Preparation Of Selenide-based Nanoarrays Toward Efficient Electrolytic Overall Water Splitting

As a new type of secondary energy,hydrogen energy has the characteristics of clean and efficient.The process of hydrogen production from electrolyzed water is the most environmentally friendly and effective way to produce hydrogen and it will be the main way to obtain hydrogen energy in the future.However,due to the high overpotential in the electrolyzed water process,the consumption of electric energy is increased.In addition,the current precious metals used as electrolyzed water catalysts in the industry are too expensive and rare,leading to the hard application in the large-scale electrolyzed water engineering.Therefore,current researchers generally choose cheap and efficient transition metal compounds as substitutes for precious metals as electrolysis water catalysts,where transition metal selenides are recognized as hydrogen evolution and oxygen evolution bi-functional electrocatalysts because of their excellent water splitting performances.However,how to design and control the morphology structure of selenides so that it can expose more active sites and improve the stability and how to choose the appropriate material and selenides composite to further enhance the electrochemical performance is still a challenge.In order to solve the above problems,considering that the LDH?Layered Double Hydroxides?has a unique structure and properties,the work of this paper will introduce the LDHs into the preparation process of the material,and use the LDH as a precursor to prepare the selenide and LDH and selenide were assembled together.Two kinds of selenide-based catalytic materials with excellent water resolving performance were obtained.Furthermore,the structure and composition of the material were finely controlled,and the intrinsic mechanism of the electrocatalytic performance of the selenide-based material was studied.In order to obtain high efficiency and stability,the work of this dissertation has made an effective exploration for the production of a mild and simple solution of water splitting catalyst.The specific research content is as follows.?1?NiCo-LDH precursor was used to prepare?Ni,Co?_0.85Se NSAs as the electrolytic water splitting catalyst.First,a NiCo-LDH array grown in-situ on nickel foam was prepared by a rapid electrosynthesis method,and then NiCo-LDH was used as a precursor to obtain?Ni,Co?_0.85Se nanosheet array.As a bifunctional catalyst,?Ni,Co?_0.85Se NSAs exhibit excellent hydrogen evolution and oxygen evolution performance.In the two-electrode system,?Ni,Co?_0.85Se NSAs need only 1.65 V to achieve a current density of 10 mA cm-2,which is very close to commercial IrO2?Pt/C and has a stability of up to 50 hours.In this work,the effect of selenization on the material was studied by changing the selenization time.Finally,it was concluded that the material properties of selenization for 8 hours are optimal,and that the selenization time is too long will result in a decrease in performance.At the same time,the nickel-cobalt ratio of?Ni,Co?_0.85Se NSAs was adjusted by changing the feeding ratio of nickel and cobalt during the preparation of LDH,and the test showed that when the nickel-cobalt feeding ratio is 1:1,?Ni,Co?_0.85Se NSAs have the best performance.Finally,by comparing the XPS spectra of nickel and cobalt before and after selenization,the intrinsic mechanism of selenide is better than that of LDH.?2?NiFe-LDH and Ni_0.85Se nanowires were composited to prepare the core-shell Ni_0.85Se@NiFe-LDH water solution.Ni_0.85Se nanowires grown in-situ on nickel foam were prepared by nickel selenization with nickel foam as the nickel source.NiFe-LDH was rapidly encapsulated on the NiO.85Se nanowires by electrosynthetic method to obtain core-shell Ni_0.85Se@NiFe-LDH.As a dual-functional catalyst,Ni_0.85Se@NiFe-LDH exhibits better hydrogen evolution and oxygen evolution performance than NiFe-LDH and Ni_0.85Se,and only needs 1.51 V at 10 mA cm-2 in two electrode systems.It is one of the best performances reported in many water-resolving materials.The work of this dissertation also regulates the NiFe-LDH coating amount on the nanowires by changing the time of NiFe-LDH electrodeposition.Through tests,it is found that the material exhibits the best performance at 50 s,which proves that the NiFe-LDH is coated too much which will cover the active site of Ni_0.85Se.Finally,by comparison with other hydrotalcite-coated materials,it is proved that the production method of Ni_0.85Se@NiFe-LDH is the most energy-saving and simple,and it has the best water-splitting performance.