Pathways towards high performance Na–O₂ batteries: tailoring graphene aerogel cathode porosity & nanostructure

Abstract

Fundamental understanding of the physical phenomena and electrochemical reactions occurring in metalair batteries is critical for developing rational approaches towards high-performing Na-O 2 battery cathodes. In this context, air cathode porosity plays a key role in battery performance, influencing oxygen supply and hence oxygen reduction and evolution reaction kinetics (ORR/OER). Graphene-based aerogels offer great versatility as air-cathodes due to their low density, high electronic conductivity and adjustable porosity. Reduced graphene aerogels with different porosities are examined where high meso-macroporosity and a narrow macropore size arrangement exhibit the best electrode performance among all studied materials (6.61 mA h cm À2 ). This is ascribed to the particular macroporous 3D structure of graphene-based electrodes, which favours the diffusion of oxygen to the defect sites in graphene sheets. An outstanding cycle life is achieved by using the pore-tuned cathode, leading to 39 cycles (486 h) at 0.5 mA h cm À2 with very low overpotential (250 mV) and efficiency over 95%. The cyclability is further increased to 745 h (128 cycles) by decreasing the capacity cut-off. This study shows that tuning of material porosity opens a new avenue of research for achieving Na-O 2 batteries with high performance by maximizing the effective area of the electrodes for the ORR/OER. Fig. 1 SEM images of the rGO (a) film and aerogels, (b) ArGO_U and (c) ArGO_N. (Inset a) Cross-sectional SEM image of rGO film.Scheme 1 Schematic illustration of the proposed mechanism as a function of the different 2D and 3D arrangements of GSs on the graphenederived cathodes.This journal is

In situ assembly of MnO2 nanosheets on sulfur-embedded multichannel carbon nanofiber composites as cathodes for lithium-sulfur batteries

“…5c. The isotherm of CNF presents a typical type-IV (IUPAC 1985) behavior with a H3-type hysteresis loop at relative pressure P/P 0 from 0.45 to 1.0, indicating the existence of narrow channel and meso/macropores, which agrees well with the TEM results [33,34] , indicating the sulfur almost completely penetrates into the porous structure of the CNF during the melt-diffusion process. As the MnO 2 content increases, the specific surface area of CNF@S/ MnO 2 -1, CNF@S/MnO 2 -2 and CNF@S/MnO 2 -3 increases from 88, 140 to 186 m 2 g −1 , respectively.…”

Controlling the Three‐Phase Boundary in Na–Oxygen Batteries: The Synergy of Carbon Nanofibers and Ionic Liquid

“…The peak at À20 ppm could also be relatedt oN aO 2 .P revious publications by Liu et al [35] and Enterríae tal. [9] assign NMR peaks corresponding to NaO 2 at À27 and À25 ppm, respectively.T hese differences can be attributed to different electrolytes being used in the studies, which werep erformed by using glyme-based electrolytes, whereas the presentw ork focuses on ionic liquid-based electrolytes so thatt he 23 Na environmentsmay be different in the two cases.…”

“…), the surface area is not the only factor that influences the overall battery performance but also the pore size and the electrode composition must be considered. [6][7][8][9] For instance, Chervin et al [6] studied the influence of the pore size on Li-oxygen batteries based on af ree-standing, carbon binder-free nanofoam cathode,a nd demonstrated that, althought he macroporous nanofoam hadl ower specifics urface area, it achieved higher discharge capacity than the mesoporousnanofoams.…”

Aqueous Cathodic Exfoliation Strategy toward Solution-Processable and Phase-Preserved MoS2 Nanosheets for Energy Storage and Catalytic Applications

“…10,11 For example, with a view to its use as a cathode in M-O2 batteries, processing graphene into suitable three-dimensional porous architectures having well-interconnected nanosheets is expected to be advantageous, since an efficient electron transport, an unimpeded access of ions and gas molecules as well as a proper accommodation of the discharge products throughout the electrode can be simultaneously attained with such architectures. 4,12 These requirements can in principle be met by using graphene foams or aerogels obtained by chemical vapor deposition (CVD) techniques that employ metal (e.g., Ni) foams acting both as a catalyst and template. 4,13,14 Unfortunately, the high temperatures and controlled synthesis atmospheres usually associated to such techniques, together with the need to remove the metal template after the synthesis step, make the CVD approach expensive and difficult to scale up.…”