Study On The Synthesis And Electrochemistry Performance Of Carbon Materials Co-doped With Heteroatoms And Transition Metals

The increased consumption of fossil fuels has led to serious energy crises and environmental problems.The development of clean and sustainable energy,energy conversion systems,and energy storage technologies is an important way to alleviate global energy demand and environmental problems.For energy conversion systems including water splitting and fuel cells,researchers are committed to developing effective catalysts for the key reactions involved in these systems,such as hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）,oxygen reduction reaction（ORR）.Noble metals（such as Pt）and/or noble metal oxides（such as Ru O₂ and Ir O₂）are currently the best-performing catalysts used in these three reactions.However,their high cost and limited reserves make these energy conversion systems unusable for large-scale commercial applications.Therefore,finding a suitable replacement for noble metal-based electrocatalysts is the key to solving the above-mentioned problems.In this thesis,several composite materials were prepared by doping transition metals and heteroatoms with MOF as the precursor,and the electrocatalytic properties were studied.（1）Cobalt phytate（PA-Co）was formed by chelating sodium phytate with transition metal cobalt,and then Zn-Co-ZIF was synthesized in its aqueous solution to form Zn-Co-ZIF@PA-Co complex attached to Zn-Co-ZIF,in which sodium phytate was used as a phosphorus source and Zn-Co-ZIF as carbon source and nitrogen source.Nitrogen-doped carbon matrix nanosheets embedded with Co₂P were obtained by controlled pyrolysis of the Zn-Co-ZIF@PA-Co complex.To improve the electrocatalytic performance of the material,a small amount of precious metal ruthenium was introduced into the system through adsorption.Finally,low content of precious metal ruthenium and Co₂P co-doped carbon nanosheets（Ru-Co₂P/NC）were obtained and used for electrocatalysis of HER,ORR,and OER.The electrochemical performance showed that the addition of low content precious metals greatly improved the catalytic performance.For HER,when the current density reaches 10 m A/cm² in the 1M KOH electrolyte,the overpotential generated decreases from 205 m V to 43 m V.For ORR,the initial potential increased from 0.889 V vs.RHE to 0.946 V vs.RHE,and the half-wave potential increased from 0.79 V vs.RHE to 0.88 V vs.RHE in 0.1 M KOH electrolyte.For OER,there is also a significant performance improvement.The improvement of performance is attributed to the addition of low content of ruthenium to change the electronic structure of the material.The carbon matrix derived from ZIF plays a key role in supporting the active site.This work provides a new idea for the design and synthesis of low-load precious metals and durable multifunctional electrocatalysts and is expected to be a new approach for large-scale commercial use of electrocatalysts.（2）The cobalt-iron Prussian blue analog（Co-Fe PBA）synthesized by the co-precipitation method is used as a template,and the surface structure of Co-Fe PBA is destroyed by ammonia etching strategy to expose more active centers.Finally,it is vulcanized in a tube furnace.During the vulcanization process,the Co²⁺and Fe³⁺in the original precursor Co-Fe PBA are converted into mixed metal sulfides,and the organic ligands are carbonized at the same time,and finally,nitrogen-doped carbon nanocubes（Co S₂-FeS₂/NC）loaded with Co S₂ and FeS₂ are obtained.And used for electrocatalysis OER,HER,and total water decomposing.The electrochemical performance shows that the heterostructure of Co S₂ and FeS₂ improves the electrocatalytic performance.At the same time,the presence of Co S₂ changes the electronic structure of FeS₂ and improves the catalytic activity.For OER,when the current density reaches 10 m A/cm² in 1M KOH electrolyte,the overpotential is 208 m V.For HER,in the 1M KOH electrolyte,when the current density reaches 10 m A/cm²,the overpotential generated is 246 m V.It is also evaluated for its use in simulating catalytic OER in seawater.At the same time,to investigate the electrocatalytic performance of other mixed transition metal sulfides,Ni S₂-FeS₂/NC and Mn S-FeS₂/NC catalysts were synthesized respectively for comparison.The results show that the Co S₂-FeS₂/NC derived from Co-Fe PBA shows the best electrocatalytic performance.This work provides an experimental basis for the design of transition metal sulfide heterostructures derived from MOFs.