Preparation Of Nickel/Cobalt Hydroxide Catalysts For Electrochemical Water Oxidation

The environmental issue has a great influence on our daily life and development of economy,splitting water into oxygen gas and hydrogen gas using high-efficient electrocatalyst is a novel route to relax energy crisis and climate change problem originating from the consumption of fossil source.The water splitting process can be divided into two sub-reactions:cathodic hydrogen evolution reaction（HER）and anodic oxygen evolution reaction（OER）.In contrast with the relatively facile cathodic hydrogen evolution,the anodic OER is a kinetically sluggish process in which electrons are involved for the formation of one oxygen molecule.Traditionally,noble metal electrocatalysts（e.g.,IrO₂,RuO₂）have been employed to reduce the large overpotential.However,the large-scale practical application is severely impeded by the scarcity and high cost of the precious catalysts.It is an important and difficult topic to design cost-efficient and high-active non-precious electro-catalysts to overcome the high kinetic barrier.In this paper,nickel and cobalt based materials with low cost,high electro-catalytic activity and electrochemical stability were employed to fabricate efficient anode catalysts.And this thesis contains three parts.1.A two-dimensional（2D）ultrathin Ni（OH）₂-Cu₂S nanosheet hybrid with hexagonal structure is in situ synthesized by hydrothermal reaction with Cu₂O used as the copper source.A two-dimensional（2D）ultrathin Ni（OH）₂-Cu₂S nanosheet is homogeneous in size with edge lengths of 20-30 nm.This catalyst exhibits a current density of 10 mA cm^-22 at an overpotential of 0.5 V and Tafel slope of 89 mV dec^-11 for water oxidation in 0.1 M KOH.Moreover,the nanosheets are stable and no deactivation is observed during the following cyclic voltammetry cycles,even up to 3500 cycles.2.A cost-effective and homogeneous synthetic method has been employed to prepare a kind of nanomesh flowersα-Co（OH）₂.The optimizedα-Co（OH）₂ nanoflowers with 12-15 nm perforation catalyst exhibit a high electrocatalytic activity and excellent stability for OER in 0.1 M KOH alkaline media with a relatively low overpotential and Tafel slope.After the 2500th cycle,nanoflowers display trivial loss of current density compared with the 100 th cycle,outperforming that most of other reported non-precious metal materials and the commercial RuO₂ catalyst for OER process.3.Based on the research and design of the above two catalysts,the Co（OH）₂ nanomaterials have beensynthesized with different sizes Cu₂O used as templates.Co（OH）₂ has been confirmed by TEM,which show that the material was found to be amorphous.The electrochemical stability of Co（OH）₂ samples is tested by i-t,after 24 h,the current density is 75.5%of the initial current density.