Abstract
Background: Fuel cells have a very low emission of greenhouse gases such as CO2, SOx etc with high efficiencies and are non-polluting energy sources. One of the current challenges is to develop inexpensive and efficient oxygen reduction reaction (ORR) materials. Extensive research has been conducted to develop platinum (Pt) loaded carbon nanomaterials for ORR applications. However, the literature is rife with inconsistencies owing to varying synthesis conditions of Pt nanoparticles, variation of carbon supports materials and indeed the ORR experiments.
Method: A comparative electrochemical analysis of various carbon supports, including commercial PtCB, pristine and Pt loaded carbon nanotubes (MWCNTs), graphene oxide (GO) and graphene nano platelets (GNP) has been conducted, to ascertain their electrochemical response towards oxygen reduction reactions under identical experimental conditions.
Results: The reduction potential (least negative) and the peak current densities for the materials follow the order of MWCNTs>GNP>GO, with the performance of pristine MWCNTs (3 mA/cm2) comparable to that of N- and B-doped MWCNTs. Furthermore, low-loading of platinum nanoparticles on the carbon supports, carried out via microwave-assisted polyol synthesis, lead to an increase in the peak reduction current density significantly at lower reduction potentials. Although the same synthesis process is used; the MWCNTs, GO and GNP support samples have different metallic Pt loadings. A comparison of ORR current densities mass normalized to Pt loading shows that Pt/MWCNTs have the highest linear sweep voltammetry (LSV) reduction current density of 900 A/g, much higher than 510 A/g of the commercial Pt-carbon black supports, and is followed by Pt/GNP and Pt/GO which have the LSV value of 500 A/g and 200 A/g LSV, respectively.