Fabrication Of Porous Carbon Nanofibers Doped By Nitrogen And Phosphorus Via Electrospinning And Its Water Oxidation Properties

Electrolysis of water is an efficient and safe method for the preparation of hydrogen energy.The oxygen evolution reaction?OER?and the hydrogen evolution reaction?HER?are two key reactions for water decomposition.Currently,the oxides of ruthenium?Ru?and iridium?Ir?,as well as platinum?Pt?and their alloys had been proved to be high-performance electrocatalysts for OER and HER,respectively.However,its scarcity,high cost and poor durability have seriously hindered its large-scale commercial application.Therefore,the development of non-precious metal materials rich in resources to replace precious metal catalysts has been widely studied.Cobalt-base multi-pore carbon nanofiber structure electrocatalysts?oxides and phosphates?have significant advantages in the field of electrolysis of water due to their large specific surface area and high content of active substances.Besides,the method of in-situ growth of active substances on the matrix with porous carbon fiber as the matrix saves the use of additional binders and greatly enhances the sustainable stability of the electrode.In this study the zeolite imidazole skeleton-67?ZIF-67?and polyacrylonitrile?PAN?were used as the basic materials,the in situ synthesis method for preparing ZIF-67@PNFs precursor was used,and then the porous carbon nanofibers electrode material of N-Co₃O₄@NPCNFs,Co P@NPCNFs and N₁-Co P@NPCNFs were synthesized through high-temperature pyrolysis,oxidation,phosphating and nitrogen-doped processing.The catalytic activity and sustainable stability as OER and HER catalysts was evaluated.The main contents are included the following three aspects:?1?Firstly,ZIF-67@PNFs precursor was prepared by electrospinning technique and in-situ synthesis method,then ZIF-67@PNFs was successfully converted into a new N-doped cobaltosic oxide@N-doped carbon nanofiber?N-Co₃O₄@NPCNFs?composite electrocatalyst by carbonization,oxidation and nitrogen doping treatment.The morphology,structure and crystal phase composition of the composite catalysts were studied by SEM,XRD and XPS.And the electrochemical experiments were conducted in 1 M KOH solution.The results showed that the specific surface area of the prepared N-Co₃O₄@NPCNFs catalyst was up to 252.33 m²g^-1,showing excellent OER catalytic activity.When the N-Co₃O₄@NPCNFs electrode reaches a current density of 10 m A cm^-2,the OER requires an overpotential of 289 m V and a Tafel slope of 78 m V dec^-1.Besides,the stability test under constant voltage showed that the electrode can maintain the durability test for 10 h.?2?Cobalt-phosphate@N-doped carbon nanofibers?Co P@NPCNFs?were synthesized by oxidizing and phosphating.The effects of different calcining temperatures of 800,900,1000?on the morphology,structure,composition and catalytic performance of Co P@NPCNFs were studied.The results showed that compared with Co P@NPCNFs-800 and Co P@NPCNFs-1000,Co P@NPCNFs-900showed the best OER performance,with an overpotential of 297 m V and Tafel slope of 77 m V dec^-1at a current density of 10 m A cm^-2.This is mainly due to the minimum ratio of amorphous carbon to graphite carbon in Co P@NPCNFs-900?I_D/I_G=1.251?and the largest specific surface area(252.33 m²g^-1).In additionally,Co P@NPCNFs-900 has a good performance of HER.The overpotential of the electrode is 144 m V,and the slope of Tafel is 62 m V dec^-1.Stability experiments showed that both for OER and HER,Co P@NPCNFs-900 maintain above 36000 s,showing good stability and durability.?3?The N-doped Co P@N-doped carbon nanofiber?N-Co P@NPCNFs?composite electrocatalyst was prepared in nitrogen atmosphere by the method of oxidizing,phosphating and nitrogen doping.The effects of sodium dihydrogen phosphate/urea ratio on the morphology,structure,composition and catalytic performance of N-Co P@NPCNFs were studied.The results showed that N₁-Co P@NPCNFs shows the best OER performance when the urea content is 1 g.When the current density reaches 10 m A cm^-2,the overpotential is only 266 m V and the Tafel slope is 70 m V dec^-1.This is mainly because when appropriate N atoms are incorporated into the Co P lattice,the ECSA,electrica,conductivity and electronic structure can by significantly adjusted so that a good synergy effect is formed between the doped N and Co P,and the N₁-Co P@NPCNFs catalyst has the largest specific surface area(282.55 m²g^-1).This study further improves the electrocatalytic performance of cobalt-based catalysts due to the N-doping method,,which has certain theoretical significance in the field of electrocatalysis.