MnO x /C and Me-MnO x /C (Me ) Ni, Mg) electrocatalysts prepared by chemical deposition of manganese oxide nanoparticles on carbon have been characterized by Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), and chemical analysis. Their Oxygen Reduction Reaction (ORR) kinetics and mechanism have been investigated in alkaline KOH solutions by using the Rotating Disk Electrode (RDE) and the Rotating Ring-Disk Electrode (RRDE) setups. Doping the MnO x /C nanoparticles with nickel or magnesium divalent cations can considerably improve their oxygen reduction activity. As a result, the Me-MnO x /C electrocatalysts exhibit ORR specific or mass activities close to the benchmark 10 wt % Pt/C from E-TEK. At low ORR current densities, the undoped MnO x /C electrocatalyst displays a reaction order with respect to P O 2 and OHof 1 and -0.5, respectively, while ∂E/∂log i is ca. -59 mV dec -1 . The ORR reaction order toward OHis unchanged with the magnesium doping, while it becomes -2 with the nickel doping. RRDE data show that doping the MnO x /C electrocatalysts directs the ORR toward the four-electron pathway. The first electrochemical step of the 4-electron ORR mechanism is probably the quasiequilibrium proton insertion process into MnO 2 leading to MnOOH, while the second electron transfer, consisting of the O 2,ads species electrosplitting, yielding O ads and hydroxide anion, is rate determining. The presence of the doping metal cations may stabilize the intermediate Mn III /Mn IV species, which assist this second charge transfer to oxygen adatoms. As a result, the ORR rate is enhanced for the Me-MnO x /C electrocatalysts: they exhibit remarkable ORR catalytic activity and yield quantitative formation of OH -(selectivity toward the 4-electron pathway).

Energy accumulation and storage is one of the most important topics in our times. This paper presents the topic of supercapacitors (SC) as energy storage devices. Supercapacitors represent the alternative to common electrochemical batteries, mainly to widely spread lithium-ion batteries. By physical mechanism and operation principle, supercapacitors are closer to batteries than to capacitors. Their properties are somewhere between batteries and capacitors. They are able to quickly accommodate large amounts of energy (smaller than in the case of batteries-lower energy density from weight and volume point of view) and their charging response is slower than in the case of ceramic capacitors. The most common type of supercapacitors is electrical double layer capacitor (EDLC). Other types of supercapacitors are lithium-ion hybrid supercapacitors and pseudo-supercapacitors. The EDLC type is using a dielectric layer on the electrode-electrolyte interphase to storage of the energy. It uses an electrostatic mechanism of energy storage. The other two types of supercapacitors operate with electrochemical redox reactions and the energy is stored in chemical bonds of chemical materials. This paper provides a brief introduction to the supercapacitor field of knowledge.

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