Synthesis and Comparative Study of Nanoporous Palladium-Based Bimetallic Catalysts for Formic Acid Oxidation

In view of the inherent limitations of current portable technology energy sources, the implementation of micro fuel cells is becoming increasingly appealing. This has generated great interest in the development of direct formic acid micro fuel cells. In this study, nanoporous Pd and four nanoporous bimetallic Pd-M catalysts with an atomic ratio of 90:10, where M = Cd, Pb, Ir, and Pt, were synthesized via a facile hydrothermal method and examined for the electrochemical oxidation of formic acid. The electrocatalytic activity of these nanoporous electrode materials was studied with the use of linear sweep voltammetry and chronoamperometry. Our chronoamperometric measurements have shown that the initial electrochemical performance of the nanoporous Pd-M electrodes toward formic acid oxidation was almost independent of the alloying materials; however, the second incorporated metal strongly affected the stability of the Pd-based electrocatalysts. The mechanisms of the oxidation of formic acid were further examined with the aid of in situ electrochemical ATR-FTIR spectroscopy. For the nanoporous Pd, PdCd, and PdPb catalysts, oxidation proceeds through the direct mechanism, whereas the indirect mechanism, along with major CO poisoning, was observed in the case of the PdIr and PdPt catalysts. The incorporation of even small amounts of Pt and Ir to Pd was found to inhibit the oxidation of formic acid. On the other hand, the addition of Pb to Pd served to promote the direct mechanism, which in turn makes these Pd-based catalysts both cost and electrocatalytically more effective.