Study On Electrochemical HER And OER By Carbon Cloth In Situ Growth CDs And Cobalt Tetroxide

The reaction of electrolytic water consists of two semi-reactions,cathodic hydrogen evolution reaction(HER)and anodic oxygen evolution reaction(OER).Many studies have sought to develop environmentally friendly and inexpensive electrocatalysts for oxygen/hydrogen reactions(OER/HER).The carbon cloth,a metal-free flexible network of intertwined carbon fibers,exhibits a large specific surface area,inspiring properties including high con-ductivity,high corrosion resistance,high chemical and mechanical stability,is a commonly used catalyst supported substrate.The active components grown directly on the carbon cloth,which is easy to regulate the morphology of electrocatalysts.In this paper,the zero-dimensional(0D)carbon quantum dots(CDs)was first grown on carbon cloth as metal-free HER electrocatalysts.Meanwhile,the Co3O4 with different morphologies were prepared by one-step hydrothermal method and annealing treatment as OER catalysts to regulate the morphology of catalysts on carbon cloth by adjusting a series of parameters.The main elements are as follows:(1)Developing hydrogen evolution reaction(HER)electrocatalysts with high activity,durability and moderate price are essential for sustainable hydrogen energy utilization.In this chapter,the 0D CDs grow directly on the carbon cloth,which can enhance electrochemical hydrogen production.We report a novel low cost,abundant source and environment CDs catalysts on CC(CD/CC)for hydrogen evolution by one-step hydrothermal method,which is synthesized via in situ grown CDs on CC.Electrochemical tests reveal that the CD/CC catalysts show outstanding HER catalytic activity with a small overpotential of 280 mV at the current density of 10 mA/cm2,a small Tafel slope of 87 mV/dec and prominent durability.Percolation theory is for the first time introduced to interpret the catalytic mechanism of the CD/CC catalysts.The special morphology assembled by the 0D carbons constitutes the percolating clusters and promote electron transport throughout the carbon cloth.Besides the nitrogen doping induced structural defects and electronic properties of the CDs themselves,the specific zero-dimension dot-shape morphology on carbon microfiber and the introduction of amide groups(CONH2)can also improve catalytic performance through lowering series resistance,increasing specific surface area,promoting electron transport,exposing more active sites,and facilitating diffusion of the electrolyte and H2.(2)We successfully synthesized Co3O4 with different morphologies on 1D carbon fiber by simple one-step hydrothermal and annealing treatment.The morphology of Co3O4 on carbon cloth can be adjusted by regulating the molar ratio of NH4F to Co(NO3)2·6H2O.By regulating the molar ratio of NH4F to Co(NO3)2·6H2O,Co3O4 can form structures such as nanosheets,nanowires,nanowire clusters and thick round nanosheets.Electrochemical tests show that the catalyst with nanowire clusters structure have the smaller overpotential,smaller charge transfer resistance and larger electrochemical active surface area,which can expose more OER active sites and promote the diffusion of electrolyte with better electrochemical OER effect.