Electrically Rearranged Birnessite-Type MnO₂by Repetitive Potential Steps and Its Pseudocapacitive Properties

Abstract

Nickel(II) ions-intercalated manganese dioxide (Ni/MnO 2 ) film with a layered structure on Pt electrode was subjected to repetitive steps between anodic (+0.8 V) and cathodic (0.0 V) potentials in different conditions. Current response during the repetitive steps varied drastically, depending on the number and duration of steps and the type of electrolyte. This behavior was accompanied by an irreversible morphological transformation of the MnO 2 film with retaining the layer structure itself. The potential steps with time durations of 10 and 10 s at +0.8 and 0.0 V, respectively, resulted in thick plates with micrometer-scale consisting of hierarchically clustered MnO 2 nanolayers. They were grown vertically to the surface of electrode. The structure thus formed exhibited much improved pseudocapacitive properties, resulting from intercalation/deintercalation of not only monovalent cations but also divalent cations. That is, the film had specific capacitances of 225 and 318 F g −1 at a scan rate of 2 mV s −1 in Na + -and Ca 2+ -containing electrolytes, respectively.

Highly Efficient K0.15MnO2 Birnessite Nanosheets for Stable Pseudocapacitive Cathodes

“…The highest specific capacitances of the K 0.15 MnO 2 /PEDOT electrode were 249 F/g (CV) and 303 F/g (CP) from half-cell measurements. These values are higher than or comparable to a variety of SC electrode materials that were measured under similar conditions, including Fe 3 O 4 /active carbon (38–90 F/g), graphene/MnO 2 -textile (∼300 F/g), Au-MnO 2 /carbon nanotubes (∼70 F/g), Li + , Na + , and K + intercalated δ-MnO 2 (140–160 F/g), δ-MnO 2 nanoplates (180–210 F/g), highly crystalline δ-MnO 2 powder (110–130 F/g), , poorly crystalline δ-MnO 2 nanostructures (∼250 F/g), a mixture of amorphous and crystalline MnO 2 nanoparticles (72–168 F/g), and Ni 2+ intercalated δ-MnO 2 (225 F/g) . The enhanced SC performance of MP nanomaterials relative to these materials (or to the baseline PC or P-only electrodes) can be attributed to a number of unique characteristics, including (i) the 2D layered architectures of K 0.15 MnO 2 that offered large electrochemically active surface areas and a reduced ion and charge diffusion length during charge/discharge processes and (ii) a conductive PEDOT coating that provided excellent interfacial contacts and highly conductive paths throughout the K 0.15 MnO 2 nanosheets for rapid electronic transport.…”

100k Cycles and Beyond: Extraordinary Cycle Stability for MnO2 Nanowires Imparted by a Gel Electrolyte

“…For electrode materials that rely on ion insertion for Faradaic charge storage, a nanowire morphology can enable higher power in either batteries or capacitors than is possible using a film of the same material. − However, the Achilles heal of such nanowires for energy storage is cycle stability. , The diminutive lateral dimension of nanowires increases their susceptibility to dissolution and corrosion, and these processes rapidly result in a loss of electrical continuity through the nanowire and an irreversible loss of capacity. In the specific case of MnO 2 an insertion metal oxide that is of interest herewe have recently reported the retention of C sp to 4000 cycles for symmetrical core@shell Au@MnO 2 all-nanowire capacitors operating at rapid voltage scan rates of 100 mV/s across a 1.2 V window in dry LiClO 4 , acetonitrile electrolytes. , Somewhat better cycle stability of up to 10 000 cycles has been reported for composites of Mn 3 O 4 nanorods and graphene.…”

Electrochemical Assembly of Ruthenium Complexes during the Multilayering Process of MnO2

“…This demonstrates that complex ions confined during immersion in water are not replaced by small Na + ions but remain immobilized in the interlayer. (4). This film is composed of wrinkled thin sheets.…”