Synthesis Of Iron-Doped Transition Metal Phosphide Electrocatalyst And Their Applications In Overall Splitting Water

Because of its unique metal-like atomic structure,transition metal phosphides（TMPs）have the advantages of stable crystal structure,good conductivity,strong redox capacity,and moderate adsorption capacity for decomposed water,which is one of the research hotspots for electrocatalytic water decomposition.However,due to the shortcomings of TMPs,such as low exposure rate at the active site of catalytic reaction and poor cycle stability,their practical application in the field of hydrogen production has been greatly restricted.In order to solve the above problems,this paper focuses on TMPs nano-electrocatalysts.By constructing a high specific surface area structure and Fe element doping method,the specific surface area of TMPs is increased,more reactive sites are exposed,the electronic structure is adjusted,and the conductivity is increased.Performance,which in turn reduces the kinetic energy barrier for water decomposition and increases the catalytic reaction rate.Various characterization methods were used to analyze the element composition,electron distribution,micro-morphology,electrocatalytic activity and stability of the prepared Fe-doped composite electrocatalyst,and further explore the mechanism of enhanced composite catalytic performance.The specific research content is as follows:1.A nickel-cobalt phosphide catalyst(abbreviated as NiCo_1-xFe_xP HHAs/NF)with a Fe-doped hyperbranched and hierarchical array structure was successfully prepared by a two-step method of hydrothermal-vapor phase phosphating based on nickel foam.The amount of Fe added to explore the optimal Fe doping ratio.The NiCo_1-xFe_xP HHAs/NF catalyst was characterized by XRD,XPS,TEM,SEM,BET and other characteristics,and its electrocatalytic hydrogen evolution（HER）and oxygen evolution（OER）performance were studied under 1 M KOH conditions.The experimental results show that when the doping amount of Fe element is 10%,NiCo0.9Fe0.1P HHAs/NF catalyst has the best HER and OER performance.When the current density is 10 mA cm^-2,the HER overpotential of the composite catalyst is 122.5 mV,OER overpotential is 269 mV,and the fully decomposed water voltage is 1.57V.The excellent catalytic activity of NiCo_0.9Fe_0.1P HHAs/NF in fully decomposed water can mainly be attributed to the unique hyperbranched hierarchical array structure and the coordinated modification of Fe element doping,which increases the specific surface area of the catalyst and provides more reactive sites.At the same time,it can also adjust the catalyst’s electron distribution,increase the catalyst’s electrical conductivity,and accelerate the reaction process,thereby improving its electrocatalytic full water splitting performance.2.Using SBA-15 as a template,a Fe-doped three-dimensional ordered mesoporous structure of a cobalt cobalt phosphide catalyst(abbreviated as 3DOMeso-Co_2-xFe_xP)was successfully prepared,and XRD,XPS,TEM,SEM,BET,etc.were used.The series of characterization methods tested and analyzed the crystal phase,structural composition,and micro-morphology of the samples.The electrocatalytic performance of HER and OER was studied under the condition of 1 M KOH.It was found that3DOMeso-Co_1.8Fe_0.2P catalyst had the best HER and OER performance when the content of Fe element was 10%.The overpotentials of HER and OER were 90.6 mV and 266.4 mV,the water voltage of the two electrodes is 1.58V(current density is 10mA cm^-2).The excellent electrocatalytic activity of 3DOMeso-Co_1.8Fe_0.2P can be mainly attributed to the large specific surface area provided by the three-dimensional ordered mesopores for the catalyst,which not only provides an open space for the catalytic reaction,but also exposes the reactive sites to the maximum.The doping of Fe element also adjusted the electronic structure,reducing the internal resistance of the catalyst and further improving the catalytic activity of the composite catalyst.3.A Fe-doped two-dimensional mesh-like porous nanosheet structure cobalt phosphide catalyst（abbreviated as 2DMesh-CoFeP-x）was successfully prepared by a two-step method of solvothermal-gas phase phosphating,and XRD,XPS,and TEM were used.A series of characterizations,such as SEM,BET,etc.,were used to test and analyze the crystal phase,structural composition,and micro-morphology of the samples.The experimental results show that the 2DMesh-CoFeP-5 catalyst with Fe doping reaction time of 5 min has the best HER and OER performance in 1 M KOH electrolyte.When the current density is 10 mA cm^-2,the HER and OER overpotentials are respectively at 79 mV and 219.7 mV,at a current density of 20 mA cm^-2,the voltage of fully decomposed water was 1.55V,and 1.5V dry batteries were successfully used to drive the fully decomposed water of the two-electrode system,showing excellent catalytic activity.The catalytic performance of 2DMesh-CoFeP-5 is mainly attributed to the two-dimensional porous mesh sieve structure,which can effectively prevent nanosheets from stacking,can provide a catalyst with a large specific surface area,and expose more reactive active sites.At the same time,Fe doping can make the catalyst The pore size of the material becomes smaller and the specific surface area becomes larger.It can also adjust the electronic structure and accelerate the electron transfer rate,thereby greatly improving the catalytic activity of fully decomposed water.