In-situ fabrication of carbon-metal fabrics as freestanding electrodes for high-performance flexible energy storage devices

Abstract

1D carbon structures are attractive due to their mechanical, chemical and electrochemical properties. Further enhancements to these structures can be made by creating structural hierarchy, producing composites with catalytically active metal nanoparticle domains -however the synthesis of these materials can be costly and complicated. Here, through the combination of inexpensive acetylacetonate salts of Ni, Co and Fe with a solution of polyacrylonitrile (PAN) which was electrospun and subsequently heat treated, self-assembling carbon-metal fabrics (CMFs) containing unique 1D hierarchical structures can be created readily. Microscopic and spectroscopic measurements show that the CMFs form through the decomposition and exsolution of metal nanoparticle domains which then catalyse the formation of carbon nanotubes through the decomposition by-products of the PAN. These weakly bound nanoparticles form structures similar to trichomes found in plants, with a combination of base-growth, tip-growth and peapod-like structures, where the metal domain exhibits a core(graphitic)-shell(disorder) 2 carbon coating where the thickness is in-line with the metal-carbon binding energy. The applicability of these carbon-metal fabrics (CMFs) was demonstrated as a cathode in an allsolid-state zinc-air battery which exhibited superior performance to pure electrospun carbon fibres, in addition to enhanced mechanical flexibility due to the enhanced surface area of the hairy fibres and their metallic nanoparticle domains which acted as bifunctional catalysts to oxygen reduction and evolution. This work therefore unlocks a potentially new category of composite metal-carbon fibre based structures for energy storage applications and beyond, which can be created in a low cost manner.

Trichome-like Carbon-Metal Fabrics Made of Carbon Microfibers, Carbon Nanotubes, and Fe-Based Nanoparticles as Electrodes for Regenerative Hydrogen/Vanadium Flow Cells

“…This is not due to electrode degradation but most likely due to electrolyte management issues such as water evaporation and/or crossover of vanadium electrolyte to the hydrogen-side half-cell. Such an improved electrolyte utilization for CMF_ELAT (∼90%), first originates from the catalytic activity of CMFs that provide surfaces enriched with nitrogenous (N 2 ) groups, which are active toward vanadium redox chemistries, and the presence of N 2 groups was previously shown via XPS and electrochemical characterization (the iron acetylacetonate and polyacrylonitrile used to process CMFs via electrospinning and pyrolysis, which produced such N 2 groups), 23 which is also in line with other reports. 24,25 Second, the trichome-like CNTs on the fibers facilitate efficient surface charge transfer and reduce polarization due to mass transfer (Figure 1h).…”

“…The presence of Fe-based nanoparticles on both trichome-like CNTs and carbon microfibers is confirmed by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM−EDS) chemical mapping as given in the Supporting Information (Figure S2). In brief, these CMFs were prepared by mixing iron acetylacetonate and PAN in N,N′-dimethylformamide (DMF), and the resulting solution was electrospun, followed by pyrolysis at 850 °C, as reported by Liu et al, 23 where the decomposition of iron acetylacetonate produced Febased nanoparticles, which then catalyzed the growth of CNTs on carbon microfibers as shown in Figures 1b,c,f and S2. These have also been extensively characterized in terms of their morphology via transmission electron microscopy and exploited in zinc/air batteries, 23 where the Fe-based nanoparticles were found to be embedded in carbon microfibers as well as at the tips of CNTs, while XPS indicated the presence of nitrogenous groups.…”

“…The presence of Fe-based nanoparticles on both trichome-like CNTs and carbon microfibers is confirmed by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM–EDS) chemical mapping as given in the Supporting Information (Figure S2). In brief, these CMFs were prepared by mixing iron acetylacetonate and PAN in N , N ′-dimethylformamide (DMF), and the resulting solution was electrospun, followed by pyrolysis at 850 °C, as reported by Liu et al, where the decomposition of iron acetylacetonate produced Fe-based nanoparticles, which then catalyzed the growth of CNTs on carbon microfibers as shown in Figures b,c,f and S2. These have also been extensively characterized in terms of their morphology via transmission electron microscopy and exploited in zinc/air batteries, where the Fe-based nanoparticles were found to be embedded in carbon microfibers as well as at the tips of CNTs, while XPS indicated the presence of nitrogenous groups.…”

“…On completion of the heat treatment, the growth of carbon nanotubes with metal nanoparticles on the electrospun microfibers can be observed, producing trichome-like carbon nanofibers or carbon-metal fabric (CMF). 23 Surface Microstructural Analyses. The surface morphology of the CMF samples was observed by a scanning electron microscope (Zeiss Leo Gemini 1525), using an in-lens detector and a 5 kV accelerating voltage.…”

Understanding of Neighboring Fe‐N4‐C and Co‐N4‐C Dual Active Centers for Oxygen Reduction Reaction

“…Moreover, the flexible Al-air battery is able to be bended at different angles (Figure S24, Supporting Information) and the solid-state Al-air battery with FeCo-N-HCN cathode could power the working small fan (Figure S25, Supporting Information). [65][66][67] Therefore, the flexible solid-state Al-air battery holds great potential in the application of flexible wearable electronic devices.…”