Preparation And Electrolytic Water Splitting Performance Of NiFe-based CeO_x Composite Catalysts

Energy crisis and environmental pollution have been two major problems faced by all countries in the word.Recently,the demand and utilization of green,clean and renewable energy have increased significantly in all countries,which have triggered exploring green and renewable energy.Hydrogen technology,being one type of high value and ecofriendly energy medium,has been considered to be one of the most promising technology towards energy revolution.Electrocatalytic water spilitting is currently an attractive mass production approach of hydrogen water,which is much cleaner,more green,and better than that of other industrial methods.Generally,electrocatalytic water spilitting includes two basic half reaction process:anodic oxygen evolution（OER）and cathodic hydrogen evolution（HER）.At present,Pt/C electrode and IrO₂/RuO₂ noble metal oxide electrodes are commercial materials with excellent the HER and OER properties.However,the large-scale development and application of these materials have been sincerely limited due to high cost and scarcity of the expensive electrodes.Therefore,the design and synthesis of non-noble metal materials are of great importance.Nickel-iron based materials have attracted a lot of concern owing to their high activity,low cost and long-term durability.However,the type of electrocatalysts have been focused on OER electrocatalysis,and in particular,their poor HER performances are unable to well-match its OER performances used bifunctional electrocatalysts for overall water splitting.In this paper,we have proposed a combination of Ni/Fe-based materials and cerium oxides as an effective way to improve the performance of dual function electrolysis water.Electrocatalytical materials were supported onto foam nickel through hydrothermal synthesis,coprecipitation,and calacination protocols,giving rise to two types of composite electrocatalysts（Ni₃Fe@CNTs/CeO_x/NF and NiFe-LDH/CeO₂/NF）.Characterizatioin was carried out in terms of composition,morphology,physical and chemical properties of the two composites,and further electrocatalytical testing was also performed for the OER,HER,and overall water splitting.The main contents of this paper are summaried as follows:（1）Preparation and electrocatalytic performance of nickel foam supported Ni₃Fe@CNTs/CeO_x:Ni₃Fe@CNTs/CeO_x/NF electrocatalyst was designed and prepared from a layered yellow green nanoscale compound（NiFeCe-LDH/NF）grown on clean nickel foam via hydrothermal synthesis,followed by calcination with melamine.The composite had a self-supporting three-dimensional interconnection structure,which provided a channel for the rapid transfer of electrons and ions,and also offered fully exposed active sites and large specific surface area for the for the OER,HER,and overall water splitting.When tested in 1.0 m KOH medium,the electrocatalyst required an attractive OER overpotential of only 195 mV at 10 mA cm^-2,and 320 mV at 50 mA cm^-2;as well as a decent HER overpotential of 125mV at 10 mA cm^-2.When further applied to the overall electrolytic water splitting as a bifunctional electrocatalyst,the composite reached 10 mA cm^-2 at voltage of 1.64 V,and also exhibied an excellent cycling stability after100 h.（2）Preparation and electrocatalytical perofrmances of foam nickel supported NiFe-LDH/CeO₂:NiFe-LDH/CeO₂ was constructed by in situ growing CeO₂nanoparticles on NiFe-LDH nanosheets,in which the CeO₂ were prepared via hydrothermal synthesis and calcination procedures.The dense CeO₂nanoparticles of the composite were interconnected with the LDH sheet structure,leading to the resulting mesoporous structure and large specific surface area,and rich catalytic active sites.When tested in 1.0 m KOH,the electrocatalyst required an OER overpotential of 253 mV and a HER overpotential of 163 mV at 10 mA cm^-2.When further applied to the overall electrolytic water splitting as a bifunctional electrocatalyst,the composite reached 10 mA cm^-2 at voltage of 1.68 V,and also achieved an excellent cycling stability of 100 h.