Effects of Electrolyte Additives on Nonaqueous Redox Flow Batteries

The widespread utilization of nonaqueous redox flow batteries is hindered by the low performance. Including some kinds of additives in electrolyte is a possible and facile solution. In this chapter, the effects of carbon dioxide gas, EC/DMC, and antimony ions on the electrochemical performance of nonaqueous redox flow batteries are disclosed. The results show that the ohmic resistance of the deep eutectic solvent (DES) electrolyte reduces significantly when adding carbon dioxide gas and EC/DMC, the percentage of reduction increases with the volume percentage of EC/DMC in electrolyte, and the reaction kinetics almost keeps unchanged for carbon dioxide gas and EC/DMC additives. For the additive of antimony ions, the electrochemical reaction kinetics of active redox couple is enhanced, the diffusion coefficient of active ions also increases, and the charge transfer resistance decreases. The antimony ions electrodeposited on the surface of graphite felt contribute a catalytic effect on the electrochemical reaction so as to improve the performance. However, due to the trade-off between the enhanced kinetics and reduced active surface area, the optimum concentration of antimony ions is found to be 15 mM. In addition, the flow battery assembled with negative electrolyte containing antimony ions exhibits 31.2% higher power density than that of pristine DES electrolyte

Eliminating micro-porous layer from gas diffusion electrode for use in high temperature polymer electrolyte membrane fuel cell

In this work, we report a simple strategy to improve the performance of high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) by eliminating the micro-porous layer (MPL) from its gas diffusion electrodes (GDEs). Due to the absence of liquid water and the general use of high amount of catalyst, the MPL in a HT-PEMFC system works limitedly. Contrarily, the elimination of the MPL leads to an interlaced micropore/macropore composited structure in the catalyst layer (CL), which favors gas transport and catalyst utilization, resulting in a greatly improved single cell performance. At the normal working voltage (0.6 V), the current density of the GDE eliminated MPL reaches 0.29 A cm2 , and a maximum power density of 0.54 W cm2 at 0.36 V is obtained, which are comparable to the best results yet reported for the HT-PEMFCs with similar Pt loading and operated using air. Furthermore, the MPLfree GDE maintains an excellent durability during a preliminary 1400 h HT-PEMFC operation, owing to its structure advantages, indicating the feasibility of this electrode for practical applications

Optimization of gas diffusion electrode for polybenzimidazole-based high temperature proton exchange membrane fuel cell: Evaluation of polymer binders in catalyst layer

Gas diffusion electrodes (GDEs) prepared with various polymer binders in their catalyst layers (CLs) were investigated to optimize the performance of phosphoric acid doped polybenzimidazole (PBI)-based high temperature proton exchange membrane fuel cells (HT-PEMFCs). The properties of these binders in the CLs were evaluated by structure characterization, electrochemical analysis, single cell polarization and durability test. The results showed that polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF) are more attractive as CL binders than conventional PBI or Nafion binder. At ambient pressure and 160 o C, the maximum power density can reach w 0.61 W cm-2 (PTFE GDE), and the current density at 0.6 V is up to ca. 0.52 A cm-2 (PVDF GDE), with H2/air and a platinum loading of 0.5 mg cm-2 on these electrodes. Also, both GDEs showed good stability for fuel cell operation in a short term durability test.Web of Scienc

Natural wood derived robust carbon sheets with perpendicular channels as gas diffusion layers in air-breathing proton exchange membrane fuel cells (PEMFCs)

Abstract Herein, a novel natural wood derived macroporous carbon sheet with three-dimension inter-connected perpendicular-channels was engineered as gas diffusion layers (w-GDLs) for air-breathing proton exchange membrane fuel cells (PEMFCs). Beneficial to the unique accessible perpendicular channels and the presence of a microporous layer, the current density reached 0.139 A/cm2 (at 0.6 V) and the maximum power density elevated up to 0.102 W/cm2 (at 0.43 V), which are comparable to the best results reported for the air-breathing PEMFCs with high Pt loadings. Furthermore, it exhibited excellent durability during preliminary constant discharge operation, demonstrating the feasibility of this w-GDL for practical applications

Eliminating micro-porous layer from gas diffusion electrode for use in high temperature polymer electrolyte membrane fuel cell

© 2016 Elsevier B.V. In this work, we report a simple strategy to improve the performance of high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) by eliminating the micro-porous layer (MPL) from its gas diffusion electrodes (GDEs). Due to the absence of liquid water and the general use of high amount of catalyst, the MPL in a HT-PEMFC system works limitedly. Contrarily, the elimination of the MPL leads to an interlaced micropore/macropore composited structure in the catalyst layer (CL), which favors gas transport and catalyst utilization, resulting in a greatly improved single cell performance. At the normal working voltage (0.6 V), the current density of the GDE eliminated MPL reaches 0.29 A cm−2, and a maximum power density of 0.54 W cm−2 at 0.36 V is obtained, which are comparable to the best results yet reported for the HT-PEMFCs with similar Pt loading and operated using air. Furthermore, the MPL-free GDE maintains an excellent durability during a preliminary 1400 h HT-PEMFC operation, owing to its structure advantages, indicating the feasibility of this electrode for practical applications

Thermal conductivity and temperature profiles of the micro porous layers used for the polymer electrolyte membrane fuel cell

The thermal conductivity and the thickness change with pressure of several different micro porous layers (MPL) used for the polymer electrolyte membrane fuel cell (PEMFC) were measured. The MPL were made with different compositions of carbon and polytetrafluoroethylene (PTFE). A one-dimensional thermal PEMFC model was used to estimate the impact that the MPL has on the temperature profiles though the PEMFC. The thermal conductivity was found to vary from as low as 0.05 up to as high as 0.12 W K 1 m 1 while the compaction pressure was varied from 4 bar and up to around 16 bar resulting in a decrease in thickness of approximately 40%. The PTFE content, which varied between 10 and 25%, did not result in any significant change in the compression or thermal conductivity. Both the thickness and the thermal conductivity changed irreversibly with compaction pressure. Considering a MPL thermal conductivity of 0.1 W K 1 m 1, a MPL thickness of 45 mm, a current density of 10 kAm 2 (1.0 A cm 2), liquid water (production and sorption), and a 30 mm membrane it was found that the MPL is responsible for a temperature increase of up to 2 C. This contribution can be lowered by integrating the MPL into the porous transport layer.Web of Scienc

Investigation of Synthesis Methods for Improved Platinum-Ruthenium Nanoparticles Supported on Multi-Walled Carbon Nanotube Electrocatalysts for Direct Methanol Fuel Cells

This book chapter reports on various catalyst synthesis methods (impregnation, polyol, modified polyol, and microwave-assisted modified polyol methods) to determine which method would result in the most electrochemically active platinum-ruthenium (PtRu) electrocatalyst supported on multi-walled carbon nanotubes (MWCNTs) for methanol oxidation reaction in an acidic medium. Different techniques were used to characterize the synthesized catalysts, including the high-resolution transmission electron microscope used for morphology and calculating particle sizes, and X-ray diffraction for determining crystalline sizes. The electroactive catalyst surface area, ECSA of the electrocatalysts was determined using cyclic voltammetry (CV), while the electroactivity, electron kinetics, and stability of the electrocatalysts towards methanol oxidation were evaluated using CV, electrochemical impedance spectroscopy, and chronoamperometry, respectively. The microwave-assisted modified polyol method produced the PtRu/MWCNT electrocatalyst with the most enhanced electrocatalytic activity compared to other PtRu/MWCNT catalysts produced by the impregnation, polyol, and modified polyol methods

Electrochemical Investigation of Heat Treated PtRu Nanoparticles Prepared by Modified Polyol Method for Direct Methanol Fuel Cell Application

In this work, heat-treated PtRu metal alloys based on multi-walled carbon nanotubes (MWCNT) were synthesized using modified polyol approach for methanol oxidation reaction (MOR) in acidic conditions at 2500, 3500, and 4500 C. The catalysts physical and electrochemical properties were investigated. The High Resolution Transmission Electron Microscopy (HR-TEM) was used to determine the shape, particle size, and particle size distribution of the catalysts, where spherical and agglomerated PtRu nanoparticles with narrow particle size distribution were observed with particle sizes ranging from 0.600 to 1.005 nm. Their crystalline sizes were assessed using the XRD with catalysts presenting a face-centered crystal structure, which is typical of platinum structures with crystalline sizes ranging from 0.500 to 1.180 nm. Energy-Dispersive Spectroscopy, (EDS), was used to identify the elements. Cyclic voltammetry (CV) was used to determine the electroactive surface area (ECSA) and MOR of the electrocatalysts, whereas electrochemical impedance spectrometry (EIS) and chronoamperometry (CA) were used to study their electro-kinetics and stability towards MOR, respectively. PtRu/MWCNT electrocatalysts alloyed at 450°C showed better electroactivity and kinetics as compared to other catalysts, evident from the highest current density of 19.872 mA/cm2 and lowest charge transfer resistance of 0.151 kΩ from CA and EIS, respectively

Membrane electrode assemblies with low noble metal loadings for hydrogen production from solid polymer electrolyte water electrolysis

High performance membrane electrode assemblies (MEAs) with low noble metal loadings (NMLs) were developed for solid polymer electrolyte (SPE) water electrolysis. The electro- chemical and physical characterization of the MEAs was performed by IeV curves, elec- trochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). Even though the total NML was lowered to 0.38 mg cm-2, it still reached a high performance of 1.633 V at 2 A cm-2 and 80 o C, with IrO2 as anode catalyst. The influences of the ionomer content in the anode catalyst layer (CL) and the cell temperature were investigated with the purpose of optimizing the performance. SEM and EIS measurements revealed that the MEA with low NML has very thin porous cathode and anode CLs that get intimate contact with the electrolyte membrane, which makes a reduced mass transport limitation and lower ohmic resistance of the MEA. A short-term water electrolysis operation at 1 A cm-2 showed that the MEA has good stability: the cell voltage maintained at ~1.60 V without distinct degradation after 122 h operation at 80 o C and atmospheric pressure.Web of Scienc