Synthesis And Research Of CoFe-based Carbon Nanotube Composites For Electrochemical Oxygen Evolution Reaction

Electrochemical water splitting as an efficient clean and reliable new energy technology to produce hydrogen includes two crucial half reactions,namely oxygen evolution reaction?OER?and hydrogen evolution reaction?HER?.However,in these two reactions,OER as a complex four-electron reaction process owns sluggish kinetics,which restricts the generation of hydrogen.Thus,the development of noble metal catalysts which are inexpensive,excellent in performance,and strongly durable to replace the noble metal catalyst?IrO₂,RuO₂?for reducing the overpotential and electrical power consumption is a pressing necessity.This paper is devoted to the construction of highly active cobalt-iron-based carbon nanotubes composites for the OER.Meawhile,the structural characteristics and electrochemical properties of electrocatalysts are systematically studied.The main content of the paper includes following three parts:1.A Facile preparation of CoFe₂O₄ nanoparticles on Polyaniline-Functioned Carbon Nanotubes as Enhanced Catalysts for Oxygen Evolution ReactionIn this work,a polyaniline-multiwalled carbon nanotubes?PANI-MWCNTs?supported,high performance CoFe₂O₄ nanoparticles?NPs?loading electrocatalyst?CoFe₂O₄/PANI-MWCNTs?is synthesized by a in-situ process at mild temperature?120°C?and room atmosphere.By electrochemical measurement,the electrocatalyst displays excellent OER activities at a low overpotential of 314 mV for 10 mA cm^-2 current density and a small Tafel slope 30.69 mV dec^-1 in1M KOH.Furthermore,this electrocatalyst exhibits remarkably long durability evaluated by continuously cycling 1000 cycles and stably working at 0.54 V?vs.Ag/AgCl?for at least 40 h.This may be because the introduction of PANI improved the synergistic effect between CoFe₂O₄ NPs and MWCNTs,thus promoting the activity and stability of the catalyst.Meanwhile,PANI provides more anchor sites to prevent the agglomeration of CoFe₂O₄ NPs.2.A lyophilized and thermal two step synthesis of Cobalt Iron alloy nanoparticles embedded in N-doped carbon nanosheets/carbon nanotubes for the oxygen evolution reactionHerein,a lyophilized and thermal two step procedure is adopted to synthesize a high-performance CoFe alloy nanoparticles embedded in N-doped carbon nanosheets interspersed with carbon nanotubes?CoFe-N-CN/CNTs?hybrid.The lyophilization step during catalysts preparation is beneficial to uniform the dispersion of carbon-like precursors and avoid the agglomeration of metal particles.Structurally,the porous carbon structure of CoFe-N-CN/CNTs hybrid not only provides high specific surface area and high porosity to intensify mass transfer,but also protects CoFe nanoparticles for superior stability in alkaline medium.The inserted CNTs not only can serve as a complementary site for the electrochemical reaction to promote electron transfer,but also can function as spacers to increase the basal spacing between graphite sheets for the effective transport of reactants.Besides,it can also enhance conductivity of the material.The N dopant affords more chemically active sites and anchor sites to accelerate catalytic reactions and deposit metal nanoparticles.And all these lead to a favorable stability and remarkable OER activities of CoFe-N-CN/CNTs composites with an overpotential of only 285 mV at the current density of 10 mA cm^-2and a Tafel slope of 51.09 mV dec^-1 in alkaline solutions,which is even superior to commercial IrO₂catalysts.3.Amorphous Cobalt-Iron double hydroxides decorated with N-Doped CNTs for efficient electrochemical exygen evolutionHerein,an amorphous Cobalt–Iron double hydroxides decorated with N doped carbon nanotubes?Am-CFDH/NCNTs?hybrid is synthesized by a facile and simple one-pot approach under room temperature.Through electrochemical measurement,the bare Am-CFDH nanocomposite has already shown a comparable OER activity to commercial IrO₂ catalyst on account of its amorphous nature and interaction between Co and Fe components.Whereas,the introduced NCNTs can provide better electrical conductivity,more anchoring sites and functional groups for enhancing the transfer of electron and reactants,preventing the agglomeration and stack of Am-CFDH to expose more active sites,and improving the synergistic effect between Am-CFDH and CNTs.Thus the Am-CFDH/NCNTs hybrid displays a favorable durability beyond 20 h and an advanced OER activity owning a small overpotential of 270 mV at 10 mA cm^-2 and a low Tafel slop of 56.88 mV dec^-1 in alkaline medium.