Rechargeable aqueous batteries are promising devices for large‐scale energy‐storage applications because of their low‐cost, inherent safety, and environmental friendliness. Among them, aqueous ammonium‐ion (NH₄⁺) batteries (AAIB) are currently emerging owing to the fast diffusion kinetics of NH₄⁺. Nevertheless, it is still a challenge to obtain stable AAIB with relatively high output potential, considering the instability of many electrode materials in an aqueous environment. Herein, a cell based on a concentrated (5.8 m) aqueous (NH₄)₂SO₄ electrolyte, ammonium copper hexacyanoferrate (N‐CuHCF) as the positive electrode (cathode), and 3,4,9,10‐perylene‐bis(dicarboximide) (PTCDI) as the negative electrode (anode) is reported. The solvation structure, electrochemical properties, as well as the electrode–electrolyte interface and interphase are systematically investigated by the combination of theoretical and experimental methods. The results indicate a remarkable cycling performance of the low‐cost rocking‐chair AAIB, which offers a capacity retention of ≈72% after 1000 cycles and an average output potential of ≈1.0 V.

The electroactivity of sodium‐rich manganese hexacyanoferrate (MnHCF) material constituted of only abundant elements, as insertion host for Li‐ and Na‐ions is herein comprehensively discussed. This material features high specific capacities (>130 mAh g⁻¹) at high potentials when compared to other materials of the same class, i.e., Prussian blue analogs. The reversible electronic and structural modifications occurring during ion release/uptake, which are responsible for such high specific capacity, are revealed herein. The in‐depth electronic and structural analysis carried out combining X‐ray diffraction and X‐ray absorption spectroscopy (XAS), demonstrates that both Fe and Mn sites are involved in the electrochemical process, being the high delivered capacity the result of a reversible evolution in oxidation states of the metallic centers (Fe³⁺/Fe²⁺ and Mn²⁺/Mn³⁺). Along with the Mn²⁺/Mn³⁺ oxidation, the Mn local environment experiences a substantial yet reversible Jahn–Teller effect, being the equatorial Mn‐N distances shrunk by 10% (2.18 Å → 1.96 Å). Na‐rich MnHCF material offers slightly higher performance upon uptake and release of Na‐ions (469 Wh kg⁻¹) than Li‐ions (457 Wh kg⁻¹), being, however, the electronic and structural transformation independent of the adopted medium, as observed by XAS spectroscopy.

A novel and reproducible protocol allows the electro-synthesis of LDHs for electro-catalytic applications.

Manganese hexacyanoferrate (MnHCF) has received increasing attention as positive electrode for both lithium- and sodium-ion storage owing to its high delivered specific capacity among the Prussian Blue Analogs (PBAs). During ion-release, the material undergoes Jahn-Teller distortion arising from the oxidation of manganese to its trivalent state. Typically, the Jahn-Teller distortion is reported to destabilize the host structure of layered and spinel manganese oxides-based electrode materials, resulting into displaying volume changes in the order of 10 – 20%, which deteriorates the cycle performance. Herein, the effect of such a distortion on MnHCF via in operando, synchrotron powder diffraction is reported. Surprisingly, only a minor volume change (about 2%) is recorded upon cycling the electrode material against lithium, highlighting the major role of the PBA framework in stabilizing the PBAs’ structure.