Design Of Co-based Hierarchical Nanowire Array For Water Splitting

Recent years,much more attention has been devoted to the application of clean energy due to the serious environmental pollution and the shortage of traditional fossil fuels.Compared with solar energy,wind energy and other new types of clean energy,hydrogen energy has many advantages such as easy to store and not affected by the weather.If hydrogen could be widely used,a series of environmental pollution problems and the shortage of fossil fuels can be solved.Among various methods of hydrogen energy production,the electrolysis of water possess many advantages such as high energy efficiency and simple operation,which is considered as the most promising method for hydrogen energy production.However,in the practical application process,the use of noble metal catalyst with high cost limits the mass production.Therefore,the preparation of a high efficient catalyst with lower cost to replace noble metal is crucial for the industrial production of water electrolysis.Transition metal oxides,due to their excellent catalytic properties and low prices are considered to be an effective alternative to noble metal oxide catalysts.Among them,Co₃O₄,Ni/Fe-hydrotalcite have been widely studied because of their excellent catalytic performance and easy to prepare.Catalytic reactions usually occur on the surface of the catalyst,so the geometry of the catalyst has great impact on the catalytic performance.Ordinary oxide catalyst ususally has poor catalytic performance due to poor conductivity or small catalyst surface area.In this paper,Co₃O_4-x and Co nanowire arrays with good conductive were prepared through the hydrothermal and calcined method,then combined with Ni/Fe-hydrotalcite which possess high catalytic activity to promote the overall catalytic through the synergistic effect.The hierarchical structure constructed can enhance the surface area of the catalyst and improve the contact of active site with the electrolyte to further improve catalytic efficiency.First,Co-based nanowire precursors were in situ grown on the stainless steel mesh by hydrothermal method.Then the Co₃O₄ nanowire arrays were prepared by calcining the precursors in air at high temperature.Finally,the Co₃O₄ nanowires were treated by Na BH4 to generate oxygen vacancies,which can improve the catalytic performance of the catalysts.The Co₃O_4-x@LDH hierarchical structure was successfully synthesized by electrodeposition of Ni/Fe-hydrotalcite on the surface of nanowires.After the IR compensation,the oxygen evolution overpotential is 272 m V and the Tafel slope is 85.5 m Vdec-1 at the current density of 30 m Acm-2.At the current density of 10 m Acm-2,the hydrogen evolution overpotential is-284 m V,the Tafel slope is-72 m Vdec-1,the catalytic performance is better than Co₃O_4-x nanowire arrays.In order to further improve the conductivity of the catalyst,Co-based nanowire precursors were calcined under argon/hydrogen atmosphere to produce metal Co nanowire arrays which possess better conductivity.The Co@LDH hierarchical structure was successfully synthesized by electrodeposition of Ni/Fe-hydrotalcite on the surface of nanowires.The Co@LDH hierarchical structure possesses good catalytic performance for full water splitting.At the 30 mAcm-2 current density,the oxygen evolution overpotential is 262 m V with a 39.8 m Vdec-1 Tafel slope and the hydrogen evolution overpotential is-265 m V with a-65 m Vdec-1 Tafel slope.And the catalytic activity is almost constant after 50000 s reaction indicating that the catalytic possess excellent stability.