Design of 3-Dimensional Hierarchical Architectures of Carbon and Highly Active Transition Metals (Fe, Co, Ni) as Bifunctional Oxygen Catalysts for Hybrid Lithium–Air Batteries

Abstract

Flexible power sources and efficient energy storage devices with high energy density are highly desired to power a future sustainable community. Theoretically, rechargeable metal−air batteries are promising candidates for the next-generation power sources. The rational design of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts with high catalytic activity is critical to the development of efficient and durable metal−air batteries. Herein, we propose a novel strategy to mass synthesize nonprecious transition-metal-based nitrogen/oxygen codoped carbon nanotubes (CNTs) grown on carbon-nanofiber films (MNO-CNT-CNFFs, M = Fe, Co, Ni) via a facile free-surface electrospinning technique followed by in situ growth carbonization. With a combination of the high catalytic activity of Fe-catalyzed CNTs and the efficient mass-transport characteristics of 3D carbon fiber films, the resultant flexible and robust FeNO-CNT-CNFFs exhibit the highest bifunctional oxygen catalytic activities in terms of a positive half-wave potential (0.87 V) for ORR and low overpotential (430 mV @ 10 mA cm −2 ) for OER. As proof-of-concept, newly designed hybrid Li−air batteries fabricated with FeNO-CNT-CNFFs as air electrode present high voltage (∼3.4 V), low overpotential (0.15 V), and long cycle life (over 120 h) in practical open-air tests, demonstrating the superiority of the freestanding catalysts and their promising potential for the applications in fuel cells and flexible energy storage devices.

Grown Carbon Nanotubes on Electrospun Carbon Nanofibers as a 3D Carbon Nanomaterial for High Energy Storage Performance

“…The growth of CNTs has confirmed via the observation of the peak at 26 ° in the XRD pattern of the 3D Co‐NS/CNTs‐carbon fibers, which indexes to the crystalline plane (002). This result also covenants with the literature ,…”

“…Furthermore, increase the pyrolysis temperature decreased the defect level in carbon structure. In disagreement with references, Ji et al . decided that 700 °C is too low to growth CNTs, where CNTs were not observed after pyrolyzed at 700 °C and long CNTs detected at 900 °C.…”

“…This result was confirmed by Chen et al, the intensity ratio of hybrid 1D CNTs/CNFs is higher than pore CNFs that verified the high graphite of the structure. The relative I D /I G of 3D FeNO‐CNTs/CNFs calcined at 900 °C is 1.139, which indicating the defects in the graphite structure …”

“…Zeolitic Imidazolate Framework‐67 (ZIF‐67) converted to CNTs through further heating treatment under Ar/H 2 atmosphere . Hybrid 3D hierarchical FeNO doped CNTs grown on CFs synthesized via electrospun of polymer solution consisting PAN and cellulose acetate (CA) dissolved DMF . The decomposition of CA released oxygen gave the porous structure of CNFs, which provided a large specific surface area for reaction and growth CNTs.…”

Structure Design and Composition Engineering of Carbon‐Based Nanomaterials for Lithium Energy Storage

“…The integration of 1D carbon‐based nanomaterials into freestanding film or 3D hierarchical structure guarantees the high output production of electrode materials with superior mechanical strength and large surface area. Ramakrishna et al prepared N/O‐codoped CNTs/CF films via a facile free‐surface electrospinning technique . This flexible and robust structure combined high catalytic activity and efficient mass‐transport characteristics.…”