Transition Metal Compound Modified Carbon Composites Materials And Electrocatalytic Performance

The development and utilization of fossil energy has promoted the development of society.Unfortunately,for the lack of awareness of resource conservation and environmental protection,human beings have fallen into the global energy crisis and environmental pollution.In order to achieve the prosperity and development of all countries,the ideal green life of human beings is crucial to seeking new and sustainable clean energy.Clean energy such as wind,tidal,solar and geothermal energy is hampering its wide range of applications due to the lack of suitable energy storage technologies.Catalysts of hydrogen evolution reaction?HER?,oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?are particularly important for promising clean energy technologies such as metal-air batteries,fuel cells and water decomposition.However,current platinum-based catalysts and ruthenium/iridium oxide noble metal catalysts hinder the further development of these materials for renewable energy technologies owing to their scarcity,high cost and poor durability.Carbon-based catalysts are the most ideal electrocatalysts for energy storage conversion because they are rich in resources and low in cost.In this paper,metal-organic frameworks?MOFs?precursor was synthesized by simple precipitation method.Core-shell nanostructured composite carbon materials composed of nitrogen-doped carbon shells-encapsulated iron-cobalt mixed metal carbides were obtained through pyrolysis of metal organic framework precursor.When the precursor was pyrolyzed at 600°C,a complete core-shell structure was obtained.Core-shell nanostructured composite carbon materials were used in the HER test with poor catalytic activity and stability.The mixed bimetallic?Co,Fe?carbide nanocluster embedded in the hollow carbon spheres was obtained after heated inorganic acid etching.The composite exhibits good electrocatalytic activity in both hydrogen evolution and oxygen reduction reactions.Hollow carbon spheres were obtained under optimized conditions for the hydrogen evolution reaction with overpotentials of 180 mV at a current density of 10 mA·cm^–2 and Tafel slope of 90mV·dec^–1 in acidic media.The hollow carbon spheres also exhibited favorable activities toward oxygen reduction with a rather high half-wave potential of 0.82 V?vs.RHE?and electron transfer number of 3.8,high methanol tolerance,and robust stability.These excellent performances demonstrate their promising potential for application in fuel cells,metal–air batteries and water splitting devices.On this basis,the core-shell structure composed of cobalt-iron mixed metal carbides coated with nitrogen-doped carbon shells was further phosphatized at a low temperature to obtain a core-shell structure composed of mixed double metal phosphide.Due to further calcination phosphating,a core-shell structure with a cavity was obtained,accompanying with accelerated movement of the metal in the nucleus,agglomeration and shrinkage.The composite was used in HER and OER with stable performance.The composite materials for hydrogen evolution reaction with overpotentials of 105 mV at the current density of 10 mA·cm^–2 and Tafel slope of 56mV·dec^–1 in acidic media.After 10,000 cycles,the polarization curves almost coincide and the stability was excellent.In oxygen evolution reaction of the composite under alkaline conditions,the overpotential was 310 mV with the current density reaches 10 mA·cm^–2,and the Tafel slope was 60 mV·dec^–1.After 10 h of testing,the current density always maintained at 70%of the original value,and the performance was relatively stable.Therefore,metal phosphide has broad application prospects in electrolyzed water and important reference value in the development of high-performance nanostructured metal phosphide direction.In summary,a series of transition metal modified carbon composites materials were obtained by pyrolysis of metal-organic framework precursors.Carbon-based composites are rich in micro/mesopores.The resulting composite exhibits excellent performance in HER,ORR and OER due to the synthesis of these channels produces many accessible active sites.Considering abundant versatility of MOFs structure,this proposed method can be extended to the rational syntheses of other multi-component nanocomposites with multifunctional properties for renewable energy storage and conversion applications.