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Doping is promising strategy for the alteration of nanomaterials to enhance their optical, electrical, and catalytic activities. The development of electrocatalysts for oxygen reduction reactions (ORR) with excellent activity, low cost and durability is essential for the large-scale utilization of energy storage devices such as batteries. In this study, MnO2 and Ni-doped MnO2 nanowires were prepared through a simple co-perception technique. The influence of nickel concentration on electrochemical performance was studied using linear sweep voltammetry and cyclic voltammetry. The morphological, thermal, structural, and optical properties  of MnO2 and Ni-doped MnO2 nanowires were examined by SEM, ICP-OES, FT-IR, XRD, UV–Vis, BET and TGA/DTA. Morphological analyses showed that pure MnO2 and Ni-doped MnO2 had flower-like and nanowire structures, respectively. The XRD study confirmed the phase transformation from ε to α and β phases of MnO2 due to the dopant. It was also noted from the XRD studies that the crystallite sizes of pure MnO2 and Ni-doped MnO2 were in the range of 2.25–6.6 nm. The band gaps of MnO2 and 0.125 M Ni-doped MnO2 nanoparticles were estimated to be 2.78 and 1.74 eV, correspondingly, which can be seen from UV–Vis. FTIR spectroscopy was used to determine the presence of functional groups and M–O bonds (M = Mn, Ni). The TGA/TDA examination showed that Ni-doping in MnO2 led to an improvement in its thermal properties. The cyclic voltammetry  results exhibited that Ni-doped MnO2 nanowires have remarkable catalytic performance for ORR in 0.1 M KOH alkaline conditions. This work contributes to the facile preparation of highly active and durable catalysts with improved catalytic performance mainly due to the predominance of nickel. Article Highlights MnO2 and Ni-doped MnO2 nanowires were synthesized via a facile co-perception approach. Nickel doping in MnO2 induces the formation of wire-like nanostructures. Nickel doping enhances the electrochemical activity and thermal stability of MnO2 nanoflowers. The addition of nickel into MnO2 promoted the catalytic activity for oxygen reduction reaction. A higher catalytic activity was achieved in 0.125 M Ni-MnO2 nanowires. Graphic abstract

Pure ZnO and Cr-doped ZnO nanoparticles have been synthesized via a facile chemical co-precipitation route and their structural, thermal characteristics were discussed systematically. In the experimental producer, the doping concentration has varied the range, 0.05–0.1 M, while calcined at 600 °C. The influence of Cr-doping on the physical characteristics of ZnO nanoparticles was investigated and addressed. As-prepared samples were analyzed via XRD, FTIR, TGA/DTA, BET, and ICP-MS. XRD analysis shows that ZnO and Cr doped ZnO nanoparticles with average particle sizes between 23 and 39 nm were successfully developed with hexagonal wurtzite structure. The FTIR spectroscopy analysis confirms the existence of chromium in the doped ZnO nanoparticles and the formation of ZnO. The TGA/DTA analysis shows that Cr–ZnO nanoparticles are more thermally stable than ZnO nanoparticles. Moreover, the dopant concentration has been analyzed via ICP-MS and showed a good agreement with the expected chromium concentration. The BET surface area measurement shows that 176.25 m2/g and 287.17 m2/g for un-doped ZnO, and 0.1 M Cr-doped ZnO nanoparticles, respectively. Hence, doping of Cr enhances the surface area and thermal stability. Thus, Cr–ZnO nanoparticles show good thermal stability, and high surface area, which is an excellent characteristices of nanomaterials. Graphic abstract

Co 3 O 4 /MnO 2 nanocomposites have been effectively synthesized via a coprecipitation route. The addition of Co 3 O 4 in MnO 2 led to a drastic change in the electrochemical properties. The electrochemical behaviors of Co 3 O 4 /MnO 2 nanocomposites have been investigated. The Co 3 O 4 /MnO 2 nanocomposite electrode exhibits high stabilities and high catalytic activities.

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