The oxygen-reduction kinetics on Vulcan XC-72 carbon-supported nanosized Pt-Cr alloy catalysts were studied using the porous rotating disk electrode technique in pure and methanol-containing electrolytes. The Vulcan XC-72 carbon-supported Pt-Cr alloy catalysts with different Pt/Cr atomic ratios were prepared via a Pt-carbonyl route. X-ray diffraction data showed that the as-prepared nanosized Pt-Cr alloy catalysts mainly have the disordered structures (solid solution) and that the lattice parameter decreases with the increase in Cr content. Energy-dispersive X-ray analysis indicated that the catalyst compositions are nearly the same as the nominal ones. The obtained Pt-Cr alloy nanoparticles are well dispersed on the surface of carbon with a relatively narrow size distribution. For example, the mean particle size of the as-prepared Pt-Cr (1:1)/C catalyst with 20 wt % metal loading is about 3.1 nm in diameter with a standard deviation of 1.3 nm, and the particle size distribution is relatively narrow. As compared to the Pt/C catalyst, the bimetallic alloy catalysts with the different Pt/Cr atomic ratios showed slightly enhanced mass activity (MA) for the oxygen reduction reaction (ORR); however, the significant enhancement in the specific activity (SA) by a factor of about 1.5-3 for the ORR was found on the Pt-Cr alloy catalysts in pure HClO 4 solution. This enhancement in SA of the Pt-based catalysts was correlated to the changes in the lattice parameter and Pt/Cr surface composition. Moreover, the bimetallic Pt-Cr alloy catalysts with the different Pt/Cr atomic ratios exhibited much higher methanol tolerance during the ORR than the Pt/C catalyst. Furthermore, the catalytic activity for methanol oxidation on the Pt-Cr alloy catalysts was much lower than that on the Pt/C catalyst. Thus, the high methanol tolerance of the carbon-supported Pt-Cr alloy catalysts for the ORR can be ascribed to the weak adsorption of methanol induced by the presence of Cr atoms in the alloys.

The oxygen reduction reaction (ORR) activity of a Ru 1.92 Mo 0.08 SeO 4 catalyst, a Vulcan XC72-supported Ru catalyst and, for comparison, a Vulcan XC72-supported Pt catalyst was studied with a rotating ring-disk electrode. The very similar reaction characteristics of the two Ru catalysts in pure and CH 3 OH-containing H 2 SO 4 electrolyte, which differ markedly from those of the Pt catalyst, indicate that the reactive centers in both Ru catalysts must be identical. They are highly selective (>95%) toward reduction to H 2 O (four electron pathway), independent of the presence of methanol. In the latter case, they are 100% selective toward the ORR, i.e., completely methanol tolerant, while the ORR on Pt catalysts is accompanied by significant CH 3 OH oxidation. Based on mass specific current densities, however, the Ru catalysts are significantly less active than the standard Pt catalysts. Only at methanol concentrations above 10-30 mM does their methanol tolerance make them more active than Pt/Vulcan. Implications for their use as cathode catalysts in a direct methanol fuel cell are discussed.

The use of high amounts of iridium in industrial proton exchange membrane water electrolyzers (PEMWE) could hinder their widespread use for the decarbonization of society with hydrogen. Nonthermally oxidized Ir nanoparticles supported on antimony-doped tin oxide (SnO 2 :Sb, ATO) aerogel allow decreasing the use of the precious metal by more than 70% while enhancing the electrocatalytic activity and stability. To date, the origin of these benefits remains unknown. Here, we present clear evidence of the mechanisms that lead to the enhancement of the electrochemical properties of the catalyst. Operando near-ambient pressure X-ray photoelectron spectroscopy on membrane electrode assemblies reveals a low degree of Ir oxidation, attributed to the oxygen spill-over from Ir to SnO 2 :Sb. Furthermore, the formation of highly unstable Ir(III) species is mitigated, while the decrease of Ir dissolution in Ir/ SnO 2 :Sb is confirmed by inductively coupled plasma mass spectrometry. The mechanisms that lead to the high activity and stability of Ir catalysts supported on SnO 2 :Sb aerogel for PEMWE are thus unveiled.