Hierarchical urchin-shaped α-MnO2 on graphene-coated carbon microfibers: a binder-free electrode for rechargeable aqueous Na–air battery

Abstract

With the increasing demand of cost-effective and high-energy devices, sodium-air (Na-air) batteries have attracted immense interest due to the natural abundance of sodium in contrast to lithium. In particular, an aqueous Na-air battery has fundamental advantage over non-aqueous batteries due to the formation of highly water-soluble discharge product, which improve the overall performance of the system in terms of energy density, cyclic stability and round-trip efficiency. Despite these advantages, the rechargeability of aqueous Na-air batteries has not yet been demonstrated when using non-precious metal catalysts. In this work, we rationally synthesized a binder-free and robust electrode by directly growing urchin-shaped MnO 2 nanowires on porous reduced graphene oxide-coated carbon microfiber (MGC) mats and fabricated an aqueous Na-air cell using the MGC as an air electrode to demonstrate the rechargeability of an aqueous Na-air battery. The fabricated aqueous Na-air cell exhibited excellent rechargeability and rate capability with a low overpotential gap (0.7 V) and high round-trip efficiency (81%). We believe that our approach opens a new avenue for synthesizing robust and binder-free electrodes that can be utilized to build not only metal-air batteries but also other energy systems such as supercapacitors, metal-ion batteries and fuel cells.

Carambola-shaped VO2 nanostructures: a binder-free air electrode for an aqueous Na–air battery

“…The electrocatalytic activities of the VGC, Pt/C and RuO 2 catalysts were investigated using a rotating ring-disk electrode (RRDE) in 0.1 M NaOH with IviumStat. The electron transfer number (n) was calculated by the following equation 13 :…”

“…Bare carbon-paper Raman spectra show two low-intensity bands at Figure S3b), which is in agreement with the observations reported in the literature. 13 The I D /I D′ band ratio also gives an information on the type of defect in coated rGO. 32 In our case, I D /I D′ ratio was calculated to be 3.17 which is due to the boundary or edge defect in rGO.…”

“…In addition, rGO was coated on the carbon paper to improve the conductivity of the system 21,22 and wettability of electrode. 13 The fabricated Naair battery with VGC air electrode displays 0.64 V overpotential gap, 81% round trip efficiency, 2.81 V terminated discharge potential, 104 mW g -1 power density at 80 mA g -1 current density, and good cyclic stability up to 50 cycles. We believe that our strategy can be used to fabricate cost-effective, large-scale and binder-free electrodes for high-performance aqueous Na-air batteries.…”

“…This behavior enables full cell discharge, resulting in enhancement of the cell performance. 13 Furthermore, the solubility of the discharged product (sodium hydroxide) in a Na-air battery with an aqueous electrolyte is higher than that of lithium hydroxide (produced in aqueous LABs), which helps to improve cyclic stability of aqueous Naair batteries. 11 However, despite various advantages of aqueous Na-air batteries, there has not been in-depth study to explore and realize new air electrode materials for costeffective high-energy devices.…”

Facile Synthesis of Single‐ and Multi‐Layer Graphene/Mn3O4 Integrated 3D Urchin‐Shaped Hybrid Composite Electrodes by Core‐Shell Electrospinning

“…In the both electrodes, the urchin-shaped structure of PANI acted as an effective pathways for the movement of electrolyte ions towards inside the electrode. [33] Higher specific capacitance value of GNP-based hybrid compared to TEGO-based electrode arises from higher content of GNP in the structure which facilitates the ion transfer to the inner layers of the electrode structure to generate electrochemical double layers between PANI and graphene layers by improving both electrode-electrolyte interactions and interfacial interactions between all components in the structure and shorten the diffusion lengths of ions. [24] The galvanostatic charge-discharge test (GCD) was performed to further evaluate the electrochemical performance of fabricated electrodes.…”