Preparation Of One-dementional Cobalt-based Nanostructured Catalysts For Water Electrolysis

Hydrogen is a clean,efficient alternative to fossil fuels for sustainable energy development,for which the promising production method is water electrolysis.For the two key processes occurred when water electrolysis,the hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）,they always used precious metal species such as Pt,RuO₂ as the catalyst,and the high-cost limited their wide applications.Thus it is particularly urgent to develop efficient,low cost water electrolysis catalysts.At present,transition metal cobalt-based chalcogenides are considered as a type of active catalyst for OER experiments.However,during electrochemical cycling,bare transition metal catalysts with exposed active surfaces are always subject to dissolution and aggregation,and the recently developed method of encapsulating the catalyst in a thin carbon coating is particularly effective in improving stability.In addition to the stability,the carbon shell can also greatly increase the conductivity of the material,especially when heteroatoms such as N and S are doped into the carbon shell,the surface electronic structure can be adjusted to reduce the local work function and change the adsorption of the intermediates.The strength,the synergistic effect between the transition metal chalcogenide core and the doped carbon shell also greatly enhances the catalytic activity,thereby improving the electrocatalytic performance involved in various reactions.A well-designed structure with the high density of the active sites is crucial for achieving high catalytic activity.In this work,we prepared Co₉S₈ nanowires which especially are encapsulated in an unusual fluffy shell layer constructed by a continuous N-,S-codoped carbon coating decorated with copious,vertically grown,short N-,S-codoped carbon nanotubes.Such a nanowire/nanofluff combined structure provides not only many voids for rapid mass transfer,but also numerous specific surfaces for loading of active sites.In the oxygen evolution reaction,the achieved catalysts exhibit remarkable catalytic performances by showing a small overpotential of 287 mV to obtain the current density of 10 mA cm^-2.Moreover,the tightly coated carbon layer also successfully prevents the dissolution and recrystallization of the Co₉S₈ nanowires.Therefore,after the long-term test in alkaline electrolyte for 30 h,the catalyst only shows a slight loss of overpotential.The fluffy carbon shell produced in this experiment provides a novel structural design,which has obvious advantages in the exposure of high-density active sites,and can be extendly used in preparation of various functional nanomaterials.The controllable preparation of the transition metal phosphides catalysts with well designed microstructures for hydrogen evolution and oxygen evolution reaction have been studied.In this work,the precursors were grown in situ on a carbon fiber paper substrate by hydrothermal method followed by phosphating to obtain CoP@CFP catalyst.This not only simplifies the synthesis process but also ensures intimate contact between the catalyst and the electrode.This method avoids the use of a polymer binder and facilitates the transfer of electrons from the membrane surface to the solution.In addition,the presence of elemental P provides a weak"ligand effect"and"group effect",which is also an important factor for the high activity of the catalyst.