Novel catalyst-support interaction for direct formic acid fuel cell anodes: Pd electrodeposition on surface-modified graphite felt

Abstract

The electrodeposition of Pd on graphite felt (GF, thickness ~3 mm in uncompressed state) was studied and the resulting catalyst was compared with Pt-Ru/GF for the electro-oxidation of formic acid. A micellar solution composed of the non-ionic surfactant Triton X-102 and an aqueous phase containing PdCl2 were utilized for the galvanostatic electrodeposition of Pd nanoparticles. The presence of the surfactant during electrodeposition coupled with pretreatment of the GF surface by a Shipley-type method (PdCl2 + SnCl2 solution) creating nucleation sites had a major impact on the Pd catalyst morphology and penetration throughout the electrode thickness, affecting, therefore, the electrocatalytic activity toward formic acid oxidation. It was found that large (~1,000 nm) Pd particles with smooth surface favored the indirect COad pathway, while Pd nanoparticles (diameter <40 nm) with rough surface, formed with surfactant and pretreatment, were much more active leading to the direct non-COad pathway. Due to pretreatment the GF surface has been modified and the effective catalytic system could be described as Pd/SnO2–Pd(PdO)/GF with possible electronic interaction between support and catalyst. In direct formic acid fuel cell (DFAFC) experiments at 333 K and 1 M HCOOH, the peak power density using the Pd/GF anode reached 852 W m−2 (57 g m−2 Pd) compared to 392 W m−2 (40 g m−2 Pd) with a commercial Pd catalyst-coated membrane (CCM). The long-term stability of Pd-based anodes was poor and inferior to Pt–Ru (4:1 at. ratio) prepared and tested under identical conditions.