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1.
Chem Commun (Camb) ; 56(12): 1831-1834, 2020 Feb 11.
Artigo em Inglês | MEDLINE | ID: mdl-31950935

RESUMO

Catalysts for the N2 reduction reaction (NRR) are at the heart of key alternative technology to the Haber-Bosch process for NH3 synthesis, and are expected to optimize the interplay between efficiency, activity and selectivity. Here, we report our recent finding that P-doped graphene shows superior NRR performances in aqueous media at present, with a remarkably large NH3 yield of 32.33 µg h-1 mgcat.-1 and a high faradaic efficiency of 20.82% at -0.65 V vs. reversible hydrogen electrode. The mechanism is clarified by density functional theory calculations.

2.
Angew Chem Int Ed Engl ; 59(2): 758-762, 2020 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-31664770

RESUMO

Electrochemical reduction of CO2 into various chemicals and fuels provides an attractive pathway for environmental and energy sustainability. It is now shown that a FeP nanoarray on Ti mesh (FeP NA/TM) acts as an efficient 3D catalyst electrode for the CO2 reduction reaction to convert CO2 into alcohols with high selectivity. In 0.5 m KHCO3 , such FeP NA/TM is capable of achieving a high Faradaic efficiency (FE CH 3 OH ) up to 80.2 %, with a total FE CH 3 OH + C 2 H 5 OH of 94.3 % at -0.20 V vs. reversible hydrogen electrode. Density functional theory calculations reveal that the FeP(211) surface significantly promotes the adsorption and reduction of CO2 toward CH3 OH owing to the synergistic effect of two adjacent Fe atoms, and the potential-determining step is the hydrogenation process of *CO.

3.
Chem Commun (Camb) ; 56(7): 1074-1077, 2020 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-31872824

RESUMO

Electrochemical N2 reduction is an environmentally friendly and sustainable approach for NH3 synthesis under mild conditions, while an efficient electrocatalyst is crucial for the N2 reduction reaction (NRR). Herein, we report Ti3+ self-doped TiO2-x nanowires on Ti mesh (Ti3+-TiO2-x/TM) as an efficient non-noble-metal NRR electrocatalyst with excellent selectivity. In 0.1 M Na2SO4, the Ti3+-TiO2-x/TM achieves a high faradaic efficiency of 14.62% with a NH3 yield of 3.51 × 10-11 mol s-1 cm-2 at -0.55 V vs. the reversible hydrogen electrode. Density functional theory calculations further reveal that introducing Ti3+ decreases the reaction energy barrier and increases the number of active sites on the TiO2 surface for the NRR.

4.
Chem Commun (Camb) ; 55(96): 14474-14477, 2019 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-31729521

RESUMO

The artificial N2 fixation to NH3 is dominated by the traditional Haber-Bosch process, which consumes large amounts of energy and natural gas with low energy efficiency and large amounts of CO2 emissions. Electrochemical N2 reduction is a promising and environmentally friendly route for artificial N2-to-NH3 fixation under milder conditions. Herein, we report that dendritic Cu acts as a highly active electrocatalyst to catalyze N2 to NH3 fixation under ambient conditions. When tested in 0.1 M HCl, such an electrocatalyst achieves a high faradaic efficiency of 15.12% and a large NH3 yield rate of 25.63 µg h-1 mgcat.-1 at -0.40 V versus a reversible hydrogen electrode. Notably, this catalyst shows high electrochemical stability and excellent selectivity toward NH3 synthesis.

5.
Angew Chem Int Ed Engl ; 58(51): 18449-18453, 2019 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-31549471

RESUMO

Titanium-based catalysts are needed to achieve electrocatalytic N2 reduction to NH3 with a large NH3 yield and a high Faradaic efficiency (FE). One of the cheapest and most abundant metals on earth, iron, is an effective dopant for greatly improving the nitrogen reduction reaction (NRR) performance of TiO2 nanoparticles in ambient N2 -to-NH3 conversion. In 0.5 m LiClO4 , Fe-doped TiO2 catalyst attains a high FE of 25.6 % and a large NH3 yield of 25.47 µg h-1 mgcat -1 at -0.40 V versus a reversible hydrogen electrode. This performance compares favorably to those of all previously reported titanium- and iron-based NRR electrocatalysts in aqueous media. The catalytic mechanism is further probed with theoretical calculations.

6.
Nanoscale ; 11(41): 19274-19277, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31215588

RESUMO

The Haber-Bosch process for industrial-scale NH3 production suffers from harsh conditions and serious CO2 release. Electrochemical N2 reduction is an alternative approach to synthesize NH3 under ambient conditions, but it requires highly-efficient electrocatalysts for the N2 reduction reaction (NRR). In this Communication, we demonstrate that WO3 nanosheets rich in oxygen vacancies (R-WO3 NSs) exhibit greatly enhanced NRR performances. In 0.1 M HCl, such R-WO3 NSs achieve a large NH3 yield of 17.28 µg h-1 mgcat.-1 and a high faradaic efficiency of 7.0% at -0.3 V vs. a reversible hydrogen electrode, much superior to the WO3 nanosheets deficient in oxygen vacancies (6.47 µg h-1 mgcat.-1 and 1.02%). Remarkably, R-WO3 NSs also show high electrochemical stability.

7.
Front Chem ; 7: 325, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31165056

RESUMO

In this work, a micron-sized three-way nitrogen-doped carbon tube covered with MoS2 nanosheets (TNCT@MoS2) was synthesized and applied in photocatalytic water splitting without any sacrificial agents for the first time. The micron-sized three-way nitrogen-doped carbon tube (TNCT) was facilely synthesized by the calcination of commercial sponge. The MoS2 nanosheets were assembled on the carbon tubes by a hydrothermal method. Compared with MoS2, the TNCT@MoS2 heterostructures showed higher H2 evolution rate, which was ascribed to the improved charge separation efficiency and the increased active sites afforded by the TNCT.

8.
Small ; 15(13): e1805103, 2019 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30773809

RESUMO

Developing anodic oxygen evolution reaction (OER) electrocatalysts with high catalytic activities is of great importance for effective water splitting. Compared with the water-oxidation electrocatalysts that are commonly utilized in alkaline conditions, the ones operating efficiently under neutral or near neutral conditions are more environmentally friendly with less corrosion issues. This review starts with a brief introduction of OER, the importance of OER in mild-pH media, as well as the fundamentals and performance parameters of OER electrocatalysts. Then, recent progress of the rational design of electrocatalysts for OER in mild-pH conditions is discussed. The chemical structures or components, synthetic approaches, and catalytic performances of the OER catalysts will be reviewed. Some interesting insights into the catalytic mechanism are also included and discussed. It concludes with a brief outlook on the possible remaining challenges and future trends of neutral or near-neutral OER electrocatalysts. It hopefully provides the readers with a distinct perspective of the history, present, and future of OER electrocatalysts at mild conditions.

9.
Nanoscale ; 11(4): 1555-1562, 2019 Jan 23.
Artigo em Inglês | MEDLINE | ID: mdl-30637419

RESUMO

Artificial N2 fixation via the Haber-Bosch process requires high temperature and high pressure at the expense of CO2 release. Electrochemical NH3 synthesis is emerging as an environmentally friendly alternative that operates under ambient conditions, calling for electrocatalysts with efficient N2 reduction reaction (NRR) performance. In this paper, we experimentally and theoretically prove that defective TiO2 on Ti mesh (d-TiO2/TM) acts as an electrocatalyst for the NRR. In 0.1 M HCl, d-TiO2/TM achieves a much higher NH3 yield of 1.24 × 10-10 mol s-1 cm-2 and FE of 9.17% at -0.15 V (versus reversible hydrogen electrode) than pristine TiO2 (NH3 yield: 0.17 × 10-10 mol s-1 cm-2; FE: 0.95%). Notably, d-TiO2/TM also shows great electrochemical stability and durability. Theoretical investigation further reveals the possible catalytic mechanism involved.

10.
Adv Sci (Weinh) ; 6(1): 1801182, 2019 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-30643719

RESUMO

NH3 is a valuable chemical with a wide range of applications, but the conventional Haber-Bosch process for industrial-scale NH3 production is highly energy-intensive with serious greenhouse gas emission. Electrochemical reduction offers an environmentally benign and sustainable route to convert N2 to NH3 at ambient conditions, but its efficiency depends greatly on identifying earth-abundant catalysts with high activity for the N2 reduction reaction. Here, it is reported that MnO particles act as a highly active catalyst for electrocatalytic hydrogenation of N2 to NH3 with excellent selectivity. In 0.1 m Na2SO4, this catalyst achieves a high Faradaic efficiency up to 8.02% and a NH3 yield of 1.11 × 10-10 mol s-1 cm-2 at -0.39 V versus reversible hydrogen electrode, with great electrochemical and structural stability. On the basis of density functional theory calculations, MnO (200) surface has a smaller adsorption energy toward N than that of H with the *N2 → *N2H transformation being the potential-determining step in the nitrogen reduction reaction.

11.
Chemistry ; 25(8): 1914-1917, 2019 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-30523656

RESUMO

Currently, NH3 production primarily depends on the Haber-Bosch process, which operates at elevated temperatures and pressures and leads to serious CO2 emissions. Electrocatalytic N2 reduction offers an environmentally benign approach for the sustainable synthesis of NH3 under ambient conditions. This work reports the development of biomass-derived amorphous oxygen-doped carbon nanosheet (O-CN) using tannin as the precursor. As a metal-free electrocatalyst for N2 -to-NH3 conversion, such O-CN shows high catalytic performances, achieving a large NH3 yield of 20.15 µg h-1 mg-1 cat. and a high Faradic efficiency of 4.97 % at -0.6 V vs. reversible hydrogen electrode (RHE) in 0.1 m HCl at ambient conditions. Remarkably, it also exhibits high electrochemical selectivity and durability.

12.
Angew Chem Int Ed Engl ; 58(5): 1340-1344, 2019 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-30537395

RESUMO

Long afterglow materials can store and release light energy after illumination. A brick-like, micrometer-sized Sr2 MgSi2 O7 :Eu2+ ,Dy3+ long-afterglow material is used for hydrogen production by the photocatalytic reforming of methanol under round-the-clock conditions for the first time, achieving a solar-to-hydrogen (STH) conversion efficiency of 5.18 %. This material is one of the most efficient photocatalysts and provides the possibility of practical use on a large scale. Its remarkable photocatalytic activity is attributed to its unique carrier migration path and large number of lattice defects. These findings expand the application scope of long afterglow materials and provide a new strategy to design efficient photocatalysts by constructing trap levels that can prolong carrier lifetimes.

13.
Inorg Chem ; 57(23): 14692-14697, 2018 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-30427664

RESUMO

Electrochemical reduction has been regarded as a sustainable strategy to tackle energy-intensive operations by the Haber-Bosch process achieving catalytic conversion of N2 to NH3 under mild conditions. However, the challenge of N2 electroconversion emphasizes the requirement of efficient electrocatalysts. In this paper, we report the development of porous bromide-derived Ag film (BD-Ag/AF) as an efficient electrocatalyst for N2 reduction reaction. During electrochemical test, Br- anions are released and adsorbed onto the surfaces of the electrode, suppressing hydrogen evolution reaction. Such BD-Ag/AF shows a high Faradaic efficiency of 7.36% at -0.6 V vs reversible hydrogen electrode in 0.1 M Na2SO4, which is higher than that (0.38%) of porous Ag film without Br- anions. Moreover, it exhibits excellent long-term electrochemical durability.

14.
Chem Commun (Camb) ; 54(92): 12966-12969, 2018 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-30382249

RESUMO

Electrochemical N2-to-NH3 fixation under ambient conditions is emerging as a promising alternative to the energy-intensive and CO2-emitting Haber-Bosch process. However, this process involves difficulty in N2 activation, underlining the demand of electrocatalysts for the N2 reduction reaction (NRR). In this work, cubic sub-micron SnO2 particles on carbon cloth (SnO2/CC) are proposed as an efficient NRR electrocatalyst for ambient N2 conversion to NH3 with excellent selectivity. Electrochemical tests reveal that SnO2/CC attains a large NH3 yield of 1.47 × 10-10 mol s-1 cm-2 at -0.8 V vs. reversible hydrogen electrode (RHE) and a high Faradaic efficiency of 2.17% at -0.7 V vs. RHE in 0.1 M Na2SO4, outperforming most reported aqueous-based NRR electrocatalysts. Notably, it also shows strong electrochemical stability.

15.
Small ; 14(48): e1803111, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30334346

RESUMO

Traditionally, ammonia (NH3 ) is synthesized via the Haber-Bosch process, which is not only commanded by harsh conditions but causes serious environmental pollution. Electrochemical reduction is recognized as a mild and environmentally benign alternative approach for NH3 synthesis, but an efficient electrocatalyst is a prerequisite for NH3 production. In this communication, the first experimental demonstration that Mn3 O4 nanocubes can be used as an efficient non-noble-metal electrocatalyst for N2 reduction reaction (NRR) at ambient conditions is reported. In 0.1 m Na2 SO4 aqueous solution, the catalyst delivers excellent NRR activity with an NH3 yield of 11.6 µg h-1 mg-1 cat. and Faradaic efficiency of 3.0% at -0.8 V versus reversible hydrogen electrode. Notably, this catalyst also possesses satisfactory durability during the electrolysis and recycling test.

16.
Chem Commun (Camb) ; 54(80): 11332-11335, 2018 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-30239537

RESUMO

NH3 is one of the most important chemicals with a wide range of applications. NH3 is mainly produced via the Haber-Bosch process, which leads to large energy consumption and carbon emission. Electrochemical reduction has emerged as an environmentally-benign and sustainable alternative for artificial N2 fixation under ambient conditions, but needs materials to effectively catalyze the N2 reduction reaction (NRR). In this communication, we report that ß-FeOOH nanorods behave as an efficient and durable NRR electrocatalyst. In 0.5 M LiClO4, such an electrocatalyst achieves a high NH3 yield of 23.32 µg h-1 mgcat.-1 and a faradaic efficiency of 6.7%, outperforming most reported aqueous-based NRR electrocatalysts under ambient conditions. Notably, this catalyst also shows good electrochemical stability and excellent selectivity. The catalytic mechanism of the NRR on the FeOOH(110) surface is further discussed using density functional theory calculations.

17.
Chem Commun (Camb) ; 54(81): 11427-11430, 2018 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-30246829

RESUMO

The industrial-scale NH3 production still heavily depends on the Haber-Bosch process which demands not only high energy consumption but emits a large amount of CO2. Electrochemical fixation of N2 to NH3 under ambient conditions is regarded as an eco-friendly and sustainable approach, but stable and efficient electrocatalysts are demanded for the N2 reduction reaction (NRR). In this work, we report our recent finding that an Ag nanosheet acts as a high-performance NRR electrocatalyst at room temperature and pressure. Electrochemical tests in 0.1 M HCl reveal that such a catalyst achieves a high Faradaic efficiency of 4.8% and a NH3 yield rate of 4.62 × 10-11 mol s-1 cm-2 at -0.60 V vs. reversible hydrogen electrode (RHE), rivaling the performances of most of the reported aqueous-based NRR electrocatalysts. Additionally, the Ag nanosheet also shows excellent selectivity, strong long-term electrochemical stability and durability.

18.
ACS Appl Mater Interfaces ; 10(34): 28251-28255, 2018 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-30117725

RESUMO

NH3 serves as an attractive hydrogen storage medium and a renewable energy sector for a sustainable future. Electrochemical reduction is a feasible ambient reaction to convert N2 to NH3, while it needs efficient electrocatalysts for the N2 reduction reaction (NRR) to meet the challenge associated with N2 activation. In this Letter, we report on our recent experimental finding that the TiO2 nanosheets array on the Ti plate (TiO2/Ti) is effective for electrochemical N2 conversion to NH3 at ambient conditions. When tested in 0.1 M Na2SO4, such TiO2/Ti attains a high NH3 yield of 9.16 × 10-11 mol s-1·cm-2 with corresponding Faradaic efficiency of 2.50% at -0.7 V vs reversible hydrogen electrode, outperforming most reported aqueous-based NRR electrocatalysts. It also shows excellent selectivity for NH3 formation with high electrochemical stability. The superior NRR activity is due to the enhanced adsorption and activation of N2 by oxygen vacancies in situ generated during electrochemical tests.

19.
Chem Commun (Camb) ; 54(73): 10340-10342, 2018 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-30151506

RESUMO

It is highly attractive to develop efficient electrocatalysts for the sensitive and selective detection of nitrite. In this communication, we report that an MnO2 nanoarray on titanium mesh (MnO2 NA/TM) is an efficient catalyst electrode for the electroreduction of nitrite. Electrochemical measurements demonstrate that the constructed MnO2 NA/TM sensor offers a superior sensing performance, having a short response time of 3 s, a wide detection range of 1.0 µM to 5.0 mM, a low detection limit of 1.5 nM (S/N = 3), and a response sensitivity of 10 301 µA mM-1 cm-2, with satisfactory selectivity, specificity, and reproducibility. This electrochemical system is also capable of catalyzing the electrochemical reduction of nitrite to NH3 with a transformation efficiency of 6%.

20.
Chem Commun (Camb) ; 54(74): 10499-10502, 2018 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-30159557

RESUMO

Metal-organic frameworks (MOFs) have emerged as attractive electrode materials for applications in energy storage and conversion, owing to their high porosity and surface area. In this communication, we report a hierarchically structured Co-MOF supported on nickel foam (Co-MOF/NF) serving as a high-performance electrode material for supercapacitors. The as-obtained Co-MOF/NF exhibits an ultrahigh areal specific capacitance of 13.6 F cm-2 at 2 mA cm-2 in 2 M KOH, exceeding those of the previously reported MOF-based materials. It also shows an excellent rate performance of 79.4% at a current density of 20 mA cm-2. An asymmetric supercapacitor (ASC) device employing Co-MOF/NF as the positive electrode and activated carbon (AC) as the negative electrode achieves a high energy density of 1.7 mW h cm-2 at a power density of 4.0 mW cm-2 with a capacitance retention of 69.7% after 2000 cycles.

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