Preparation Of Platinum Based And Carbon Based Catalysts And Their Application In Electrocatalysis

Fossil energy is still the main source of energy in today's society.Due to the limited reserves of fossil energy and the environmental pollution caused by its extensive use,it has become an urgent need to seek new energy and explore energy storage or conversion equipment with high performance.Fuel cells and metal-air batteries,as new types of energy equipment,have the advantages of stable operation,environmental friendliness,and high energy density,and have attracted more attention.Take fuel cells as an example,methanol oxidation reaction(MOR)and oxygen reduction reaction(ORR)are the key reactions in fuel cells because their slow reaction kinetic limit the performance of the cells.Platinum(Pt)catalyst is recognized as a highly active electrocatalyst,whereas,it's low reserves,high price,instability and other factors limit the commercial application of the fuel cells.Thus,it is very urgent to design new,efficient and low-cost electrocatalysts.Based on the above background and current research hotspots,various researches have been performed in this dissertation to reduce the cost of catalysts and improve the activity and stability of catalysts,including the construction of Pt-based catalysts with special morphology(section 1 and section 2),heteroatom doped carbon catalysts(section 3),single-atom catalysts(section 4)and rare earth phosphate catalysts(section 5).The details are as follows:(1)Platinum-copper alloy tetradecahedrons(Pt-Cu TNs)with hollow structures were prepared by a novel,simple and efficient method.The thickness of Pt-Cu TNs shell and the content ratio of Pt and Cu can be accurately controlled by this method.The formation mechanism of Pt-Cu TNs was also studied in detail.The results show that Pt-Cu TNs has higher MOR electrocatalytic activity,stability and CO poisoning resistance than commercial platinum catalysts.This can be ascribed to its large specific surface area,abundant active sites and synergistic effect among metal components.(2)Hollow PtPdCu trimetallic octahedrons(PtPdCu HTOs)nanoparticles were rapidly synthesized at room temperature using cuprous oxide as a template.Due to the hollow and porous structure of PtPdCu HTOs and their composition advantages,the catalyst showed higher ORR electrocatalytic activity and stability than commercial Pt black in an acidic medium.(3)Ultrathin carbon nanosheet superstructure(BN/C)with high B,N-doping level were prepared by hard template method.In an alkaline medium,the BN/C catalyst has an excellent ORR activity(half-wave potential(E1/2):0.8 V vs RHE),which is similar to that of Pt/C catalyst.The BN/C catalyst also shows great electrocatalytic stability and satisfactory methanol tolerance.This excellent performance is attributed to the structure and composition characteristics of BN/C,including the large surface area(1085 m2 g-1),hierarchically porous structure,the synergistic effect of the B,N codoping and high content of ORR active species.Furthermore,a rechargeable Zn-air battery device comprising BN/C catalyst and RuO2 with a liquid electrolyte shows superior performance(open-circuit potential:1.36 V,peak power density:115 mW cm-2),as well as excellent durability(14 days' operation for1000 cycles).Moreover,a solid-state Zn-air battery containing BN/C catalyst and RuO2 shows good cycling durability under different bending states,indicating excellent practicability in wearable devices.(4)The atomically dispersed Co sites anchored on interconnected B,N doped carbon nanotubes(CoN4/B,N-C nanotubes)were prepared with the assistance of salt template.The CoN4/B,N-C nanotubes exhibit excellent ORR electrocatalytci activity in alkaline medium(half-wave potential:0.87 V vs RHE,surpassing that of commercial Pt/C:0.84 V vs RHE),but also show outstanding stability(only 1 mV degrade can be observed after 10,000 cycles).These excellent ORR performances derive from the efficient synergy of atomically dispersed Co active sites,unique 3D tubelike assembly structure and large specific surface area.Moreover,the CoN4/B,N-C nanotubes assisted by RuO2 as an air cathode can enable rechargeable Zn-air batteries with larger power density(125.0 mW cm-2),higher specific capacity(746.8 mA h gzn-1),and better cycling stability than those of conventional Pt/C+RuO2-based Zn-air batteries.(5)A nitrogen doped carbon material loading with lanthanum phosphate nanoparticles(LaPO4-N/C)was prepared.It is found that LaPO4-N/C is a new ORR catalyst with better performance than commercial Pt/C.The experimental results show that the catalytic process of the LaPO4-N/C catalyst is a synergistic catalytic mechanism between LaPO4 and N/C components.More specifically,the LaPO4 adsorbs and activates O2 molecule,and produces an appropriate amount of HO2-species through a two-electron reduction reaction.Then,the HO2-species are rapidly transferred to N/C and further converted to OH-.It provides a new idea for the design and development of new and efficient non-noble metal ORR catalysts.