Comparison of Charge Storage Properties of Prussian Blue Analogues Containing Cobalt and Copper

Amanda Rensmo,Jennifer R Hampton

doi:10.3390/met9121343

Abstract

Prussian blue analogues are of great interest as alternative battery materials because of their long life cycle and potential use of earth-abundant elements. In this work, thin film mixed-metal hexacyanoferrates (HCFs) based on NiCo and NiCu alloys were fabricated in an all electrochemical process. The structure and composition of the samples were characterized, along with the charge storage capacity and kinetics of the charge transfer reaction. For both NiCo-HCF and NiCu-HCF samples, the total charge capacity increased with the substitution of Ni with more Co or Cu, and the increase was larger for Cu samples than for Co samples. On the other hand, the charge storage kinetics had only a modest change with substituted metal, and these effects were independent of the amount of that substitution. Thus, the mixed-metal HCFs have promise for increasing overall storage capacity without negatively influencing the rate capability when used in battery applications.

Highlights

Prussian blue analogues (PBAs) and other open framework intercalation compounds have been the subject of increasing interest as promising battery materials [1,2,3,4,5,6]
The general formula for PBAs can be written as A j Mk [M0 (CN)6 ]l, where M and M0 are transition metals, A is a counter cation, and the stoichiometry depends on the identities of M, M0, and A, as well as the number of cyanometalate vacancies incorporated into the structure [7]
The results showed that samples fabricated from NiCu alloys yield a significantly higher charge capacity those from

Summary

Introduction

Prussian blue analogues (PBAs) and other open framework intercalation compounds have been the subject of increasing interest as promising battery materials [1,2,3,4,5,6]. The general formula for PBAs can be written as A j Mk [M0 (CN)6 ]l , where M and M0 are transition metals, A is a counter cation, and the stoichiometry depends on the identities of M, M0 , and A, as well as the number of cyanometalate vacancies incorporated into the structure [7]. Supercapacitive behavior occurs in these materials when the metal centers change oxidation state, accompanied by the intercalation or deintercalation of counter cations. In the subset of PBAs known as hexacyanoferrates (HCFs), where M0 = Fe, one possible redox reaction is [7,8] h i h i. The wide variety of transition metals that can be substituted for M and M0 makes tuning the properties of PBA materials a possibility. By changing the transition metals, the potential of the redox reactions can be adjusted [9]. Mixed-metal PBAs have been produced, where either M and M0 or both metals are occupied by a mixture of elements rather than just one, providing additional degrees of tunability [8,13,14,15,16,17,18]

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Discussion

Conclusion