Stable cycling of a 4 V-class potassium-ion battery is demonstrated with a highly concentrated potassium bis(fluorosulfonyl)amide 1,2-dimethoxyethane solution as an electrolyte. Not only graphite and K2Mn[Fe(CN)6] half cells but also graphite//K2Mn[Fe(CN)6] full cells filled with the electrolyte exhibit higher coulombic efficiency and better cyclability than those of KPF6/carbonate ester solutions.

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Potassium manganese hexacyanoferrate (KMnHCF) can be used as a positive electrode for potassium‐ion batteries because of its high energy density. The effect of particle size and [Fe(CN)6]n− vacancies on the electrochemical potassium insertion of KMnHCFs was examined through experimental data and theoretical calculations. When nearly stoichiometric KMnHCF was synthesized and tested, smaller particle sizes were found to be important for achieving superior electrochemical performance in terms of capacity and rate capability. However, even in the case of larger particles, introducing a suitable number of anion vacancies enabled KMnHCF to exhibit comparable electrode performance. Electrochemical tests and density functional theory calculations indicated that anion vacancies contribute to the enhancement of K+ ion diffusion, which realizes good electrochemical performance. Structural design, including crystal vacancies and particle size, is the key to their high performance as a positive electrode.

Electrophoresis of a Corynebacterium glutamicum membrane preparation in the presence of sodium dodecyl sulfate, followed by staining for peroxidase activity (heme staining), showed only one band at about 28 kDa. This 28 kDa protein was purified from C. glutamicum membranes by chromatography in the presence of decylglucoside using DEAE-Toyopearl and hydroxylapatite columns, as the sole c-type cytochrome in the bacterium. The cytochrome showed an alpha band at 551 nm, and its E(m, 7) was about 210 mV. A QcrCAB operon encoding the subunits of a putative quinol cytochrome c reductase was found 3'-downstream of ctaE encoding subunit III of cytochrome aa(3) in the C. glutamicum genome. The deduced amino acid sequence of qcrC, composed of 283 amino acid residues, contained two heme C-binding motifs and was in agreement with partial peptide sequences obtained from the 28 kDa protein after V8 protease digestion. We propose to name this protein cytochrome cc. The presence of cytochrome cc is a common feature of high G+C content Gram-positive bacteria, since we could confirm this protein by electrophoresis; homologous QcrCAB operons are also known in Mycobacterium and Streptomyces. QcrA and qcrB of C. glutamicum encode the Rieske Fe-S protein and cytochrome b, respectively, although these proteins were not co-purified with cytochrome cc. The phylogenetic tree of cytochromes b and b(6) show that C. glutamicum cytochrome b, along with those of other bacteria in the high G+C group, is rather different from the Bacillus counterparts, but highly similar to the Deinococci and Thermus cytochromes. This indicates that there is a fourth group of bacteria in addition to the three clades: proteobacterial cytochrome b, cyanobacterial b(6) and green sulfur-low G+C Gram-positive bacteria.

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