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1.
J Am Chem Soc ; 2020 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-32279490

RESUMO

Exploring efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) in alkaline media is critical for developing anion exchange membrane electrolyzers. The key to a rational catalyst design is understanding the descriptors that govern the alkaline HER activity. Unfortunately, the principles that govern the alkaline HER performance remain unclear and are still under debate. By studying the alkaline HER at a series of NiCu bimetallic surfaces, where the electronic structure is modulated by the ligand effect, we demonstrate that alkaline HER activity can be correlated with either the calculated or the experimental-measured d band center (an indicator of hydrogen binding energy) via a volcano-type relationship. Such correlation indicates the descriptor role of the d band center, and this hypothesis is further supported by the evidence that combining Ni and Cu produces a variety of adsorption sites, which possess near-optimal hydrogen binding energy. Our finding broadens the applicability of d band theory to activity prediction of metal electrocatalysts and may offer an insightful understanding of alkaline HER mechanism.

2.
Proc Natl Acad Sci U S A ; 116(47): 23404-23409, 2019 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-31685626

RESUMO

Phase transitions in halide perovskites triggered by external stimuli generate significantly different material properties, providing a great opportunity for broad applications. Here, we demonstrate an In-based, charge-ordered (In+/In3+) inorganic halide perovskite with the composition of Cs2In(I)In(III)Cl6 in which a pressure-driven semiconductor-to-metal phase transition exists. The single crystals, synthesized via a solid-state reaction method, crystallize in a distorted perovskite structure with space group I4/m with a = 17.2604(12) Å, c = 11.0113(16) Å if both the strong reflections and superstructures are considered. The supercell was further confirmed by rotation electron diffraction measurement. The pressure-induced semiconductor-to-metal phase transition was demonstrated by high-pressure Raman and absorbance spectroscopies and was consistent with theoretical modeling. This type of charge-ordered inorganic halide perovskite with a pressure-induced semiconductor-to-metal phase transition may inspire a range of potential applications.

3.
J Am Chem Soc ; 141(37): 14772-14779, 2019 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-31450888

RESUMO

We report here, and rationalize, a synergistic effect between a non-noble metal oxide catalyst (CuO) and high-frequency ultrasound (HFUS) on glucose oxidation. While CuO and HFUS are able to independently oxidize glucose to gluconic acid, the combination of CuO with HFUS led to a dramatic change of the reaction selectivity, with glucuronic acid being formed as the major product. By means of density functional theory (DFT) calculations, we show that, under ultrasonic irradiation of water at 550 kHz, the surface lattice oxygen of a CuO catalyst traps H· radicals stemming from the sonolysis of water, making the ring-opening of glucose energetically unfavorable and leaving a high coverage of ·OH radical on the CuO surface, which selectively oxidizes glucose to glucuronic acid. This work also points toward a path to optimize the size of the catalyst particle for an ultrasonic frequency that minimizes the damage to the catalyst, resulting in its successful reuse.

4.
ACS Appl Mater Interfaces ; 11(12): 11722-11735, 2019 Mar 27.
Artigo em Inglês | MEDLINE | ID: mdl-30838855

RESUMO

In this study, graphene nanosheet-supported ultrafine Cu nanoparticles (NPs) encapsulated with thin mesoporous silica (Cu-GO@m-SiO2) materials are fabricated with particle sizes ranging from 60 to 7.8 nm and are systematically investigated for the oxidative coupling of amines to produce biologically and pharmaceutically important imine derivatives. Catalytic activity remarkably increased from 76.5% conversion of benzyl amine for 60 nm NPs to 99.3% conversion and exclusive selectivity of N-benzylidene-1-phenylmethanamine for 7.8 nm NPs. The superior catalytic performance along with the outstanding catalyst stability of newly designed catalysts are attributed to the easy diffusion of organic molecules through the porous channel of mesoporous SiO2 layers, which not only restricts the restacking of the graphene nanosheets but also prevents the sintering and leaching of metal NPs to an extreme extent through the nanoconfinement effect. Density functional theory calculations were performed to shed light on the reaction mechanism and to give insight into the trend of catalytic activity observed. The computed activation barriers of all elementary steps are very high on terrace Cu(111) sites, which dominate the large-sized Cu NPs, but are significantly lower on step sites, which are presented in higher density on smaller-sized Cu NPs and could explain the higher activity of smaller Cu-GO@m-SiO2 samples. In particular, the activation barrier for the elementary coupling reaction is reduced from 139 kJ/mol on flat terrace Cu(111) sites to the feasible value of 94 kJ/mol at step sites, demonstrating the crucial role of the step site in facilitating the formation of secondary imine products.

5.
Nat Commun ; 10(1): 572, 2019 02 04.
Artigo em Inglês | MEDLINE | ID: mdl-30718514

RESUMO

Exploring robust catalysts for water oxidation in acidic electrolyte is challenging due to the limited material choice. Iridium (Ir) is the only active element with a high resistance to the acid corrosion during water electrolysis. However, Ir is rare, and its large-scale application could only be possible if the intrinsic activity of Ir could be greatly enhanced. Here, a pseudo-cubic SrCo0.9Ir0.1O3-δ perovskite, containing corner-shared IrO6 octahedrons, is designed. The Ir in the SrCo0.9Ir0.1O3-δ catalyst shows an extremely high intrinsic activity as reflected from its high turnover frequency, which is more than two orders of magnitude higher than that of IrO2. During the electrochemical cycling, a surface reconstruction, with Sr and Co leaching, over SrCo0.9Ir0.1O3-δ occurs. Such reconstructed surface region, likely contains a high amount of structural domains with corner-shared and under-coordinated IrOx octahedrons, is responsible for the observed high activity.

6.
J Phys Chem Lett ; 9(14): 3878-3885, 2018 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-29938512

RESUMO

The past few years have witnessed unprecedented rapid improvement of the performance of a new class of photovoltaics based on halide perovskites. This progress has been achieved even though there is no generally accepted mechanism of the operation of these solar cells. Here we present a model based on bistable amphoteric native defects that accounts for all key characteristics of these photovoltaics and explains many idiosyncratic properties of halide perovskites. We show that a transformation between donor-like and acceptor-like configurations leads to a resonant interaction between amphoteric defects and free charge carriers. This interaction, combined with the charge transfer from the perovskite to the electron and hole transporting layers results in the formation of a dynamic n-i-p junction whose photovoltaic parameters are determined by the perovskite absorber. The model provides a unified explanation for the outstanding properties of the perovskite photovoltaics, including hysteresis of J-V characteristics and ultraviolet light-induced degradation.

7.
ACS Appl Mater Interfaces ; 10(10): 8574-8584, 2018 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-29437377

RESUMO

Copper oxides have been of considerable interest as electrocatalysts for CO2 reduction (CO2R) in aqueous electrolytes. However, their role as an active catalyst in reducing the required overpotential and improving the selectivity of reaction compared with that of polycrystalline copper remains controversial. Here, we introduce the use of selected-ion flow tube mass spectrometry, in concert with chronopotentiometry, in situ Raman spectroscopy, and computational modeling, to investigate CO2R on Cu2O nanoneedles, Cu2O nanocrystals, and Cu2O nanoparticles. We show experimentally that the selective formation of gaseous C2 products (i.e., ethylene) in CO2R is preceded by the reduction of the copper oxide (Cu2OR) surface to metallic copper. On the basis of density functional theory modeling, CO2R products are not formed as long as Cu2O is present at the surface because Cu2OR is kinetically and energetically more favorable than CO2R.

8.
Nat Commun ; 8: 15271, 2017 05 12.
Artigo em Inglês | MEDLINE | ID: mdl-28497786

RESUMO

Plasmonics has attracted tremendous interests for its ability to confine light into subwavelength dimensions, creating novel devices with unprecedented functionalities. New plasmonic materials are actively being searched, especially those with tunable plasmons and low loss in the visible-ultraviolet range. Such plasmons commonly occur in metals, but many metals have high plasmonic loss in the optical range, a main issue in current plasmonic research. Here, we discover an anomalous form of tunable correlated plasmons in a Mott-like insulating oxide from the Sr1-xNb1-yO3+δ family. These correlated plasmons have multiple plasmon frequencies and low loss in the visible-ultraviolet range. Supported by theoretical calculations, these plasmons arise from the nanometre-spaced confinement of extra oxygen planes that enhances the unscreened Coulomb interactions among charges. The correlated plasmons are tunable: they diminish as extra oxygen plane density or film thickness decreases. Our results open a path for plasmonics research in previously untapped insulating and strongly-correlated materials.

9.
Adv Mater ; 28(8): 1559-66, 2016 Feb 24.
Artigo em Inglês | MEDLINE | ID: mdl-26676965

RESUMO

Skin-inspired haptic-memory devices, which can retain pressure information after the removel of external pressure by virtue of the nonvolatile nature of the memory devices, are achieved. The rise of haptic-memory devices will allow for mimicry of human sensory memory, opening new avenues for the design of next-generation high-performance sensing devices and systems.


Assuntos
Biomimética/instrumentação , Equipamentos e Provisões Elétricas , Memória , Sensação/fisiologia , Pele , Condutividade Elétrica , Humanos , Pressão
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