Preparation and electrode properties of novel redoxable nanosheets of Mn–Ni oxide with and without vacancy defects

Abstract

As potential cathode materials for thin-film energy storage devices, MnNi oxide nanosheets with the chemical composition H 0.46 Mn 0.81 Ni 0.19 O 2 (M81N19) were prepared. Upon restacking in HNO 3 aqueous solution and re-exfoliation, the MnNi oxide nanosheets produced the novel H 0.58 Mn 0.81 Ni 0.13 O 2 (M81N13) nanosheets with vacancy defects. The chemical composition of the nanosheets was characterized using X-ray absorption spectroscopy, inductively coupled plasma atomic emission spectroscopy, and thermogravimetry. The sizes of the M81N19 and M81N13 nanosheets were compared, and no structural change was observed after Ni dissolution from the nanosheets. The optical properties, the local structure and the electrochemical properties when used as cathodes in Li-ion batteries of the M81N19 and M81N13 nanosheets, were compared.

Enhancement in the Charge-Transfer Kinetics of Pseudocapacitive Iridium-Doped Layered Manganese Oxide

“…The x = 0.20 analogue, K y Mn 0.8 Ir 0.2 O 2 , could not be synthesized as a single phase under the same synthetic conditions. It is noted that while birnessite manganese oxide substituted with Co, Mo, Ru, and so forth has been reported, − this is the first successful synthesis of Ir-substituted birnessite manganese oxide.…”

“…Manganates are poorly conductive; thus, the specific capacitance is strongly dependent on the electrode thickness; extremely thin films show specific capacitance as high as ∼1000 F g –1 , , while films with practical mass loadings show moderate values, that is, ∼200 F g –1 . , While conductive additives such as acetylene black are added to the electrode to assist the conduction of electrons, the conductivity of manganese oxide can also be improved by doping with other metals. Doping birnessite with other transition metals such as Co, Mo, Ru, and so forth is an effective method to increase the electronic conductivity and leads to an increase in capacitance. − For example, cobalt-doped birnessite electrodes prepared by electrodeposition exhibit a specific capacitance of 170 F g –1 at 2 mV s –1 , which is almost 3 times higher than that of the nondoped birnessite MnO 2 . Ruthenium-doped MnO 2 nanosheets synthesized by exfoliation of Ru-doped birnessite-type K x MnO 2 have also shown promising results, showing a 1.4 times increase in specific capacitance by 10 mol % doping with Ru …”

Structural Distortion in MnO2 Nanosheets and Its Suppression by Cobalt Substitution

“…Replotting the UV-Vis spectra in Tauc form allowed estimation of the direct allowed band gaps of C23M77NS and M100NS as 2.75 and 2.62 eV, respectively. We recently reported a direct allowed band gap of 2.66 eV for H 0.46 Mn 0.81 Ni 0.19 O 2 nanosheets in which the valence state of Mn is 3.9 [ 24 ]. The observed absorption bands here are due to the d-d transition of Mn 4+ , and any difference in the corresponding peak wavelength would be mainly caused by structural distortion of the MnO 6 octahedra, as further discussed below.…”

“…MnO 2 nanosheets have been reported to have a hexagonal CdI 2 -type structure [ 23 ], and density functional theory (DFT) calculations have been conducted using such a CdI 2 -type structure as the initial structure [ 18 ]. We recently reported that Mn–Ni oxide nanosheets have a distorted crystal structure due to the cooperative Jahn–Teller effect of Mn 3+ [ 24 ], which suggests the possibility that MnO 2 nanosheets also exhibit a distorted crystal structure. The results of DFT calculations are greatly affected by the crystal structure used, since fundamental information on the structures of these systems is important for rationalizing and eventually predicting their physical properties.…”

Elucidating the Active Sites and Synergies in Water Splitting on Manganese Oxide Nanosheets on Graphite Support

“…The MnO 2 NS consists of Mn-O 6 octahedral units connected by shared octahedral edges forming a highly anisotropic 2D layer with a thickness of approximately 0.7 nm and a typical lateral size in the micrometer range. [29,30] Thus, the loading of MnO 2 NS on HOPG forms a nearly ideal 2D model catalyst surface with broad terraces and NS step-edges with minimal height. [31] First, we present the increase in total electrochemical activity due to the presence of MnO 2 NS compared to pure HOPG using linear sweep voltammetry, illustrated in a Tafel plot.…”