Catalyst Structure Design And Performance Research Based On Different Oxygen Reduction Reaction Pathways

The electrocatalytic oxygen reduction reaction plays a crucial role in the sustainable development of energy storage and energy conversion.However,due to its complexity involving the multi-electron transfer and multi-proton coupling,problems such as slow kinetics and poor 2e-/4e-path selectivity hinder its application in fuel cells,zinc-air batteries and H2O2 production.The urgent need to design advanced electrocatalysts that can accelerate the ORR kinetic process is a major challenge.Fe-NC and Co-NC catalysts have emerged as promising candidates due to their unique geometric and electronic structures,which ensure maximum atom-utilization efficiency and distinct oxygen adsorption.Herein,this thesis proposes precisely tuned coordination structure strategies to significantly improve the catalyst’s intrinsic activity and 2e/4e-path selectivity by rational design on the active site structures of Fe-NC and Co-NC.Additionally,the relationship between the active site structure and ORR activity is explored.The main advances of this research are summarized as follows:(1)Fe(Co2nd)-NC catalysts with well-defined N3-Fe-N-Co active sites were successfully prepared by a one-pot method.The Co coordination in the second shell allows for manipulation of the positive shift of the Fe center charge state,driving a closer distance from the d-band center to the Fermi energy level,thereby offering the optimal adsorption of OOH*adsorption to lowercase-determining step energy barrier of Fe(Co2nd)-NC,which ultimately improves the ORR intrinsic activity.The as-prepared Fe(Co2nd)-NC enables an excellent ORR activity with a halfwave potential of 0.948 V in 0.1 M KOH and 0.846 V in 0.1 M H2SO4,respectively.Especially,serving as a cathode in fuel cells and ZABs,it delivered an outstanding peak power density of 0.92 W cm-2 and 218 mW cm-2,respectively.Moreover,the specific capacity of ZABs can reach 915 mA h g-1 at 5 mA cm-2,with superior long-term durability over 680 h.This chapter of work paves the way for enriching the second shell layer ligand modification strategy,gaining a deeper insight into the ORR catalyst active site reconfiguration process,as well as designing advanced ORR electrocatalysts.(2)NH3-assisted high-temperature carbonization strategy was adopted to successfully construct NH3-Co-NC catalysts with multiple active sites.The adjacent carbons with a high loading of pyridinic nitrogen led to the electronic structure rearrangement of the external carbonnitrogen structure in NH3-Co-NC catalyst,which optimizes the adsorption and desorption capacity of the oxygen intermediate OOH*,leading to enhanced H2O2 selectivity.In 0.1 M H2SO4,the H2O2 selectivity of NH3-Co-NC remained above 90%,with yields up to 907.5 mmol h-1 gcat.1 at 0.1 V vs.RHE potential in H-type electrolytic cells._This chapter provides a novel design idea and method for designing electrocatalysts with high 2e-ORR selectivity and intrinsic activityproducing preparation of hydrogen peroxide.