Synthesis And Electrocatalysis Performance Of Cobalt-based Nanocomposites

In recent years,energy crisis and environmental problems have greatly threated the sustainable development of human society,therefore development of clean,renewable and high efficient new energy can solve the problem.Among varieties of new technologies,fuel cell has drown great attention due to its high efficiency of energy conversion.But the cathode of fuel cell,that is oxygen reduction reaction?ORR?,is a slow kinetics reaction.It is high time to develop effective electrocatalysts toward oxygen reduction reaction.Another energy technology,electrochemical water splitting,is an important method to for production of H₂.Although noble platinum?Pt?and its composites are acknowledged as the most efficient electrocatalysts for hydrogen evolution reaction?HER?,the rarity,high cost and insufficient stability limit their large-scale applications.On the other hand,the oxygen evolution reaction?OER?,a crucial half-reaction in water splitting,is often considered as the bottleneck of water splitting due to its sluggish kinetics.Therefore,it is highly desired to exploit earth-abundant catalysts with both OER and HER performance to improve water splitting application.Transition metals,especially Co-based nanomaterials with unique physical and chemical properties,are widely used in electrocatalysis.In this paper,we explored a variety of Co-based nanocomposites,focusing mainly on the preparation process and their electrocatalytic properties.The contents of this paper includes the following three parts:1.In-situ fabrication of Co nanoparticles embedded 3D N-enriched mesoporous carbon foam electrocatalyst with enhanced activity and stability towards oxygen reduction reactionIn this work,a well-designed high-performance catalyst for ORR was synthesized via a facile one step Co-MOF carbonization method,in which Co-MOF was prepared using the cobalt acetate tetrahydrate and2,2'-bipyridyl-5,5'-dicarboxylic acid?H₂bpydc?as the only raw materials and H₂bpydc as the favorable carbon and nitrogen source for in situ nitrogen doping and metallic cobalt reduction.The resultant 3D mesoporous carbon foam catalyst with embedded Co nanoparticles?CoN-CF?is enriched with nitrogen,which exhibits high specific surface area and abundant N-doping active sites for catalytic ORR.In particular,the optimized CoN-CF-700 sample displays the best catalytic performances including onset potential of 0.94 V,half-wave potential of 0.85 V,long-term durability and superior resistance to methanol poisoning.The demonstrated synthetic strategy provides a new insight into easy-synthesis and high-economy routes for metal-N-C catalysts and a deeper understanding of the effects of microstructures on catalytic mechanisms.2.Facile sequential ion exchange strategy to synthesize CoSe₂/FeSe₂double-shelled hollow nanocuboids for highly active and stable oxygen evolution reactionIn this work,we report for the first time on a novel multicomponent metal selenide electrocatalyst based on CoSe2/FeSe2 double-shelled hollow nanocuboids?CoSe₂/FeSe₂ DS-HNCs?with highly oxidative Co³⁺species,which is synthesized via a facile sequential ion exchange strategy.The solid Co-precursor nanocuboids are first converted into the intermediate Co₂[Fe?CN?₆]with a mesoporous and double-shelled hollow structure produced through a facile ligand exchange at room temperature,and then the final CoSe₂/FeSe₂ DS-HNCs are obtained by a subsequent Se ion exchange reaction.The intermediate product of Co₂[Fe?CN?₆]plays an important role not only in constructing double-shelled hollow structure but also in providing the Fe source for the growth of the final multicomponent metal selenides.Benefiting from the nanosized double-shelled hollow structure and mesoporous double-metal selenide shells with highly oxidative Co³⁺species,the as-prepared CoSe₂/FeSe₂ DS-HNCs exhibit superior OER performance to state-of-the-art metal selenides,including a small overpotential of 240 mV at the current density of 10 mA cm^-2 and the excellent electrochemical durability over 50 h.This work opens up a new avenue towards developing highly active multicomponent noble-metal-free electrocatalysts.3.Self-sacrifice template to construct porous Mo-doped Co?OH?₂nanosheet-crossed nanotubes for efficient overall water splitting.In this work,MoO₃ nanorod template was first prepared by a simple hydrothermal method and then a core-shell structure was prepared with Co-MOF growth on the surface of MoO₃ nanorods at room temperature.Finally,porous Mo-doped Co?OH?₂ nanosheet-crossed nanotubes were prepared by a simple reaction with NaMoO₄ at 85 ^oC.The as-prepared Mo-doped Co?OH?₂ NS-NTs showed excellent catalytic performance and stability of OER and HER and achieved overall water spliting.