Prussian Blue Analogues (PBAs) have gathered renewed interest recently because of their unique electrochemical properties, several of which are highly desirable for energy storage¹. These intriguing properties arise from the interaction of the crystal structure with inserting ions. The general electrochemical equation for the insertion of an alkali metal into a PBA is given by:

A_xP^J[R^K(CN)₆]_1−y · wH₂O + A⁺ + e⁻ → A_x+1P^J[R^K−1(CN)₆]_1−y · wH₂O

where A is an alkali-metal ion, and P and R are transition-metal ions octahedrally coordinated to six cyanide ligands via the nitrogen and carbon atom, respectively (Figure 1). The value y is the fraction of vacancies in the hexacyanoferrate complex ion (the primary lattice defect). Water can also be present, both as zeolitic and coordinated to deficiently bonded metal ions at vacancies.

Figure 1: Schematic representation of the crystal structure of PBAs. The green and dark-blue atoms are transition-metal ions at the R site and P site, respectively. Gray atoms are carbon and light-blue atoms are nitrogen.

In my talk, I will show how these exciting properties are linked to the structural diversity of PBAs² and how their chemistry can be tuned to adapt their electrochemistry to a variety of energy storage applications^3,4, with focus on K-ion batteries^5–7.

References

1. Hurlbutt, K., Wheeler, S., Capone, I. & Pasta, M. Prussian Blue Analogs as Battery Materials. Joule vol. 2 1950–1960 (2018).
2. Cattermull, J., Pasta, M. & Goodwin, A. L. Structural complexity in Prussian blue analogues. Materials Horizons 8, 3178–3186 (2021).
3. Wheeler, S., Capone, I., Day, S., Tang, C. & Pasta, M. Low-Potential Prussian Blue Analogues for Sodium-Ion Batteries: Manganese Hexacyanochromate. Chemistry of Materials 31, 2619–2626 (2019).
4. Hurlbutt, K., Giustino, F., Pasta, M. & Volonakis, G. Electronic Structure and Electron-Transport Properties of Three Metal Hexacyanoferrates. Chemistry of Materials 33, 7067–7074 (2021).
5. Fiore, M. et al. Paving the Way toward Highly Efficient, High-Energy Potassium-Ion Batteries with Ionic Liquid Electrolytes. Chemistry of Materials 32, 7653–7661 (2020).
6. Dhir, S., Wheeler, S., Capone, I. & Pasta, M. Outlook on K-Ion Batteries. Chem 6, 2442–2460 (2020).
7. Cattermull, J. et al. Revealing the structural complexity of Prussian blue analogues: the case of K2Cu[Fe(CN)6]. ChemRxiv (2022) doi:10.26434/chemrxiv-2022-zr5nn.