Synthesis Of Cobalt-based Nanostructures And Nickel Phosphides For Electrochemical Water Splitting

Electricity-driven water splitting to produce hydrogen fuels and oxygen is considered as the most promising technologies for sustainable energy due to its high calorific value,zero-emission and renewable character.Especially,hydrogen energy is believed to be the most representative green energy and has been received extensive attention.In the past decade,hydrogen production technology,such as photoelectrochemical water splitting,although it has made some progress through utilizing high-efficiency electrocatalysts for hydrogen evolution and oxygen evolution,the HER performnaces is not very satisfied compared to commercial Pt/C catalyst.As a result,exploiting low-cost,large sacle and high HER performances electrocatalysts still remain a challenging nowadays.This thesis are focused on the synthesis of cobalt-based nanostructures and nickel phosphide catalysts and their electrochemical HER performances.The main research contents are as following:1.The hydrothermal method was used to produce CoMoOx nanorods,a layer of ZIF-67 was grown on the nanorod during the subsequent water bath to obtain CoMoO_X@ZIF-67.Wherein,TAA act as S resource to modulate different S doping amounts.Results have shown that the non-metallic element S can adjust the electron distribution of the 3d orbit of the metals Co and Mo in CoMoOx through different amounts of S doping,which take great influence on HER and OER properties.After long-term electrocatalytic cycling,the materials showed excellent HER and OER stability.In addition,an overall water splitting device was assembled,then the current density of 10 and 20 mA cm^-2can be quickly achieved at a small cell voltage of 1.57 V and 1.63 V,respectively,and remains stable for at least 12 h at 10 mA cm^-2.2.A kind of CoOOH/Ni foam?NF?was synthesized via a simple electrodeposition method,after a hydrothermal-sulfurization process,then,a kind of sheet-like Co-O-S/NF composite was obtained.The prepared samples are characterized by XRD,SEM,TEM,XPS techniques.Results indicated that S doping maybe produce a active center of the S-Co,and increase the contact area between catalyst and electrolyte.In addition,the facile sulfurization makes itself incomplete amorphous.We tested the final product for HER property in 1 M KOH and found that the overpotentials are 118 mV and 177 mV at current density of 10 mA cm^-2,20 mA cm^-2,respectively.Moreover,its HER activity remains almost constant after 24 h cycling at 10 mA cm^-2testing condition.3.In this chapter,first,the layered Ni precursor was synthesized by hydrothermal method,and then a three-dimensional NiPx microsphere can be formed through high temperature phosphidation treatment.Results have shown that it is difficult to obtain pure phase through the high-temperature phosphidation treatment.Moreover,the HER property was conducted in0.5 M H₂SO₄,electrochemical data demonstrated that its HER performances can be modulated via changing the Ni/P molar ratios and the phosphidation temperatures,results found that the overpotential is 131 m V at a current density of 10 mA cm^-2,and the CV curve remains stable after 3000 cycles.