Copper Electroactivity in Prussian Blue-Based Cathode Disclosed by Operando XAS

The electronic and structural evolution of copper hexacyanoferrate (CuHCF) cathode material was studied by operando X-ray absorption spectroscopy (XAS) simultaneously at both Fe and Cu K edges during a full galvanostatic cycle. The full set of XAS data collected during the electrochemical process was analyzed by a combined chemometric approach using the multicurve resolution analysis with the alternate least squares algorithm. Using this joint approach and by applying a simultaneous multiple edge fitting procedure, it was possible to clarify the participation of both copper and iron centers to the redox processes and to analyze their local environment. The structural modifications occurring in CuHCF along with the redox processes are entirely reversible, with the steady multiplicity of Fe-C-N-Cu linear chains evidencing the structural stability of the material during cycling.