Preparation Of Graphdiyne-supported Catalysts And Their Electrocatalysis For Oxygen Reduction Reactions

The design and development of green,efficient and commercial energy conversion devices has become an important strategy in order to solve the current fossil energy shortages and environmental degradation problems faced by mankind.The fuel cell is an energy conversion device that can convert the chemical energy in the fuel into electric energy in a green and efficient manner without being restricted by the Carnot effect.Oxygen reduction reaction(ORR),as the basic step of fuel cell(Cathodic reaction),needs a right catalyst to accelerate the reaction efficiency due to its slow kinetic process.Therefore,the design and preparation of high–efficiency ORR electrocatalysts to improve its kinetics and thereby improve fuel cell performance has become the key.At present,although noble metal catalysts such as Pt,Ir,Ru,etc.are considered effective catalysts for ORR,the high price and their scarcity have hindered the promotion and commercialization of noble metal catalysts.Therefore,the design and synthesis of ORR catalysts with lower cost,more stability and high activity is of strategic significance in the future.Graphdiyne(GDY)is a new type of carbon material with a unique alkyne bond structure,which provides the possibility for the design and development of new ORR catalysts.This thesis first prepared N–doped GDY(NGDY),and then used NGDY as a catalyst carrier to prepare NGDY supported Fe catalyst(Fe–NGDY);also prepared GDY hollow spheres(GDYHS),and used poly diene dimethyl ammonium chloride(PDDA)functionalized its surface to achieve PDDA functionalized GDYHS(PDDA–GDYHS)catalyst;Then the electrocatalytic performance of Fe–NGDY and PDDA–GDYHS catalysts for ORR was studied.The details are as follows:1.A NGDY supported Fe catalyst(Fe–NGDY)was prepared to study its ORR catalytic performance.Firstly,NGDY was obtained by pyrolysis of melamine and GDY,and then Fe³⁺ions were chemically reduced using Na BH₄ aqueous solution on the surface of NGDY to synthesize Fe–NGDY catalyst.SEM showed that the catalyst had a unique 3D layered nanostructure.HRTEM,XRD tests showed that Fe element was evenly distributed on the surface of the catalyst without being in the form of aggregated particles.The results of Raman and XPS showed that the catalyst maintained the molecular structure of GDY and contained sp-hybridized N elements,and Fe elements mainly existed in the structure of Fe–N.The ORR catalytic performance test of this catalyst by CV,RDE under alkaline conditions showed that Fe–NGDY catalyst had good catalytic activity for ORR under alkaline conditions,with E_onset=0.95 V(vs.RHE),E_1/2=0.83 V,which had comparable activity to commercialized Pt/C.Accelerated durability tests(ADTs)showed that Fe–NGDY catalyst showed better stability than Pt/C catalysts.Using the K–L formula to calculate the number of transferred electrons n of Fe–NGDY as 3.9,indicating that Fe–NGDY had excellent 4e selectivity.Studies had shown that the active site of Fe–NGDY catalyst might be Fe–N structure.This thesis uses GDY as the raw material to establish a method to synthesize non–precious metal ORR catalysts with N–doped GDY as the carrier,which provides a new strategy for the design and synthesis of non–precious metal catalysts.2.PDDA functionalized GDY nano hollow spherical shell(PDDA–GDYHS)was prepared to study its ORR catalytic performance.PDDA was used to functionalize the surface of the GDY spherical shell synthesized by the template method to obtain PDDA–GDYHS catalyst.TEM and SEM images showed that PDDA–GDYHS maintains the original Si O₂ spherical structure and had a 3D honeycomb structure in aggregated form.The ORR catalytic performance test of this catalyst by CV,RDE under alkaline conditions showed that PDDA–GDYHS catalyst had good catalytic activity for ORR under alkaline conditions,with E_onset=1.0 V(vs.RHE),E_1/2=0.85 V,which was equivalent to that of commercial Pt/C catalysts.ADTs showed that the PDDA–GDYHS catalyst had good stability.Through electrochemical testing of PDDA–GDYHS catalyst synthesized at 700–1000°C,the results showed that the best catalytic performance appears when the synthesis temperature is 800°C.Raman and XPS spectroscopic characterization showed that the PDDA–GDYHS catalyst retains the molecular structure of GDY and the acetylene bond structure in the catalyst was the key to the high ORR activity of the catalyst.This may be due to the rich electronic structure of acetylenic bonds,which could carry out effective charge transfer with the quaternary amino groups on the polyelectrolyte.This thesis will offer a new method for the design and synthesis of non–metallic catalysts,and provided new thoughts for the graphdiyne–based catalysts activity source.