Design And Preparation Of Highly Efficient And Stable Co₃S₄-Based Electrocatalysts For Hydrogen Evolution Reaction

Hydrogen energy with high-energy density and zero-carbon emission is considered as a promising alternative clean energy to tackle effectively the significant puzzle of sustainable development of human society caused by energy exhaustion and serious eneroviemental pollution.Electrochemical water splitting,as a promising hydrogen production method with tadvantages of high-efficiency,green,and high-purity,has attracted great interest in the past decades.Developing highly active and durable electrocatalysts is essential for realizing the energy conversion between electric energy and chemical energy stored in H₂.Earth-abundant and low-cost cobalt-based compounds still suffer from the problem of insufficient intrinsic catalytic activity and durability,which is promsing to be sloved by optimizing their electronic structure.Therefore,this paper major fouse on solving the scientific problem of how to effectively adjust electronic structure and further enhace the intrinsic catalytic activity of Co₃S₄-based compounds.Firstly,Co₃S₄/CC HER electrocatalyst with good conductivity was prepared.Then,highly HER efficient and stable P-Co₃S₄/CC was successfully obtained by doping P atoms into Co₃S₄/CC.The theoretical calculations and experimental results further illustrated the in-deth mechanism of the improvement of HER performance for the prepared cobalt-based compounds.Hence,this work has provided an easy-to-operate and feasible design strategy to further explore the efficient and stable cobalt-based compounds and even other non-novle metal-based electrocatalysts.The main contents of the paper are as follows:（1）Co precursor nanoneedle array（Co precursor/CC）was grown vertically on a clean carbon cloth（CC）by the chemical bath deposition method（CBD）,then the Co precursor/CC was converted into Co₃S₄/CC without damaging the nanoneedle array structure by hydrothermal reaction and the crystalline of Co₃S₄ was well preserved.The in-situ growning on CC of the spinel structure Co₃S₄ with good conductivity can increasethe electron transfer speed and avoide the blocking of active sites due to the use of binders.Electrochemical test results show that the HER activity of Co₃S₄/CC significantly improved superior to that of Co precursor/CC.The Co₃S₄/CC nanoneddle arrays require the overpotential under10 m A cm^-2 is 182 m V and Tafel slope is 135.1 m Vdec^-1,and it can operate stably at10 m A cm^-2 over 24 h in 1 M KOH solution.（2）On the basis of chapter（1）,P-Co₃S₄/CC nanoneedle arrays were prepared by solid-gas reaction in a tube furnace under Ar atmosphere.The phase and composition characterization results shown that the morphology and crystal structure of the as-prepared electrocatalyst were well maintained,and phosphorus eletment was successfully doped into Co₃S₄/CC.The P-Co₃S₄/CC shown the excellent HER performance with only require an ultrasmall overpotential of 65 m V to provide 10 m A cm^-2 and a low Tafel slope of76.6 m Vdec^-1during HER process.Furthermore,it can operate stably with 25 hours in 1 M KOH under various test current density.The experimental results and theoretical calculations illustrate that substituting part of S atoms in spinel-type Co₃S₄with P atoms can effectively tune their electronic structure to obtain a higher concentration of catalytic sites(the Co²⁺ion),activate the absorbed water molecules on the tetrahedron Co²⁺ions,and accelerate the charge transfer,thereby evidently promoting the HER activity of P-Co₃S₄/CC.This work has uncovered the mystery of the catalytic mechanism and the real active site of spinel-structured Co₃S₄ during the HER process in alkaline electrolyte and has served an easy-to-operate and feasible design strategy to enhance the HER electrocatalytic activity of spinel-structured compounds by doping nonmetal elements to adjust their electronic structure and improve their intrinsic catalytic activity.