Design And Properties Of Catalytic Water Splitting Electrode Materials

Water splitting is an efficient way to produce clean energies.It often involves two half reactions,which are hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.These reactions involve multi-step electron transfers,thus requiring the highly efficient catalytic materials to reduce their kinetics barriers,and thereby to accelerate the whole water splitting reaction.In this dissertation,I designed a series of catalytic electrode materials for OER and HER via improving their structures,components,and interfaces.The main research achievements are listed as follows:A mild oxidation and doping method was developed to prepare a three-dimensional nitrogen and sulfur co-doped graphite foam.This foam has high conductivity and strength;and the porous structure in its interlayer can promote the transportation of ions and desorption of bubbles.It also has excellent electrochemical activities,thus can be directly used as a self-supported conductive electrode.Its catalytic performance for OER in an alkaline media is much higher than that of reported carbon-based catalysts.A simple and fast electrochemical method was developed to produce a three-dimensional NiFe/graphene composite electrode.This electrode has an interpenetrated and open porous architecture,which is in favor of exposing the active sites,transporting ions in the electrolyte,and desorbing the generated bubbles.The activity,kinetics,and stability of this electrode for catalytic OER in an alkaline media are much higher than those of commercial Iridic oxide catalyst.A controllable electrodeposition method was developed to prepare a n ultrathin layer of NiFe alloy on the surface of silicon?Si?electrode.This NiFe alloy works as both protective and catalytic layer of Si,and can efficiently improve the interfaces of Si and electrolyte.It provides large band bending at NiFe/Si interface and high efficiency of hole injection at NiFe/electrolyte interface.Thus,the prepared photoanode has an outstanding performance for photoelectrochemical catalysis of OER.In an alkaline media and one sun illumination,the onset-potential of this photoanode for OER is 620 mV far ahead that of common electrocatalysis.It can also keep continuous working for more than 100 h in an alkalescent solution.A hydrothermal method was used to prepare two polymorphs of nickel hydroxides?Ni?OH?₂?,which are used as co-catalysts to adsorb on the surface of Pt electrode,and finally inducing the Ni?OH?₂/Pt composite electrodes.Among them,the?-Ni?OH?₂ has strong hydrogen bonding interactions with water molecules and strong charge transfers with Pt substrate,thus largely improving the activity and stability of?-Ni?OH?₂/Pt electrode for catalysis of HER in an alkaline media.A versatile and industrializable method was developed to produce a large-area graphene-bimetal composite film.This film has superior conductivity,flexibility,and strength,thus can be directly used as the catalytic electrode.The film electrode delivered excellent performance to catalytic OER and HER even at a low mass loading,largely improving the conversion efficiency of active metal centers.The assembled two-electrode full water splitting system has a low cell voltage and high stability?more than 200 h?;these performances are much superior to those of the commercial Pt/C||IrO₂ system.