Bimetallic core–shell Ag@Pt nanoparticle-decorated MWNT electrodes for amperometric H2 sensors and direct methanol fuel cells

Bimetallic core–shell Ag@Pt nanoparticles (NPs) attached on multiwall carbon nanotube (Ag@Pt-MWNT) were synthesized via the formation of Ag NPs on a MWNT surface through chemical reduction and subsequent galvanic replacement of Ag with PtCl62−. The successful synthesis of Ag@Pt-MWNT was confirmed by probing chemical compositions, absorption, and microstructures using various material analysis methods (UV–vis, SEM, EDS, and TEM). The bimetallic particles were found to have a core–shell structure in the TEM image: an Ag core with an average size of approximately 7 nm was enclosed by a shell composed of small Pt NPs. The electrochemical surface area of the Ag@Pt-MWNT-modified glassy carbon electrode was 896 cm2/mg, which was 1.5 times higher than that of commercial 20 wt% Pt-C (E-Tek). The Ag@Pt-MWNTs electrode also exhibited a higher peak current for methanol oxidation than those of comparable Pt-MWNT and Pt-C under the same amount of Pt loading, thus providing evidence for its higher electrocatalytic activity and CO tolerance. Furthermore, an amperometric gas-sensing electrode was fabricated by filtering an Ag@Pt-MWNT solution on a porous PTFE sheet. The as-fabricated electrode displayed a high sensitivity of 1.1 μA/ppm in H2 detection and an excellent linear response over the wide concentration range of 5–1000 ppm, together with fairly good detection times and long-term stability. This enhanced performance was correlated and discussed to be a result of the unique nanostructural features of the Ag@Pt core–shell structure with a porous Pt layer and the strong anchoring of the bimetallic NPs on the activated MWNT surface, which provides a highly active surface area and effective interactions between Ag and Pt.