Assembly Of Hierarchical Structured Electrodes Based On Fe,Co,Ni And Their Application For Electrocatalytic Water Splitting

The gradual depletion of fossil energy and the consequent environmental problems have become the most urgent issues to be solved in the course of human social development.Hydrogen is recognized as one of the most promising energy carriers in the exploration of sustainable energy development.Optical/electrocatalytic splitting of water to produce hydrogen is one of the cleanest methods.However,the optimal electrocatalysts for the electrocatalytic water splitting are noble metal materials.Their high price and low reserves limit the development of hydrogen production industry.Transition metal compounds have attracted more and more attention from scholars due to their advantages of cheapness,high availability and stability.In order to optimize the performance of the electrocatalysts based on transition metal compounds,the composition,structure,morphology and system control of the transition metal compounds have become the mainstream of this research field.Herein,based on the regulation of the composition of the transition metal compounds and the design of the structure,self-supported hierarchical structure electrodes based on transition metal oxides,sulfides,and hydroxides were prepared.They are mainly applied to the anode reaction of water splitting,and we also explores its application in cathodic reaction electrocatalysis.The content of the dissertation is divided into the following two parts:preparation and characterization of FeCoNi ternary layered metal hydroxide and NiCo₂O₄ composite hierarchical structure electrode?FeCoNi-LTH/NiCo₂O₄/CC?,and preparation and characterization of NiCo layered double metal hydroxide and NiCo₂S₄composites hierarchical structure electrode?NiCo-LDH/NiCo₂S₄/CC?.For the FeCoNi-LTH/NiCo₂O₄/CC hierarchical structure electrode,NiCo₂O₄nanoneedle array was prepared,and then the FeCoNi ternary layered metal hydroxide nanosheet was loaded on the surface of the nanoneedles by a cathodic electrodeposition method.This ternary layered metal hydroxides have superior properties to LDH materials,and the assembly of hierarchical structures provides the electrode with a large electrochemical active surface area and a smooth mass transport path.These advantages make it an excellent OER electrocatalyst and own performance for HER electrocatalysis,and it can be used to electrocatalyze the overall water splitting in alkaline solution.In OER,this electrode requires an overpotential of only 302 mV to achieve a current density of 50 mA cm^-2with excellent stability.In HER,it only requires an overpotential of 151 mV to achieve a current density of 20 mA cm^-2with excellent stability.When this electrode is used as the anode and cathode of an overall water splitting cell,only an voltage of 1.65 V is required to reach a current density of 50 mA cm^-2.For the NiCo-LDH/NiCo₂S₄/CC hierarchical structure electrode,sulfides were used for nanoneedle array substrate to further enhance its electrocatalysis activity.NiCo-LDHs electrodeposited on it ensure the stability of NiCo₂S₄,and the stability of the entire electrode is excellent.The characterization and test results show that the electrode is one of the most outstanding non-noble metal-based electrocatalysts up to now.In the OER process,only 254 mV of overpotential is needed to achieve a current of 50 mA cm^-1.It is only required an overpotential of 168 mV for NiCo-LDH/NiCo₂S₄/CC to reach a current of 50 mA cm^-2in HER.It was found that the excellent performance of these two kinds of hierarchical structure electrodes mainly comes from the following aspects:?1?The hierarchical structure exposes a large number of active sites and enhances the mass transfer process.?2?Good contact between materials at all stages leads to a rapid charge transfer process.?3?The active substance oxyhydroxide formed during the reaction further promotes the reactivity.These factors bring excellent performance to both electrodes and provide good ideas for the design and preparation of transition metal based electrocatalysts.