Origin of High Activity and Durability of Twisty Nanowire Alloy Catalysts under Oxygen Reduction and Fuel Cell Operating Conditions.

The ability to control the surface composition and morphology of alloy catalysts is critical for achieving high activity and durability of catalysts for oxygen reduction reaction (ORR) and fuel cells. This report describes an efficient surfactant-free synthesis route for producing a twisty nanowire (TNW) shaped platinum-iron (PtFe) alloy catalyst (denoted as PtFe TNWs) with controllable bimetallic compositions. PtFe TNWs with an optimal initial composition of ∼24% Pt are shown to exhibit the highest mass activity (3.4 A/mgPt, ∼20 times higher than that of commercial Pt catalyst) and the highest durability (<2% loss of activity after 40 000 cycles and <30% loss after 120 000 cycles) among all PtFe-based nanocatalysts under ORR or fuel cell operating conditions reported so far. Using ex situ and in situ synchrotron X-ray diffraction coupled with atomic pair distribution function (PDF) analysis and 3D modeling, the PtFe TNWs are shown to exhibit mixed face-centered cubic (fcc)-body-centered cubic (bcc) alloy structure and a significant lattice strain. A striking finding is that the activity strongly depends on the composition of the as-synthesized catalysts and this dependence remains unchanged despite the evolution of the composition of the different catalysts and their lattice constants under ORR or fuel cell operating conditions. Notably, dealloying under fuel cell operating condition starts at phase-segregated domain sites leading to a final fcc alloy structure with subtle differences in surface morphology. Due to a subsequent realloying and the morphology of TNWs, the surface lattice strain observed with the as-synthesized catalysts is largely preserved. This strain and the particular facets exhibited by the TNWs are believed to be responsible for the observed activity and durability enhancements. These findings provide new insights into the correlation between the structure, activity, and durability of nanoalloy catalysts and are expected to energize the ongoing effort to develop highly active and durable low-Pt-content nanowire catalysts by controlling their alloy structure and morphology.

Effect of Chuanminshen violaceum polysaccharides and its sulfated derivatives on immunosuppression induced by cyclophosphamide in mice.

One hundred mice were randomly divided into five groups. The mice in one group were injected with physiological saline as the normal control group. The mice in the other four groups were injected with physiological saline, sulfated Chuanminshen violaceum polysaccharides (SCVP), Chuanminshen violaceum polysaccharide (CVP) and astragalus polysaccharide (AP) once daily for 7 d and then with cyclophosphamide (CY) in the last 3 d. The serum cytokine level, apoptosis protein expressions, spleen lymphocyte proliferation, changes in peripheral blood T-cell subsets, and immune organ index were then measured. Results showed that SCVP and CVP can overcome CY-induced immunosuppression by promoting spleen lymphocyte proliferation, raising serum IFN-γ and IL-2 levels, enlarging immune organ indexes, and decreasing excessive apoptosis. Moreover, SCVP and CVP showed the potential to treat autoimmune diseases based on CD4(+)/CD8(+) ratios. Results suggested that SCVP and CVP exhibited the potential to treat autoimmune and immunosuppression diseases.