Synthesis,electrochemical Sensing And Electrocatalytic Hydrogen Evolution Of Keggin-type Polyoxometalates Based Metal Organic Framework Composites Electrode Materials

Polyoxometalate-based metal-organic frameworks(POMOFs)contain both high porosity of MOFs and the remarkable redox activity of POMs,which have been attracted much attention in the electrochemical field.Generally,most POMOFs materials are powders which were attached onto the surface of glassy carbon electrode with Nafion or PTFE for electrochemical process.Nevertheless,there are some drawbacks could degrade the electrochemical performance during the electrocatalytic measurement like:(1)The polymer binder may increase the series resistance and block active sites;(2)poor dispersity of crystals powders or the weak connection between crystals powder and substrates.To overcome these difficulties,in our work,the POMOFs materials were grown on the carbon cloth firmly to form a uniform crystal film through a facile one-step solvothermal method and used as conductive electrode materials to apply in electrochemical sensor and hydrogen evolution reaction(HER).The main research work is as follows:(1)Keggin-type heteropolyacids having small size can act as guest molecule to encapsulate in cavity of HKUST-1 to construct POMOFs that can increase the rigidity of MOFs structure,avoid MOFs dissolution in the electrolyte and improve its electrochemical stability.CC is a conductive substrate due to its excellent conductivity and superb corrosion resistance in harsh electrolytes.In this experiment,three electroactive polyoxometalate-based metal-organic frameworks(POMOFs)films in situ grown on carbon cloth(NENU-3/CC,NENU-5/CC and PMo12@PW12@HKUST-1/CC)were synthesized by a facile one-step solvothermal method.Furthermore,three POMOFs/CC were characterized by PXRD,SEM,XPS,IR and TGA.(2)NENU-3/CC and NENU-5/CC were used in the electrocatalytic reduction of bromate.The results of amperometric detection of NENU-3/CC to bromate show a high sensitivity of 45.11 ?A cm-2 mM-1 and a low detection limit of 0.55?M.Furthermore,NENU-5/CC can exhibit a detection limit of 1.18 ?M,and a high sensitivity of 18.83 ?A cm-2 mM-1.As a result,the amperometric determination demonstrate that two as-synthesized POMOFs/CC films as working electrode materials exhibit good sensitivity,selectivity,stability,reproducibility and repeatability to detect bromate as sensor materials.Simultaneously,in the analysis of real water samples,the detection results of NENU-3/CC and NENU-5/CC are close to those of traditional ion chromatography(IC).Thus,it is feasible for the bromate analysis in real samples using our prepared sensor.(3)The PMo12@PW12@HKUST-1/CC was converted into polymetallic phosphide(Cu-Mo-W-P/CC)through a phosphidation process,and the Cu-Mo-W-P/CC directly acted as working electrode to apply in hydrogen evolution reaction(HER)over a wide pH range.Simultaneously,NENU-3/CC and NENU-5/CC as contrast samples were changed to Cu-W-P/CC and Cu-Mo-P/CC under high phosphating temperature,respectively.The results show that the electrocatalytic activity of Cu-Mo-W-P/CC is better than that of Cu-W-P/CC and Cu-Mo-P/CC.The performance may be attributed to Cu-Mo-W-P/CC combine the excellent catalytic activity of WP,MoP,Cu3P and high conductivity of CC.Therefore,Cu-Mo-W-P/CC exhibits good electrocatalytic activity and stability.