Highly Dispersed Pt Catalysts Supported On Atomically Dispersed Zn,Fe,N-Doped Carbon Nanometerials For Fuel Cells

As a new type of energy conversion device,fuel cell has become one of the important equipments for solving energy shortage and environmental problems due to its advantages of high energy conversion efficiency,environmental friendliness,and renewable fuel.It has a broad application prospect.At present,the catalysts commonly used in fuel cells are composed of carbon-supported Pt nanoparticles.However,the scarce reserves,high price,poor dispersion,and low utilization rate of Pt make the catalysts cost high,which seriously restricts the large-scale application of fuel cells.To accelerate the commercial development of fuel cells,we must increase the dispersion of Pt and reduce the loading of Pt to reduce the cost of catalysts firstly.Therefore,the development of Pt-based catalysts with high dispersion and high utilization rate is of great significance to the industrialization of fuel cells.Bases on this background,two highly dispersed Pt-based catalysts were explored in this thesis.Pt/Zn Fe NC catalyst with highly dispersed Pt nanoparticles were successfully prepared using atomically dispersed Zn,Fe,N doped carbon materials as the support.The study found that a large number of Zn and Fe single atoms on the surface of the Zn Fe NC support can be used as nucleation centers to induce the nucleation growth of Pt atoms,thus avoiding the direct reduction of Pt atoms on existing Pt atoms and improving the dispersion of Pt in the catalyst.The strong interaction between the abundant N element in the Zn Fe NC support and Pt atoms anchors the Pt atoms firmly on the surface of the carbon support,making it difficult for Pt nanoparticles to migrate and agglomerate,improving Pt utilization and stability.TEM images shows that when the Pt loading in the Pt/Zn Fe NC catalyst is 19.87%,the Pt nanoparticles are uniformly dispersed on the surface of the support without agglomeration,with the particle sizeaveraged at 2.24 nm.Adjusting the Pt loading from 0 to 20%,the particle size is successfully controlled within1.5 nm-2.5 nm.The highly dispersed Pt-based catalyst has a high atom utilization rate and excellent catalytic activity toward oxygen reduction reaction in acid media.The ESCA of Pt/Zn Fe NC catalyst is 141.88 m²/g,which was about 2 times that of commercial Pt/C.In the oxygen reduction reaction,when the electrode load was 1.46μg,the half-wave potential reached 0.851 V.Based on the above research,by reducing the amount of metal salt precursor adsorption,the multi-atomic Pt Ru catalyst（MA-Pt Ru/Zn Fe NC）with 100%atom utilization efficiency was successfully prepared.HAADF-STEM shows that Pt and Ru are aggregated in the form of multiple single atoms into uniformly dispersed nanostructures with the size of about 2 nm.XAFS analysis shows that each Pt atom is coordinated with approximately 2.7 N atoms and 4.1 Pt/Ru atoms,and each Ru atom is coordinated with approximately 4.2 N atoms and 0.8 Pt/Ru atoms.The bimetallic multi-atomic Pt Ru catalyst combines the advantages of monoatomic catalyst and alloy nanoparticle catalyst,has extremely high metal utilization and excellent catalytic activity in methanol oxidation.The ECSA of MA-Pt Ru/Zn Fe NC catalyst is 164.52 m² g^-1,which is 3 times that of commercial Pt Ru/C.After adjusting the Ru loading in the catalyst,the ECSA of the catalyst did not decrease with the increase of Ru loading,which proved that the Zn Fe NC support can simultaneously adsorb Pt and Ru metals,and the newly added Ru atoms did not cover the reduction of Pt atoms.In methanol oxidation reaction,the mass activity of MA-Pt Ru/Zn Fe NC catalyst is 0.578 m A ug^-1 Pt,which is 4 times that of the commercial Pt Ru/C.After 2000 cycles of accelerated aging,the ECSA only decayed by 5%,proving the superior stability of the bimetallic multi-atomic Pt Ru catalyst.The bimetallic multi-atomic catalyst provides a new research direction for improving metal utilization and reducing catalyst cost.