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Fe nanoparticles immobilized on polyaniline-covered carbon nanotube (CNT) surfaces (Fe NPs–PANI/CNT) are prepared by reducing FeCl 3 in the mixing solution of aniline and CNT. Significantly, the structure of such composites can be effectively optimized by pretreating FeCl 3 with sodium citrate (CA). In the absence of CNTs, we found these two routes have large differences in reduction behaviors and different PANI states with varied conductivities. Therefore, the self-assembly mechanism in the preparation is proposed and the controlled self-assembly manner in the pretreating route is disclosed. Under acid condition, both catalysts demonstrate high oxygen reduction reaction (ORR) activity with four-electron pathway, and high electrochemical durability, revealing a promising application in the proton exchange membrane fuel cells. However, the high Tafel slopes relating to the surface red-ox couple and porous conductivity are still the main obstacles to improve their ORR dynamic, and more efforts on these aspects are needed to drive non-noble catalyst application in future. [ABSTRACT FROM AUTHOR]

To drive the Fe-based application for the Oxygen Reduction Reaction (ORR) in alkali media, this work found the Carbon Nanotube supported Fe-Polyaniline (Fe-PANI/CNT) catalyst from controlled Molecular Self-assembly (MS) method is comparable to the commercial Pt/C catalyst in mass current density and ORR stability, but with large gap on specific current density. This can be due to that the controlled MS method help establish the most active site of Fe-N coordination in the PANI pore, whose hydrophilic state inhibits O 2 transfer and whose poor conductivity restricts O 2 utilization jointly. In the meanwhile, we revealed that the enormous impact of OH adsorption (OH ad ) on ORR activity and stability, exhibiting negative results on the Pt/C catalyst but beneficial results for Fe-based catalysts, especially in the “indirect 2e+2e pathway” relating to the inner and outer-sphere electron transfer processes. All these progress facilitate the clarification for the structure-catalysis and encourage preparation towards controlled MS methods. [ABSTRACT FROM AUTHOR]

Abstract: This paper established an in-situ synthesis strategy that the mixing solution of aniline, CNTs and CoCl2 was directly reduced to prepare polyaniline-cobalt-carbon nanotube (PANI-Co-CNT) electrocatalyst. Furthermore, this strategy was effectively modified by pretreating CoCl2 precursor with citric acid (CA), forming 2-4nm cobalt nanoparticles uniformly distributed on PANI-CNT support with porous structure. The control experiments revealed various PANI states in the growth stage, further proposing the self-assembly mechanisms in these two routes with and without CA pretreatment. These two PANI-Co-CNT electrocatalysts were also checked by oxygen reduction reaction (ORR) in acid environment, to corroborate their basically 4-electron processes. Inspiringly, the large activity and stability for the pretreated route could be comparable with those of the advanced electrocatalysts. All these progresses lay a bottom-up approach for future electrocatalysts. [Copyright &y& Elsevier]