Synthesis And Structure-activity Relationship Of Nano-assembled Non-precious Metal Oxygen-involved Electrocatalyst

With increasing energy consumption and environmental problems,it is urgent to find other feasible and renewable energy technologies.Some recently emerged devices without the emission of pollutants,e.g.,fuel cells,metal-air batteries,and water splitting,are promising for efficient energy conversion and storage,and environmental remediation.Highly efficient electrocatalysts for various reactions,especially oxygen reduction reaction(ORR)and/or oxygen evolution reaction(OER)are essential for realizing the commercialization of the above-mentioned energy technologies as electrocatalysts are necessary to promote the key electrochemical catalytic reactions involved in these devices.Generally,Pt-based catalysts exhibit excellent ORR performance in both acidic and alkaline media,while Ru and Ir oxides based catalysts are considered as the best OER catalysts.However,the high cost and scarcity of these precious metals have limited their commercial applications.Therefore,the development of low-cost non-precious metal-based catalysts or carbon-based metal-free catalysts with efficient catalytic activity and long-term stability to reduce/replace Pt-or Ru/Ir-based catalysts has attracted worldwide attention.Based on the above considerations,in this thesis,a series of non-precious metal-based electrocatalysts with excellent electrochemical catalytic activity towards OER and/or ORR were designed and synthesized through facile synthesis methods.The relationship between their morphology/structure/composition and the catalytic activity was also studied in detail,providing both experimental and theoretical guidelines for the preparation of other high-performance non-precious metal-based electrocatalysts.The main contents of the thesis are listed as follows:1.The non-precious CoS_1.097-B electrocatalyst of CoS_1.097 embedded in flower-like biomass derived from red blood cells(RBCs)was synthesized via a one-step hydrothermal method with low-cost precursors.The resulted CoS_1.097-B catalyst with a thickness of only 15 nm has a large specific surface area,showing better OER performance.The generated CoS_1.097-B exhibits enhanced OER performance and stability with a onset potential of 1.43 V vs.RHE,a low Tafel slope of 83 m V dec^-1,superior to commercial RuO₂.2.The electrocatalyst of CoFe₂O₄ nanoparticles embeded in a carbon tube with high-nitrogen content(N-CoFe₂O₄-NC)was obtained by the pyrolysis of the nitrogen-contained precursor in the presence of ammonia gas.The obtained N-CoFe₂O₄-NC has a large specific surface area and high electrical conductivity,making it a promising alternative to Pt-based catalysts towards ORR.The onset potential for N-CoFe₂O₄-NC is 0.98V vs.RHE,and the half-wave potential is 0.86V vs.RHE,which is comparable to commercial Pt/C.In addition,CoFe₂O₄ particles are fixed by the N doped carbon layer,which was unlikely to dissolve or aggregate during the electrocatalysis,resulting in good stability.3.By combining carbon nanotubes and layered hydroxides via"adsorption-alkalization-reduction"strategy,a defect-rich heterojunction catalyst of CNT@Ni Co LDH-OV was obtained.The combination of the experimental results and theoretical calculation illustrate that CNT@NiCo LDH-OV has high electrical conductivity and electron transfer efficiency due to the existence of carbon nanotubes,heterojunctions and oxygen vacancies,and therefore exhibits excellent OER performance and stability.CNT@NiCo LDH-OV displays outstanding OER performance with an overpotential of 257 m V vs.RHE and a low Tafel slope for 51 m V dec^-1,superior to commercial RuO₂ and some other electrocatalysts in the literature.In summary,a series of non-precious metal electrocatalysts with well-defined morphologies,compositions,and structures have been synthesized via simple methods.All of the catalysts exhibited superior catalytic performance towards ORR and/or OER.Meanwhile,the relationship between the composition/structure and performance has also been intensively studied,providing both theoretical and experimental guidelines for designing other high-performance non-precious metal-based electrocatalysts for OER/ORR and beyond in the future.