Unveiling the charge storage mechanisms of Co-based perovskite fluoride in a mild aqueous electrolyte.

This study is an in-depth exploration of the charge storage mechanisms of KCoF 3 in 1 M Na 2 SO 4 mild aqueous electrolytes via an array of ex situ / in situ physicochemical/electrochemical methods, especially the electrochemical quartz crystal microbalance (EQCM) technique, showing a combination of conversion, insertion/extraction and adsorption mechanisms. Specifically, during the first charge phase, Co(OH) 2 is formed/oxidized into amorphous CoOOH and Co 3 O 4 , and then CoOOH undergoes partial proton extraction to yield CoO 2 , which is simultaneously accompanied by the transformation of Co 3 O 4 into CoOOH and (hydrated) CoO 2 . During the first discharge process, the partial insertion of H + into (hydrated) CoO 2 leads to the formation of CoOOH and Co 3 O 4 , with the conversion of Co 3 O 4 into CoOOH and both Co 3 O 4 and CoOOH undergoing further transformations into (hydrated) Co(OH) 2 via the insertion of H + . This work offers valuable references for the development of aqueous energy storage.