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Here two chemical reduction pathways to synthesize the vinylene carbonate (VC) and poly(VC) reduction products are investigated, with the precise aim of further deciphering the lithium-ion battery solid electrolyte interphase (SEI) layer composition and the associated reduction mechanisms. The liquid synthesis pathway offers the opportunity of varying the concentration of Li-4,4′-Di- tert -butylbiphenyl reducing agent, whereas the dry synthesis pathway by ball milling allows to solve issues related to solvent-induced side reactions and washing procedure. As a result, the two syntheses do not unveil the same reduction mechanisms, favouring either carboxylate or carbonate salts as the major end product. The latter pathway is very efficient in terms of providing SEI-layers products resulting in well-defined IR spectra and comparisons with simulated spectra enable us to obtain IR fingerprints of the Li di-vinylene di-carbonate (LDVD) compound. Taken together the synthesis procedures provide information on conditions favouring radical polymerization and further poly(VC) reduction into Li 2 CO 3 and polyacetylene. Overall, this chemical simulation of SEI-layers formation assists in a proper characterization of the SEI-layers created on graphite surfaces by their IR spectra showing that Li 2 CO 3 , LDVD and poly(VC) are all present in different proportions dependent on the VC content in the electrolyte. • Li 2 CO 3, Li divinylene dicarbonate and poly(VC) are all VC-derived SEI-layer compounds. • Poly(VC) can be reduced into Li 2 CO 3 and polyacetylene. • Dry ball milling with Li is helpful to synthesize SEI reduction compounds. • Radical polymerization processes prevail in presence of small amount of VC radicals. • EC also participates to the SEI formation in presence of electrolyte with 2 wt% VC. [ABSTRACT FROM AUTHOR]

Abstract Anode electron transfer efficiency is one of the main bottlenecks in determining the performance of microbial fuel cells (MFCs). Here, we report for the first time a novel design of a silicon solar cell equipped MFC with one-dimensional TiO 2 /Fe 2 O 3 photoanode and conventional bioanode to overcome the constraints of using traditional anodes. The novel MFC has the maximum power density of 638.3 mW m−2, which is nearly 7.6 times higher than that of general MFCs (84.2 mW m−2). In addition, the novel MFC achieves 90.9% removal of hexavalent chromium Cr(VI) with concentration of 50 ppm within 13.5 h, and this rate is significantly high at 3.67 g m−3 h−1. Efficient microbial oxidation and photoelectrocatalysis are realized after constructing the SSC with double-anode MFC, thereafter leading to enhanced electron transfer to the external circuit. In addition, the electrons are driven by the built-in electric field in silicon solar cell, in which system barriers are resolved at the same time. Power output and Cr(VI) reduction efficiency are both remarkably enhanced. Such a novel MFC strategy provides new directions for designing new systems that can increase the efficiency of MFCs by utilizing solar energy economically, which further suggest great potential in environmental remediation. Graphical abstract Image 1 Highlights • A SSC coupled double anodes novel MFC constructed for the first time. • Increment of electrons overcame the bottlenecks in traditional MFC. • Decreased transfer barrier realized after utilizing solar energy by SSC. • The maximum power density was 7.6 times higher than that in general MFC. • Such system exhibited high reduction rate (3.67 g m−3 h−1) for Cr(VI) wastewater. [ABSTRACT FROM AUTHOR]

Abstract Flexible all-solid-state supercapacitors with specific energy higher than 1 mW h cm−3 after long-term cycles remain a hot research topic in energy storage systems. In this paper, free-standing reduced graphene oxide/polypyrrole films are produced at the ice/ethanol interface following by hydrogen iodide reduction. The reduced graphene oxide/polypyrrole films are featured with high specific surface area, three-dimensional porosity, and tunable thickness and electronic conductivity. The typical flexible all-solid-state supercapacitor based on reduced graphene oxide/polypyrrole films exhibits a high volumetric specific capacitance of 17.3 F cm−3 and a high specific energy of 2.40 mW h cm−3 with corresponding specific power of 136.1 mW cm−3 at a current density of 3 mA cm−2 (ca. 10 A g−1). After 10,000 cycles at 3 mA cm−2, the capacitance retention of the typical flexible supercapacitor retains 73.2%. The enhanced electrochemical properties of the flexible supercapacitors are attributed to the high specific surface area, three-dimensional porosity, and the synergistic effect between reduced graphene oxide and polypyrrole with respect to the composite films. Graphical abstract Image 1 Highlights • Free-standing rGO/PPy films are produced at the ice/ethanol interface. • rGO/PPy films have high specific surface area and three-dimensional porosity. • rGO/PPy-based flexible supercapacitors exhibit high volumetric specific capacitance. • rGO/PPy-based flexible supercapacitors exhibit high volumetric specific energy. [ABSTRACT FROM AUTHOR]

Abstract SiO x has emerged as an important alternative to silicon as the high capacity anode host to store lithium due to its smaller volume change upon lithiation. However, conventional synthesis methods generally require harsh reaction conditions, making its production in industrial scale much challenging. Herein, a safe, economical and scalable approach is developed for SiO x using highly abundant natural silica as starting material via a magnesio-mechanochemical reduction process induced by ball-milling. The as-prepared SiO x is intrinsically porous and comprised of mixed nano clusters of SiO 2 and Si. Upon lithiation, SiO 2 nano domains convert into lithium silicates and Li 2 O, which help to absorb Si volume expansion and participate in the formation of a stable solid electrolyte interface. Such synergistic effect leads to exceptional cycling stability up to 2000 cycles with 71.3% capacity retention under 4 A g−1. After blending with graphite, a high areal capacity of 2.64 mAh cm−2 demonstrates stable cycling of 89.7% retention over 200 cycles with an high initial Coulombic efficiency of 82.3%, implying the feasibility for practical applications. Structural and compositional characterizations reveal the involved chemistry and evolution mechanism of the formed solid electrolyte interface upon cycling, providing guidelines of designing future silicon-based materials for future Li-ion batteries. Graphical abstract Image 1 Highlights • Synthesis of nano SiO x from natural silica by facile ball milling. • Exceptional long-term cycling stability up to 2000 cycles was demonstrated. • Superb structural stability derived from intrinsic porosity and the grown stable SEI. • Blending with graphite exhibited application feasibility with high areal capacity. [ABSTRACT FROM AUTHOR]

Abstract The Ag 4 Sn and Ag 3 Sn intermetallics are successfully synthesized by combining electrochemical deposition and dealloying methods. The Ag 4 Sn and Ag 3 Sn possess a half-wave potential of 0.810 mV and 0.790 mV respectively for the oxygen reduction reaction in alkaline media, which are comparable to the commercial Pt/C (0.837 mV). In term of the durability, the Ag 4 Sn retains a half-wave potential of 0.775 mV after 5000 potential cycles, which is superior to Pt/C of 0.784 mV. The better catalytic activity and durability are mainly attributed to the ensemble effect and strong chemical bond in the AgSn ordered intermetallic structure. The catalytic activity is hardly influenced by methanol or ethanol in alkaline media with alcohol concentrations up to 1.0 M. Therefore, a membraneless alkaline zinc-air battery and direct alcohol fuel cell can operate with Ag 4 Sn and Ag 3 Sn intermetallics as the cathode catalysts, which allow the anode fuel to freely enter the cathode. A high power density is delivered by the membraneless alkaline fuel cells with zinc, methanol or ethanol as anode fuels. The excellent alcohol-tolerance is beneficial to the oxygen reduction reaction of alkaline fuel cells and makes the AgSn intermetallics a promising candidate to replace Pt-based electrocatalysts for oxygen reduction reaction. Highlights • AgSn intermetallics were successfully synthesized by an electrochemical method. • AgSn intermetallics exhibited excellent ORR activity and stability. • AgSn intermetallics showed superior tolerance to alcohol than commercial Pt/C. • High catalytic properties are attributed to ensemble effect and ordered structure. • Membraneless alkaline fuel cells based on selective catalysts were designed. [ABSTRACT FROM AUTHOR]

We report a simple and convenient method for the synthesis of functionalized graphene nanosheets/carbon nanotubes networks (G/CNTs-200) through chemical oxidation followed by low temperature treatment reduction. The G/CNTs-200 sample has the unique hybrid structure consisting of 1D carbon nanotubes as the continuous conductive networks and 2D functionalized graphene nanosheets as pseudocapacitive materials. Significantly, such unique hybrid structure ensures high surface area and suitable oxygen functional groups without obviously sacrificial conductivity. As a result, the G/CNTs-200 electrode exhibits a specific capacitance of 202 F g −1  at a current density of 0.5 A g −1 , which is almost five times higher than that of pure CNTs (40 F g −1 ). Interestingly, it can keep a high capacitance retention ratio of 60% at a current density of 50 A g −1 in 6 mol L −1 KOH aqueous electrolyte. More importantly, a symmetric device based on G/CNTs-200 electrodes delivers an energy density of 11.7 W h kg −1 and excellent electrochemical stability in 1 mol L −1 Na 2 SO 4 aqueous electrolyte. Therefore, this work holds a great promise for the design and large-scale production of CNTs-based electrode materials for high performance supercapacitors. [ABSTRACT FROM AUTHOR]

For proton exchange membrane fuel cells (PEMFCs), instability of Pt-based catalysts due to carbon support corrosion is a critical issue that limits their wide application. Alternative corrosion resistant supports, such as metal oxides, have been investigated in conductive carbon containing matrix and demonstrated improved stability. This study probes systematically the effects of TiO 2 support particle size (5, 18, and 30 nm) and Pt content (6, 12, and 37 wt%) on the oxygen reduction reaction (ORR) activity and stability of the Pt/TiO 2 catalyst in the absence of corrosive carbon. The average Pt nanoparticle size increases with increased TiO 2 support size and Pt content. For 12 wt% Pt loading, with increasing support size the ECSA increases from 4.91 to 7.23 m 2 g P t − 1 , 6.5%–10.6% of the predicted electrochemical surface area, respectively. This result suggests that there is an increased support contribution with increased TiO 2 support size to improve Pt accessibility. The mass and area specific ORR activities are the highest for the 12 wt% Pt on 30 nm TiO 2 , 0.083 A m g P t − 1 and 1134.56 μ A c m P t − 2 , respectively. Accelerated stress testing results in only a 5.9% loss in ECSA for the 12 wt% Pt/TiO 2 (30 nm) catalyst. [ABSTRACT FROM AUTHOR]

A horizontal Zn-air battery has been designed to enable the use of physically decoupled and catalytically efficient ORR and OER electrodes for discharge and charge, respectively. The horizontal design features a horizontally positioned ORR electrode and a vertically positioned OER electrode, allowing effective management of oxygen transport and pressure. The ORR catalyst (MnOx) and OER catalyst (Co-Fe alloy) are fabricated via one-step electrodeposition on carbon paper and Ni foam, respectively. MnOx is identified as a combination of Mn 3 O 4 nanorods and α-Mn 2 O 3 spheres. Co-Fe is deposited as a solid solution film with an oxidized surface. Electrochemical tests show that both catalysts have comparable or even better activity than their commercial Pt-Ru catalyst counterpart. The catalysts are cycled at 20 mA cm −2 to examine their durability. Cycling potential affects catalyst durability, with improved lifetime under separate ORR and OER conditions compared with the full ORR-OER voltage range. The fabricated catalysts are assembled into a Zn-air battery for discharge-charge cycling tests and show the same average efficiency (58%) as commercial Pt-Ru catalysts. [ABSTRACT FROM AUTHOR]

A previous study is focused on high temperature cycling of industrially manufactured Li-ion pouch cells (NMC-111/Graphite) with different electrolytes at 80 °C [JPS 373 (2018) 172–183]. Within this article the same test set-up is used, with cells stored for 30 days at different open circuit potentials and various electrolytes instead of electrochemical cycling. The most pronounced cell degradation (capacity fade and resistance increase) happens at high potentials. However appropriate electrolyte formulations are able to suppress ageing conditions by forming passivating surface films on both electrodes. Compared with electrochemical cycling at 80 °C, cells with enhanced electrolytes only show a slight resistance increase during storage and the capacity fade is much lower. Additionally it is shown for the first time, that the resistance is decreasing and capacity is regained once these cells are cycled again at room temperature. This is not the case for electrolytes without additives or just vinylene carbonate (VC) as an additive. It is further shown that the resistance increase of cells with the other electrolytes is accompanied by a reduction of the cell volume during further cycling. This behaviour is likely related to the reduction of CO 2 at the anode to form additional SEI layer components. [ABSTRACT FROM AUTHOR]

Lithium-sulfur (Li-S) batteries are regarded as a potential next-generation energy storage system but they are hampered by low active-material utilization, polysulfide shuttling, and rapid capacity fade. We present here the use of lightweight boron- and nitrogen-doped reduced graphene oxide (B-rGO, N-rGO) coated separators to suppress polysulfide diffusion and enhance active material utilization at high sulfur contents. B-rGO and N-rGO are synthesized through a facile modified Hummer's method involving the exfoliation of graphite sheets. Upon reduction, the carbon forms valuable interlayers with dynamic spacings for polysulfide trapping. Freeze-drying is utilized to preserve the structure of the pillow-like carbon, which is then slurry-coated onto a separator and placed against a sulfur cathode. The advantages of boron and nitrogen and their affinity towards polysulfides is compared while noting the lighter carbon coatings with good electrochemical stability. The cells attain a loading of 4.0 mg cm −2 with a high sulfur content of 66.5 ± 0.5 wt % on including the weight of the coatings. After a long cycle life of 400 cycles, N-rGO and B-rGO are still able to maintain a specific capacity of, respectively, 430 mA h g −1 and 367 mA h g −1 . [ABSTRACT FROM AUTHOR]

The study exploits the functional advantages of vanadium with variable oxidation states to extract maximum energy from Li 3 V 2 (PO 4 ) 3 /HHC composite containing human hair derived carbon. Vanadium, present in the form of V 3+ in Li 3 V 2 (PO 4 ) 3 stabilizes itself electrochemically as V 4+ by forming LiV 2 (PO 4 ) 3 through oxidation in the potential range 3.0–4.5 V and as V 1+ by forming Li 7 V 2 (PO 4 ) 3 due to the reduction of V 3+ into V 1+ in the 0.01–3.0 V region, thus qualifying LVP as a rocking chair electrode. In other words, Li 3 V 2 (PO 4 ) 3 /HHC composite demonstrates itself as anode and as cathode for lithium-ion batteries. Li 3 V 2 (PO 4 ) 3 /HHC cathode exhibits ultra high capacity, excellent rate capability at 50C and retains about 99% capacity up to 1000 cycles. As anode, Li 3 V 2 (PO 4 ) 3 /HHC delivers a capacity of 428 mAh g −1 at 50 mA g −1 and tolerates 5 A g −1 condition up to 1000 cycles with a negligible capacity fade. The dual electrode behavior of Li 3 V 2 (PO 4 ) 3 /HHC may be attributed to the unique architecture of HHC that provides high electronic conductivity, facilitates rapid diffusion of lithium ions and admits volume changes during intercalation/deintercalation. More importantly, HHC is a cheap and eco-friendly carbon additive derived from filthy human hair, which in turn offers ample scope for the commercial exploitation of title electrode. [ABSTRACT FROM AUTHOR]

Li-rich layered oxides are promising cathode materials for advanced Li-ion batteries because of their high specific capacity and operating potential. In this work, the Li-rich layered oxide Li 1·2 Mn 0·54 Ni 0·13 Co 0·13 O 2 (LMNC), is modified via a carbonization-reduction process (yielding the corresponding reduced compound denoted LMNC-R). Compared to the pristine oxide, LMNC-R delivers significantly enhanced initial discharge capacity/columbic efficiency, remarkably improved rate performance with an accelerated Li + diffusion rate, and significantly increased capacity/voltage retention. The specific energy density and energy retention after 100 cycles increase from 378.2 Wh kg −1 and 47.7% for LMNC to 572.0 Wh kg −1 and 71.3%, respectively, for LMNC-R. The enhancement in the electrochemical performance of LMNC-R can be attributed to the synchronous formation of the oxygen non-stoichiometric Li 2 MnO 3-δ component and to the carbon/spinel double coating layer in the material that resulted from the post-treatment process. Thus, the carbonization-reduction modification process can be used to tailor the structural evolution procedure and to suppress the metal ion dissolution of the Li-rich layered oxide during cycling. [ABSTRACT FROM AUTHOR]

A strategy for tuning the surface property of Single Walled Carbon Nanotubes (SWNTs) for enhanced methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR) along with methanol tolerance is presented. The surface functionality is tailored using controlled acid and base treatment. Acid treatment leads to the attachment of carboxylic carbon (CC) fragments to SWNT making it hydrophilic (P3-SWNT). Base treatment of P3-SWNT with 0.05 M NaOH reduces the CCs and makes it hydrophobic (P33-SWNT). Pt catalyst supported on the P3-SWNT possesses enhanced MOR whereas that supported on P33-SWNT not only enhances ORR kinetics but also possess good tolerance towards methanol oxidation as verified by the electrochemical technique. [ABSTRACT FROM AUTHOR]

Nano-Co 3 O 4 decorated with gold nanoparticles is synthesized by a simple method of in-situ reduction of HAuCl 4 by sodium citrate for energy storage application, and the effect of gold content in the product on electrochemical performance is investigated in detail. Introducing gold nanoparticles into nano-Co 3 O 4 bulk would contribute to reduce internal resistance of charge transmission. The results show that after in-situ reduction reaction gold nanoparticles imbed uniformly into nano-Co 3 O 4 with irregular nanoparticles. The gold nanoparticles decorated nano-Co 3 O 4 exhibits specific capacitance of 681 F g −1 higher than that of pristine Co 3 O 4 of 368 F g −1 . It is interesting that a good cycle life with the specific capacitance retention of 83.1% is obtained after 13000 cycles at 5 A g −1 , which recovers to initial specific capacitance value when the test current density is turned to 2 A g −1 . In addition, the device of asymmetric supercapacitor, assembled with gold nanoparticles decorated nano-Co 3 O 4 as the positive electrode and activated carbon as the negative electrode, exhibits good energy density of 25 Wh kg −1 , which is comparable to the asymmetric device assembled with normal nano-Co 3 O 4 , or the symmetric device assembled just with activated carbon. [ABSTRACT FROM AUTHOR]

This study deals with the synthesis and characterization of V-doped, TiO 2 supported Pt catalyst (Pt/V-TiO 2 ) for oxygen reduction reaction (ORR) and its in-situ performance investigation in proton exchange membrane (PEM) fuel cell. Pt/V-TiO 2 nanocomposite catalyst is prepared via a facile sol-gel and microwave assisted, modified chemical reduction route and its performance is compared with the undoped TiO 2 supported catalyst, Pt/TiO 2 prepared in an identical way. The prepared Pt/V-TiO 2 and Pt/TiO 2 catalysts are employed as cathode catalyst in PEM fuel cell and compared with standard Pt/C catalyst. Their comparative studies are conducted with physical and electrochemical techniques. In-situ electrochemical characterization studies show improved ORR catalytic activity of Pt/V-TiO 2 compared to Pt/TiO 2 . Furthermore, both Pt/TiO 2 and Pt/V-TiO 2 are more stable than Pt/C when subjected to 6000 voltammetric cycles in the range of 0.2–1.2 V vs . standard hydrogen electrode in operating fuel cell conditions, losing only <20% of its electrochemical surface area as compared to 50% loss exhibited by Pt/C. This study thus demonstrates Pt/V-TiO 2 nanocomposite material as a potential cathode catalyst for PEM fuel cell with immense scope for further investigation. [ABSTRACT FROM AUTHOR]

For practical applications of graphene-based materials in flexible supercapacitors, a technological breakthrough is currently required to fabricate high-performance graphene paper by a facile method. Herein, highly conductive (∼6900 S m −1 ) graphene paper with loose multilayered structure is produced by a high-efficiency in-situ chemical reduction process, which assembles graphite oxide suspensions into film and simultaneously conducts chemical reduction. Graphene papers with different parameters (including different types and doses of reductants, different thicknesses and areas of films) are successfully fabricated through this in-situ chemical reduction method. Meanwhile, the influences of the graphene papers with different parameters upon the supercapacitor performance are systematically investigated. Flexible supercapacitor based on the graphene paper exhibits high areal capacitance (152.4 mF cm −2 at current density of 2.0 mA cm −2 in aqueous electrolyte), and excellent rate performance (88.7% retention at 8.0 mA cm −2 ). Furthermore, bracelet-shaped all-solid supercapacitor with fascinating cycling stability (96.6% retention after 10 000 cycles) and electrochemical stability (an almost negligible capacity loss under different bending states and 99.6% retention after 4000 bending cycles) is established by employing the graphene paper electrode material and polymer electrolyte. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) represent a promising approach for remediation of toxic vanadium (V) contaminated environment. Herein, enhanced V(V) reduction and bioelectricity generation are realized in MFCs with biocathode. Synergistically electrochemical and microbial reductions result in the nearly complete removals of V(V) within 7 d operation with initial concentration of 200 mg L −1 . Maximum power density of 529 ± 12 mW m −2 is obtained. Electrochemical tests reveal that biocathode promotes electron transfers and reduces charge transfer resistance. XPS analysis confirms that V(IV) is the main reduction product, which precipitates naturally under neutral conditions. High-throughput 16S rRNA gene sequencing analysis indicates that the newly appeared Dysgonomonas is responsible for V(V) reduction and Klebsiella contributes mainly to bioelectricity generation in MFCs with biocathode. This study further improves the performance of remediating V(V) contaminated environment based on MFC technology. [ABSTRACT FROM AUTHOR]

N-doped microporous carbon as an exceptional metal-free catalyst from waste biomass ( banana peel as representative ) was obtained via fast catalysis carbonization, followed by N-doping modification. The method achieves a relatively high C conversion efficiency of ∼41.9%. The final carbon materials are doped by N (∼3 at.%) and possess high surface area (∼1097 m 2 g −1 ) and abundant micropores. Compared to commercial Pt/C materials, the as-prepared carbon catalyst exhibits a comparable electrocatalytic activity and much better stability. Furthermore, the metal-free catalyst loaded Zn-air battery possesses higher discharge voltage and power density as compared with that of commercial Pt/C. This novel technique can also be readily applied to produce metal-free carbon catalysts from other typical waste biomass (e.g., orange peel, leaves) as the carbon sources. The method can be developed as a potentially general and effective industrial route to transform waste biomass into high value-added microporous carbon with superior functionalities. [ABSTRACT FROM AUTHOR]

Composite electrode materials Li[Li 0.13 Ni 0.2 Mn 0.47 Co 0.2 ]O 2 (LNMC)–CeO 2 –С are obtained by the coprecipitation of Co, Ni, Mn and Ce hydroxides followed by the coating of LNMC–CeO 2 composites with pyrolytic carbon. The introduction of 5% CeO 2 promotes the reduction of LNMC grain size from 190–230 to 100–170 nm and the corresponding increase in the electrochemical capacity of LNMC-CeO 2 composite. The pyrolytic coating consists of the network of 2–5 nm polymer-carbon particles at the surface of LNMC crystallites. The electrochemical impedance spectroscopy data, which was performed after the galvanostatic cycling, demonstrated considerably lower charge transfer resistance of the carbon-coated composites compared to the bare LNMC and the LNMC-CeO 2 composites. The values of the discharge capacity of LNMC-CeO 2 -C composites are superior to the capacity of LMNC-CeO 2 and LMNC-C composites at all discharge rates (C/10 – 5C). The increase of the upper boundary of potentials to 4.8 V after cycling at 5C (U – 2÷4.6 V) promotes the increase of low rate electrochemical capacity of LNMC-CeO 2 -C composite to 220 mAh g −1 . [ABSTRACT FROM AUTHOR]

We have investigated the electroconversion of glycerol in alkaline medium using bimetallic M50@Pt50 nanocatalysts (where M = Ru, Sn or Ni) supported on multi-walled carbon nanotubes. The electrocatalysts have been synthesized via an electrostatically oriented co-reduction method in which self-assembly of the positively charged metal species (Sn, Ni and Ru) into the internal catalyst level and of the negatively charged platinum species towards the outer layer afford nanocatalysts with the desired morphology. The physicochemical characterizations have confirmed the atomic ratios, the metal loadings, and the spherical shape of the nanoparticles with average diameter lying between 2 and 3 nm. In terms of electrochemical performance, the Ni@Pt composition displays the highest electrochemically active surface area, the best relation between the peak current and the onset oxidation potential in the presence of glycerol (275 mA mg −1 Pt and −492 mV vs. Hg/HgO/OH − ), and the most remarkable electrochemical stability in chronoamperometric tests. Long-term experiments to evaluate the oxidation of glycerol and analysis of the products indicate that the different electrocatalysts synthesized herein efficiently perform the electroconversion of glycerol at high rates and generate of value-added products. [ABSTRACT FROM AUTHOR]

The aim of the paper is to present a promising approach for recycling high value-added metals from the cathode materials of spent LIBs. The synthesis process of NCM cathode material enlightened us to apply reduction roasting to break LiNi x Co y Mn z O 2 into simple compounds or metals. Accordingly, the effect of several factors such as temperature, carbon dosage and roasting time is assessed on the leaching efficiency of valuable metals. The roasted products are analyzed by XRD and SEM-EDS, and the results show that the cathode material after reduction roasting is primarily transformed into Li 2 CO 3 , Ni, Co and MnO. However, the solubility of Li 2 CO 3 is relatively low, so carbonated water leaching is used to treat the roasted products. Then the filtrate is evaporated for the preparation of pure Li 2 CO 3 , and residue is leached to recycle other metals with H 2 SO 4 . The results indicate that, after roasted at 650 °C for 3 h with 19.9% carbon dosage, 84.7% Li is preferentially recovered via carbonated water leaching, and more than 99% Ni, Co and Mn are recycled via acid leaching without adding reductant. Finally, the products of Li 2 CO 3 , NiSO 4 , CoSO 4 and MnSO 4 are obtained. The process have great potential for industrial-scale recycling from spent LIBs. [ABSTRACT FROM AUTHOR]

Direct borohydride fuel cells (DBFCs) exhibit the potential for a wide range of applications due to their high energy and power density; however, the hydrolysis of BH 4 − significantly limits the use of DBFCs. In this paper, PdNi x -B/carbon nanotubes (PdNi x -B/CNTs) (x = 0, 0.3, 0.6, 0.9) composites have been prepared by a chemical reduction method in which PdNi x -B nanoparticles of approximately 3.5 nm are grown on the surface of carbon nanotubes. A cell was assembled with PdNi x -B/CNTs as the anode catalyst, a polymer fibre membrane (PFM) as a substitute for the Nafion membrane and LaNiO 3 as the cathode catalyst. The results show that the Ni element displays an ability to balance the competition between the hydrolysis and oxidation of BH 4 − . A peak power density of 105 mW cm −2 (x = 0.9) was achieved at 25 °C. However, the highest fuel efficiency of 69% was achieved at x = 0.3, and the corresponding power density was 87 mW cm −2 , which represents the best comprehensive performance of these DBFCs. [ABSTRACT FROM AUTHOR]

We report a novel magnetic field assisted chemical reduction method for the synthesis of boron-doped Ni/Fe nano-chains as promising catalysts for the oxygen evolution reaction (OER). The boron-doped Ni/Fe nano-chains were synthesised in a one step process at room temperature using NaBH 4 as a reducing agent. The addition of boron reduced the magnetic moment of the intermediate synthesis products and produced nano-chains with a high specific surface area of 73.4 m 2 g −1 . The boron-doped Ni/Fe nano-chains exhibited catalytic performance superior to state-of-the-art Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3−δ perovskite and RuO 2 noble metal oxide catalysts. The mass normalized activity of the boron-doped Ni/Fe nano-chains measured at an overpotential of 0.35 V was 64.0 A g −1 , with a Tafel slope of only 40 mV dec −1 . The excellent performance of the boron-doped Ni/Fe nano-chains can be attributed to the uniform elemental distribution and highly amorphous structure of the B-doped nano-chains. These results provide new insights into the effect of doping transition-metal based OER catalysts with non-metallic elements. The study demonstrates a facile approach to prepare transition metal nano-chains using magnetic field assisted chemical reduction method as cheap and highly active catalysts for electrochemical water oxidation. [ABSTRACT FROM AUTHOR]

Chemically regenerative redox cathode (CRRC) polymer electrolyte fuel cells (PEFCs), where the direct reduction of oxygen is replaced by an in-direct mechanism occurring outside of the cell, are attractive to study as they offer a solution to the cost and durability problems faced by conventional PEFCs. This study reports the first detailed characterization of a high performance complete CRRC PEFC system, where catholyte is circulated between the cathode side of the cell and an air-liquid oxidation reactor called the “regenerator”. The catholyte is an aqueous solution of phosphomolybdovanadate polyoxoanion and is assessed in terms of its performance within both a small single cell and corresponding regenerator over a range of redox states. Two methods for determining regeneration rate are proposed and explored. Expressing the regeneration rate as a “chemical” current is suggested as a useful means of measuring re-oxidation rate with respect to the cell. The analysis highlights the present limitations to the technology and provides an indication of the maximum power density achievable, which is highly competitive with conventional PEFC systems. [ABSTRACT FROM AUTHOR]

The design of efficient non-Pt counter electrode (CE) materials is highly desired in field of dye sensitized solar cell (DSC). Herein, by combining the catalytic features of N doped carbon (NC) and CoNi alloy, CoNi alloy incorporated porous N doped carbon hybrid (CoNi-NC) is synthesized for application as catalytic CE of DSC. Benefiting from the proper meso-/macroporosity with high electroactive surface area, the CoNi-NC electrode demonstrates apparently higher electrocatalytic activity for iodine reduction reaction (IRR) over pyrolyzed Pt electrode. As a consequence, the DSC based on CoNi-NC CE yields a power conversion efficiency ( PCE ) of 7.6%, which is superior over that of Pt CE based cell (7.2%), highlighting the bright potential of CoNi-NC in efficient and economical CE of DSC. [ABSTRACT FROM AUTHOR]

Enzymatic biobatteries can be implanted in living organisms to exploit the chemical energy stored in physiological fluids. Generally, commonly-used electron donors (such as sugars) are ubiquitous in physiological environments, while electron acceptors such as oxygen are limited due to many factors including solubility, temperature, and pressure. The wide range of solid-state cathodes, however, may replace the need for oxygen breathing electrodes and serve in enzymatic biobatteries for implantable devices. Here, we have fabricated a glucose biobattery suitable for in vivo applications employing a glucose oxidase (GOx) anode coupled to a solid-state Prussian Blue (PB) thin-film cathode. PB is a non-toxic material and its electrochemistry enables fast regeneration if used in a secondary cell. This novel biobattery can effectively operate in a membraneless architecture as PB can reduce the peroxide produced by some oxidase enzymes. The resulting biobattery delivers a maximum power and current density of 44 μW cm − 2 and 0.9 mA cm − 2 , respectively, which is ca. 37% and 180% higher than an equivalent enzymatic fuel cell equipped with a bilirubin oxidase cathode. Moreover, the biobattery demonstrated a stable performance over 20 cycles of charging and discharging periods with only ca. 3% loss of operating voltage. [ABSTRACT FROM AUTHOR]

A three-dimensional reduced graphene oxide (3D-RGO) material has been successfully prepared by a facile hydrothermal method and is employed as the negative additive to curb the sulfation of lead-acid battery. When added with 1.0 wt% 3D-RGO, the initial discharge capacity (0.05 C, 185.36 mAh g −1 ) delivered by the battery is 14.46% higher than that of the control cell (161.94 mAh g −1 ); and the cycle life under the high-rate partial-state-of-charge (HRPSoC) condition is significantly improved by more than 224% from 8142 to 26,425 cycles. In comparison to the conventional carbon additions like the activated carbon and acetylene black, the 3D-RGO also exhibits the highest initial discharge capacity, the best rate capabilities and the longest HRPSoC cycling life. Finally, we propose a possible mechanism for 3D-RGO to suppress lead-acid battery sulfation, where the abundant pore structure and excellent conductivity of 3D-RGO may have a synergistic effect on facilitating the charge and discharge process of negative plate. [ABSTRACT FROM AUTHOR]

As a simple and versatile method, diffusion driven Layer-by-Layer assembly (dd-LbL) is developed to assemble graphene oxide (GO) into three-dimensional (3D) structure. The assembled GO macrostructure can be reduced through a hydrothermal treatment and used as a high volumetric capacitance electrode in supercapacitors. In this report we use rGO framework created from dd-LbL as a scaffold for in situ polymerization of aniline within the pores of the framework to form rGO/polyaniline (rGO/PANI) composite. The rGO/PANI composite affords a robust and porous structure, which facilitates electrolyte diffusion and exhibits excellent electrochemical performance as binder-free electrodes in a sandwich-configuration supercapacitor. Combining electric double layer capacitance and pseudo-capacitance, rGO/PANI electrodes exhibit a specific capacitance of 438.8 F g −1 at discharge rate of 5 mA (mass of electrodes were 10.0 mg, 0.5 A g −1 ) in 1 mol L −1 H 2 SO 4 electrolyte; furthermore, the generated PANI nanoparticles in rGO template achieve a higher capacitance of 763 F g −1 . The rGO/PANI composite electrodes also show an improved recyclability, 76.5% of capacitance retains after recycled 2000 times. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of liquid toluene to methylcyclohexane (MCH) was investigated using a membrane electrode assembly (MEA) and high active-area catalysts commonly used in proton exchange membrane fuel cells (PEMFC). The current density on Pt/C was higher than on PtRu/C, which was comparable to that of alkaline water electrolysis. The potential of hydrogen evolution was shifted negatively by the presence of toluene and MCH. Therefore, the toluene reduction reaction was almost perfectly separated from the hydrogen evolution reaction. Toluene was perfectly reduced to MCH at around 0 V vs. RHE on PtRu/C and no by-products were detected in the solutions after electrolysis. MCH was produced at a Faradaic efficiency of more than 96% by carefully keeping the potential above −30 mV vs. RHE. Through this electrolytic process, we were able to reduce the concentration of toluene from 100% to 7.6%. [ABSTRACT FROM AUTHOR]

The poisoning effects of 5 ppm CH 3 Br in the air on the spatial performance of a proton exchange membrane fuel cell (PEMFC) were studied using a segmented cell system. The presence of CH 3 Br caused performance loss from 0.650 to 0.335 V at 1 A cm −2 accompanied by local current density redistribution. The observed behavior was explained by possible bromomethane hydrolysis with the formation of Br − . Bromide and bromomethane negatively affected the oxygen reduction efficiency over a wide range of potentials because of their adsorption on Pt, which was confirmed by XPS. Moreover, the PEMFC exposure to CH 3 Br led to a decrease in the anode and cathode electrochemical surface area (∼52–57%) due to the growth of Pt particles through agglomeration and Ostwald ripening. The PEMFC did not restore its performance after stopping bromomethane introduction to the air stream. However, the H 2 /N 2 purge of the anode/cathode and CV scans almost completely recovered the cell performance. The observed final loss of ∼50 mV was due to an increased activation overpotential. PEMFC exposure to CH 3 Br should be limited to concentrations much less than 5 ppm due to serious performance loss and lack of self-recovery. [ABSTRACT FROM AUTHOR]

The choice of electrolyte solvent is expected to play a key role in influencing the lithium-oxygen battery performance. The electrochemical performances of three electrolytes composed of lithium bis (trifluoromethane sulfonyl) imide (LiTFSI) salt and different solvents namely, ethylene carbonate/propylene carbonate (EC/PC), tetra ethylene glycol dimethyl ether (TEGDME) and dimethyl sulfoxide (DMSO) are investigated by assembling lithium oxygen cells. The electrolyte composition significantly varied the specific capacity of the battery. The choice of electrolyte also influences the overpotential, cycle life, and rechargeability of the battery. Electrochemical impedance spectra, cyclic voltammetry, and chronoamperometry were utilized to determine the reversible reactions associated with the air cathode. [ABSTRACT FROM AUTHOR]

Manipulating basal plane structure of graphene for advanced energy conversion materials design has been research frontier in recent years. By extending size of defects in the basal plane of graphene from atomic scale to nanoscale, graphene with in-plane holes can be synthesized by multiple steps oxidation and reduction of defective graphene oxide at low concentration. These complicated and low yield synthetic methods largely limited research and applications of holey graphene based high performance energy conversion materials. Inspired by graphene in-plane holes formation mechanism, an easy and scalable synthetic approach has been proposed in this work. By oxidizing widely available defective graphite mineral under high concentration, holey graphene oxide has been scalable synthesized. Through simple reduction of holey graphene oxide, nitrogen doped holey graphene with high volumetric capacitance of 439 F/cm 3 was obtained. We believe this breakthrough can provide a feasible synthetic approach for further exploring the properties and performance of holey graphene based materials in variety of fields. [ABSTRACT FROM AUTHOR]

Carbon-supported Rh porphyrins catalyze the oxidation of carbon monoxide by water-soluble electron acceptors. The rate of this reaction is plotted as a function of the redox potential of the electron acceptor. The rate increases with an increase in the redox potential until it reaches a plateau. This profile can be explained in terms of the electrocatalytic CO oxidation activity of the Rh porphyrin. The removal of CO from CO(2%)/H 2 by a solution containing a carbon-supported Rh porphyrin and an electron acceptor is examined. The complete conversion of CO to CO 2 is achieved with only a slight amount of Rh porphyrins. Rh porphyrin on carbon black gives higher conversion than that dissolved in solution. This reaction can be used not only to remove CO in anode gas of stationary polymer electrolyte fuel cells but also to regenerate a reductant in indirect CO fuel cell systems. [ABSTRACT FROM AUTHOR]

In this study, the reduction processes of nickel oxide at different temperatures were investigated using nickel-film anode to study the influences of reduction temperature on the initial performances and stability of nickel-yttria-stabilized zirconia anode. Compared to conventional nickel-yttria-stabilized zirconia composite cermet anode, nickel-film anode has the advantage of direct observation at nickel-yttria-stabilized zirconia interface. The microstructural changes were characterized by scanning electron microscopy. The reduction process of nickel oxide is considered to be determined by the competition between the mechanisms of volume reduction in nickel oxide-nickel reaction and nickel sintering. Electrochemical impedance spectroscopy was applied to analyze the time variation of the nickel-film anode electrochemical characteristics. The anode performances and microstructural changes before and after 100 hours discharging and open circuit operations were analyzed. The degradation of nickel-film anode is considered to be determined by the co-effect between the nickel sintering and the change of nickel-yttria-stabilized zirconia interface bonding condition. [ABSTRACT FROM AUTHOR]

TiO 2 -reduced graphene oxide (rGO) nanocomposite (TiO 2 -rGO) is fabricated by microwave-assisted forced hydrolysis and examined as prospective electrode for energy storage applications, especially in Li-ion battery (LIB) and Li-ion capacitor (LIC). First, the uniformly distributed nanoscopic TiO 2 particulates (∼3 nm) over rGO nanosheets is evaluated as anode in half-cell assembly to ascertain the Li-insertion behavior and found that ∼0.68 mol Li (∼227 mAh g −1 ) is reversible. Then, “rocking-chair” type LIB is fabricated with spinel LiMn 2 O 4 cathode, and the LiMn 2 O 4 /TiO 2 -rGO assembly exhibits high capacity (∼120 mAh g −1 at 0.1 C rate), good rate capability (∼53 mAh g −1 at 1 C rate), and excellent cycleability (∼90% initial reversible capacity after 1000 cycle) as well. Similarly, the LIC is also constructed with activated carbon cathode, and such configuration delivered a maximum energy density of ∼50 Wh kg −1 with ∼82% retention after 4000 cycles. The synergistic effect of both rGO and anatase nanoparticles provides excellent energy efficiency and battery performance in different kind of Li-ion based energy storage devices. [ABSTRACT FROM AUTHOR]

A 2D Ti 3 C 2 MXene is introduced into NaAlH 4 to improve its hydrogen storage properties for the first time. In the presence of Ti 3 C 2 , the operating temperatures for hydrogen storage in NaAlH 4 are remarkably reduced, and the hydrogenation/dehydrogenation kinetics are significantly enhanced. The onset dehydrogenation temperature of the 7 wt% Ti 3 C 2 -containing NaAlH 4 sample is reduced to 100 °C, and hydrogen recharging starts at 50 °C. Approximately 4.7 wt% hydrogen is released from the NaAlH 4 -7 wt% Ti 3 C 2 sample within 100 min at 140 °C, and the dehydrogenated sample absorbs 4.6 wt% hydrogen within 60 min at 120 °C. However, pristine NaAlH 4 only absorbs 0.4 wt% hydrogen under identical conditions. Further cycling measurements show significantly improved cycling stability for the Ti 3 C 2 -containing NaAlH 4 ; the hydrogenation/dehydrogenation behaviour remains nearly constant after 10 cycles. XRD and XPS analyses reveal that the Ti 3 C 2 reacts with NaAlH 4 and is reduced to metallic Ti and Ti 3+ species, which are responsible for the lowered operating temperatures and improved dehydrogenation/hydrogenation kinetics. [ABSTRACT FROM AUTHOR]

Exploiting cost-effective and efficient counter electrodes (CEs) for the reduction of triiodide (I 3 − ) has been a persistent objective for the development of dye-sensitized solar cells (DSSCs). Here, we propose a strategy for the synthesis of nitrogen and sulfur dual-doped porous carbon (N/S-PC) via a thermal annealing approach by using melamine as N source, and basic magnesium sulfate (BMS) whiskers as S source and templates. Benefiting from the high surface area, unique interconnected structural feature and synergistic effects of N/S dual-doping, the N/S-PC shows excellent electrocatalytic activity toward I 3 − reduction, which has simultaneously been confirmed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization measurements. The DSSC devices with N/S-PC CEs exhibit a PCE up to 7.41%, which is higher than that of DSSC devices with single heteroatom (N or S) doped CEs and even Pt CEs (7.14%). [ABSTRACT FROM AUTHOR]

The reduction of oxygen transfer resistance through porous components consisting of a gas diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL) is very important to reduce the cost and improve the performance of a PEFC system. This study involves a systematic examination of the relationship between the oxygen transfer resistance of the actual porous components and their three-dimensional structure by direct measurement with FIB-SEM and X-ray CT. Numerical simulations were carried out to model the properties of oxygen transport. Moreover, based on the model structure and theoretical equations, an approach to the design of new structures is proposed. In the case of the GDL, the binder was found to obstruct gas diffusion with a negative effect on performance. The relative diffusion coefficient of the MPL is almost equal to that of the model structure of particle packing. However, that of CL is an order of magnitude less than those of the other two components. Furthermore, an equation expressing the relative diffusion coefficient of each component can be obtained with the function of porosity. The electrical conductivity of MPL, which is lower than that of the carbon black packing, is considered to depend on the contact resistance. [ABSTRACT FROM AUTHOR]

In this work, we develop a two-dimensional, transient model to investigate the mechanisms of ion-transport through a porous separator in VRFBs and their effects on battery performance. Commercial-available separators with pore sizes of around 45 nm are particularly investigated and effects of key separator design parameters and operation modes are explored. We reveal that: i) the transport mechanism of vanadium-ion crossover through available separators is predominated by convection; ii) reducing the pore size below 15 nm effectively minimizes the convection-driven vanadium-ion crossover, while further reduction in migration- and diffusion-driven vanadium-ion crossover can be achieved only when the pore size is reduced to the level close to the sizes of vanadium ions; and iii) operation modes that can affect the pressure at the separator/electrode interface, such as the electrolyte flow rate, exert a significant influence on the vanadium-ion crossover rate through the available separators, indicating that it is critically important to equalize the pressure on each half-cell of a power pack in practical applications. [ABSTRACT FROM AUTHOR]

A new nanocomposite formulation of the iron-based anode for alkaline secondary batteries is proposed. For the first time, FeS nanoparticles anchored on reduced graphene oxide (RGO) nanosheets are synthesized via a facile, environmentally friendly direct-precipitation approach. In this nanocomposite, FeS nanoparticles are anchored uniformly and tightly on the surface of RGO nanosheets. As an alkaline battery anode, the FeS@RGO electrode delivers a superior high-rate charge/discharge capability and outstanding cycling stability, even at a condition without any conductive additives and a high electrode loading of ∼40 mg cm −2 . At high charge/discharge rates of 5C, 10C and 20C (6000 mA g −1 ), the FeS@RGO electrode presents a specific capacity of ∼288, 258 and 220 mAh g −1 , respectively. Moreover, the FeS@RGO electrode exhibits an admirable long cycling stability with a superior capacity retention of 87.6% for 300 cycles at a charge/discharge rate of 2C. The excellent electrochemical properties of the FeS@RGO electrode can be stemmed from the high specific surface area, peculiar electric conductivity and robust sheet-anchored structure of the FeS@RGO nanocomposite. By virtue of its superior fast charge/discharge properties, the FeS@RGO nanocomposite is suitable as an advanced anode material for high-performance alkaline secondary batteries. [ABSTRACT FROM AUTHOR]

Versatile and ductile conductive carbonized cotton fabrics decorated with reduced graphene oxide (rGO)/manganese dioxide (MnO 2 ) are prepared in this paper. In order to endow multifunction to cotton fabric, graphene oxide (GO) is deposited on cotton fibers by simple dip-coating route. MnO 2 nanoparticles are assembled on the surface of cotton fabric through in-situ chemical solution deposition. MnO 2 /GO@cotton fabrics are carbonized to achieve conductive fabric (MnO 2 /rGO@C). The morphologies and structures of obtained fabrics are characterized by SEM, XRD, ICP and element analysis, and their electro-properties including electro-chemical, electro-heating and electro-mechanical properties are evaluated. The MnO 2 /rGO@C yields remarkable specific capacitance of 329.4 mA h/g at the current density of 100 mA/g, which is more than 40% higher than that of the control carbonized cotton fabric (231 mA h/g). Regarding electro-heating properties, the temperature of MnO 2 /rGO@C fabric could be monotonically increased to the steady-state maximum temperatures (ΔT max ) of 36 °C within 5 min under the applied voltage 15 V while the Δ T max = 17 °C of the control case. In addition, MnO 2 /rGO@C exhibits repeatable electro-mechanical properties and its normalized resistance ( R − R 0 )/ R 0 could reach 0.78 at a constant strain (curvature = 0.6 cm −1 ). The MnO 2 /rGO@C fabric is versatile, scalable, and adaptable to a wide variety of smart textiles applications. [ABSTRACT FROM AUTHOR]

In this study, a metastable form of vanadium dioxide, denoted as VO 2 (B), has been successfully synthesized under solvothermal condition. However, the as-received VO 2 (B) suffers from fast capacity fading and poor high-rate performance. In order to overcome these problems, the as-received VO 2 (B) is solvothermally treated with reduced graphene oxide (rGO) to produce VO 2 (B)/rGO composite. As a result, the resulting electric conductivity of the VO 2 (B)/rGO composite is improved to ∼10 −4 cm S −1 (from ∼10 −7 S cm −1 for the as-received VO 2 (B)). Electrochemical data of the VO 2 (B)/rGO composite, tested in both Li and Na cells, shows markedly enhanced electrochemical performance compared to bare VO 2 (B). The effect of electro-conducting rGO is more evident at high rates. [ABSTRACT FROM AUTHOR]

Black TiO 2 with various nanostructures and phase constitutions have been reported to exhibit excellent photocatalytic and photoelectrochemical (PEC) performance. Here, we report the fabrication of black nanostructured TiO 2 B through hydrogen plasma assisted reduction and its enhanced PEC properties for the first time. Both the obtained TiO 2 B and black TiO 2 B are single crystalline nanowires, while the black TiO 2 B samples exhibit much stronger visible and infrared light absorption. The optimal black TiO 2 B sample obtained by hydrogen plasma treatment at 425 °C yields a photocurrent density of 0.85 mA cm −2 , a rather low onset potential of −0.937 V Ag/AgCl and a high applied bias photon-to-current efficiency (ABPE) of 0.363%, which is far superior to the TiO 2 B (0.15 mA cm −2 photocurrent, −0.917 V Ag/AgCl onset potential and 0.138% ABPE). The significantly enhanced PEC performance of the black TiO 2 B is ascribed to the introduction of moderate surface oxygen vacancies. These results indicate that the black TiO 2 B is a promising material for PEC application and solar energy utilization. [ABSTRACT FROM AUTHOR]

It has been found that carbonaceous materials containing a transition metal coordinated by 4 nitrogens in the square-planar configuration (metal–N 4 site) on the surface possessed a catalytic activity for various electrochemical reactions related to energy conversion and storage; i.e., oxygen reduction, hydrogen evolution, and quite recently, the electrode reactions in vanadium redox flow batteries (VRFB). The catalyst for the VRFB positive electrode discharge reaction, i.e., the dioxovanadium ion reduction, was formed by coating the surface of cup-stack carbon nanotubes with a carbonaceous thin film with the Fe–N 4 site generated by the sublimation, deposition, and pyrolysis of iron phthalocyanine. In this study, the influence of the physical properties of the catalyst on the electrochemical reactions was investigated to optimize the coating. With an increase in the coating, the specific surface area increased, whereas the pore size decreased. The surface Fe concentration was increased in spite of the Fe aggregation inside the carbon matrix. The catalytic activity enhancement was achieved due to the increase in the specific surface area and the surface Fe concentration, but was lowered due to the decrease in the pore size, which was disadvantageous for the penetration of the electrolyte and the mass transfer. [ABSTRACT FROM AUTHOR]

To evaluate the reliability of solid oxide fuel cell (SOFC) stacks during operation, the stress field in the stack must be known. During operation the stress field will depend on time as creep processes relax stresses. The creep of reduced Ni-YSZ anode support at operating conditions has been studied previously. In this work a newly discovered creep phenomenon taking place during the reduction is reported. This relaxes stresses at a much higher rate (∼×10 4 ) than creep during operation. The phenomenon was studied both in three-point bending and uniaxial tension. Differences between the two measurements could be explained by newly observed stress promoted reduction. Finally, samples exposed to a small tensile stress (∼0.004 MPa) were observed to expand during reduction, which is in contradiction to previous literature. These observations suggest that release of internal residual stresses between the NiO and the YSZ phases occurs during reduction. The accelerated creep should practically eliminate any residual stress in the anode support in an SOFC stack, as has previously been indirectly observed. This phenomenon has to be taken into account both in the production of stacks and in the simulation of the stress field in a stack based on anode supported SOFCs. [ABSTRACT FROM AUTHOR]

This paper describes a diagnostic tool for in-situ characterization of the rate and distribution of hydrogen transfer leaks in Polymer Electrolyte Membrane (PEM) fuel cell stacks. The method is based on reducing the air flow rate from a high to low value at a fixed current, while maintaining an anode overpressure. At high air flow rates, the reduction in air flow results in lower oxygen concentration in the cathode and therefore reduction in cell voltages. Once the air flow rate in each cell reaches a low value at which the cell oxygen-starves, the voltage of the corresponding cell drops to zero. However, oxygen starvation results from two processes: 1) the electrochemical oxygen reduction reaction which produces current; and 2) the chemical reaction between oxygen and the crossed over hydrogen. In this work, a diagnostic technique has been developed that accounts for the effect of the electrochemical reaction on cell voltage to identify the hydrogen leak rate and number of leaky cells in a fuel cell stack. This technique is suitable for leak characterization during fuel cell operation, as it only requires stack air flow and voltage measurements, which are readily available in an operational fuel cell system. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide/carbon nanotubes (CNTs) sponge (GCNTS) is fabricated via a simple freeze drying of graphene oxide/CNTs mixed solution and subsequent thermal treatment in nitrogen atmosphere, and used as anodes for sodium-ion batteries (SIBs) for the first time. The morphology, structure and electrochemical performance of GCNTS are characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, nitrogen adsorption-desorption isotherms, galvanostatic charge/discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy, respectively. The results show that GCNTS with 20 wt % CNTs has a highest charge capacity of 436 mA h g −1 after 100 cycles at a current density of 50 mA g −1 and even at a high current density of 10 A g −1 , a capacity of 195 mA h g −1 is maintained after 7440 cycles. The high capacity, excellent rate performance and long life cycling enable the GCNTS to be a promising candidate for practical SIBs. [ABSTRACT FROM AUTHOR]

Developing efficient, readily available, and sustainable electrocatalysts for oxygen reduction reaction (ORR) in neutral medium is of great importance to practical applications of microbial fuel cells (MFCs). Herein, a porous nitrogen-doped carbon material with encapsulated Fe-based nanoparticles (Fe-N x /C) has been developed and utilized as an efficient ORR catalyst in MFCs. The material was obtained through pyrolysis of a highly porous organic polymer containing iron(II) porphyrins. The characterizations of morphology, crystalline structure and elemental composition reveal that Fe-N x /C consists of well-dispersed Fe-based nanoparticles coated by N-doped graphitic carbon layer. ORR catalytic performance of Fe-N x /C has been evaluated through cyclic voltammetry and rotating ring-disk electrode measurements, and its application as a cathode electrocatalyst in an air-cathode single-chamber MFC has been investigated. Fe-N x /C exhibits comparable or better performance in MFCs than 20% Pt/C, displaying higher cell voltage (601 mV vs. 591 mV), maximum power density (1227 mW m −2 vs. 1031 mW m −2 ) and Coulombic efficiency (50% vs. 31%). These findings indicate that Fe-N x /C is more tolerant and durable than Pt/C in a system with bacteria metabolism and thus holds great potential for practical MFC applications. [ABSTRACT FROM AUTHOR]

Surface conductive engineering on Li 2 S is critical for construction of advanced cathodes of lithium-sulfur batteries. Herein, we construct a high-performance Li 2 S-based composite cathode with the help of three-dimensional reduced graphene oxide (3D-rGO) network and outer carbon coating. Typically, the Li 2 S@C particles are uniformly embedded into 3D-rGO to form a binder-free 3D-rGO-Li 2 S@C cathode by the combination of a liquid solution-evaporation coating and PVP (Polyvinyl Pyrrolidone) carbonization. The 3D-rGO-Li 2 S@C cathode exhibits a high initial discharge capacity of 856 mAh g −1 at 0.1C, superior cycling stability with a capacity of 388.4 mAh g −1 after 200 cycles at 1C, corresponding to a low capacity fading rate. It is demonstrated that the outer conductive coating is effective and necessary for electrochemical enhancement of Li 2 S cathodes by improving electrical conductivity and prohibiting polysulfide from shuttling during cycling. [ABSTRACT FROM AUTHOR]

MnO 2 /reduced graphene oxide (rGO) nanocomposites were synthesized via a simple solution method at room temperature for use in Li-ion batteries. Owing to the mesoporous features as well as the high electrical conductivity of rGO, the overall electronic and ionic conductivities of the nanocomposite were increased, resulting in improved electrochemical properties in terms of specific capacity, rate capability, and cyclability. In particular, as-prepared nanocomposites showed 222 and 115 mAh g −1 at a current density of as high as 5 and 10 A g −1 , and the specific capacitance was well maintained after 400 cycles. In addition, MnO 2 , via composite formation with rGO, permitted the additional conversion reaction between MnO and Mn 3 O 4 , resulting in the reduction of the initial irreversible capacity despite the high first discharge capacity caused by the large specific surface area. [ABSTRACT FROM AUTHOR]