Prussian Blue analogue materials for energy conversion and storage

A global trend towards decarbonisation of energy provision is driving the exploitation of renewable sources, such as photovoltaics and wind power. As the amount of energy produced by those plants heavily depends on external conditions, such as weather, season or time of day, the grid needs to be stabilized in order to dependably provide the power demanded. Grid-scale battery systems are a solution to this problem. By storing excess produced energy and releasing it when the demand is higher than production, these systems buffer the volatility of renewable energy sources.

Today's dominating battery designs often rely on scarce elements, which prevents the widespread usage of these established systems for large-scale applications. Therefore, a new class of materials, Prussian blue analogues, was proposed as a promising electrode material for these use cases. Their many desirable properties include long cycle life, the abundance of constituting elements and fast charge/discharge rates which enable a high power output. These arise from the open-framework crystal structure exhibiting large interstitial sites which are connected by wide pathways. Apart from these, the crystal structure includes two distinct sites occupied by transition metal atoms, which are fundamental for the electrochemical activity. A variety of elemental species can be chosen, which allows for the tailoring of materials to specific applications.

During the synthesis of these materials, subtle changes in parameters such as temperature or chemical environment result in Prussian blue analogue materials exhibiting different structural properties, which in turn affects the electrochemical performance. For example, it was shown that the concentration of unoccupied transition metal sites (vacancies) has a drastic effect on the electrochemistry of electrodes during cycling.

This work aims at an in-depth investigation of the correlation between crystallographic features of Prussian blue analogues and their electrochemical properties. The structural, chemical and morphological investigation will be carried out using X-ray powder diffraction (both ex-situ and in-situ) in-house and at beamline I11 at the Diamond Light Source, neutron diffraction at the ISIS Neutron and Muon source, solid-state NMR, Raman spectroscopy and electron microscopy. Advanced electrochemical characterization techniques will be employed such as Electrochemical Impedance Spectroscopy (EIS), Galvanostatic Intermittent Titration Technique (GITT) and variety of potentiostatic and galvanostatic techniques. This experimental analysis will be complemented by theoretical materials modelling by means of density functional theory (DFT).

The results of this work will help to identify desirable structural features including a targeted synthesis route and will accelerate the design and tailoring of new Prussian blue analogues by shedding light on the fundamental relationships between their structure and electrochemistry.

This project falls within the EPSRC energy research area.