Research On Electrocatalysis Properties Of Porous Carbon Materials Doped With Heteroatoms

The solar,wind,water and other clean renewable energy sources are difficult to meet people's daily needs due to the restrict of location and influence of daylight.Hydrogen energy is considered as the ultimate energy in human society because of its high energy density,abundant sources and zero pollution.The most efficient and promising way to prepare and utilize hydrogen energy is using electrochemical energy storage and conversion technologies,including water splitting and hydrogen-oxygen fuel cells.Currently,electrode reactions involved in electrochemical energy storage and conversion technologies all require efficient electrocatalysts to improve the efficiency of electrochemical energy storage and conversion,including HER,OER and ORR.Over the years,researchers are developing low-cost and efficient electrocatalyst for efficient large-scale application of clean and renewable energy,but the best catalyst in the electrode reaction is still precious metal catalysts.For example,Pt and Pt alloy catalysts are the best catalysts in HER and ORR,Ru and Ir-based catalysts are the best OER catalysts.However,the scarcity and high-cost of noble metal catalysts limit their large-scale commercial application,thus hindering the development of electrochemical energy storage and conversion technology.At present,hetero-atom-doped carbon-based catalysts are considered as promising catalysts due to their abundant sources of carbon materials,various of heteroatoms,good morphology and chemical stability.According to the demand of the catalytic electrodes,a series of heteroatom doped porous carbon catalyst are synthesized through designing precursor molecular with various of composition and structure.The electrochemical performance of the obtained catalysts for HER,OER and ORR are also investigated by electrochemical test.The catalytic mechanism and application are researched by DFT calculation and assembling Zn-air battery.The research results are summarized as follows:Firstly,hyperbranched cobalt phthalocyanine was synthesized by in situ method and nano SiO₂ templates were embedded into hyperbranched cobalt phthalocyanine to form H-CoPc/SiO₂ precursor.The trace Co,N co-doped porous carbon catalyst Co@NG-T was obtained by pyrolyzing the precursor at different temperatures and subsequent etching treatment.The results showed no agglomeration of Co nanoparticles owing to the chemical bond anchoring of phthalocyanine ring,which inhibited the migration and aggregation of Co atoms.The catalyst Co@NG-800 obtained at the carbonization temperature of 800^oC exhibits best HER activity than that of Co@NG-700,Co@NG-900and control sample NG-800.This work may provide a method for preparing transition metal,N co-doped porous carbon-based catalysts with high atom utilization efficiency.Secondly,owing to the significantly inferior activity of Co@NG-800 catalyst compared with Pt/C,the ruthenium-supported nitrogen-doped carbon catalyst with higher HER-activity was synthesized by the strategy of increasing the intrinsic activity of the catalyst and the number of active sites.Ru@NG,a carbon-based catalyst supported by ultrafine Ru clusters,was obtained by pyrolyzing the mixture of 4-aminphthalocyanine ruthenium?RuPc-NH₂?and GO,with a load of more than 23wt%of Ru.It was found that the chemical anchoring of Ru atoms by phthalocyanine ring and the space confinement of graphene could effectively inhibit the migration-agglomeration of Ru atoms during pyrolyzing process.The average particle size of Ru clusters was about 1.03nm.The performance of HER showed that the overpotential of Ru@NG in 1.0M KOH solution was only 20mV,better than that of Pt/C catalyst,and even among one of the best reported alkaline HER catalysts.The overpotential in 0.5M H₂SO₄ solution was only 42mV,which also showed excellent HER activity.The stability test showed that after 10h i-t test in acidic or alkaline environment,the current retention rate was above 80%,and there were no significant shifts in LSV curves before and after i-t test.It was found that Ru@NG had higher catalytic activity was attributed to its more catalytic activity sites,revealed by Cu-UPD method.Thirdly,in the research of metal-free carbon-based catalysts for ORR,PPSS served as sulfur and carbon sources was selected for preparing N,S co-doped porous carbon catalyst?N,S@C_x-T?.By optimizing the content of SiO₂ in the precursor,it was found that when the content of SiO₂ was moderate,a regular honeycomb structure porous carbon was obtained.This kind of structure was conducive to exposing more catalytic active sites and mass transfer in the catalytic reaction process.In addition,N,S@C_M-1000 pyrolyzed at 1000^oC showed better ORR catalytic activities than other catalysts obtained at different pyrolysis temperature.The XPS and Raman spectra revealed that the dominated Graphitic N,Pyridinic N and Thiophene-S species in N,S@C_M-1000 with higher graphitization degree are the reasons why N,S@C_M-1000 exhibit best ORR catalytic activity.The zinc-air battery assembled by N,S@C_M-1000 catalyst also showed high open circuit voltage?1.37V?,excellent discharge performance and maximum power density(90mW cm^-2).This work provides an alternative approach for the future recycling of high-performance polymers.Finally,no precious metal based-catalyst exhibit highly efficient bifunctional oxygen catalytic performance for rechargeable zinc air battery.Therefore,RuCo oxide alloy embedded in nitrogen doped CNT as a bifunctional oxygen catalyst was synthesized.The prepared RuCoOx@Co/N-CNT catalyst exhibits a robust ORR and OER performance with an overpotential gap??E?of 0.79V.It was found that the doping of Ru and oxidation treatment could tune the electronic structure of the active sites of catalysts,so as to improve the ORR and OER activities of catalysts.The zinc-air batteries assembled with RuCoO_x@Co/N-CNT also exhibit high OCP,charge and discharge cycle performance and maximum power density(93mW cm^-2).DFT calculation results show that Ru doping and oxidation treatment could promote charge transfer to adjacent carbon atoms of nitrogen atoms on the surface of carbon nanotubes,thus regulate the electronic structure of active site and promote the adsorption/separation of oxygen.