Reversible electrochemical potassium-ion intercalation in P2-type NaCoO was examined for the first time. Hexagonal NaCoO platelets prepared by a solution combustion synthesis technique were found to work as an efficient host for K intercalation. They deliver a high reversible capacity of 82 mA h g, good rate capability and excellent cycling performance up to 50 cycles.

Reversible intercalation of Zn ions in tetragonal K1.33Mn8O16 delivers 312 mA h g−1 capacity at a galvanostatic cycling rate of 0.1C with an average voltage of 1.5 V.

Noble-metal-free, bifunctional catalysts are essential to develop high-performance, cost-effective water-splitting systems. The current work explores the bifunctional electrocatalytic behavior of two sodium cobalt phosphate systems, namely, NaCoPO 4 and Na 2 CoP 2 O 7 , prepared by solution combustion synthesis (SCS) for the first time. Formation of phase-pure orthorhombic maricite NaCoPO 4 (space group: Pnma) and orthorhombic Na 2 CoP 2 O 7 (space group: Pna2 1 ) was confirmed by Rietveld refinement. The electrocatalytic activity of maricite NaCoPO 4 and Na 2 CoP 2 O 7 was investigated by using linear sweep voltammetry with a rotating disk electrode (RDE). The oxygen reduction reaction (ORR) activities of these sodium cobalt phosphates are comparable to Vulcan carbon black and Pt/C. Oxygen evolution reaction (OER) activity of Na 2 CoP 2 O 7 is dominant compared to NaCoPO 4 and Pt/C. The Tafel slope, electron-transfer number, and stability of the sodium-metal phosphates were calculated in different concentrations of Na + -containing aqueous electrolyte. The bifunctional activity and good stability of the sodium cobalt phosphates stem from cobalt ions and stabilization of the catalytic centers by the phosphate frameworks. The present work demonstrates sodium cobalt phosphates as alternate costeffective, novel electrocatalysts for efficient OER/ORR activity in alkaline solution.

We report the synthesis, crystal structure, thermal response, and electrochemical behavior of the Prussian blue analogue (PBA) K 2 Cu[Fe(CN) 6 ]. From a structural perspective, this is the most complex PBA yet characterized: its triclinic crystal structure results from an interplay of cooperative Jahn–Teller order, octahedral tilts, and a collective “slide” distortion involving K-ion displacements. These different distortions give rise to two crystallographically distinct K-ion channels with different mobilities. Variable-temperature X-ray powder diffraction measurements show that K-ion slides are the lowest-energy distortion mechanism at play, as they are the only distortion to be switched off with increasing temperature. Electrochemically, the material operates as a K-ion cathode with a high operating voltage and an improved initial capacity relative to higher-vacancy PBA alternatives. On charging, K + ions are selectively removed from a single K-ion channel type, and the slide distortions are again switched on and off accordingly. We discuss the functional importance of various aspects of structural complexity in this system, placing our discussion in the context of other related PBAs.

A P3-type K0.48Mn0.4Co0.6O2 oxide forms a 3 V economical cathode for potassium-ion batteries, having a discharge capacity of 64 mA h g−1 coupled with excellent cycling stability.