182 m V at the current density is 10 m A cm^-2,and the overpotential at a current density of 40 m A cm^-2 is lower than commercial Pt/C.The mass activity of Pt-NPs@NPCNs-Co is 2.8 times that of commercial Pt/C at the overpotential of 50 m V.DFT calculation shows that the coordination Co atom can indirectly modulate the electronic structure of Pt NPs,promote the water dissociation step,thereby improving the HER kinetics.