Ultra-stable Pt cathode catalysts in ultra-low Pt loading proton exchange membrane fuel cells were synthesized by facile carbon encapsulation.

Direct alcohol fuel cells play a pivotal role in the synthesis of catalysts because of their low cost, high catalytic activity, and long durability in half-cell reactions, which include anode (alcohol oxidation) and cathode (oxygen reduction) reactions. However, platinum catalysts suffer from CO tolerance, which affects their stability. The present study focuses on ultrafine Pt nanoparticles stabilized by flowerlike MoS2/N-doped reduced graphene oxide (Pt@MoS2/NrGO) architecture, developed via a facile and cost-competitive approach that was performed through the hydrothermal method followed by the wet-reflux strategy. Fourier transform infrared spectra, X-ray diffraction patterns, Raman spectra, X-ray photoelectron spectra, field-emission scanning electron microscopy, and transmission electron microscopy verified the conversion to Pt@MoS2/NrGO. Pt@MoS2/NrGO was applied as a potential electrocatalyst toward the anode reaction (liquid fuel oxidation) and the cathode reaction (oxygen reduction). In the anode reaction, Pt@MoS2/NrGO showed superior activity toward electro-oxidation of methanol, ethylene glycol, and glycerol with mass activities of 448.0, 158.0, and 147.0 mA/mgPt, respectively, approximately 4.14, 2.82, and 3.34 times that of a commercial Pt–C (20%) catalyst. The durability of the Pt@MoS2/NrGO catalyst was tested via 500 potential cycles, demonstrating less than 20% of catalytic activity loss for alcohol fuels. In the cathode reaction, oxygen reduction reaction results showed excellent catalytic activity with higher half-wave potential at 0.895 V versus a reversible hydrogen electrode for Pt@MoS2/NrGO. The durability of the Pt@MoS2/NrGO catalyst was tested via 30 000 potential cycles and showed only 15 mV reduction in the half-wave potential, whereas the Pt@NrGO and Pt–C catalysts experienced a much greater shift (Pt@NrGO, ∼23 mV; Pt–C, ∼20 mV).

A novel structure-catalytic activity correlation of platinum and palladium alloys is reported in this study.Metals with similar covalent radius (Pt and Pd) were alloyed with metals of lesser covalent radius (Fe and Co). The ternary alloys namely, PtFeCo and PdFeCo were synthesized by a solvothermal method. The structural properties such as lattice parameters and compressive strain of these electrocatalysts were evaluated by XRD and SAED analysis. Particle size and pattern of dispersion of these catalysts in Vulcan XC-72 carbon were characterized by TEM. The composition of the alloys was identified by ICP-OES and EDX techniques. Electrochemical properties such as ECSA, oxygen reduction reaction activity and kinetic parameters were assessed by CV and RDE studies. Structural and electroactivity of both alloys were compared with their respective bulk metal catalysts (20 wt% Pt/C, 20 wt% Pd/C). The lattice strain was calculated from the decrease in lattice parameters of alloys compared with those of pure metals. It is observed that PdFeCo/C shows more compressive strain than PtFeCo/C which is reflected in the greater improvement in ORR activity than that of PtFeCo/C catalyst. ORR studies revealed that both alloys and their pure metals follow a four electron transfer mechanism. The kinetic parameters such as mass and specific activities are calculated from the Tafel slope of ORR. Pt/C, PtFeCo/C and PdFeCo/C electrocatalysts have Tafel slope values ($120 mV dec À1 ) indicative of one electron transfer as the rate determining step. The mass and specific activities of PdFeCo/C show higher increments than those of PtFeCo/C compared to their respective metals. The results of ORR studies reflect that lattice strain is an important factor to improve the catalytic activity of the electrocatalyst. Single cell polarizations were carried out at 60, 70 and 80 C with PtFeCo/C and PdFeCo/C as cathode electrocatalysts. Both ternary alloy electrocatalysts show higher performance than pure metal catalysts. At 80 C, PtFeCo/C and PdFeCo/C register a power density of 713 mW cm À2 and 437 mW cm À2 respectively.