Carbon supported PdO with improved activity and stability for oxygen reduction reaction in alkaline solution

Abstract

A series of PdO/C catalysts were prepared by using the PdCl2 and Mn3O4/C as the precursors. The physical properties and the catalytic activity toward the oxygen reduction reaction (ORR) in alkaline media of the prepared PdO/C catalysts were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), as well as transmission electron microscopy (TEM) and the electrochemical techniques. The results show that, with the reaction time increasing, the main species PdO forms on the surface of carbon accompanied by a decreasing of the Mn content, implying a replacement of Mn3O4 with PdO on the carbon surface. The morphology of the irregular aggregates composed of PdO nanoparticles (about 2.3nm) is similar to that of Mn3O4 particles. The PdO/C catalyst with the reaction time of 4h and the Mn content of 0.03wt.% (PdO/C-4h) exhibits the highest activity toward the ORR, with the onset potential and the half-wave potential of the ORR shifting positively about 0.017V and 0.020V, respectively, compared to those on the commercial Pd/C (20wt. %, E-TEK). The specific and mass current densities for the ORR obtained at 0.850V (vs. RHE) on the PdO/C-4h catalyst are about 2.64mAcmPd−2 and 1.11mAμgPd−1, respectively, being about 2.67 and 2.18 times to those on the Pd/C. After 2000 potential cycles between 0.424V and 1.124V for accelerated aging tests, the better catalytic stability of the PdO/C-4h catalyst toward the ORR over the Pd/C is observed, with the half-wave potential of the ORR shifting negatively only about 0.013V, less than that on the latter one. All these findings demonstrate that the catalytic activity and stability of PdO/C-4h catalyst for the ORR are superior to those of the commercial Pd/C, and the PdO/C-4h catalyst would be a promising candidate for the non-platinum catalysts in alkaline media.