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1.
Nano Lett ; 19(10): 6894-6903, 2019 10 09.
Artigo em Inglês | MEDLINE | ID: mdl-31547661

RESUMO

The defect engineering of noble metal nanostructures is of vital importance because it can provide an additional yet advanced tier to further boost catalysis, especially for one-dimensional (1D) noble metal nanostructures with a high surface to bulk ratio and more importantly the ability to engineer the defect along the longitudinal direction of the 1D nanostructures. Herein, for the first time, we report that the defect in 1D noble metal nanostructures is a largely unrevealed yet essential factor in achieving highly active and stable electrocatalysts toward fuel cell reactions. The detailed electrocatalytic results show that the Pd-Sn nanowires (NWs) exhibit interesting defect-dependent performance, in which the defect-rich Pd4Sn wavy NWs display the highest activity and durability for both the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations reveal that a large number of surface vacancies/agglomerated voids are the driving forces for forming surface grain boundaries (GBs) within Pd4Sn WNWs. These electronic active GB regions are the key factors in preserving the number of Pd0 sites, which are critical for minimizing the intrinsic site-to-site electron-transfer barriers. Through this defect engineering, the Pd4Sn WNWs ultimately yield highly efficient alkaline ORR and MOR. The present work highlights the importance of defect engineering in boosting the performance of electrocatalysts for potentially practical fuel cells and energy applications.

2.
Nat Commun ; 10(1): 3782, 2019 Aug 22.
Artigo em Inglês | MEDLINE | ID: mdl-31439841

RESUMO

Three-dimensional bimetallic nanoframes with high spatial diffusivity and surface heterogeneity possess remarkable catalytic activities owing to their highly exposed active surfaces and tunable electronic structure. Here we report a general one-pot strategy to prepare ultrathin octahedral Au3Ag nanoframes, with the formation mechanism explicitly elucidated through well-monitored temporal nanostructure evolution. Rich crystalline defects lead to lowered atomic coordination and varied electronic states of the metal atoms as evidenced by extensive structural characterizations. When used for electrocatalytic methanol oxidation, the Au3Ag nanoframes demonstrate superior performance with a high specific activity of 3.38 mA cm-2, 3.9 times that of the commercial Pt/C. More intriguingly, the kinetics of methanol oxidation on the Au3Ag nanoframes is counter-intuitively promoted by carbon monoxide. The enhancement is ascribed to the altered reaction pathway and enhanced OH- co-adsorption on the defect-rich surfaces, which can be well understood from the d-band model and comprehensive density functional theory simulations.

3.
ACS Nano ; 12(11): 11625-11631, 2018 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-30481970

RESUMO

Exploring high-performance and cost-efficient electrocatalysts with unusual metastable phase offers opportunities for improving the electrochemical hydrogen generation, while it remains a great challenge to achieve them with desirable activity and stability. Herein, we report that the doping engineering in a metastable, hexagonal-close-packed nickel (hcp Ni) electrocatalyst is a largely unrevealed yet important factor in achieving an extremely active and stable electrocatalyst toward alkaline hydrogen evolution reaction (HER). Theoretical predications and experimental results suggest that, while the stability of metastable hcp Ni electrocatalyst can be largely improved via the manganese (Mn) doping due to the lower formation energy and lattice stabilization, the MnO/hcp Ni surface promotes the HER via intrinsic favorable H2O adsorption and fast water dissociation kinetics. Consequently, the Mn-doped hcp Ni electrocatalyst shows a small overpotential of 80 mV at 10 mA/cm2 and a low Tafel slope of 68 mV/dec. The result is even approaching that of the commercial Pt/C, being one of the best reported non-noble metal HER electrocatalysts in alkaline media. Under long-term chronopotentiometry measurement, such electrocatalyst can endure at least 10 h with negligible activity decay and structure change. The present work demonstrates the dimension in boosting the electrocatalysis by doping engineering of metastable electrocatalysts.

4.
ACS Appl Mater Interfaces ; 10(45): 38799-38806, 2018 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-30339345

RESUMO

Room-temperature storage and transportation of microorganisms maximize the power of microorganisms in healthcare, energy, and environment. Recently, paper-based biotechnologies have been developed to enable room-temperature storage of a variety of nonliving biosystems such as diagnostic devices and cell-free systems. Herein, room-temperature storage of living microorganisms is realized by an electrospun nonwoven paper containing convex region, which is composed of coiled microfibers with dense distribution of microorganisms. Microorganisms are encapsulated into the microfibers and remain intact after electrospinning. Poly(ethylene oxide) is used as polymer matrix, and glycerol and dextran are used as additives. When the contents of glycerol and dextran are optimized as 5 and 0.4%, the room-temperature time is prolonged to 2 days, more than 8 folds as compared with the control group. Upon demand, the microorganisms can be activated by adding water and used for culturing microorganisms directly. Furthermore, mechanisms which account for microbial activity and storage are studied. Our microfiber-based strategy is universal for the room-temperature storage of prokaryotic and eukaryotic microorganisms in the solid formulation. Besides, our microorganism/polymer complex structures represent novel living materials via a bottom-up strategy, which are of great potential for new biomedical applications.


Assuntos
Membranas Artificiais , Técnicas Microbiológicas/métodos , Manejo de Espécimes/métodos , Dextranos/química , Escherichia coli/fisiologia , Glicerol/química , Técnicas Microbiológicas/instrumentação , Polietilenoglicóis/química , Manejo de Espécimes/instrumentação , Temperatura Ambiente
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