Research And Application Of Electrochemical Performance Of Non-metallic Carbon And Transition Metal Materials

In the current infrastructure of energy,non-renewable fossil energy still stands a dominant position,resulting in environmental pollution,limate warming and other issues.Developing clean and renewable new energy is the key to solve these issues.Hydrogen,as an effective energy carrier,is considered as a new energy source with potential to replace traditional fossil fuels.Hydrogen from water electrolysis has attracted wide attention in the scientific community.Hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?are cathodic and anodic reactions for water electrolysis,respectively.Because of the slow kinetics process of the both reactions,catalysts are needed to reduce the activation energy of the reactions.Nowadays,Pt-based and RuO₂ are the best catalytic materials for HER and OER,respectively.However,their wide applications are limited by the lack of earth reserves and poor catalytic stability.Therefore,efforts should be made to develop non-precious metal materials and even non-metallic materials to promote the application of water electrolysis.This thesis mainly designed and prepared non-metallic functional carbon materials and transition metal compounds catalytic materials,studied their application in the electrolysis of aquatic hydrogen production,and discussed in detail the structure,morphology and catalytic mechanism of the materials.The main work and research results are as follows:?1?HER catalytic performance of HT-AFNG.Specifically,HT-AFNG?highly torn amine functionalized nitrogen doped graphene?has been synthesized by a simple procedure involving the synthesis of the AFNG through the hydrothermal reaction and the subsequent tearing of the AFNG through the ball milling in the presence of KOH.The obtained HT-AFNG shows improved catalytic activity for the HER.Its amine functionalized and nitrogen doped structure plays an important role in the high performance of the HT-AFNG,since the amine group lowers the|?G_H*|value of the HT-AFNG and increases the electron transfer capability of the NG.Additionally,the highly torn structure also makes a big contribution on the improved catalytic activity of the HT-AFNG.That is because the highly torn structure facilitates the formation of a solid with a porous morphology,which enables a good accessibility of the active sites for the HER.?2?HER and OER catalytic performance of sulfur-nitrogen co-doped graphene supported cobalt-nickel sulfide composite catalyst?rGO@SN-CoNi₂S₄?.The rGO@SN-CoNi₂S₄ is synthesized simply via a one-step hydrothermal method.As a bifunctional catalyst,rGO@SN-CoNi₂S₄ exhibits excellent electrocatalytic performance of HER and OER under alkaline conditions,and has lower precipitation potential?35 mV vs RHE and 290 mV vs RHE,respectively?,which is obviously superior to monometallic sulfides and shows excellent stability.The CoNi₂S₄ particles are encapsulated and embedded in graphene,which effectively avoide its corrosion and detachment in the catalytic process.At the same time,the doping of sulfur and nitrogen heteroatoms can effectively adjust the electronic properties between metal sulfide and graphene,accelerate the electron transfer rate,and maximize the high conductivity of metal sulfide in the catalytic process.?3?HER and OER catalytic performance of cobalt-iron based compounds?CoFe₂O₄,CoFe and CF-P?.The cobalt-iron based compounds?CoFe₂O₄,CoFe alloy and CF-P cobalt iron metal phosphide?are synthesized by pyrolysis-reduction/phosphating method on the basis of template method.The spindle morphology of MIL-88 MOF is retained and secondary nanoparticles are formed on the surface.By comparing the electrochemical catalytic performance of the three catalysts,it can be found that the metal phosphide CF-P exhibits the best HER catalytic performance in acidic and alkaline electrolytes,with the precipitation potential of 90 mV vs RHE and 149 mV vs RHE,respectively.At the same time,OER test results shows that it also has the best catalytic performance,and the precipitation potential is290 mV vs RHE.Through analysis,it is found that the synergistic effect between the two phosphides in CF-P improves the material properties,and the secondary particles after high temperature sintering are beneficial to further exposure of active sites and ion transport.?4?HER and OER catalytic performance of nickel foam supported cobalt phosphide/nickel phosphide?Co₂P-Ni₂P/NF?.The Co₂P-Ni₂P/NF is synthesized by simple low-temperature phosphating method and shows a fascinating catalytic bifunctionality for HER and OER.When used as the catalyst for the HER,the Co₂P-Ni₂P/NF exhibits an onset potential of 18 mV vs RHE.When used as the catalyst for the OER,the Co₂P-Ni₂P/NF only needs overpotential of 230 mV vs RHE to deliver a current density of 50 mA cm^-2.The systematic analysis shows the changes of the structure and morphology of the Co₂P-Ni₂P/NF during in the initial periods of HER and OER.Specifically,the surface roughening and the formation of M-P-O?M=Co and Ni?at the surface can be observed when the Co₂P-Ni₂P/NF is used for the HER after 10 cycles of the CV scans,and the surface roughening and the formation of a thin layer of amorphous MOOH?M=Co and Ni?at the surface can be observed when the Co₂P-Ni₂P/NF is used for the OER after 10 cycles of the CV scans.The surface roughening and formation of M-P-O and MOOH may be responsible for the Co₂P-Ni₂P/NF with enhanced catalytic activity for the HER and OER.Additionally,the Co₂P-Ni₂P/NF is also usable as both the cathode and anode for the water splitting electrolyzers and shows enhanced performance for overall water splitting.This thesis mainly focuses on the exploration of water electrolysis catalyst performance and catalytic mechanism.The non-metallic carbon-based electrolytic water cathode catalytic materials and three bifunctional catalytic materials,rGO@SN-CoNi₂S₄,CF-P and Co₂P-Ni₂P/NF,have been synthesized.These studies are of great significance to the design and commercial application of catalytic materials for water electrolysis.