In-Situ Engineering Nickel Cobalt Based Transition Metal Chalcogenides And Their Electrocatalytic Performance

With the increased serious energy shortage and environmental pollution,as well as the requirements of environmental protection and future modern society,the transformation of China’s energy industry to renewable and sustainable energy has become very urgent.With the proposal of the concepts of carbon peak and carbon neutralization,hydrogen energy is bound to become the pillar of the future energy system.Compared with the disposable and non-renewable conventional fossil fuels,hydrogen is the lightest and richest element in the universe.Noticeably,it can be obtained from the inexhaustible water and renewable energy,and has been considered as one of the best clean energy carriers.At present,the electrolysis for water splitting for has the obvious advantages and huge application potential for H₂ production.Normally,the water splitting process can be divided into hydrogen evolution（HER）and oxygen evolution（OER）reactions,which are expected to meet large-scale commercial applications for H₂ generation.However,the most common catalytic electrode relies heavily on rare and expensive Pt,Ir and Ru-based noble metals,which hinders the industrial hydrogen production.Although transition metal compounds have been widely explored to replace precious metals for water electrolysis,only a few electrocatalysts can achieve the required activity and stability under the harsh conditions for the commercial electrolytic cells.Therefore,it is urgent to design the transition metal catalysts for realizing the cost-effective and robust hydrogen preparation.In this thesis,transition metal chalcogenides are in-situ constructed on the surface of transition metal foam（nickel iron or nickel cobalt）by the combination protocols（e.g.,atmospheric pressure dielectric barrier discharge plasma,oil bath method,precipitation standing method and hydrothermal method）.Meanwhile,the relationships among the reaction condition,material structure and electrocatalytic performance are investigated.The relevant research contents are listed as follows:（1）A stable and efficient heterostructured bifunctional electrocatalyst of NiTe-NiSe is successfully synthesized on the Ni-Fe foam by using an innovative,green and simple one-step hydrothermal method.Thanks to the hollow flower-shaped catalyst assembled with nanosheets,the active surface area of optimized electrode material is 20 times larger than that of a single NiTe/NFF or NiSe/NFF,causing low overpotentials for delivering a current density of 10 m A cm^-2(j₁₀)in the hydrogen（HER,76 m V）and oxygen（OER,164 m V）evolution processes.The OER activity of NiTe-NiSe/NFF exceeds that of benchmarked Ru O₂ even at a moderate current density region above j₁₁₅.In addition,pushed with a current density of j₁₀,the H₂ and O₂production rates are 2.07 mmol h^-1 and 0.90 mmol h^-1,respectively,which are superior to many reported transition-metal based catalysts.Noteworthy,the cell assembled with NiTe-NiSe/NFF only require 1.49 V to drive a current density of j₁₀,which is superior to that of a noble metal based electrolytic cell（1.55 V,Pt/C/NFF||Ru O₂/NFF）.In addition,NiTe-NiSe electrode still shows a high catalytic activity and stability after10000 CV cycles test and undergoing 100 h I-t process stimulated with j₁₀₀.Based on the experimental results and DFT calculations,the unexpected high catalytic performance of NiTe-NiSe/NFF is attributed to the formed heterointerfaces and mismatched crystal lattice of NiTe,which effectively optimize the electronic structure through the phase synergy and cause a low adsorption free energy for the reactive intermediates.Noted that the NiTe-NiSe nanosheet catalysts with low cost,high HER/OER performance and stability can be prepared by using an advanced interface engineering with only one step of tellurium selenidation,which provides a new idea for the design of non-noble metal electrocatalysts.（2）The nickel cobalt foam is pretreated by atmospheric pressure plasma,then the indium based precursor is grown by a unique combination of oil bath and precipitation methods,and then the highly efficient hydrogen evolution catalyst of In-Ni₃Se₄-CoSe₂/PNCF is obtained by a selenidation approach.Thanks to the customized hollow carambola morphology and the enhanced synergy on the heterogeneous interface after indium doping,the catalyst exhibits an excellent electrocatalytic performance for the hydrogen evolution reaction.At the current densities of 10,100 and 1000 m A cm^-2,the HER overpotentials are only 30,184 and362 m V,respectively.Meanwhile,the obtained catalyst has a rapid reaction kinetics,indicated by a small Tafel slope value of 33.6 m V dec^-1.Especially,when the current density is smaller than 18 m A cm^-2,the electrocatalytic activity of In-Ni₃Se₄-CoSe₂/PNCF is better than that of Pt/C.At the same time,the H₂ evolution rate of optimized catalyst pushed with j₁₀ is about 2.37 mmol h^-1,which is superior to the recently reported high-performance catalysts.In addition,the Ni₃Se₄-CoSe₂ is sprouted from the microgrooves and rough surface of PNCF,which greatly enhances the combining intensity between In-Ni₃Se₄-CoSe₂ and PNCF.After a continuous reaction in 1.0 M KOH with j₁₀₀ for more than 100 hours,the physio-chemical structure and electrochemical activity are almost unchanged.Meanwhile,a long-term stable operation over 50 h is performed in a simulated industrial working environments(85℃,30%KOH,j₅₀₀),which is also supported by the unchanged in-situ Raman spectroscopy curves.Importantly,this work provides new insights into the design of high-performance electrocatalysts for hydrogen production via intentional heteroatom doping,which is expected to be extended to other field of energy catalysis.