No abstract

To propel the commercialization of fuel cells, the development of efficient nonprecious metal catalysts, specifically cathodic oxygen reduction catalysts, is turning into reality because the great advancements have been made on nitrogen-doped carbon materials recently. In this study, we demonstrated that nitrogen-doped hollow carbon nanoparticles (N-HCNPs) exhibit excellent electrocatalytic performance for oxygen reduction reaction (ORR) in alkaline fuel cells. Cyclic voltammetry and rotating ring-disk electrode voltammetry showed that the ORR activity of N-HCNPs approaches that of commercial Pt–C catalyst and is much better compared with nitrogen-free counterparts due to the incorporation of nitrogen atoms into graphitic structures. Kinetic studies indicated that the involvement of nitrogen induces a totally different oxygen adsorption mechanism and a four-electron dominated reaction pathway for N-HCNPs in comparison with nitrogen-free HCNPs, very similar to the observations in Pt–C. Moreover, N-HCNPs exhibited good operation stability and excellent tolerance to methanol crossover and CO poisoning for ORR superior to that of Pt–C. Our findings suggest that N-HCNPs catalyst is a promising alternative for the Pt-based catalysts in fuel cells.

NH3 emissions were limited strictly because of the threat for human health and sustainable development. Pt/Al2O3 and Pt/CeZrO2 were prepared by the impregnation method. Differences in surface chemical states, reduction ability, acid properties, morphological properties, reaction mechanisms, and ammonia oxidation activity were studied. It indicated that Pt species states were affected by different metal–support interactions. The homogeneously dispersed Pt species over Pt/Al2O3 exposed Pt(111) because of weak metal–support interactions; there even existed an obvious interface between Pt and Al2O3. While obscure even an overlapped interface was observed over Pt/CeZrO2, resulting in the formation of PtO because of the oxygen migration from CeZrO2 to Pt species (confirmed by CO-FTIR, the cycled H2-TPR and transmission electron microscopy results). It was noteworthy that different reaction mechanisms were induced by different states of Pt species; NH was the key intermediate species for ammonia oxidation reaction over Pt/Al2O3, but two kinds of intermediates, N2H4 and HNO, were observed for Pt/CeZrO2. It consequently resulted in the obvious distinction of the NH3-SCO catalytic performance; the light-off temperatures of NH3 over Pt/Al2O3 and Pt/CeZrO2 were 231 and 275 °C, respectively, while the maximum N2 selectivity (65%) was obtained over Pt/CeZrO2, it was obviously better than that over Pt/Al2O3.

Capped chelating organic molecules are presented as a design principle for tuning heterogeneous nanoparticles for electrochemical catalysis. Gold nanoparticles (AuNPs) functionalized with a chelating tetradentate porphyrin ligand show a 110-fold enhancement compared to the oleylamine-coated AuNP in current density for electrochemical reduction of CO to CO in water at an overpotential of 340 mV with Faradaic efficiencies (FEs) of 93 %. These catalysts also show excellent stability without deactivation (<5 % productivity loss) within 72 hours of electrolysis. DFT calculation results further confirm the chelation effect in stabilizing molecule/NP interface and tailoring catalytic activity. This general approach is thus anticipated to be complementary to current NP catalyst design approaches.

ObjectiveThe aim of this study was to evaluate the mechanical and biological properties of orthodontic bonding agents containing silver- or zinc-doped bioactive glass (BAG) and determine the antibacterial and remineralization effects of these agents.MethodsBAG was synthesized using the alkali-mediated solgel method. Orthodontic bonding agents containing BAG were prepared by mixing BAG with flowable resin. Transbond™ XT (TXT) and Charmfil™ Flow (CF) were used as controls. Ion release, cytotoxicity, antibacterial properties, the shear bond strength, and the adhesive remnant index were evaluated. To assess the remineralization properties of BAG, micro-computed tomography was performed after pH cycling.ResultsThe BAG-containing bonding agents showed no noticeable cytotoxicity and suppressed bacterial growth. When these bonding agents were used, demineralization after pH cycling began approximately 200 to 300 µm away from the bracket. On the other hand, when CF and TXT were used, all surfaces that were not covered by the adhesive were demineralized after pH cycling.ConclusionsOur findings suggest that orthodontic bonding agents containing silver- or zinc-doped BAG have stronger antibacterial and remineralization effects compared with conventional orthodontic adhesives; thus, they are suitable for use in orthodontic practice.