The reversible deposition-dissolution reactions of zinc in several “water-in-salt” (WIS)-based electrolytes were monitored and compared using an electrochemical quartz microbalance (EQCM). These WIS electrolytes, irrespective of composition, promote reversible zinc deposition with high Coulombic efficiency. The mass change on the electrode, the local viscosity, and the change in the water content differ among electrolyte compositions, possibly because of phase separation to a solid zinc salt-water precipitate induced by the local concentration change of electrolyte during zinc dissolution.

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The dependence of the impedances of lithium phosphorous oxynitride (LiPON) thin film and solid electrolyte interphase (SEI) formed by decomposition of some electrolytes on the electrode potential was investigated by electrochemical impedance spectroscopy. A LiPON thin film was prepared on a Ni electrode by radio frequency magnetron sputtering of Li₃PO₄ under nitrogen atmosphere. The resistance of the LiPON thin film decreased with lowering the electrode potential in an ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing 1 M LiTFSA. The similar potential dependence of the impedance of the SEI formed in 1 M LiTFSA/BMPTFSA was observed, suggesting that the Li⁺ carrier density in the LiPON thin film and SEI increased with lowering the electrode potential probably due to the doping of Li⁺ from the electrolyte into the thin Li⁺ conductors in order to compensate the negative charge on the electrode. On the other hand, the potential dependence of the SEI formed in LiTFSA-tetraglyme (G4) solvate ionic liquid was insignificant because of the high concentration of Li⁺ in the SEI and electrolyte. The resistance of the SEI formed in 1 M LiClO₄/EC (ethylene carbonate) + DMC (dimethyl carbonate) (1 : 1 vol%) did not depend on the electrode potential, suggesting the thin and highly Li⁺ conductive SEI is formed in the organic electrolyte.

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Mg plating/stripping reaction in Mg[N(CF₃SO₂)₂]₂/glyme based solution is studied by electrochemical quartz crystal microbalance method. During the cyclic voltammetry, the apparent mass decrease is observed in spite of the negative scan. The irregular response also appears in the Mg plating reaction with low constant current density apply. In the cases, Mg plating takes place locally and the size of each plating is relatively large of about 50 µm. The cross-sectional image of the plated Mg is tree-like structure, i.e., the large Mg crystal connects to the substrate with small contact area. From the results, we conclude that the specific Mg morphology causes the restoring force to the quartz substrate, resulting in the apparent mass decrease.

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For polymer electrolyte fuel cell cathodes, highly durable supports are required to prevent catalyst degradation in supports. In this study, as model Pt catalysts, 2–10 wt% Pt was deposited on Magnéli-phase niobium-doped macroporous Ti₄O₇ (Nb–Ti₄O₇) mounted on glassy carbon rods using the coaxial arc plasma deposition method. The morphologies of 2, 5, and 10 wt% Pt catalysts showed the hemisphere fine particles, islands with ca. 1.4 nm diameter and ca. 2.4 nm thickness, and films with ca. 3.3 nm thickness, respectively. During start/stop accelerated durability tests (ADTs) of 5000 cycles following the Fuel Cell Commercialization Conference of Japan protocol, Pt was slightly agglomerated; consequently, the morphologies of the 2, 5, and 10 wt% Pt catalysts were island-like with 3.5 nm thickness, chain bead-like with 4 nm thickness, and film-like with 4 nm thickness, respectively. This slight agglomeration led to good durability during the ADTs. Herein, the oxygen reduction reaction (ORR) mass activity (MA) values at 0.9 V vs. reversible hydrogen electrode (RHE) of the 2, 5, and 10 wt% Pt catalysts were 79, 60, and 36 A g_Pt^-1 after 5000 cycles ADT, respectively, which had declining ratios after 5000 cycles were 32 %, 17 %, and 0 %, respectively. The island-like and film-like Pt/Nb–Ti₄O₇ presented activity and durability comparable to a Pt/C catalyst, which was 42 A g_Pt^-1 (0.9 V vs. RHE) with a 12 % of declining ratio after the ADTs. The durability of the MA suggested that the different affinity caused by different crystal faces led to the slight agglomeration of 2, 5, and 10 wt%_Pt/Nb–Ti₄O₇ catalysts. These catalysts showed electrochemical surface areas (ECSAs) of 36, 27, and 29 m² g⁻¹ after the ADTs, with declining ratios as low as 20 %, 6 %, and 0 %, respectively. All Pt/Nb–Ti₄O₇ catalysts showed higher durability of the ECSAs than the Pt/C catalyst, which was 68 m² g⁻¹ with a 30 % declining ratio after the ADT. Different from common Pt nanoparticle catalysts, which agglomerate into large spherical Pt particles, the slight agglomeration was caused by the interconnection of the deposits and supplemented by a limited increase in the diameter or thickness. The island-like morphology of Pt with a limited thickness presented both high durability and activity among the Pt/Oxide catalysts.

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The anodic dissolution (electropolishing) of pure metallic nickel and cobalt in choline chloride-propylene glycol eutectic mixture at a mole ratio of 1 : 3 by holding the voltage at 0.9 V for 40 min at 25 °C. The electrochemical study was further studied by recording a steady-state in the form of I-t profile for both metals. Mass transport is the cause of electropolishing and has been proved from the obtained steady-state. The process of electropolishing makes the metallic surface to be resistive to degradation by corrosion. For characterization of the prepared electropolished surface, two microscopic techniques were used; namely, scanning electron and atomic force microscopies. The SEM images have exhibited relatively high-quality electropolished surfaces in both cases of the surface. The Arithmetic mean roughness (Ra) from the AFM are 198.8 and 132.6 nm for polished surfaces of nickel and cobalt, respectively and Ra are 200.1 and 102.2 nm for unpolished regions of nickel and cobalt, respectively.

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