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1.
Chem Commun (Camb) ; 56(20): 3061-3064, 2020 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-32048685

RESUMO

Four crystal phases of ruthenium-boron intermetallics, including Ru7B3, RuB, Ru2B3 and RuB2, are selectively synthesized. With the increase in boron content for the ruthenium-boron intermetallics, Ru-B hybridization interactions decrease. And their hydrogen-evolution electrocatalytic performances are compared, with those of RuB2 exhibiting the best electrocatalytic activity and stability.

2.
Artigo em Inglês | MEDLINE | ID: mdl-31899847

RESUMO

A theoretical and experimental study gives insights into the nature of the metal-boron electronic interaction in boron-bearing intermetallics and its effects on surface hydrogen adsorption and hydrogen-evolving catalytic activity. Strong hybridization between the d orbitals of transition metal (TM ) and the sp orbitals of boron exists in a family of fifteen TM -boron intermatallics (TM :B=1:1), and hydrogen atoms adsorb more weakly to the metal-terminated intermetallic surfaces than to the corresponding pure metal surfaces. This modulation of electronic structure makes several intermetallics (e.g., PdB, RuB, ReB) prospective, efficient hydrogen-evolving materials with catalytic activity close to Pt. A general reaction pathway towards the synthesis of such TM B intermetallics is provided; a class of seven phase-pure TM B intermetallics, containing V, Nb, Ta, Cr, Mo, W, and Ru, are thus synthesized. RuB is a high-performing, non-platinum electrocatalyst for the hydrogen evolution reaction.

3.
ACS Appl Mater Interfaces ; 11(45): 42006-42013, 2019 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-31633901

RESUMO

One of the key objectives in PEM electrolysis technology is to reduce iridium loading and to improve iridium mass activity at the side of oxygen evolution electrocatalysis. 6H-phase, Ir-based perovskite (6H-SrIrO3) is known to be a promising alternative to the IrO2 catalyst, and developing effective strategies to further enhance its catalytic performance is needed. Here we present that a significant enhancement in electrocatalytic activity for the oxygen evolution reaction of 6H-SrIrO3 can be achieved by cobalt incorporation. A suitable amount of cobalt dopants results in a decreased formation temperature of 6H-SrIrO3 from 700 to 500 °C and thereby a decreased thickness of platelike particles for the material. Besides the morphological effect, the cobalt incorporation also increases the coverage of surface hydroxyl groups, regulates the Ir-O bond covalency, and modulates the oxygen p-band center of the material. This synergistic optimization of the morphological, surface, and electronic structures makes the cobalt-doped 6H-SrIrO3 catalyst give a 3-fold increase in iridium mass activity for oxygen evolution reaction in comparison with the undoped 6H-SrIrO3 under acidic conditions.

4.
Chem Commun (Camb) ; 55(59): 8627-8630, 2019 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-31282506

RESUMO

A family of twelve monometallic diborides, containing transition metals from group IVB elements to group VIII elements, and Ni-W bimetallic diborides are synthesized via a molten salt-assisted method. Their trend in activity for the hydrogen evolution reaction is studied, with Ni-W bimetallic diborides acting as the most efficient, nonprecious electrocatalysts.

5.
Angew Chem Int Ed Engl ; 58(33): 11409-11413, 2019 Aug 12.
Artigo em Inglês | MEDLINE | ID: mdl-31187910

RESUMO

The fundamental understanding and rational manipulation of catalytic site preference at extended solid surfaces is crucial in the search for advanced catalysts. Herein we find that the Ru top sites at metallic ruthenium surface have efficient Pt-like activity for the hydrogen evolution reaction (HER), but they are subordinate to their adjacent, less active Ru3 -hollow sites due to the stronger hydrogen-binding ability of the latter. We also present an interstitial incorporation strategy for the promotion of the Ru top sites from subordinate to dominant character, while maintaining Pt-like catalytic activity. Our combined theoretical and experimental studies further identify intermetallic RuSi as a highly active, non-Pt material for catalyzing the HER, because of its suitable electronic structure governed by a good balance of ligand and strain effects.

6.
Nanoscale ; 11(21): 10257-10265, 2019 May 30.
Artigo em Inglês | MEDLINE | ID: mdl-31112185

RESUMO

The development of nonprecious and efficient catalysts to boost the oxygen reduction reaction (ORR) is imperative. However, the majority of previously reported approaches suffered from a complicated fabrication procedure, both time consuming and difficult to scale up. Herein, large-scale iron ion embedded polyaniline fibers were successfully fabricated as precursors for preparing iron/nitrogen co-doped fibrous porous carbons (Fe/NPCFs) through an interfacial engineering strategy at room temperature. As ORR electrocatalysts in an alkaline medium (0.1 M KOH), Fe/NPCFs display a positive half-wave potential of 0.827 V (vs. RHE), and high limited current density (up to 5.76 mA cm-2), which are better than those of commercial Pt/C (E1/2 = 0.815 V, JL = 5.47 mA cm-2). Also, Fe/NPCFs exhibit a high ORR catalysis activity (E1/2 = 0.632 V, JL = 5.07 mA cm-2) in acidic medium (0.5 M H2SO4). When used as an air cathode in a primary Zn-air battery, high power density (158.5 mW cm-2) and specific capacity (717.8 mA h g-1) can be easily achieved, outperforming the commercial Pt/C.

7.
Angew Chem Int Ed Engl ; 58(23): 7631-7635, 2019 Jun 03.
Artigo em Inglês | MEDLINE | ID: mdl-30775830

RESUMO

Simultaneous realization of improved activity, enhanced stability, and reduced cost remains a desirable yet challenging goal in the search of oxygen evolution electrocatalysts in acid. Herein we report iridium-containing strontium titanates (Ir-STO) as active and stable, low-iridium perovskite electrocatalysts for the oxygen evolution reaction (OER) in acid. The Ir-STO contains 57 wt % less iridium relative to the benchmark catalyst IrO2 , but it exhibits more than 10 times higher catalytic activity for OER. It is shown to be among the most efficient iridium-based oxide electrocatalysts for OER in acid. Theoretical results reveal that the incorporation of iridium dopants in the STO matrix activates the intrinsically inert titanium sites, strengthening the surface oxygen adsorption on titanium sites and thereby giving nonprecious titanium catalytic sites that have activities close to or even better than iridium sites.

8.
Nat Commun ; 9(1): 5236, 2018 12 07.
Artigo em Inglês | MEDLINE | ID: mdl-30531797

RESUMO

The widespread use of proton exchange membrane water electrolysis requires the development of more efficient electrocatalysts containing reduced amounts of expensive iridium for the oxygen evolution reaction (OER). Here we present the identification of 6H-phase SrIrO3 perovskite (6H-SrIrO3) as a highly active electrocatalyst with good structural and catalytic stability for OER in acid. 6H-SrIrO3 contains 27.1 wt% less iridium than IrO2, but its iridium mass activity is about 7 times higher than IrO2, a benchmark electrocatalyst for the acidic OER. 6H-SrIrO3 is the most active catalytic material for OER among the iridium-based oxides reported recently, based on its highest iridium mass activity. Theoretical calculations indicate that the existence of face-sharing octahedral dimers is mainly responsible for the superior activity of 6H-SrIrO3 thanks to the weakened surface Ir-O binding that facilitates the potential-determining step involved in the OER (i.e., O* + H2O → HOO* + H+ + e¯).

9.
ChemSusChem ; 11(19): 3486-3494, 2018 Oct 11.
Artigo em Inglês | MEDLINE | ID: mdl-30091281

RESUMO

Semiconductor electrodes integrated with cocatalysts are key components of photoelectrochemistry (PEC)-based solar-energy conversion. However, efforts to optimize the PEC device have been limited by an inadequate understanding of the interface interactions between the semiconductor-cocatalyst (sem|cat) and cocatalyst-electrolyte (cat|ele) interface. In our work, we used ferrihydrite (Fh)-modified Ti-Fe2 O3 as a model to explore the transfer process of photogenerated charge carriers between the Ti-Fe2 O3 -Fh (Ti-Fe2 O3 |Fh) interface and Fh-electrolyte (Fh|ele) interface. The results demonstrate that the biphasic structure (Fh/Ti-Fe2 O3 ) possesses the advantage that the minority hole transfer from Ti-Fe2 O3 to Fh is driven by the interfacial electric field at the Ti-Fe2 O3 |Fh interface; meanwhile, the holes reached at the surface of Fh can rapidly inject into the electrolyte across the Fh|ele interface. As a benefit from the improved charge transfer at the Ti-Fe2 O3 |Fh and Fh|ele interface, the photocurrent density obtained by Fh/Ti-Fe2 O3 can reach 2.32 mA cm-2 at 1.23 V versus RHE, which is three times higher than that of Ti-Fe2 O3 .

10.
ACS Appl Mater Interfaces ; 10(35): 29795-29804, 2018 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-30095885

RESUMO

The cation substitutional doping of metal oxide semiconductors plays pivotal roles in improving the gas sensing performances, but the doping effect on surface sensing reaction is still not well understood. In this study, indium oxides doped with various heteroatoms are investigated to obtain in-depth understanding of how doping (or the resulting change in the electronic structure) alters the surface-absorbed oxygen chemistry and subsequent sensing process. The experimental results reveal that energy level of In2O3 can be modulated by introduction of these dopants, some of which (e.g., Al, Ga, and Zr) lead to the elevation of Fermi level, whereas others (e.g., Ti, V, Cr, Mo, W, and Sn) bring about relative drop in Fermi level. However, only the former can improve the response to formaldehyde, indicating a strong link between Fermi level and sensing properties. Mechanistic study suggests that the elevation of Fermi level increases energy level difference between oxide semiconductor and oxygen molecules and facilitates the surface absorption of oxygen species, resulting in superior formaldehyde sensing activity. Especially, Al-doped In2O3 exhibits remarkably enhanced sensing performances toward formaldehyde at low working temperature (150 °C) with high response, good selectivity, ultralow limit of detection (60 ppb), and short response time (2-23 s). Our findings not only promote the understanding of sensing reaction process and its correlation with the semiconductor electronic structure but also offer a general guideline for large-scale screening of promising oxide semiconductor-based sensing materials for gas detection.

11.
Nat Commun ; 9(1): 2609, 2018 07 04.
Artigo em Inglês | MEDLINE | ID: mdl-29973591

RESUMO

Although a number of nonprecious materials can exhibit catalytic activity approaching (sometimes even outperforming) that of iridium oxide catalysts for the oxygen evolution reaction, their catalytic lifetimes rarely exceed more than several hundred hours under operating conditions. Here we develop an energy-efficient, cost-effective, scaled-up corrosion engineering method for transforming inexpensive iron substrates (e.g., iron plate and iron foam) into highly active and ultrastable electrodes for oxygen evolution reaction. This synthetic method is achieved via a desired corrosion reaction of iron substrates with oxygen in aqueous solutions containing divalent cations (e.g., nickel) at ambient temperature. This process results in the growth on iron substrates of thin film nanosheet arrays that consist of iron-containing layered double hydroxides, instead of rust. This inexpensive and simple manufacturing technique affords iron-substrate-derived electrodes possessing excellent catalytic activities and activity retention for over 6000 hours at 1000 mA cm-2 current densities.

12.
Sci Rep ; 8(1): 4478, 2018 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-29540797

RESUMO

Amorphous Ni-Mn bimetallic hydroxide film on the three-dimensional nickle foam (NF)-supported conductive Ni3S2 nanosheets (denoted as Ni-Mn-OH@Ni3S2/NF) is successfully synthesized by an ultrafast process (5 s). The fascinating structural characteristic endows Ni-Mn-OH@Ni3S2/NF electrodes better electrochemical performance. The specific capacitance of 2233.3 F g-1 at a current density of 15 A g-1 can achieve high current density charge and discharge at 20/30 A g-1 that the corresponding capacitance is 1529.16 and 1350 F g-1, respectively. As well as good cycling performance after 1000 cycles can maintain 72% at 15 A g-1. The excellent performance can be attributed to unique surface modification nanostructures and the synergistic effect of the bimetallic hydroxide film. The impressive results provide new opportunity to produce advanced electrode materials by simple and green route and this material is expected to apply in high energy density storage systems.

13.
ChemSusChem ; 11(1): 276-284, 2018 01 10.
Artigo em Inglês | MEDLINE | ID: mdl-28968003

RESUMO

Although NiCoP has attracted much attention in the field of electrocatalysis, the study of its photocatalytic activity and mechanism have been somewhat limited. NiCoP/g-C3 N4 , synthesized by simple one-pot method, is a highly efficient photocatalyst for hydrogen production from water. NiCoP/g-C3 N4 exhibits a hydrogen evolution rate of 1643 µmol h-1 g-1 , which is 21 times higher than that of bare g-C3 N4 . The excellent performance is due to a combination of improved separation efficiency and effective charge transfer efficiency. The photogenerated charge behavior is characterized by the surface photovoltage (SPV), transient photovoltage (TPV), and photoluminescence spectroscopy. The photogenerated charge transport is investigated by electrochemical impedance spectroscopy and polarization curve. Moreover, the effective charge transfer efficiency was measured according to the mimetic apparent quantum yield. SPV and TPV measurements, whereby 10 vol % of a triethanolamine-water mixture was added into the testing system, were taken to simulate the real atmosphere for photocatalytic reaction, which can give rise to the photogenerated charge transfer process. A possible photocatalytic mechanism was also proposed. This study may provide an efficient theoretical basis to design transition metal phosphide cocatalyst-modified photocatalysts.


Assuntos
Cobalto/química , Hidrogênio/química , Níquel/química , Nitrilos/química , Fósforo/química , Processos Fotoquímicos , Catálise , Espectroscopia Dielétrica , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Espectroscopia Fotoeletrônica , Difração de Raios X
14.
ACS Appl Mater Interfaces ; 10(1): 696-703, 2018 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-29227088

RESUMO

The hydrogen evolution reaction (HER) is involved in energy-intensive water- and chlor-alkali electrolyzers, and thus, highly active and stable HER electrocatalysts in alkaline media are needed. Titanates, a family of representative two-dimensional materials with negatively charged main layers, are chemically and structurally stable under strongly basic conditions, but they have never been shown to have electrocatalytic activity for HER. Herein, we report that intercalating 3d metal cations, including Fe3+, Co2+, Ni2+, and Cu2+ ions, into the interlayer regions of titanates yields efficient and robust electrocatalysts for the alkaline HER. The intercalation of 3d metal cations in titanates is achieved by rapid cation-exchange reaction between Na+-containing titanates and 3d metal cations at room temperature. Among the 3d metal-intercalated titanates we synthesize, the Co2+-containing material is found to show the best electrocatalytic activity. Experimental and theoretical results reveal that the strong electronic interaction between 3d metal cations and negatively charged main [TiO6]∞ layers renders good catalytic activity to the outermost oxygen atoms in the [TiO6]∞ layer, further making 3d metal-intercalated titanate an efficient electrocatalyst for the HER.

15.
J Am Chem Soc ; 139(36): 12370-12373, 2017 09 13.
Artigo em Inglês | MEDLINE | ID: mdl-28686430

RESUMO

Developing nonprecious hydrogen evolution electrocatalysts that can work well at large current densities (e.g., at 1000 mA/cm2: a value that is relevant for practical, large-scale applications) is of great importance for realizing a viable water-splitting technology. Herein we present a combined theoretical and experimental study that leads to the identification of α-phase molybdenum diboride (α-MoB2) comprising borophene subunits as a noble metal-free, superefficient electrocatalyst for the hydrogen evolution reaction (HER). Our theoretical finding indicates, unlike the surfaces of Pt- and MoS2-based catalysts, those of α-MoB2 can maintain high catalytic activity for HER even at very high hydrogen coverage and attain a high density of efficient catalytic active sites. Experiments confirm α-MoB2 can deliver large current densities in the order of 1000 mA/cm2, and also has excellent catalytic stability during HER. The theoretical and experimental results show α-MoB2's catalytic activity, especially at large current densities, is due to its high conductivity, large density of efficient catalytic active sites and good mass transport property.

16.
Adv Mater ; 29(22)2017 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-28370573

RESUMO

Developing nonprecious oxygen evolution electrocatalysts that can work well at large current densities is of primary importance in a viable water-splitting technology. Herein, a facile ultrafast (5 s) synthetic approach is reported that produces a novel, efficient, non-noble metal oxygen-evolution nano-electrocatalyst that is composed of amorphous Ni-Fe bimetallic hydroxide film-coated, nickel foam (NF)-supported, Ni3 S2 nanosheet arrays. The composite nanomaterial (denoted as Ni-Fe-OH@Ni3 S2 /NF) shows highly efficient electrocatalytic activity toward oxygen evolution reaction (OER) at large current densities, even in the order of 1000 mA cm-2 . Ni-Fe-OH@Ni3 S2 /NF also gives an excellent catalytic stability toward OER both in 1 m KOH solution and in 30 wt% KOH solution. Further experimental results indicate that the effective integration of high catalytic reactivity, high structural stability, and high electronic conductivity into a single material system makes Ni-Fe-OH@Ni3 S2 /NF a remarkable catalytic ability for OER at large current densities.

17.
ACS Appl Mater Interfaces ; 9(19): 16335-16342, 2017 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-28436643

RESUMO

Nitric oxide (NOx, including NO and NO2) is one of the most dangerous environmental toxins and pollutants, which mainly originates from vehicle exhaust and industrial emission. The development of sensitive NOx gas sensors is quite urgent for human health and the environment. Up to now, it still remains a great challenge to develop a NOx gas sensor, which can satisfy multiple application demands for sensing performance (such as high response, low detection temperature, and limit). In this work, ultrathin In2O3 nanosheets with uniform mesopores were successfully synthesized through a facile two-step synthetic method. This is a success due to not only the formation of two-dimensional (2D) nanosheets with an ultrathin thickness of 3.7 nm based on a nonlayered compound but also the template-free construction of uniform mesopores in ultrathin nanosheets. The sensors based on the as-obtained mesoporous In2O3 ultrathin nanosheets exhibit an ultrahigh response (Rg/Ra = 213) and a short response time (ca. 4 s) toward 10 ppm NOx, and a quite low detection limit (10 ppb NOx) under a relatively low operating temperature (120 °C), which well satisfies multiple application demands. The excellent sensing performance should be mainly attributed to the unique structural advantages of mesopores and 2D ultrathin nanosheets.

18.
Adv Mater ; 29(13)2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-28128868

RESUMO

Superefficient water-splitting materials comprising sub-nanometric copper clusters and quasi-amorphous cobalt sulfide supported on copper foam are reported. While working together at both the anode and cathode sides of an alkaline electrolyzer, this material gives a catalytic output of overall water splitting comparable with the Pt/C-IrO2 -coupled electrolyzer.

19.
Chem Commun (Camb) ; 53(10): 1619-1621, 2017 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-28094354

RESUMO

Room-temperature crystallization, a mild and energy-efficient process, shows important application potentials for developing functional materials. We significantly accelerated the crystallization of amorphous TiO2 at room temperature by storing photogenerated electrons and the resulting porous anatase titania exhibits ultrahigh surface areas up to 736 m2 g-1.

20.
ACS Appl Mater Interfaces ; 9(5): 4692-4700, 2017 Feb 08.
Artigo em Inglês | MEDLINE | ID: mdl-28084720

RESUMO

The design of appropriate composite materials with unique surface structures is an important strategy to achieve ideal chemical gas sensing. In this paper, efficient and selective detection of formaldehyde vapor has been realized by a gas sensor based on porous GaxIn2-xO3 nanofibers assembled by small building blocks. By tuning the Ga/In atomic ratios in the materials, crystallite phase, nanostructure, and band gap of as-obtained GaxIn2-xO3 nanofibers can be rationally altered. This further offers a good opportunity to optimize the gas sensing performances. In particular, the sensor based on porous Ga0.6In1.4O3 nanofibers assembled by small nanoparticles (∼4.6 nm) exhibits best sensing performances. Toward 100 ppm formaldehyde, its highest response (Ra/Rg = 52.4, at 150 °C) is ∼4 times higher than that of the pure In2O3 (Ra/Rg = 13.0, at 200 °C). Meanwhile, it has superior ability to selectively detect formaldehyde against other interfering volatile organic compound gases. The significantly improved sensing performance makes the Ga0.6In1.4O3 sensor very promising for selective detection of formaldehyde.

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