| Silver complexes are valuable for applications in fluorescence,magnetism and catalysis due to their fascinating geometric structures and abundant chemical properties.The variable valence,unique electronic structure and redox properties of silver ions have allowed silver complexes to demonstrate potential applications in electrocatalysis,energy storage and electrochemical sensing.Currently,the precious metal-based catalysts with excellent electrocatalytic performance suffer from high cost and low reserves;secondary,alloy-based and semiconductor-based oxides are restricted in large-scale applications owing to factors such as poor stability,lower activity and less readily modifiable.Therefore,the development of silver complex electrocatalytic materials with novel structures,superior catalytic activity and easily tunable are of great practical significance,and would expand the research field of silver complexes and provide innovative ideas for the design of electrochemical catalysts.On this basis,the thesis designs and synthesizes structurally diverse novel silver complexes using azaheterocyclic silver complexes as the research target.Research on the electrocatalytic water splitting and electrochemical sensing performance of silver complex modified electrode materials and exploration of the relationship between silver complex structure and electrocatalytic activity.The specific research content are as follows:(1)The bis[1-(pyridin-3-ylmethyl)-benzimidazol-2-ylmethyl]thioether(3py-bbs)and bis[1-(pyridin-4-ylmethyl)-benzimidazol-2-ylmethyl]thioether(4py-bbs)are selected as the organic ligands.With aromatic polyacids(H2BDC=terephthalic acid,H2FA=fumaric acid,H2PIA=isophthalic acid,H3BTC=trimesic acid,H2IP=5-hydroxyisophthalic acid)as auxiliary ligands.Two types of nitrogen heterocyclic silver complexes were synthesized by the natural volatilization method by modulation of the amount of organic ligands,namely the binuclear silver complexes 1-6 and the silver coordination polymers 7-11:[Ag2(3py-bbs)2(BDC)]·2H2O(1)[Ag2(4py-bbs)2(PIA)]·CH3CN(2)[Ag2(4py-bbs)2(IP)]·C2H5OH·4H2O(3)[Ag2(4py-bbs)2(BDC)]·2CH3CN·2H2O(4)[Ag2(4py-bbs)2(FA)]·3C2H5OH(5)[Ag2(4py-bbs)2(Br)2](6){[Ag2(3py-bbs)2(FA)]·2C2H5OH·2H2O}n(7){[Ag2(3py-bbs)2(PIA)]·5H2O}n(8){[Ag2(3py-bbs)2(IP)]·2CH3CN·H2O}n(9){[Ag2(3py-bbs)2]·(BTC)·4CH3CN·H2O}n(10){[Ag3(4py-bbs)(BTC)]·2H2O}n(11)Structural analysis shows that the silver complexes 1-6 are binuclear structures,7-10 are one-dimensional chain coordination polymers,while 11 is a two-dimensional layered coordination polymer.The central silver ions of complexes 1-3 all have a triple-coordinated planar triangular geometry,the central silver ions of complexes 4-10 have a tetrahedral structure with four-coordinated deformations,and the central silver ion of complex 11 has both a linear structure with two-coordinations and a triple-coordinated planar triangular structure.The main ligands are all ligated in bidentate chelate coordination pattern in complexes 1-6,the main ligands in 7-9 have the μ2-(κ1N,N’:κ1N)coordination pattern,the main ligands in 10 have a μ3-(κ1N:κ1N,N’:κ1N)coordination pattern,whereas the main ligands in 11 have μ4-(κ1N:κ1N:κ1N:κ1N)coordination mode.The Ag-Ag bond is present in both complexes 6 and 11.The binuclear silver complexes 1-6 could be linked by π-π stacking to form a one-dimensional supramolecular chain structure.Through the structural analysis,it was demonstrated that the amount ratio of the primary ligand to the central ion and the steric hindrance may affect the coordination pattern of the silver ions,resulting in structural differences in the silver complexes.(2)The silver complex 1-11 was mixed with acetylene black,added with nafion as a binder and coated on the surface of the glassy carbon electrode(GCE)to prepare a silver complex/acetylene black/Nafion modified glassy carbon electrode(1～11-GCE).The electrocatalytic hydrogen evolution reaction(HER)activity of silver complex-modified electrode materials was investigated using cyclic voltammetry(CV),linear scanning voltammetry(LSV)and electrochemical impedance spectroscopy(EIS).The overpotential values(η10)of 1～11-GCE at a current density of 10 mA cm-2 were positively shifted by 191～355 mV with a Tafel slope of 182～260 mV dec-1 in a 0.5 M H2SO4 solution at 293 K compared to the unmodified bare electrode bare-GCE,indicating that the silver complex modified electrode exhibited better electrocatalytic hydrogen precipitation activity and the order of electrocatalytic HER activity was:two-dimensional>one-dimensional>binuclear silver complex.Further analysis of the structure-activity relationship of the complexes leads to the following conclusion:the higher the dimensionality of the silver complex skeleton structure(the higher the dispersion of the central ion),the higher the hydrogen evolution reaction activity.The silver complexes with two or three coordination are more active than the silver complexes with four coordination,probably due to the fact that the silver complexes with two or three coordination are easily deformed to form active intermediates during the catalytic process,while tetrahedral structure of four coordination is more difficult to deform.(3)The electrocatalytic oxygen evolution reaction(OER)performance of silver complex-modified electrode materials 1～11-GCE were carried out simultaneously using similar electrochemical experimental methods.The OER overpotential values(η10)of 1～11-GCE were negatively shifted by 238～399 mV and the Tafel slope was significantly lower at 0.5 M H2SO4 solution at 293 K compared to the unmodified bare electrode bare-GCE.This suggests that silver complexes 1-11 display improved OER electrocatalytic kinetic properties.In particular,the η10 value of 11-GCE during OER was reduced by maximum 399 mV in comparison to bare electrode bare-GCE,indicating that complex 11 has favourable oxygen evolution activity and electrocatalytic OER stability.The analysis of the data revealed that the order of electrocatalytic OER and HER activity of the silver complexes was essentially the identical,both being related to the degree of dispersion of the active sites of the complexes and the coordination modes of the central silver ions.(4)The electrochemical recognition properties of 1～11-GCE were investigated by chronoamperometry,which demonstrated that the silver complexes 1-11 all showed varying degrees of recognition of H2O2.Specifically,9-GCE and 11-GCE exhibited a significant response to H2O2 over a wide linear range of 0.35～4000 μM,with detection limits of 0.17242 and 0.26592 μM,sensitivities of 33.35697 and 41.36053 μA mM-1 and linear correlation coefficients of 0.99589 and 0.99287.In the presence of a series that interferes,9-GCE and 11-GCE simultaneously exhibit excellent specificity and stability.Electrochemical experiments have demonstrated the potential of 9-GCE and 11-GCE as electrochemical sensors for the quantitative analysis of H2O2.In summary,the design of the main ligand,dosage ratio of the main ligand to central ion and selection of the auxiliary ligands were employed to synthesise 11 novel silver complexes.The silver complex/acetylene black/Nafion modified glassy carbon electrode(1～11-GCE)was prepared and the electrocatalytic HER,OER and H2O2 recognition performance of complex modified electrode 1～11-GCE was investigated.The results suggested that the silver complexes 1-11 all have excellent electrochemical activity and mechanism of electrocatalysis was speculated based on the well-defined structure of the complexes.The present work opens up new avenues for the development of silver complexes containing nitrogen heterocyclic ligands in the field of electrocatalysis. |
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