The development of effective catalysts for the oxygen reduction reaction (ORR) is crucial for improving the performance of fuel cells. Efficient carbon-supported Pt-Co nanocatalysts were successfully prepared by a generic two-step method: (i) electroless deposition of a Co-P coating on Vulcan XC72R carbon powder and (ii) subsequent spontaneous partial galvanic replacement of Co by Pt, upon immersion of the Co/C precursor in a chloroplatinate solution. The prepared Pt-Co particles (of a core-shell structure) are dispersed on a Vulcan XC-72 support, forming agglomerates made of nanoparticles smaller than 10 nm. The composition and surface morphology of the samples were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) as well as transmission electron microscopy (TEM). The crystal structures of the Co-P/C precursor and Pt-Co/C catalyst were investigated by X-ray diffraction (XRD). XPS analysis was performed to study the chemical state of the surface layers of the precursor and catalyst. The electrochemical behavior of the Pt-Co/C composites was evaluated by cyclic voltammetry (CV). Linear sweep voltammetry (LSV) experiments were used to assess the catalytic activity towards the ORR and compared with that of a commercial Pt/C catalyst. The Pt-Co/C catalysts exhibit mass-specific and surface-specific activities (of jm = 133 mA mg−1 and jesa = 0.661 mA cm−2, respectively) at a typical overpotential value of 380 mV (+0.85 V vs. RHE); these are superior to those of similar electrodes made of a commercial Pt/C catalyst (jm = 50.6 mA mg−1; jesa = 0.165 mA cm−2). The beneficial effect of even small (<1% wt.%) quantities of Co in the catalyst on Pt ORR activity may be attributed to an optimum catalyst composition and particle size resulting from the proposed preparation method.
Banti et al. (Wed,) studied this question.