ABSTRACT:We have designed and synthesized a polyaniline (PANI)-decorated Pt/C@PANI core−shell catalyst that shows enhanced catalyst activity and durability compared with nondecorated Pt/C. The experimental results demonstrate that the activity for the oxygen reduction reaction strongly depends on the thickness of the PANI shell and that the greatest enhancement in catalytic properties occurs at a thickness of 5 nm, followed by 2.5, 0, and 14 nm. Pt/C@PANI also demonstrates significantly improved stability compared with that of the unmodified Pt/C catalyst. The high activity and stability of the Pt/C@PANI catalyst is ascribed to its novel PANIdecorated core−shell structure, which induces both electron delocalization between the Pt d orbitals and the PANI π-conjugated ligand and electron transfer from Pt to PANI. The stable PANI shell also protects the carbon support from direct exposure to the corrosive environment. P roton exchange membrane fuel cells (PEMFCs) are regarded as ideal candidates for stationary and mobile power generation because of their high energy conversion efficiencies and low environmental impact.1 However, the insufficient electrocatalytic activity and durability of Pt cathode catalysts still remains a major obstacle for PEMFC applications.2 At present, the most commonly used cathode catalysts are highly dispersed 2−5 nm Pt nanoparticles (NPs) supported on carbon. However, Pt NPs suffer from poor durability because of the rapid and significant loss of platinum electrochemical surface area (ECSA) over time due to corrosion of the carbon support, Pt dissolution, Ostwald ripening, and aggregation. and optimization of the catalyst structure to increase the exposure of Pt NPs to the three-phase zone. 7 Although these methods have been proposed to enhance the catalytic activity and durability, the development of a Pt-based catalyst with both good durability and high mass activity remains a challenge.Conducting polymers such as polypyrrole (PPy) and polyaniline (PANI) have received special attention in fuel cell applications because of their unique π-conjugated structures, which lead to good environmental stability, high electrical and proton conductivity in acidic environments, and unique redox properties. 8 Recently, Deki and co-workers 9 reported the preparation of a Pt/electroconductive-polymer-loaded carbon composite that improved the durability of electrodes in fuel cells. In that study, Pt(NH 3 ) 4 2+ was absorbed onto carbon and used to oxidize aniline while reducing the Pt(NH 3 ) 4 2+ itself. The Pt and PANI were thoroughly mixed together throughout the entire polymerization process. Accordingly, nearly all of the Pt NPs in the prepared Pt/PANI/C composite, except those present on the outermost catalyst layer, were embedded inside the PANI rather than exposed to the outside. Thus, some of the Pt NPs could not be utilized by the fuel cell, and the Pt/PANI/ C composites showed poor oxygen reduction reaction (ORR) activity; indeed, no Pt behavior was observed in cyclic voltammograms (CVs) of ...

No abstract

Nitrogen-doped carbon nanotubes (NCNTs) have been successfully synthesized via the direct solid pyrolysis of Zn-Fe-ZIF and the N content, N doped state, diameter and formation temperature of the NCNTs can be finely tuned by mixing Zn-Fe-ZIF with proper amounts of dicyandiamide (DCDA). DCDA serves as the extra nitrogen supplier and favors the formation of NCNTs at relatively low temperature due to its inducing effect for graphitic structure. The synthesized NCNTs, with iron species and high amounts of graphitic N, exhibit higher catalytic activity than commercial Pt/C as oxygen reduction electrocatalysts in alkaline solution.