Preparation Of Transition Metal Hydroxide And Oxide Electrodes For Electrocatalysis And Photoelectrocatalysis By Electrospray Deposition

With rapid growth of the society,the demand and consumption of resources are increased.Energy shortage,environmental pollution and the greenhouse effect become severe.To solve these problems,scientists are trying to use inexhaustible solar energy,through electrochemical or photoelectrochemical water splitting,to produce clean energy hydrogen.However,the preparation of catalytic materials far cannot satisfy the actual needs of the industrial mass production.As a result,the preparation of highly efficient energy conversion and storage devices can be a major challenge in the catalytic field.Electrospray deposition technology is a kind of green and efficient thin film preparation method in the atmosphere.It can produce microstructure with high throughput and low consumption.In this technology,ion source produce charged droplets under electric field.Then the droplets deposited on the conductive substrates,forming uniform film.By adjusting the parameters in the process of deposition,electrospray deposition process can be controlled to prepare films of different properties and performance.Film materials made by electrospray deposition can be efficiently applied in the catalysis field.This work uses ferric nitrate and nickel nitrate and conductive glass?FTO?as precursors and substrates to produce three different kinds of FeCo?OH?_x thin film materials for electric catalytic oxygen evolution via electrospray deposition method in different ways.Through X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,scanning electron microscope?SEM?and transmission electron microscopy?TEM?characterization,it is found that the three FeCo?OH?_x films have different chemical composition and different microstructure.In electrochemical performance test,the current density of one FeCo?OH?_x film can reach 10 mA/cm² under the overpotential of only 355 mV.Then we make the electrospray source produce charged droplet of smaller size by adjusting the experimental parameters.Smaller droplets on the substrate with different diffusion and drying process,can prepare FeCo?OH?_x film with different surface structure,which can get the higher electrochemical activity for oxygen evolution reaction at the same time.In photoelectrochemical water splitting system,low charge transfer capability and surface recombination of the positive and negative charge are the main factor limiting the performance of photoanodes.We synthesized TiO₂ nanorod array?TiO₂NRAs?on the FTO via hydrothermal method as the photoanode material.Then we use the TiO₂ NRAs as substrates in the electrospray process to improve photoelectrochemical performance.First we prepared Co₃O₄/TiO₂ heterojunction,the build-in electric field at the interface of the two phases can drive charge transfer,resulting in enhanced photoelectrochemical performance.It is worth noting that the electrosprayed Co₃O₄ deposited selectively on the top of TiO₂ nanorods.In addition,surface states of the electrode can serve as recombination center for positive and negative charges and lower the photoelectrochemical activity.We modified TiO₂NRAs by Al₂O₃ as passivation layer through electrospray deposition technology.this method can effectively passivate surface states of the TiO₂ NRAs and double the photoelectrochemical activity of the pristine photoanode.