Investigation on the effect of catalyst on the electrochemical performance of carbon felt and graphite felt for vanadium flow batteries

The role of catalysts in vanadium flow batteries (VFBs) has been studied by introducing bismuth (Bi) nanoparticles on carbon felt (CF) and graphite felt (GF). The electrocatalytic activity and VFBs performance of CF and GF before and after modification with Bi nanoparticles are investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and VFB single cell charge-discharge test. The results show that CF exhibits the much higher electrocatalytic activity than GF, due to its higher amount of C-OH and quaternary nitrogen groups and more defect sites. Bi nanoparticles can effectively improve the electrocatalytic activity of CF and GF, especially GF, towards V2+/V3+ redox couple in VFBs. As a result, energy efficiency of a VFB with GF, electrodes can be improved significantly by modification with Bi due to the dramatically reduced electrochemical polarization. However, the energy efficiency of a VFB with CF electrodes rarely changes after introduction of Bi nanoparticles, due to the fact that dominant limitation in a VFB with CF electrodes is ohmic polarization, and the reduced charge transfer resistance is not enough to improve the performance of this VFB remarkably. Therefore, CF is a more suitable electrode material for commercialized VFBs due to its higher electrocatalytic activity and lower cost. (C) 2015 Elsevier B.V. All rights reserved

A hierarchical porous electrode using a micron-sized honeycomb-like carbon material for high capacity lithium-oxygen batteries

A micron-sized honeycomb-like carbon material (MHC) is prepared in a facile way using nano-CaCO3 as a hard template. A novel electrode for lithium-oxygen batteries is fabricated and displays a superior discharge capacity as high as 5862 mA h g(-1). The higher electrode space utilization is attributed to its hierarchical pore structure, with intrinsic mesopores in the MHC particles for Li2O2 depositions and macropores among them for oxygen transport

Iridium incorporated into deoxygenated hierarchical graphene as a high-performance cathode for rechargeable Li-O-2 batteries

A novel Li-O-2 cathode was designed with a nanocrystal iridium catalyst functionalized on the purposely deoxygenated surfaces of hierarchical graphene. Due to the synergistic effect between the ORR/OER activity and deoxygenated porous supporter, this cathode exhibited excellent battery performance, cycling 150 times with a limited capacity of 1000 mA h g(-1) at a current density of 2000 mA g(-1)

Free-Standing Thin Webs of Activated Carbon Nanofibers by Electrospinning for Rechargeable Li-O-2 Batteries

Free-standing activated carbon nanofibers (ACNF) were prepared through electrospinning combining with CO2 activation and then used for nonaqueous Li-O-2 battery cathodes. As-prepared ACNF based cathode was loosely packed with carbon nanofibers complicatedly overlapped. Owing to some micrometer-sized pores between individual nanofibers, relatively high permeability of O-2 across the cathode becomes feasible. Meanwhile, the mesopores introduced by CO2 activation act as additional nucleation sites for Li2O2 formation, leading to an increase in the density of Li2O2 particles along with a size decrease of the individual particles, and therefore, flake-like Li2O2 are preferentially formed. In addition, the free-standing structure of ACNF cathode eliminates the side reactions about PVDF. As a result, the Li-O-2 batteries with ACNF cathodes showed increased discharge capacities, reduced overpotentials, and longer cycle life in the case of full discharge and charge operation. This provides a novel pathway for the design of cathodes for Li-O-2 battery

Nitrogen enriched mesoporous carbon as a high capacity cathode in lithium-oxygen batteries

Nitrogen enriched mesoporous carbon (N-MCS) with extremely high mesopore volume and nitrogen content is prepared through a one-step hard template method. The N-MCS cathode shows excellent discharge performance in lithium-oxygen batteries. The pore space is better utilized due to its optimized pore structure and uniformly incorporated N

Hierarchical Micron-Sized Mesoporous/Macroporous Graphene with Well-Tuned Surface Oxygen Chemistry for High Capacity and Cycling Stability Li–O₂ Battery

Nonaqueous Li–O₂ battery is recognized as one of the most promising energy storage devices for electric vehicles due to its super-high energy density. At present, carbon or catalyst-supporting carbon materials are widely used for cathode materials of Li–O₂ battery. However, the unique electrode reaction and complex side reactions lead to numerous hurdles that have to be overcome. The pore blocking caused by the solid products and the byproducts generated from the side reactions severely limit the capacity performance and cycling stability. Thus, there is a great need to develop carbon materials with optimized pore structure and tunable surface chemistry to meet the special requirement of Li–O₂ battery. Here, we propose a strategy of vacuum-promoted thermal expansion to fabricate one micron-sized graphene matrix with a hierarchical meso-/macroporous structure, combining with a following deoxygenation treatment to adjust the surface chemistry by reducing the amount of oxygen and selectively removing partial unstable groups. The as-made graphene demonstrates dramatically tailored pore characteristics and a well-tuned surface chemical environment. When applied in Li–O₂ battery as cathode, it exhibits an outstanding capacity up to 19 800 mA h g^–1 and is capable of enduring over 50 cycles with a curtaining capacity of 1000 mA h g^–1 at a current density of 1000 mA g^–1. This will provide a novel pathway for the design of cathodes for Li–O₂ battery