113Cd NMR for determination of the local electronic and structural states of the Prussian blue

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we demonstrated that 113Cd NMR can be used as a sensitive local structural probe to monitor the lithium intercalation/deintercalation process inside a model PBA electrode based on {Cd-NC-Fe} units. The experimental observations are in agreement with the expected trends: (i) the Fe(III)/Fe(II) redox reaction is reversible; (ii) the maximum Li+ intercalation corresponds to a full reduction of the Fe sites. However, new cadmium sites with lower chemical shifts are found upon lithiation. Importantly the NMR study sheds light on the underlying electronic structure, in particular the possible occurrence of a fast charge transfer between Fe(III)/Fe(II) in the lithiated PBA. This feature might also be found in other FeM PBA materials where the redox active sites are also the Fe ions. Further investigations on various PBA electrodes are now required to clarify this peculiar electronic state.

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