In-situ Preparation And Electrocatalytic Performance Study Of Nickel-cobalt Phosphide

Precious metal based catalysts have an excellent hydrogen（HER）and oxygen（OER）evolution performance,but they also have some disadvantages such as limited reserves in the earth,high price and easy shedding during the electrocatalysis process,which limit their industrial applications.Therefore,it is very necessary to find efficient,stable and cheap non-noble metal catalysts for replacing the noble metal materials.Relevant research works show that transition metals and their compounds have excellent electrocatalytic performances,among which transition metal phosphides（TMP）,especially nickel-cobalt based compounds,have attracted wide attention because of their excellent electrocatalytic activity and stability.However,in the process of constructing phosphide,the unfriendly environment steps affect its future industrialization,so it is urgent to explore the green method for in-situ engineering highly efficient nickel-cobalt phosphide and the structure-activity relationship of related materials.In the first part of this thesis,in view of the defects of unstable catalyst and environmental pollution caused by residual metal ions in the current two-step preparation method of TMP,we proposed to fabricate N-doped nickel-cobalt phosphide（N-NiCoP_x）by using Ni-Co foam（NCF）as substrate and metal source,and combining in-situ hydrothermal method with pure water and plasma-enhanced phosphating method.The optimized N-NiCoP_x/NCF catalyst has excellent HER and OER evolution performances,and the overpotentials are 23 m V and 298 m V respectively at the current density of 10 m A cm^-2,while they are only 191 m V and 410 m V when the current density is 400 m A cm^-2.In addition,the catalyst has good stability and corrosion resistance under a long-term I-t test.Meanwhile,the preparation method avoids residual heavy-metal ions in the fabrication process of electrocatalyst,thus reducing the pollution to ecological environment and the preparation cost,which provides a new idea for in-situ engineering electrocatalyst.Furthermore,the obtained catalyst is expected to be used as an efficient and stable bifunctional catalyst for overall water splitting.Based on the theoretical results mentioned above,we notice that the formed phase interfaces of nickel-cobalt phosphide are very beneficial to improve the electrocatalytic activity.Therefore,we constructed a three-phases transition metal phosphide in the second part of this thesis.In brief,using a simple electrodeposition method to deposit tin（Sn）on the surface of NCF,and then in-situ growing Sn Pi@CoP-Ni₅P₄/NCF multiphase electrocatalyst on the foam surface by direct phosphating method.The obtained electrocatalysis experiments show that the catalyst has excellent oxygen evolution performances in an alkaline electrolyte（1M KOH）,and the overpotential under a current density of 10 m A cm^-2 is only 180 m V.In addition,the excellent electrocatalytic activity of electrocatalyst is also manifested by the fact the overpotential at a high current density of 600 m A cm^-2 is only 264 m V,far exceeding that of a commercial noble metal catalyst of Ru O₂.Meanwhile,the electrocatalysts can continuously run for 10⁴ cycles and maintain a stably I-t testing for 50 hours at a low current density(10 m A cm^-2)and high current density(100 m A cm^-2).This work reveals that heterogeneous interfaces are closely related to the electrocatalytic performance of materials,and the construction of heterogeneous transition metal compounds with rich heterojunctions is beneficial to improve the hydrogen or oxygen evolution performances of electrocatalysts.