Synthesis And Electrocatalytic Performance Of CoSn?OH?₆-and NiSn?OH?₆-Derived Selenide And Its Composites

As a method with high efficiency and zero pollution for producing high-purity hydrogen and oxygen,water splitting has become a research hotspot in electrochemical field.Pt-based electrocatalysts reveal impressive and excellent properties for hydrogen evolution reaction?HER?,but their rareness and ultra-high price seriously limit their scalable industrial applications.In recent years,transition-metal chalcogenides?TMCs?,cobalt selenide?or nickel selenide? with excellent HER performance has been reported in many previous literatures.However,the cobalt selenide?or nickel selenide? is prone to agglomeration in the HER,resulting in the decrease in catalytic activity.Moreover,the conductivity of cobalt selenide?or nickel selenide? is not good enough.The charge transfer rate is slow,which severely limits the catalytic performance.In this work,CoSn?OH?₆ and NiSn?OH?₆ were used as precursors to synthesize cobalt?or nickel? selenide-based composite catalyst through rational structural design.The HER performance of these catalysts has been systematically investigated.The major research contents and conclusions are as follows:1.CoSn?OH?₆ was used as the precursor,which was then transformed as hollow nanobox by chemical etching.Then,the CoSe₂-SnSe₂ nanoboxes?CSB? has been synthesized by in-situ selenization and the HER performance of CSB has been studied.After that,the reduced graphene oxide-wrapped CoSe₂-SnSe₂ hollow nanoboxes?RCSB? have been synthesized through adding graphene oxide to the CSB synthesis process.Compared to the bare CoSe₂-SnSe₂ nanoboxes,the RCSB shows better HER performance with a low onset potential of ¹70 mV vs RHE and a high current density of 34.7 mA cm^-2?at²50 mV vs RHE?.In addition,the Tafel slope of RCSB decreases from 70.3 mV dec^-1?CSB? down to 36.7 mV dec^-1.And the RCSB exhibits excellent electrocatalytic stability even after 1500 CV cycles and 16-hour current-time measure.2.The graphene/Ni_0.85Se-SnO₂?GNS? microsphere has been synthesized by facile hydrothermal method.The electrochemical measurements show that the GNS catalyst has excellent catalytic activity.GNS has a high current density of 30.55 mA cm^-2 at-300 mV vs RHE.In addition,its Tafel slope is only 35.8 mV dec^-1.Even after 1000 CV cycles and 20 hours current-time curve measure,the GNS shows outstanding long-term stability.And the morphology of GNS remains nearly unchanged.The graphene nanosheets of GNS not only substantially improve the conductivity of catalyst,but also sustain the morphology in the process of HER.3.The acidified carbon nanotubes were added during the synthesis process of the NiSn?OH?₆ precursor.And a novel porous and conductive electrocatalyst,carbon nanotubes/Ni_0.85Se-SnO₂ networks?CNSN?,has been synthesized by a facile solvothermal method.The carbon nanotubes in the CNSN not only guarantee the excellent electronic conductivity but also improve the dispersity of Ni_0.85Se-SnO₂nanoparticles.The electrochemical results show that the CNSN catalyst has excellent catalytic activity with a high current density of 40.84 mA cm^-2 at-300 mV vs RHE and an ultra-low Tafel slope of 33.2 mV dec^-1,which is comparable to that of commercial Pt/C electrocatalysts.Among the previously reported Ni_0.85Se-based electrocatalysts for HER,the CNSN has the lowest Tafel slope.