Copper Hexacyanoferrate Thin Film Deposition and Its Application to a New Method for Diffusion Coefficient Measurement

Abstract

The use of Prussian blue analogues (PBA) materials in electrochemical energy storage and harvesting has gained much interest, necessitating the further clarification of their electrochemical characteristics. However, there is no well-defined technique for manufacturing PBA-based microelectrochemical devices because the PBA film deposition method has not been well studied. In this study, we developed the following deposition method for growing copper hexacyanoferrate (CuHCFe) thin film: copper thin film is immersed into a potassium hexacyanoferrate solution, following which the redox reaction induces the spontaneous deposition of CuHCFe thin film on the copper thin film. The film grown via this method showed compatibility with conventional photolithography processes, and the micropattern of the CuHCFe thin film was successfully defined by a lift-off process. A microelectrochemical device based on the CuHCFe thin film was fabricated via micropatterning, and the sodium ion diffusivity in CuHCFe was measured. The presented thin film deposition method can deposit PBAs on any surface, including insulating substrates, and it can extend the utilization of PBA thin films to various applications.

Resolving the Seeming Contradiction between the Superior Rate Capability of Prussian Blue Analogues and the Extremely Slow Ionic Diffusion

“…The charge storage properties of PBAs are largely determined by the presence of spacious vacancies and percolated three-dimensional (3D) channels in their structures. ,,− The large voids in the PBA structure have been stereotypically considered to be responsible for the exceptionally high diffusivities of Na + , K + , Rb + , Cs + , and NH 4 + ions. Accordingly, the kinetics of ionic diffusion in PBA structures have been extensively studied in both aqueous − and non-aqueous − media. Values of diffusion coefficients ( D ) on the order of 10 –8 cm 2 s –1 were reported for insertion of K + from an aqueous solution into electrodeposited films of nickel (NiHCF) and copper (CuHCF) hexacyanoferrates. , D values in PBA films were reported to be on the order of 10 –9 cm 2 s –1 for K + in iron hexacyanoferrate (FeHCF) ,, and NiHCF, , Na + in FeHCF, NiHCF, and CuHCF, Rb + in FeHCF and NiHCF, Cs + in FeHCF and NiHCF, NH 4 + in FeHCF, and Li + in NiHCF .…”

“…Accordingly, the kinetics of ionic diffusion in PBA structures have been extensively studied in both aqueous − and non-aqueous − media. Values of diffusion coefficients ( D ) on the order of 10 –8 cm 2 s –1 were reported for insertion of K + from an aqueous solution into electrodeposited films of nickel (NiHCF) and copper (CuHCF) hexacyanoferrates. , D values in PBA films were reported to be on the order of 10 –9 cm 2 s –1 for K + in iron hexacyanoferrate (FeHCF) ,, and NiHCF, , Na + in FeHCF, NiHCF, and CuHCF, Rb + in FeHCF and NiHCF, Cs + in FeHCF and NiHCF, NH 4 + in FeHCF, and Li + in NiHCF . A number of reports give lower, but still high compared to those of other solid ion insertion hosts, D values of 10 –10 to 10 –11 cm 2 s –1 for the insertion of monovalent ions into FeHCF films from aqueous solutions. ,, Similarly high values of diffusion coefficients (10 –9 to 10 –11 cm 2 s –1 ) were reported for ionic transport in PBA particles with greatly reduced lattice water contents in carbonate-based and ether-based electrolytes. − , …”

“…Values of diffusion coefficients (D) on the order of 10 −8 cm 2 s −1 were reported for insertion of K + from an aqueous solution into electrodeposited films of nickel (NiHCF) and copper (CuHCF) hexacyanoferrates. 11,15 D values in PBA films were reported to be on the order of 10 −9 cm 2 s −1 for K + in iron hexacyanoferrate (FeHCF) 8,9,21 and NiHCF, 16,17 Na + in FeHCF, 9 NiHCF, 16 and CuHCF, 22 Rb + in FeHCF 9 and NiHCF, 16 Cs + in FeHCF 9 and NiHCF, 16 NH 4 + in FeHCF, 9 and Li + in NiHCF. 16 A number of reports give lower, but still high compared to those of other solid ion insertion hosts, D values of 10 −10 to 10 −11 cm 2 s −1 for the insertion of monovalent ions into FeHCF films from aqueous solutions.…”

Dendritic Copper Current Collectors as a Capacity Boosting Material for Polymer-Templated Si/Ge/C Anodes in Li-Ion Batteries

“…In order to gauge the effect of the presumably largely enhanced surface area of dendritic copper, its electroactive area is measured. The typically performed voltammetry of ferri/ferrocyanide (K 3 [Fe­(CN) 6 and K 4 [Fe­(CN) 6 ]) redox couple is not an option in this case due to their reaction with the copper surface to cupric ferrocyanide leading to the formation of a thin film on the Cu electrode surface . Instead, CV of KOH is performed as done by Diao and co-workers and the team of Ambrose. , In their work, they evidenced that the third anodic peak at around 0.05 V vs Ag/AgCl showed the highest linearity related to the peak current when the surface area was the varying parameter.…”

Editorial for Special Issue: Highly Efficient Energy Harvesting Based on Nanomaterials

“…This study provided new insight into design of cost-effective, novel, metal-free electrocatalysts. Yun et al [7] introduced a thin film deposition method for copper hexacyanoferrate (CuHCFe) thin film, a Prussian blue analogue (PBA). PBAs are widely used in electrochemical energy storage and various energy harvesting applications due to their fast kinetics.…”