Silver montmorillonite conducting polymer composite materials as low-cost oxygen reduction catalysts

Abstract

Throughout the globe, researchers are in quest of electro-catalysts for oxygen reduction reaction (ORR) in order to develop cathode materials for fuel cells (FCs). Although the anodic half-reactions of FCs are fast enough for oxidation of any fuel on cheap catalysts, ORR at the cathode is a slow process even with expensive platinum-based catalysts. Development of low-cost electro-catalysts with reasonably fast kinetics for (ORR) is desirable if fuel cell power is to be utilised in practice. The present study is based on the preparation and characterisation of silver-based electro-catalysts towards ORR. Simple chemical processes were developed to prepare three different electronically conducting nano-composites. Aniline, pyrrole or 3,4-ethyldioxythiophene (EDOT) in between the layer space of silver [Ag (I)] ion exchanged montmorillonite (MMT) undergoes spontaneous polymerisation. During the polymerisation process, Ag(I) cations are reduced to form metallic silver, while aniline, pyrrole or EDOT monomers are converted to polyaniline (PANI), polypyrrole (PPY) and poly (3,4-ethylenedioxythiphene) (PEDOT), respectively. The prepared composites were extensively characterised by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), X-ray photoelectron spectroscopy (XPS), conductivity measurements, AC-impedance and electrochemical analyses. Electrochemical studies showed that composites are good candidates towards ORR in alkaline electrolyte medium. Ag/MMT/PEDOT showed the best performance in catalytic properties. All three composites showed better performances than that of typical Ag/C composites with a similar mass loading of silver. Although the performances of the cheap composites are somewhat lower when compared to commercially available Pt/C, the performance is sufficient to use the materials as cheap alternatives for FC cathodes.

Pyrolyzed Iron-Cobalt/Polyaniline on Bentonite Clay as Electrocatalyst for Oxygen Reduction Reaction

“…Figure 1 There are a handful of studies that investigated the utility of clays as support for ORR electrocatalysts [12][13][14][15][16][17]. These studies showed that the ORR peak for such materials are positioned at approximately -0.4 V [16,17,21]. Furthermore, this cathodic peak cannot be attributed to the reduction of the conductive polymer since PANI in this study was degraded during pyrolysis.…”

“…In an alkaline environment, the direct ORR involving 4e-produces hydroxides (OH-) which is an intermediate of the reaction [20]. According to Senarathna and Rajapakse [17], ORR occurs more suitably in alkaline media, with metals such as Fe and Co able to aid in the degradation of hydroxide ions. This situation makes the ORR potential close in value to the theoretical oxygen electrode potential [17].…”

“…According to Senarathna and Rajapakse [17], ORR occurs more suitably in alkaline media, with metals such as Fe and Co able to aid in the degradation of hydroxide ions. This situation makes the ORR potential close in value to the theoretical oxygen electrode potential [17]. The CV profiles (Fig.…”

“…1) of the various pyrolyzed catalysts in O 2saturated 0.1M KOH media are shown. Figure 1 There are a handful of studies that investigated the utility of clays as support for ORR electrocatalysts [12][13][14][15][16][17]. These studies showed that the ORR peak for such materials are positioned at approximately -0.4 V [16,17,21].…”

“…Mineral clays have high cation-exchange capacity, high electrical conductivity, and large surface area [12][13][14][15][16][17]. The characteristics of clay makes it a good template for producing carbon-clay nanocomposites after pyrolysis.…”