Preparation And Performance Of Co-based Catalysts For Electro-reduction Of H₂O₂

As a liquid oxidant,hydrogen peroxide（H₂O₂）is more convenient to transport than gas oxidant,and has lower requirements on storage containers.Applying it to fuel cells can reduce the operating cost.The commonly used gas oxidant O₂has four electron transfers during reduction,while the reduction process of H₂O₂only has two electron transfers.Therefore,H₂O₂reduction requires less activation energy,and the theoretical voltage of H₂O₂reduction is higher,which can provide greater current density.However,the electroreduction reaction rate of H₂O₂is relatively slow,and H₂O₂is easy to self-decompose,which restricts the development of H₂O₂oxidizer fuel cells.It is necessary to develop an inexpensive catalyst that has high-efficiency catalytic activity for the electroreduction reaction of H₂O₂,but does not catalyze its decomposition.In this thesis,a variety of Co-based transition metal oxide catalysts were prepared on the basis of carbon cloth and nickel foam,and the catalytic behavior of each catalyst on the electroreduction of H₂O₂was studied.The main work is as follows:The polyhedron ZIF-67 was obtained by the stirring and standing method,and the ZIF-67 was calcined in argon and air successively to prepare Co₃O₄@NC composite material.When the calcination temperature in air is 300°C,the material maintains the original polyhedral structure while adding some new pore structures on the surface.Drop the material onto the carbon cloth substrate to obtain Co₃O₄@NC/CC-300 electrode.In 3 mol L^-1NaOH and 0.5 mol L^-1H₂O₂,the reduction current density on the Co₃O₄@NC/CC-300 electrode is basically stable at 249 mA cm^-2under a voltage of-0.8 V.The porous structure shortens the ion transfer path,and N doping improves the wettability of the material,making the electrode and the electrolyte more fully contact.The nano-cluster bimetallic transition metal oxide CoMn₂O₄is grown on the foamed nickel substrate by hydrothermal and air calcination methods,and Co-nano particles are deposited on the surface to obtain a Co-CoMn₂O₄/Ni foam electrode.When the electrodeposition time is 30 min,the distribution of Co particles is the most uniform and the electrode performance is the best.The synergistic effect of Co and Mn helps to improve the performance of the electrode,and the addition of Co element improves the conductivity of the electrode.In 3 mol L^-1NaOH and 0.5 mol L^-1H₂O₂solution,the reduction current density on the Co-CoMn₂O₄/Ni foam-30 electrode is basically stable at 324 mA cm^-2under a voltage of-0.8 V.The reduced graphene oxide（rGO）and nickel foam were combined by hydrothermal method to obtain rGO@Ni foam substrate.The wrinkles of the rGO nanosheets increase the surface area of the foamed nickel.The nano-flower-like Co₃O₄was prepared on the surface of the rGO@Ni foam substrate by hydrothermal again.Through a simple in-situ reduction method,the Co elemental layer is reduced on the Co₃O₄surface to obtain the Co-Co₃O₄/rGO@Ni foam electrode.The electrochemical performance test results show that the Co-Co₃O₄/rGO@Ni foam electrode has a higher catalytic activity for the H₂O₂electroreduction reaction.In 2 mol L^-1NaOH and 0.5 mol L^-1H₂O₂solutions,applying a voltage of-0.8 V,the reduction current density on the electrode reached 455 mA cm^-2.