Improved methanol electro-oxidation reaction on PdRh-PVP/C electrodes

Here we report on the organometallic synthesis of polyvinylpyrrolidone (PVP)-stabilized palladium-rhodium nanostructures that display high electrochemical properties when used as carbon-supported electrodes (Pd_xRh_1-x-PVP/C) for methanol oxidation reaction (MOR). These nanostructures were synthesized by hydrogenation of the tris(dibenzylideneacetone)dipalladium(0) (Pd₂(dba)₃) and tris(allyl) rhodium (Rh(η³-C₃H₅)₃) complexes, in tetrahydrofuran (THF) under mild reaction conditions (room temperature and 3 bar H₂) and in the presence of PVP as stabilizer. The influence of methanol concentration (0.5, 1.0 and 2.0 M) as well as different scan rates (5–100 mV s⁻¹) was evaluated to determine changes in the stability and catalytic activity. The organometallic approach and the use of PVP for the preparation of PdRh electrode materials promoted the formation of highly dispersed nanostructures, that led to a remarkably enhanced methanol electro-oxidation in alkaline medium. This high catalytic behavior can reasonably arise from a synergistic effect between Pd and Rh metals as, under the applied conditions, Rh is expected to enhance the Pd ability to oxidize methanol to CO₂ (oxophilic character) as well as the catalyst stability. From all the evaluated electrode materials, Pd₈Rh₂-PVP/C electrode showed the highest mass activity at high methanol concentration (2.0 M) and low scan rate (10 mV s⁻¹). This catalyst showed a performance up to 26 times higher than that of Pd-PVP/C and interestingly an electroactivity superior to that of previously reported PdRh catalysts.