Observing the Structural Evolution of Quasi-Monolayer Pt Shell on Pd Core in the Electrocatalytic Oxygen-Reduction Reaction.

The use of a quasi-monolayer Pt shell (Ptqms) on a Pd core (Pdc) can reach cost and activity targets for the electrocatalytic oxygen-reduction reaction (ORR). The structure of PdcPtqms in the ORR will vary; however, direct observation of this issue is scarce. Here, during cyclic staircase voltammetry (ranging from 0.5 to 1.15 VRHE) in 0.1 M O2-saturated HClO4, the structure of PdcPtqms was monitored by in situ X-ray absorption spectroscopy. The qualitative and quantitative structural information clearly exhibits a complete picture that Ptqms will directly restructure to form Pt clusters and holes, while Pdc almost remains stable. These findings identify the initial structural evolution of PdcPtqms in the ORR, highlighting the importance of protecting Pdc in the development of high-performance PdcPtqms electrocatalysts.

Incorporation of Al2O3, GO, and Al2O3@GO nanoparticles into water-borne epoxy coatings: abrasion and corrosion resistance.

Nano-Al2O3 particles and graphene oxide (GO) nanosheets were modified by 3-aminopropyltriethoxysilane (KH550), and then dispersed in epoxy resin, and finally modified-Al2O3/epoxy, modified-GO/epoxy and modified-Al2O3@GO/epoxy composite coatings were prepared on steel sheets by the scraping stick method. The microstructure, phase identification, surface bonding and composition of the nanoparticles were characterized by SEM, XRD, FT-IR, and Raman spectroscopy, respectively. The hardness of the coating was assessed by the pencil hardness method. The abrasion resistance of the coating was tested by a sand washing machine. The corrosion resistance of the coating was assessed using salt spray, a long-period immersion test, potentiodynamic polarization curves and electrochemical impedance spectra. With the addition of a small amount of nanoparticles, the dispersion of nanoparticles in the epoxy resin was good. When the content of nano-Al2O3 particles was equal to 1.5 wt%, the particles in the epoxy exhibited the best dispersion and stability. However, the GO and Al2O3@GO nanofillers in the epoxy resin exhibited poor dispersion and stability. The hardness, abrasion and corrosion resistance of the composite coatings were improved with the addition of a small amount of nanoparticles, but the performance began to decline after exceeding a certain content range of the nanoparticles. A relatively good abrasion resistance for the coatings was obtained when the content of Al2O3, GO and Al2O3@GO after modification was 1.5 wt%, 0.2 wt% and 0.4 wt%, respectively. The corrosion resistance of the coatings doped with nano-Al2O3 particles was better than that of the coatings incorporating GO nanosheets and Al2O3@GO hybrids. The corrosion mechanism of the composite coatings in 3.5 wt% NaCl solution was addressed and studied.