An easy and effective method for producing low methanol-crossover membranes is developed by dispersing sulfonated graphene oxide (SGO) into a Nafion matrix. A SGO/Nafion mixture with low SGO content ...exhibits unique viscosity behavior and allows for better SGO dispersion within the Nafion. After film casting, the composite membranes show lower methanol and water uptakes, a reduced swelling ratio, improved proton conductivity in low relative humidity, and extremely high methanol selectivity, which can be implemented in direct methanol fuel cells (DMFCs). The regular backbone of the composite membrane shows a higher storage modulus, increased α-relaxation (transition temperature), and improved tolerance to pressure during membrane electrode assembly (MEA). The small angle X-ray spectra indicate the shrinkage of the ionic clusters in the composite membranes, which thus reduce methanol crossover. The hybrid membranes applied to DMFCs demonstrate performances superior to that of the commercial Nafion 115 in 1 M and 5 M methanol solutions.
•Sulfonated graphene oxide/Nafion hybrid membranes have been prepared by blending.•The viscosity of SGO/Nafion is dramatically enhanced for well-dispersed SGO.•The composite membranes have high methanol selectivity and reduced swelling ratio.•The composite membrane shows better performance than Nafion 115 on DMFC test.
The question of whether the metal chalcogenides (phosphides) that have been acknowledged to be efficient materials for bifunctional electrocatalysts really perform as the active species or just ...“pre-catalysts” has been debated. Herein, a series of operando measurements, including in situ X-ray absorption spectroscopy, liquid-phase transmission electron microscopy, and in situ Raman spectroscopy, were conducted to unravel in real time the structural and chemical stability of P-substituted CoSe2 electrocatalysts under both hydrogen and oxygen evolution reactions (HER and OER, respectively) in an alkaline electrolyte. It can be conclusively revealed that, in an alkaline electrolyte, the P-substituted CoSe2 electrocatalyst was acting as the “pre-catalyst” rather than the real reactive species. The introduction of phosphorus is speculated to generate more vacancies or defects around Co cations in the initial CoSe2 and considerably facilitates the structural transformation into the “real reactive species”, such as metallic cobalt (for HER) and cobalt oxyhydroxide (for OER).
The dynamics of polysulfide (PS) dissolution and re-deposition during electrochemical charge/discharge of the lithium-sulfur (Li–S) cell has been investigated in a quantitative manner based on ...in-operando transmission X-ray microscopy (TXM) analysis of dimensional variations of S particles in working cells that have been subjected to different depths of charge/discharge. Extensive shrinkage and expansion of S particles have been observed to result from PS dissolution and re-deposition, respectively. The dissolution rate of PS is found to have complex dependence on the Li content, being significantly higher for the stoichiometries of LiS8 and Li2S4 than those between Li2S8 and Li2S6. PS re-deposition is nucleation-limited, leading to considerable aggregation of the S-containing active mass and enormous dimensional variations of active particles. These two consequences may impose threat to the cycle stability of the electrode. Possible benefit of introducing favorable nucleation sites is discussed.
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•Polysulfide (PS) dissolution and re-deposition in working Li–S electrode is studied.•Particle size variation of S electrode is monitored by transmission X-ray microscopy.•Extensive shrinking and expansion of S particles are observed.•Solubility of PS is strongly dependent on Li content.•PS re-deposition is nucleation-limited and leads to sulfur aggregation.
With regard to the best electro-chemical efficiency of an active direct methanol fuel cell (DMFC), the stacks and their balance of plant (BOP) are complex to build and operate. The yield of making ...the large-scale stacks is difficult to improve. Therefore, a portable power station made of multiple simpler planar type stack modules with only appropriate semi-active BOPs was developed. A planar stack and its miniature BOP components are integrated into a semi-active DMFC stack module for easy production, assembly, and operation. An improved energy management system is designed to control multiple DMFC stack modules in parallel to enhance its power-generation capacity and stability so that the portability, environmental tolerance, and long-term durability become comparable to that of the active systems. A prototype of the power station was tested for 3600 h in an actual outdoor environment through winter and summer. Its performance and maintenance events are analyzed to validate its stability and durability. Throughout the test, it maintained the daily average of 3.3 W power generation with peak output driving capability of 12 W suitable for Internet of Things (IoT) applications.
Abstract
One challenge for realizing high-efficiency electrocatalysts for CO
2
electroreduction is lacking in comprehensive understanding of potential-driven chemical state and dynamic ...atomic-configuration evolutions. Herein, by using a complementary combination of in situ/operando methods and employing copper single-atom electrocatalyst as a model system, we provide evidence on how the complex interplay among dynamic atomic-configuration, chemical state change and surface coulombic charging determines the resulting product profiles. We further demonstrate an informative indicator of atomic surface charge (
φ
e
) for evaluating the CO
2
RR performance, and validate potential-driven dynamic low-coordinated Cu centers for performing significantly high selectivity and activity toward CO product over the well-known four N-coordinated counterparts. It indicates that the structural reconstruction only involved the dynamic breaking of Cu–N bond is partially reversible, whereas Cu–Cu bond formation is clearly irreversible. For all single-atom electrocatalysts (Cu, Fe and Co), the
φ
e
value for efficient CO production has been revealed closely correlated with the configuration transformation to generate dynamic low-coordinated configuration. A universal explication can be concluded that the dynamic low-coordinated configuration is the active form to efficiently catalyze CO
2
-to-CO conversion.
In this study, ordered mesoporous carbons (OMCs) with different pore structures, namely 2D hexagonal CMK-3 and 3D cubic CMK-8 prepared by the nanocasting method using mesoporous silicas SBA-15 and ...KIT-6 as hard templates, respectively, in their pure forms are used as anode materials in lithium ion batteries (LIBs) to evaluate the role of mesoporous structures in their electrochemical performances. The results demonstrate that the CMK-8 electrode exhibits a higher reversible capacity and better cycling stability and rate capability, as compared to the CMK-3 electrode, due to its unique 3D cubic mesostructure. The initial capacities of 1884 and 964 mA h g
−1
are obtained for the CMK-8 and CMK-3 electrodes, respectively. The CMK-8 electrode exhibits a higher capacity value (around 37.4% higher) than the CMK-3 electrode at the 100
th
cycle. The enhanced electrochemical performance of CMK-8 is mainly attributable to its unique 3D channel networks, which are beneficial for efficient Li storage and volume change. Although CMK-3 is the most investigated OMCs used in LIBs, herein we demonstrate that CMK-8 is a better carbon matrix for the fabrication of the electrode materials composed of mesoporous carbons.
Hollow nanostructures are a particularly interesting class of materials that have unusual chemical and physical characteristics that are determined by their shape and composition. A facile procedure ...for the hollow Pt nanosphere catalysts with nanochannels was developed; the catalysts can be simply prepared at room temperature with silver nanoparticles as sacrificial templates. The incomplete shell of hollow nanospheres may provide the interior surface for the catalytic reaction, and the high surface area of Pt nanospheres leads to a higher catalytic activity. Consequently, these results demonstrate a simple route to enhance the catalytic efficiency of Pt catalysts by a simple improvement.
In this study, two unique organic–inorganic hybrids are synthesized and optimized to obtain a new type of hybrid blend membrane. A soft hybrid is obtained from reaction of polyetheramine (M-2070) and ...(3-glycidyloxypropyl)trimethoxysilane (GLYMO), whereas a hard hybrid is prepared from reactions of polyetherdiamine (ED2003), poly(ethylene glycol) diglycidyl ether (PEGDGE) and GLYMO. Both hybrids are finally blended with poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-HFP)) to get the hybrid blend membrane and plasticized with 1M LiPF6 in EC/DEC. The successful synthesis of the hybrid blend membrane structure is established from 13C and 29Si solid-state NMR spectroscopy. FTIR results reveal the interactions of different groups of the hybrid blend membrane. The hybrid blend electrolyte possesses maximum ionic conductivity value of 6.9mScm−1 at 30°C and is electrochemically stable up to 5V. The electrochemical performance of the hybrid blend electrolyte assemble in a battery cell with the LiFePO4 cathode exhibits a good cycle life of over 200 cycles with an initial discharge capacity of 150mAhg−1. In addition, coulombic efficiency of 97–99% is maintained for the whole cycles. Our results demonstrate that the present hybrid blend electrolyte can be a potential candidate serving as an effective electrolyte in lithium-ion batteries.
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•A new blend electrolyte is prepared by blending of two organic–inorganic hybrids.•The blend electrolyte exhibits a maximum ionic conductivity value of 6.9mScm−1.•The blend electrolyte is electrochemically stable up to 5V.•The test cell exhibits an initial discharge capacity of 150mAhg−1 at 0.2C.•The test cell shows good cycling performance of over 200 cycles.
Sulfonated polytriazole (SPTA) in which the acidic sulfonic acid and basic triazole groups act as physical crosslinking sites within a polymer backbone has been successfully prepared, for use as a ...proton exchange membrane, using the click reaction. The acid-base interactions of the SPTA membranes leads to the formation of well-dispersed ionic clusters and the random distribution of ion channels with good connectivity resulting in lower methanol permeabilities at ambient temperatures and similar or higher proton conductivities than Nafion 117 at 80 °C in conditions of near zero relative humidity. Proton conductivities (
σ) of 0.149 S cm
−1 at 80 °C and 9 × 10
−5 S cm
−1 in anhydrous conditions together with low methanol permeability (
P) at 0.1 × 10
−6 cm
2 s
−1 that are comparable or superior to Nafion 117 (
σ
T
=80 : 0.151 S cm
−1; σ
RH=0
: 3 × 10
−5 S cm
−1;
P
T
=30: 1.31 × 10
−6 cm
2 s
−1) were achieved. Additionally, the selectivity of SPTA is approximately four times higher than that of Nafion 117, thus it may have potential for use in direct methanol fuel cells (DMFCs).
Incorporation of sulfonic acid (acidic) and triazole (basic) groups as physical crosslinking sites in polymer backbone lead to the formation of well-dispersed ionic clusters and random distribution of ion channels with good connectivity, resulting in membranes with lower methanol permeabilities at ambient temperatures and similar or higher proton conductivities than Nafion 117 at 80 °C in conditions of near zero relative humidity. SPTA membranes are capable of conducting protons under anhydrous conditions by Grotthuss mechanism of proton transfer.
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► SPTA membranes have been prepared using the click reaction. ► Sulfonic acid and triazole groups as physical crosslinking sites in SPTA membranes. ► Acid-base interactions lead to the formation of well-dispersed ionic clusters. ► Acid-base interactions lead to the random distribution of ion channels. ► SPTA membranes conduct protons under anhydrous conditions by Grotthuss mechanism.
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