Effective Construction Of Dual-Functional Nickel-Iron-Cobalt-Based Phosphide Catalysts And Performance Of Electrochemical Water Splitting

With the improvement of human living standards and industrialization,the demand for energy has been increasing.Currently,energy derived from non-renewable energy sources such as coal and oil,promotes the economic development.At the same time,it has caused serious environmental problems.Therefore,it is an effective way to explore renewable energy sources to replace fossil fuels.Hydrogen energy,with high energy densit y and no pollution,is considered a new energy source.Hydrogen production by overall water splitting is considered to be the simplest and most efficient method.Overall water splitting usuall y includes two half res ponses:hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.However,the high energy barrier seriously hinders the efficiency of overall water splitting.Thus,it is necessary to prepare efficient catalysts to solve this problem.Currently,the best electrocatal ysts are noble metal catal ysts such as Ir O₂ and Pt/C,but the high price and rarit y limit the actual application of these catal ysts.Due to friendly environmentally,high efficiency and low cost,transition metal-based catalysts have gained wide attention among various researchers.Therefore,three efficient and stable transition metal-based nanocomposites are introduced in this paper,and the performances of HER and OER are studied for overall water splitting.The specific contents and conclusions of this paper are as follows:The CoP@NC nanocomposite a re obtained by the method of low-temperature phosphorylation,on the basis of ZIF-67 as the template and precursor.In CoP@NC,cobalt ions,with good dispersion prosperity,achieve the doping of nitrogen,and after low-temperature phosphorylation,the thin layer-like structure of the surface increases the specific surface area.It is revealed that CoP@NC-350 has the most outstanding HER and OER catalytic activity in alkaline environment by electrochemical performance characterization,which further illustrated by SEM,TEM,XRD,and XPS characterization.Thus,CoP@NC-350 is assembled as a bipolar electrocatalyst to test the overall water splitting performance.The results showed that a low voltage of only 1.69 V could obtain 10 m A cm^-2.It is demonstrated that low-temperature phosphorylation is considered as an effective method to get transition metal-based overall water splitting catal ysis.NiFe-LDHs are synthesized by hydrothermal method,and NiFe P/Ce Ox LDHs catalysts are constructed by electrodeposition and low-temperature phosphating method.The multilayered sheet structure of NiFe-LDHs provides more catalytic active sites,and the conductivity of the catalyst is further enhanced after phosphorylation.The unique 3D structure of nickel foam binds strongly to the catalyst,which reduces resistance generation.NiFe P/Ce Ox LDHs combines the advantages of NiFe-LDHs and phosphides and exhibit excellent HER and OER catalytic performance and cycling stability in alkaline conditions,which is superior to similar electrocatalysts.NiFe P/Ce Ox reaches a current density of 10 m A cm^-2with only 1.59 V,and after 40 h,the voltage hardly rises.The La_0.5Sr_0.5CoO₃@MoS₂ nanocomposites are obtained by sol-gel and hydrothermal methods,and the effects of the synthesis methods on the microscopic morphology of the catalysts are investigated.By SEM and electrochemical performance characterization,it is concluded that the electrochemical performance of La_0.5Sr_0.5CoO₃ made by sol-gel method is excellent,and the MoS₂ is compounded on its surface by hydrothermal method to get La_0.5Sr_0.5CoO₃@MoS₂ heterogeneous structure.MoS₂ improves the conductivity and mass transfer capability of the catalysts.In alkaline conditions,the HER and OER performances of La_0.5Sr_0.5CoO₃@MoS₂ are tested and the current density of 10 m A cm^-2is 228 m V and 349 m V,respectively.The La_0.5Sr_0.5CoO₃@MoS₂ is assembled as a two-electrode catalyst for electrochemical water splitting and the current density of 10 m A cm^-2 is obtained at a low voltage of only 1.65 V under alkaline conditions,showing an excellent total hydrolysis performance.