Search

Uncontrolled lithium (Li) deposition has hampered the evolution of Li‐metal electrode‐based Li‐batteries. In this work, we report the differences of a guided Li deposition with a size change of the square hole micro‐patterns carved on the Li‐metal surface with two different dimensions using a simple stamping method. Li deposition is preferentially initiated on the top edge for the smaller pattern and on the bottom for the larger pattern. Although the two patterns lead to a more uniform utilization of the Li, the larger pattern shows a higher cycling stability within a LiFePO4/Li cell than that of the smaller one indicating that initiating the Li deposition from the bottom of the hole is more efficient in confining the deposited Li. Based on the impedance analysis of the compressed Li electrodes, we suggest that the guided Li deposition on the bottom of the hole is attributed to a large contrast in the resistance of native surface passivation layer between the top and hole surfaces. This improved understanding can further advance guided Li deposition induced by surface patterns for high performance Li‐metal batteries. As a model study for understanding the guiding effect of Li‐metal deposition to specific sites on the patterns, two different sized square hole patterned Li‐metal electrodes (MP‐Lis) are manufactured. It demonstrates that the change in the passivation film on the Li surface driven by the mechanical deformation is a key factor to induce the guided Li deposition of MP‐Lis, though the shapes of patterns are the same. [ABSTRACT FROM AUTHOR]

Lithium (Li) metal is one of the most promising candidates for the anode in high-energy-density batteries. However, Li dendrite growth induces a significant safety concerns in these batteries. Here, a multifunctional separator through coating a thin electronic conductive film on one side of the conventional polymer separator facing the Li anode is proposed for the purpose of Li dendrite suppression and cycling stability improvement. The ultrathin Cu film on one side of the polyethylene support serves as an additional conducting agent to facilitate electrochemical stripping/deposition of Li metal with less accumulation of electrically isolated or 'dead' Li. Furthermore, its electrically conductive nature guides the backside plating of Li metal and modulates the Li deposition morphology via dendrite merging. In addition, metallic Cu film coating can also improve thermal stability of the separator and enhance the safety of the batteries. Due to its unique beneficial features, this separator enables stable cycling of Li metal anode with enhanced Coulombic efficiency during extended cycles in Li metal batteries and increases the lifetime of Li metal anode by preventing short-circuit failures even under extensive Li metal deposition. [ABSTRACT FROM AUTHOR]

Abstract: The effect of cathode gas diffusion media with microporous layers (MPLs) on direct methanol fuel cell (DMFC) performances is studied by combining electrochemical analysis and physicochemical investigation. The membrane electrode assemblies (MEAs) using MPL-modified cathode gas diffusion layers (GDLs, GDL-1) showed slightly better performances (117mWcm−2) at 0.4V and 70°C than commercial GDL (SIGRACET® product version: GDL-35BC, SGL Co.) DMFC MEAs (110mWcm−2). This might be due to high gas permeability, uniform pore distributions, and low water transport coefficient including methanol crossover. For GDL-1, the air permeability was 31.0cm3 cm−2 s−1, while the one for SGL 35BC GDLs was 21.7cm3 cm−2 s−1. Also, the GDL-1 in the pore-size distribution diagrams had distinct peaks due to more uniform distributions of macropores and micropores with smaller holes between aggregates of carbon particles compared to GDL-35 BC as confirmed by SEM images. Furthermore, the MEA using GDL-1 for the cathode had a lower water transfer coefficient compared to an MEA with a commercial 35 BC GDL. [Copyright &y& Elsevier]

Abstract: Electrochemical analysis of a commercial polymer electrolyte membrane fuel cell (PEMFC), operated at varying cathode relative humidity (RH) and current density, has been conducted to understand the factors that affect power performance when the PEMFC is operated with a dry-air feed. With a change in the cathode RH from 80 to 4%, the electrochemical area and double-layer capacitance of the cathode are reduced by 9 and 8%, respectively. This indicates that exclusion of the catalyst layer (CL) of the cathode from proton access occurs to some extent at low RH. It does not, however, explain the observed increase in activation loss. For the dry-air feed, the ionic resistances of the membrane and cathode CL are comparable in magnitude. Impedance analyses show that drying of the cathode at low RH and low current density leads not only to an increase in the ionic resistance of the CL, but also to increases in both charge-transfer and mass-transfer resistances. The simultaneous decrease in all the resistance components with decrease in the air permeability of the cathode diffusion layer highlights the importance of cathode design for operation with dry-air feed. [Copyright &y& Elsevier]

[Display omitted] • IrO 2 -based CL shows rapid initial performance loss during constant current operations. • The cause of the initial degradation is the detachment of the IrO 2 -based CL. • Higher interactions between ionomer binders and catalysts suppress initial degradation. • The ion-conducting group of ionomers plays an important role in binding to the IrO 2. • IrO 2 -based CL mixed with Nafion and QPC-TMA showed high stability. A durable catalyst layer (CL) is essential for the successful commercialization of anion exchange membrane water electrolyzers (AEMWEs). However, AEMWEs often exhibit a large performance drop in the early stage of operation, which has not been clearly understood. Herein, we unravel the root cause of the initial degradation for a typical anode CL composed of a quaternized polycabozole-trimethyl amine (QPC-TMA) anion exchange ionomer and IrO 2 nanoparticles. Post-mortem and electrochemical analysis reveal that the detachment of the IrO 2 nanoparticles from the CL and the interfacial delamination of the CL from the porous transport layer (PTL) surface are responsible for the initial degradation. Nafion (ionomer) as a co-binder prevents the initial degradation by increasing the mechanical integrity and interfacial adhesion of the CL, thereby indicating a strong binder effect on the initial degradation. Molecular dynamics and density functional theory calculations elucidate that the binding energy of QPC-TMA on IrO 2 or PTL surface is much smaller than that of the Nafion ionomer, because the ionomer–catalyst or ionomer–PTL interaction is sterically hindered for the bulky TMA group. This study motivates structural designing of anion exchange ionomers with strong binding abilities to address the initial degradation problem. [ABSTRACT FROM AUTHOR]

There is increasing interest in vanadium redox flow batteries (VRFBs) for large scale-energy storage systems. Vanadium electrolytes which function as both the electrolyte and active material are highly important in terms of cost and performance. Although vanadium electrolyte technologies have notably evolved during the last few decades, they should be improved further towards higher vanadium solubility, stability and electrochemical performance for the design of energy-dense, reliable and cost-effective VRFBs. This timely review summarizes the vanadium electrolyte technologies including their synthesis, electrochemical performances, thermal stabilities, and spectroscopic characterizations and highlights the current issues in VRFB electrolyte development. The challenges that must be confronted to further develop vanadium electrolytes may stimulate more researchers to push them forward. [ABSTRACT FROM AUTHOR]

Vanadium redox flow batteries (VRFBs) are attracting increasing amounts of attention for energy storage applications. However, their electrochemical performance capabilities have not been closely analyzed because proper reference electrodes remain elusive. In this work, we report the resistor design of a dynamic hydrogen electrode (DHE) for VRFBs which enables the in-situ monitoring of the positive and negative electrode potential. Due to the presence of multiple redox couples at the reference electrode inserted into the VRFB membrane, the adjustment of the current flowing through the DHE with the resistor is the key factor when attempting to maintain a stable and steady hydrogen reduction reaction at the DHE during repeated charge and discharge processes. With the insertion of the DHE into the membrane, the electrochemical properties of the positive and negative electrode/electrolyte can be individually analyzed. Thus, the DHE design provides an effective electrochemical analysis platform for VRFB research. [ABSTRACT FROM AUTHOR]

Ce-based materials have been widely used as a radical scavenger to improve the chemical durability of the membrane in polymer electrolyte fuel cells; however, any negative effects from Ce ions on power performance have not been reported as an issue before except for ionomer contamination by Ce3+. Herein, we propose and experimentally demonstrate the detrimental effect of Ce4+ on the Pt/C catalyst. Due to the strong oxidation power of Ce4+, Pt and carbon are subjected to oxidative decomposition under contact with Ce4+. Based on the electrochemical and spectroscopic analyses of the Pt/C stored in Ce3+ and Ce4+ electrolyte, Pt2+ dissolution and carbon corrosion by Ce4+ are verified. As a result, the active surface area and oxygen reduction reaction activity of Pt/C are considerably reduced after storage in the Ce4+ electrolyte. Additionally, at the membrane electrode assembly level, it is demonstrated that the Ce4+ leached out from the CeO 2 causes a significant power performance decay along with the loss of the active surface area and an increase in the charge transfer resistance. The newly-found detrimental effect of Ce4+ on the Pt/C catalyst emphasizes the importance of preventing Ce4+ dissolution to improve the membrane durability by Ce-containing radical scavengers. Image 1 • ORR activity of Pt/C is decreased when it is in contact with Ce4+ ion. • Pt dissolution and carbon corrosion by Ce4+ are verified by spectroscopic analyses. • In MEA level, Ce4+ leached from CeO 2 significantly reduces MEA performance. [ABSTRACT FROM AUTHOR]