Résumé
Here, we report a rare example of an Fe-based MOF capable of accommodating K$^{+}$ ions electrochemically within its layered framework, achieving low polarization, high capacity utilization (similar to 0.8 electrons exchanged per Fe), and stable cycling performance. In situ Mössbauer spectroscopy and operando XRD analyses revealed that the observed electrochemical storage arises from the Fe$^{3+}$/Fe$^{2+}$ redox couple with polyphasic transformations.