Controlled Preparation Of Fe-Ni Nanorods Anchoring On Graphene Architectures And Its Application In Overall Water Splitting

The reaction mechanism of Hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),as two half-reactions of overall water splitting,has been well studied.In alkaline solution,the metal oxygen-species in-situ growed on the surface of materials have been demonstrated as the real active sites for transition metal-based catalyst,especially the high valence species.To reduce the overpotential of overall water splitting and realize the technique in practical applications,the development of new catalytic materials with excellent water splitting performance has attracted the attention.In this thesis,FeNi alloy/carbon nanorods,surface oxidized FeNi alloy nanorods supported on graphene aerogel and functionalized FeNi nanorods supported on graphene aerogel were successfully synthesized by optimizing the synthetic methods and adjusting the surface electronic structure of the catalyst,The effects of activation temperature,metal loading content and the structure of carbon materials on the electrochemical properties of the catalysts are studied.From the perspective of synthetic methods and optimal electronic structure,this thesis mainly includes three parts as below.1.In order to develop the poor stability of transition metal alloys catalyst during OER process,this chapter aims to prepare the catalyst with high OER catalytic stability through introducing conductive carbon material In this chapter,FeNi/carbon nanorods(FeNi3@C)are prepared by combining simple hydrothermal and thermal activation methods.The changes of the material structure and surface chemical environment after activation treatment are elucidated by physical characterization.Meanwhile,the excellent OER catalytic activity and stability of FeNi3@C are proved by cyclic voltarnmetry and CA tests in alkaline solution,such as lower overpotential and faster charge transfer ability.To reach the current desnity of 10 mA cm-2,the overpotential of FeNi3@C is only 250 mV with the Tafel slope is only 84.9 mV dec-1.Therefore,the introduction of carbon material can significantly improve the catalytic stability of the catalytic material.2.The utilization of the active site of the catalyst can be reduced by the agglomeration phenomenon of transition metal alloys.To solve this issue in previous chapter,a porous graphene aerogel is introduced and FeNi nanorods can uniformly disperse on the pore walls of the aerogel through optimizing the synthetic conditions.Herein,surface oxidized FeNi nanorods supported on graphene aerogel(FeNi-O-rGA)was successfully prepared by hydroth ermal and high temperature activation.The porous structure can expand the contact area between electrolyte and catalyst material,and improve the electrolyte diffusion and electron transport rate.The catalyst with excellent performance can be controllably prepared by adjusting the ratio of metal to carbon substrate and regulating the conductivity and proton transfer rate.When the mass ratio of metal to graphene is 1:4,FeNi-O-rGA shows the best catalytic performance in alkaline solution.To derive the current density of 10 mA cm-2,the overpotential of FeNi-O-rGA is only 215 mV and the Tafel slope is 50.9 mV dec-1.The good electrochemical stability of FeNi-O-rGA is confirmed by 1000 CV curves and CA test for 15 h.This method provides a guideline for preparing the catalyst of transition metal supported graphene aerogels with excellent OER performance.3.Transition metal supported graphene aerogels only show excellent catalytic activity of OER,and the HER catalytic activity should be further improved to satisfy the requirement of overall water splitting.In this chapter,the functionalized FeNi nanorods supported on graphene aerogels are constructed,which can show both good OER and HER properties in electrocatalytic water splitting.A new nanorod-shaped FeNi MOF was prepared through the optimal synthetic method,and FeNi phosphides nanorods supported on phosphorus doped graphene aerogels(FeNi2P-C/P-rGA)are prepared by hydrothermal,freeze-drying methods and thermal activation apporaches.The negatively charged phosphorus atoms and positively charged metal atoms can work together as proton acceptor and hydride acceptor centers after introducing the heteroatom P.The regulated electronic structure and the improved electrical conductivity of the material can guarantee the further improvement of HER catalytic performance.Due to the unique porous structure and optimized surface electronic structure,to reach the current density of 10 mA cm-2,FeNi2P-C/P-RGA catalyst can exhibit excellent OER performance(overpotential of 210 mV and Tafel slope 50.9 mV dec-1)and good HER performance(overpotential of 93 mV and Tafel slope of 98 mV dec-1)in alkaline solution.The excellent water splitting performance of the catalyst can provide a theoretical knowledge for the further preparation of functionalized transition metal-supported graphene aerogels with excellent catalytic performance.This thesis mainly studies the controllable preparation of transition metal nanorods supported carbon materials and the subsequent functionalization treatment methods,etc.,which elaborates the influence of the important factors in the preparation process on the catalytic performance of the materials,such as temperature,metal content and carbon material ratio,phosphide.This method provides a theoretical basis for the preparation of transition metal-based catalysts with excellent HER and OER catalytic performance,provides a guarantee for their practical application in future,and further promotes their commercialization progress.