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1.
Angew Chem Int Ed Engl ; 58(34): 11779-11784, 2019 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-31225687

RESUMO

In this study, mechanical vibration is used for hydrogen generation and decomposition of dye molecules, with the help of BiFeO3 (BFO) square nanosheets. A high hydrogen production rate of ≈124.1 µmol g-1 is achieved under mechanical vibration (100 W) for 1 h at the resonant frequency of the BFO nanosheets. The decomposition ratio of Rhodamine B dye reaches up to ≈94.1 % after mechanical vibration of the BFO catalyst for 50 min. The vibration-induced catalysis of the BFO square nanosheets may be attributed to the piezocatalytic properties of BFO and the high specific surface area of the nanosheets. The uncompensated piezoelectric charges on the surfaces of BFO nanosheets induced by mechanical vibration result in a built-in electric field across the nanosheets. Unlike a photocatalyst for water splitting, which requires a proper band edge position for hydrogen evolution, such a requirement is not needed in piezocatalytic water splitting, where the band tilting under the induced piezoelectric field will make the conduction band of BFO more negative than the H2 /H2 O redox potential (0 V) for hydrogen generation.

2.
ACS Appl Mater Interfaces ; 11(14): 13214-13224, 2019 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-30888151

RESUMO

Porous carbons represent a typical class of electrode materials for electric double-layer capacitors. However, less attention has been focused on the study of the capacitive mechanism of electrochemically active surface oxygen groups rooted in porous carbons. Herein, the degree and variety of oxygen surface groups of HNO3-modified samples (N-CS) are finely tailored by a mild hydrothermal oxidation (0.0-3.0 mol L-1), while the micro-meso-macroporous structures are efficiently preserved from the original sample. Thus, N-CS is a suitable carrier for separately discussing the contribution of oxygen functional groups to the electrochemical property. The optimized N-CS shows a high capacitance of 279.4 F g-1 at 1 A g-1, exceeding 52.8% of pristine carbon sphere (CS) (182.8 F g-1 at 1 A g-1) in KOH electrolyte. On further deconvoluting the redox peaks of cyclic voltammetry curves, we find that the pseudocapacitance not only associates with the surface-controlled faradic reaction at high scan rate but also dramatically stems from the diffusion-controlled capacitance through potassium and hydroxyl ion insertion/deinsertion into the underutilized micropores at low scan rate. The assembled supercapacitor based on N-CS presents a stable energy density of 5 Wh kg-1 over a wide range of power density of 250-5000 W kg-1, which is higher than 0.0N-CS in KOH electrolyte. In TEABF4 electrolyte, the N-CS supercapacitor has an energy density of 26.9 Wh kg-1 at the power density of 1350 W kg-1 and exhibits excellent cycling stability with a capacitance retention of 93.2% at 2 A g-1 after 10 000 cycles. These results demonstrate that surface oxygen groups alter the capacitive mechanism and contribution of porous carbons.

3.
ChemSusChem ; 12(7): 1443-1450, 2019 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-30724477

RESUMO

Sn-based electrocatalysts are promising for the electrochemical CO2 reduction reaction (CO2RR), but suffer from poor activity and selectivity. A hierarchical structure composed of ultrathin SnOx nanosheets anchored on the surface of the commercial multiwalled carbon nanotubes (MWCNTs) is synthesized by a simple hydrothermal process. The electrocatalytic performance can be further tuned by functionalization of the MWCNTs with COOH, NH2 , and OH groups. Both SnOx @MWCNTs-COOH and SnOx @MWCNTs-NH2 show excellent catalytic activity for CO2 RR with nearly 100 % selectivity for C1 products (formate and CO). SnOx @MWCNTs-COOH has favorable formate selectivity with a remarkably high faradaic efficiency (FE) of 77 % at -1.25 V versus standard hydrogen electrode (SHE) and a low overpotential of 246 mV. However, SnOx @MWCNTs-NH2 manifests increased selectivity for CO with higher current density. Density functional theory calculations and experimental studies demonstrate that the interaction between Sn species and functional groups play an important role in the tuning of the catalytic activity and selectivity of these functionalized electrocatalysts. SnOx @MWCNTs-COOH and SnOx @MWCNTs-NH2 both effectively inhibit the hydrogen evolution reaction and prove stable without any significant degradation over 20 h of continuous electrolysis at -1.25 V versus SHE.

4.
ACS Appl Mater Interfaces ; 11(7): 6881-6889, 2019 Feb 20.
Artigo em Inglês | MEDLINE | ID: mdl-30676728

RESUMO

The electrochemical reduction of CO2 at ambient conditions provides a latent solution of turning waste greenhouse gases into commodity chemicals or fuels; however, a satisfactory ion-conducting membrane for maximizing the performance of a CO2 electrolyzer has not been developed. Here, we report the synthesis of a sequence of hydroxide-conductive polymer membranes, which are based on polymer composites of poly(vinyl alcohol)/Guar hydroxypropyltrimonium chloride, for use in CO2 electrolysis. The effect of different membrane functional groups, including thiophene, hydroxybenzyl, and dimethyloctanal, on the efficiency and selectivity of CO2 electroreduction to formate is thoroughly evaluated. The membrane incorporating thiophene groups exhibits the highest Faradaic efficiency of 71.5% at an applied potential of -1.64 V versus saturated calomel electrode (SCE) for formate. In comparison, membranes containing hydroxybenzyl and dimethyloctanal groups produced lower efficiencies of 67.6 and 68.6%, respectively, whereas the commercial Nafion 212 membrane was only 57.6% efficient. The improved efficiency and selectivity of membranes containing thiophene groups are attributed to a significantly increased hydroxide conductivity (0.105 S cm-1), excellent physicochemical properties, and the simultaneous attenuation of formate product crossover.

5.
ACS Appl Mater Interfaces ; 11(1): 578-587, 2019 Jan 09.
Artigo em Inglês | MEDLINE | ID: mdl-30525371

RESUMO

The exploitation of a high-activity and low-cost bifunctional catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as the cathode catalyst is a research priority in metal-air batteries. Herein, a novel bifunctional hybrid catalyst of hortensia-like MnO2 synergized with carbon nanotubes (CNTs) (MnO2/CNTs) is controllably synthesized by reasonably designing the crystal structure and morphology as well as electronic arrangement. On the basis of these strategies, the hybrid accelerates the reaction kinetics and avoids the change of structures. As expected, MnO2/CNTs exhibit a remarkable ORR and OER activity [low ORR Tafel slope: 71 mV dec-1, low OER Tafel slope: 67 mV dec-1, and small potential difference (Δ E): 0.85 V] and a long-term stability, which should be attributed to its unique morphology, K+ ions in the 2 × 2 tunnels, and synergistic effect between MnO2 and CNTs. Notably, in zinc-air batteries (ZABs), aluminum-air batteries (AABs), and magnesium-air batteries (MABs), the composite shows high power density (ZABs: 243 mW cm-2, AABs: 530 mW cm-2, and MABs: 614 mW cm-2) and large specific capacities (793 mA h gZn-1, 918 mA h gAl-1, and 878 mA h gMg-1). Importantly, the rechargeable ZABs reveal small charge-discharge voltage drop (0.81 V) and strong cycle durability (500 h), which are better than the noble-metal Pt/C + IrO2 mixture catalyst (the voltage drop: 1.15 V at first and 2 V after 100 h). These superior performances together with the simple synthetic method of the hybrid reveal great promise in large-power energy storage and conversion equipment.

6.
ACS Appl Mater Interfaces ; 10(35): 29593-29598, 2018 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-30096225

RESUMO

As a potential solution to ubiquitous energy concerns, anion-exchange membranes (AEMs) have been widely used as the electrolyte in alkaline fuel cells (AFCs), and significant refinement of AEMs has been achieved in the past few decades. However, it remains unknown whether AEMs can be used as an electrolyte in a solid-state supercapacitor or zinc-air battery. A low-cost alkaline exchange membrane electrolyte composed of chitosan and poly(diallyldimethylammonium chloride) that possesses a high OH- conductivity (0.024 S cm-1), strong alkaline stability (216 h at 8 M KOH), good thermal stability, and low degree of anisotropic swelling, was found to provide a high electrochemical performance in all-solid-state devices. Prototypes of the solid AFC with the membrane shows superior stability over 500 h. The carbon nanotube-based all-solid-state supercapacitor with the membrane generated a rectangular cyclic voltammetry curve up to 10 V s-1 and excellent cycling stability of 4000 cycles with 84% specific capacitance retention. The all-solid-state zinc-air battery demonstrates high power density (48.9 mW cm-2). These advantages indicate that the membrane is a promising electrolyte for all-solid-state electrochemical devices.

7.
Nanoscale ; 10(28): 13626-13637, 2018 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-29979460

RESUMO

Central to commercializing metal-air batteries is the development of highly efficient and stable catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this study, a composite catalyst with a unique interpenetrating network (denoted as NiCo2O4@MnO2-CNTs-3) was synthesized and exhibited better bifunctional activity (ΔE = 0.87 V) and durability than both Pt/C and Ir/C catalysts. The improved performance arises from three factors: (i) MnO2 promotes the ORR while NiCo2O4 facilitates the OER; (ii) carbon nanotubes improve the electronic conductivity; and (iii) the highly porous structure enables the adsorption-desorption of O2 and enhances the structural stability. As a result, the primary and rechargeable Zn-air battery affords a high power density and specific capacity (722 mA h g-1), an outstanding discharge stability (255 mW cm-2 after 1000 cycles) and a high cycling stability (over 2280 cycles). Electron microscopy and electrochemical analysis revealed that the degradation of the rechargeable Zn-air battery performance resulted from the damage of the air electrode and the hydrogen evolution reaction on the zinc electrode. A flexible Zn-air battery employing a solid-state electrolyte showed an exciting stability (540 cycles) and high power density (85.9 mW cm-2), suggesting that the anion exchange membrane effectively prevents the migration of Zn2+ ions and the deposition of carbonates.

8.
ACS Appl Mater Interfaces ; 10(18): 15591-15601, 2018 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-29616793

RESUMO

The design of efficient, durable, and affordable catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is very indispensable in liquid-type and flexible all-solid-state zinc-air batteries. Herein, we present a high-performance bifunctional catalyst with cobalt and manganese oxides supported on porous carbon (Co3O4/MnO2/PQ-7). The optimized Co3O4/MnO2/PQ-7 exhibited a comparable ORR performance with commercial Pt/C and a more superior OER performance than all of the other prepared catalysts, including commercial Pt/C. When applied to practical aqueous (6.0 M KOH) zinc-air batteries, the Co3O4/MnO2/porous carbon hybrid catalysts exhibited exceptional performance, such as a maximum discharge peak power density as high as 257 mW cm-2 and the most stable charge-discharge durability over 50 h with negligible deactivation to date. More importantly, a series of flexible all-solid-state zinc-air batteries can be fabricated by the Co3O4/MnO2/porous carbon with a layer-by-layer method. The optimal catalyst (Co3O4/MnO2/PQ-7) exhibited an excellent peak power density of 45 mW cm-2. The discharge potentials almost remained unchanged for 6 h at 5 mA cm-2 and possessed a long cycle life (2.5 h@5 mA cm-2). These results make the optimized Co3O4/MnO2/PQ-7 a promising cathode candidate for both liquid-type and flexible all-solid-state zinc-air batteries.

9.
Chem Soc Rev ; 46(5): 1427-1463, 2017 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-28165079

RESUMO

High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO2 emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO2 electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult C[double bond, length as m-dash]O double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO2 conversion and utilization. Here, we discuss in detail the approaches of CO2 conversion, the developmental history, the basic principles, the economic feasibility of CO2/H2O co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO2 electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.

10.
Sci Rep ; 6: 33590, 2016 09 20.
Artigo em Inglês | MEDLINE | ID: mdl-27646032

RESUMO

α-MnO2 nanotubes-supported Co3O4 (Co3O4/MnO2) and its carbon nanotubes (CNTs)-hybrids (Co3O4/MnO2-CNTs) have been successfully developed through a facile two-pot precipitation reaction and hydrothermal process, which exhibit the superior bi-functional catalytic activity for both ORR and OER. The high performance is believed to be induced by the hybrid effect among MnO2 nanotubes, hollow Co3O4 and CNTs, which can produce a synergetic enhancement. When integrated into the practical primary and electrochemically rechargeable Zn-air batteries, such a hybrid catalyst can give a discharge peak power density as high as 450 mW cm(-2). At 1.0 V of cell voltage, a current density of 324 mA cm(-2) is achieved. This performance is superior to all reported non-precious metal catalysts in literature for zinc-air batteries and significantly outperforms the state-of-the-art platinum-based catalyst. Particularly, the rechargeable Zn-air battery can be fabricated into all-solid-state one through a simple solid-state approach, which exhibits an excellent peak power density of 62 mW cm(-2), and the charge and discharge potentials remain virtually unchanged during the overall cycles, which is comparable to the one with liquid electrolyte.

11.
Phys Chem Chem Phys ; 18(28): 18665-9, 2016 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-27350564

RESUMO

A new type of Fe, N-doped hierarchically porous carbons (N-Fe-HPCs) has been synthesized via a cost-effective synthetic route, derived from nitrogen-enriched polyquaternium networks by combining a simple silicate templated two-step graphitization of the impregnated carbon. The as-prepared N-Fe-HPCs present a high catalytic activity for the oxygen reduction reaction (ORR) with onset and half-wave potentials of 0.99 and 0.86 V in 0.1 M KOH, respectively, which are superior to commercially available Pt/C catalyst (half-wave potential 0.86 V vs. RHE). Surprisingly, the diffusion-limited current density of N-S-HPCs approaches ∼7.5 mA cm(-2), much higher than that of Pt/C (∼5.5 mA cm(-2)). As a cathode electrode material used in Zn-air batteries, the unique configuration of the N-Fe-HPCs delivers a high discharge peak power density reaching up to 540 mW cm(-2) with a current density of 319 mA cm(-2) at 1.0 V of cell voltage and an energy density >800 Wh kg(-1). Additionally, outstanding ORR durability of the N-Fe-HPCs is demonstrated, as evaluated by the transient cell-voltage behavior of the Zn-air battery retaining an open circuit voltage of 1.48 V over 10 hours with a discharge current density of 100 mA cm(-2).

12.
Sci Rep ; 5: 15252, 2015 Oct 20.
Artigo em Inglês | MEDLINE | ID: mdl-26482415

RESUMO

A novel synthesis containing microwave-assisted HCl etching reaction and precipitating reaction is employed to prepare hierarchical hollow SnO2@TiO2 nanocapsules for anode materials of Li-ion batteries. The intrinsic hollow nanostructure can shorten the lengths for both ionic and electronic transport, enlarge the electrode surface areas, and improving accommodation of the anode volume change during Li insertion/extraction cycling. The hybrid multi-elements in this material allow the volume change to take place in a stepwise manner during electrochemical cycling. In particular, the coating of TiO2 onto SnO2 can enhance the electronic conductivity of hollow SnO2 electrode. As a result, the as-prepared SnO2@TiO2 nanocapsule electrode exhibits a stably reversible capacity of 770 mA hg(-1) at 1 C, and the capacity retention can keep over 96.1% after 200 cycles even at high current rates. This approach may shed light on a new avenue for the fast synthesis of hierarchical hollow nanocapsule functional materials for energy storage, catalyst and other new applications.

13.
Sci Rep ; 5: 13310, 2015 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-26347981

RESUMO

A hollow hybrid Ni-Fe-O nanomaterial (NiFe2O4) is synthesized using a precursor of metal-organic frameworks through a simple and cost-effective method. The unique hollow nanocage structures shorten the length of Li-ion diffusion. The hollow structure offers a sufficient void space, which sufficiently alleviates the mechanical stress caused by volume change. Besides, the hybrid elements allow the volume change to take place in a stepwise manner during electrochemical cycle. And thus, the hierarchical hollow NiFe2O4 nanocage electrode exhibits extraordinary electrochemical performance. The stable cyclic performance is obtained for all rates from 1 C to 10 C. Even when the current reaches 10 C, the capacity can also arrive at 652 mAhg(-1). Subsequently, a specific capacity of ca. 975 mAhg(-1) is recovered when the current rate reduces back to 1 C after 200 cycles. This strategy that derived from NMOFs may shed light on a new route for large-scale synthesis of hollow porous hybrid nanocages for energy storage, environmental remediation and other novel applications.

14.
Chem Soc Rev ; 44(21): 7484-539, 2015 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-26050756

RESUMO

Electrolytes have been identified as some of the most influential components in the performance of electrochemical supercapacitors (ESs), which include: electrical double-layer capacitors, pseudocapacitors and hybrid supercapacitors. This paper reviews recent progress in the research and development of ES electrolytes. The electrolytes are classified into several categories, including: aqueous, organic, ionic liquids, solid-state or quasi-solid-state, as well as redox-active electrolytes. Effects of electrolyte properties on ES performance are discussed in detail. The principles and methods of designing and optimizing electrolytes for ES performance and application are highlighted through a comprehensive analysis of the literature. Interaction among the electrolytes, electro-active materials and inactive components (current collectors, binders, and separators) is discussed. The challenges in producing high-performing electrolytes are analyzed. Several possible research directions to overcome these challenges are proposed for future efforts, with the main aim of improving ESs' energy density without sacrificing existing advantages (e.g., a high power density and a long cycle-life) (507 references).

15.
Chem Soc Rev ; 43(2): 631-75, 2014 Jan 21.
Artigo em Inglês | MEDLINE | ID: mdl-24186433

RESUMO

This paper reviews recent progress made in identifying electrocatalysts for carbon dioxide (CO2) reduction to produce low-carbon fuels, including CO, HCOOH/HCOO(-), CH2O, CH4, H2C2O4/HC2O4(-), C2H4, CH3OH, CH3CH2OH and others. The electrocatalysts are classified into several categories, including metals, metal alloys, metal oxides, metal complexes, polymers/clusters, enzymes and organic molecules. The catalyts' activity, product selectivity, Faradaic efficiency, catalytic stability and reduction mechanisms during CO2 electroreduction have received detailed treatment. In particular, we review the effects of electrode potential, solution-electrolyte type and composition, temperature, pressure, and other conditions on these catalyst properties. The challenges in achieving highly active and stable CO2 reduction electrocatalysts are analyzed, and several research directions for practical applications are proposed, with the aim of mitigating performance degradation, overcoming additional challenges, and facilitating research and development in this area.

16.
Chem Soc Rev ; 42(13): 5768-87, 2013 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-23640049

RESUMO

In this review, we examine the most recent progress and research trends in the area of alkaline polymer electrolyte membrane (PEM) development in terms of material selection, synthesis, characterization, and theoretical approach, as well as their fabrication into alkaline PEM-based membrane electrode assemblies (MEAs) and the corresponding performance/durability in alkaline polymer electrolyte membrane fuel cells (PEMFCs). Respective advantages and challenges are also reviewed. To overcome challenges hindering alkaline PEM technology advancement and commercialization, several research directions are then proposed.

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