Ordered alloy formation for Pt3Fe/C, PtFe/C and Pt5.75Fe5.75Cuy/CO2-reduction electro-catalysts

Carbon supported Pt3Fe, PtFe and Pt5.75Fe5.75Cu catalysts are prepared via the impregnation of Fe and/or Cu-nitrate precursor salts onto a preformed nano-sized Pt/C catalyst. They are referred to as Pt3Fe/C, PtFe/C and Pt5.75Fe5.75CU/C catalysts and the subscripts refer to the nominal Pt, Fe and Cu atomic ratios. The final catalysts are obtained by annealing the impregnated samples in a H-2 enriched atmosphere. Pt5.75Fe6.75/C, Pt5.75Cu6.75/C and Pt5.75Fe5.75Cu2/C catalysts were also made. The as-prepared catalysts are characterized using X-ray diffraction, transmission electron microscopy, standard electrochemical methods and probed for the electrochemical O-2 reduction reaction (orr). Rietveld analyses reveal that [Fm-3m] Pt, cubic [Pm-3m] Pt3Fe and tetragonal [P4/mmm] PtFe structure types are made. In case of the Pt5.75Fe5.75Cu/C catalyst, a nano-sized carbon-supported single-phase catalyst of [P4/mmm] structure is found to be made at 800 degrees C, with Pt and Fe ordered on separate lattice planes, while Cu is distributed randomly onto both Pt and Fe atomic planes. The PtFe/C equivalent catalyst contains in addition a separate Fe phase as well as a slightly disordered [P4/mmm] phase. Pt5.75Fe6.75/C forms a disordered cubic [Fm-3m] alloy structure. The activity toward the orr was measured after 70 potential cycling, which can cause beneficial changes to the catalysts. In case of the specific orr activity, a dependence on the catalyst series is observed as follows: Pt5.75Fe5.75Cu/C [P4/mmm] > PtFe/C [P4/mmm] > Pt3Fe/C [Pm-3 m] approximate to Pt5.75Fe6.75/C [Fm-3m] > Pt/C [Fm-3m]. The highest orr mass activities are also found for the Pt5.75Fe5.75CU/C and subsequently for the PtFe/C catalysts. Estimated orr activities are well within the range reported in the literature. In fact the specific orr activities compare to results reported for so called de-alloyed catalyst that are among the highest orr mass activities reported in the recent literature. (C) 2012 Published by Elsevier Ltd.