Hydrous manganese oxide with promising pseudocapacitive behavior was deposited on a carbon substrate at anodic potentials of 0.5-0.95 V vs. saturated calomel electrode ͑SCE͒ in 0.25 M Mn(CH 3 COO) 2 solution at 25°C. The effects of the deposition potential on the material characteristics and electrochemical performances of the hydrous manganese oxide prepared were investigated. Porous manganese oxide with higher crystallinity was formed at a lower deposition potential. When the deposition potential was 0.8 V SCE or higher, the deposited oxide consisted of an inner layer with a laminated structure and a rough outer layer with nodules on the surface. X-ray photoelectron spectroscopy was also carried out to examine the chemical state of the deposited oxide. Analytical results indicated that the oxide was composed of both trivalent and tetravalent manganese oxides at a deposition potential of 0.5 V SCE. However, the tetravalent manganese oxide became the dominant species in the film deposited at above 0.65 V SCE. The manganese oxide formed at 0.5 V SCE exhibited a specific capacitance as high as 240 F/g, as evaluated by cyclic voltammetry ͑CV͒ with a potential scan rate of 5 mV/s in 2 M KCl at 25°C. Increasing the CV scan rate reduced the specific capacitance. Only about 70% of the capacitance at 5 mV/s could be maintained when the CV scan rate was increased to 100 mV/s, for all the manganese oxide electrodes prepared. Moreover, a high deposition potential gave rise to a low specific capacitance of the manganese oxide formed.

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With the aid of supercritical carbon dioxide (scCO 2 ), which has gas-like diffusivity, extremely low viscosity, and near-zero surface tension, highly dispersed Pd nanoparticles (NPs) can be directly synthesized on carbon nanotubes (CNTs). Due to the excellent wettability between scCO 2 and the carbon surface, the deposited Pd NPs are uniformly distributed and tightly anchored on CNTs, which do not require pretreatment. The decoration density of NPs on carbon can be easily regulated by adjusting the Pd(hfa) 2 precursor to CNT ratio, with the particle size of Pd remaining almost constant (no significant crystal growth or aggregation occur). The prepared Pd NPs on CNTs show excellent activity toward hydrogen spillover as compared to those fabricated using conventional processes. With the superior utilization of NPs, a smaller amount of Pd is required, reducing both costs and environmental impact. The proposed scCO 2 -assisted protocol for constructing NP/carbon nanostructures is effective, versatile, and potentially scalable, making it useful for further exploitation in a variety of applications.

A metallic aluminum ͑Al͒ layer was successfully electrodeposited onto a magnesium ͑Mg͒ alloy in a Lewis acidic aluminum chloride-1-ethyl-3-methylimidazolium chloride ͑AlCl 3 -EMIC͒ ionic liquid under a galvanostatic condition at room temperature. Effects of deposition current density on material characteristics of the deposited layers were explored by means of a scanning electron microscope and an X-ray diffractometer. In addition, the improvement in corrosion resistance of the Mg alloy due to the Al coating was evaluated by electrochemical measurements and a salt spray test. The electrochemical impedance spectroscopic data indicated that a bare Mg alloy had a polarization resistance of only 470 ⍀ cm 2 in 3.5 wt % NaCl solution, whereas the Al-coated Mg sample showed its resistance as high as 8700 ⍀ cm 2 in the same environment. Moreover, it was also found that the Al layer deposited at a lower current density was more compact and uniform when compared to that deposited at a higher current density; consequently, this coating revealed a superior protection capability for the Mg substrate against corrosion.

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Iron addition was attempted in this study to improve the pseudo-capacitive property of Mn oxides. The oxides were prepared on graphite substrates by anodic deposition. The deposition solutions were 0.25 M manganese acetate ͓Mn͑CH 3 COO͒ 2 ͔ aqueous solutions with various amount of FeCl 3 ͑up to 0.15 M͒. Crystal structure and surface morphology of the deposited oxides were examined by X-ray diffraction and scanning electron microscopy, while their chemical state was analyzed by X-ray photoelectron spectroscopy and X-ray absorption near edge structure. Moreover, specific capacitances of the oxide electrodes were determined by cyclic voltammetry in 2 M KCl electrolyte. Experimental results indicated that the incorporated iron presented as divalent and trivalent forms in the binary oxides. Although iron addition did not change the nanocrystalline structure of the deposited Mn oxide, it caused the chemical state and surface morphology variations of the oxide electrodes. Consequently, their pseudo-capacitive performances were modified. The optimum specific capacitance of 212 F g −1 was found for the oxide deposited in the solution containing 0.05 M FeCl 3. The value was 21% higher than that of the plain Mn oxide. Capacitance-retained ratio of the oxide after 1000 charge-discharge cycles was also improved from 70 to 85% because of iron addition.

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