Investigation Of Core-Shell Structure, Low Platinum Loading Catalysts For Fuel Cells Using A Facile Pulse Electrodeposition Approach

Low temperature fuel cells, represented by proton exchange membrane fuel cell（PEMFC）, are ideal power support for vehicles and portable devices for the merits of high power density, low operation temperature and quick startup. So far Pt-based nanomaterials have been often used as the anode and cathode electrocatalysts in fuel cells. However, the high cost and scarcity of Pt are one of the most important factors that block the large-scale commercialization of this technology. Core-shell structured catalysts of fuel cells, synthesized by depositing a monolayer or multiple layer of Pt（or Pt alloy） on a relatively cheap core metal nanoparticle, are a new type of low-Pt catalysts that can greatly reduce the Pt-loading and lower the cost. They are therefore recognized as the most promising candidate to achieve large-scale application of proton exchange membrane fuel cell. Thus, the investigation of the core-shell structured low-platinum catalysts has become a significant topic in fuel cell field.We have established a scale-up synthesis method using pulse elctrodeposition technique to prepare a series of Ru₃M@Pt/NrGO（M=Fe, Co, Ni, Cu） core-shell structured electrocatalysts and studied their catalytic activity towards the methanol oxidation reaction. The structure, morphology and performance of the prepared catalysts were characterized using the means as X-ray diffraction（XRD）, transmission electron microscopy（TEM）, thermogravimetry（TGA）, rotating disk electrode（RDE）.Firstly, the milligram-scale synthesis of Pd@Pt /C catalysts was demonstrated using the pulse electrodeposition method. The core material was a homemade 20 wt.% Pd/C catalyst that was synthesized by an organic colloid method. Then Pt was deposited on the core material through a pulse electrodeposition process in a electrolyte solution containing 2 mM H2PtCl6/H2 O, 0.1 M Na2SO4, 0.1 M sodium citrate and PVP. The electrochemical surface area（ECSA） of the prepared Pd@Pt/C catalyst can reach 115.58 m2/g, which is much higher than that of JM Pt/C（55.4 m2/g）. Moreover, the prepared Pd@Pt/C catalyst shows 3 times higher mass activity than commercial JM Pt/C catalyst towards the oxygen reduction reaction（ORR）.Secondly, the gram-scale synthesis of Pd@Pt/C, Ru@Pt/C and PdRu@Pt/C catalysts was demonstrated using the pulse electrodeposition method. The core materials, Pd/C, Ru/C and PdRu/C nanoparticles, were synthesized using the organic colloid method, impregnation method and NaBH4 reduction method, respectively. Then Pt was deposited on the core materials through a pulse electrodeposition process in a electrolyte solution containing 3.8 mM K2PtCl4/H2 O, 0.1 M Na2SO4, 0.1 M sodium citrate and PVP. The effects of pulse frequency, Ton/Toff, deposition time and solvent on the activity of the prepared catalysts were investigated as well. The half-wave potential towards the ORR of the prepared Pd@Pt/C（0.595 V vs. Ag/AgCl） and PdRu@Pt/C（0.615 V） catalysts were 10 m V and 20 mV higher than that of the commercial JM Pt/C catalyst（0.585 V）, respectively. It was found that the mass activity of the prepared Pd@Pt/C（0.254 A/gPt） and PdRu@Pt/C（0.3 A/gPt） were higher than that of the commercial JM Pt/C catalyst（0.2 A/gPt）, wheras the mass activity of the prepared Ru@Pt/C was comparable to that of the commercial JM Pt/C catalyst.Thirdly, the synthesis of a series of Ru₃M@Pt/NrGO（M=Fe,Co,Ni,Cu） catalysts was demonstrated using the pulse electrodeposition method. The core materials were homemade Ru₃M/NrGO（M=Fe, Co, Ni, Cu） nanoparticles that were prepared using a impregnation reduction method. Then Pt was deposited on the core materials through a pulse electrochemical deposition process carried out on a glassy carbon electrode（the diameter is ca. 5 mm） in a electrolyte solution containing 0.5 M Pt（NH3）4Cl2/H2 O, 0.1 M Na2SO4 and 0.1 M sodium citrate. We studied the catalytic activity of the prepared Ru₃M@Pt/NrGO catalysts towards the methanol oxidation reaction, and found that Ru₃Ni/NrGO showed the best activity.