The electrochemical kinetics of advanced materials are metered mechanistically by how charge transfer or accumulation occurs at the electrode/electrolyte interface. Fundamental insights garnered from traditional voltammetric techniques superimpose information on charge-storage mechanisms, but impedance spectroscopy can provide deeper insight into charge-storage kinetics beyond the electrode/electrolyte interface. Mirroring the work of Bai and Conway, which tracked pseudoinductive effects as a function of both frequency and potential,^1,2 we similarly track the colors of capacitance in a protocol we designate ‘3D Bode Analysis.’ This impedance variant can distinguish double-layer response, pseudocapacitance, and battery-like faradaic reactions at device-relevant electrodes.^3–7 For <10 nm coatings of lithium manganese oxide on a 3D aperiodic carbon architecture, we could identify the respective potential windows for pseudocapacitance and battery-like reactions.⁴ Mapping the respective impedance signatures of electroprecipitated zinc hydroxide sulfate in Zn²⁺-containing electrolytes provides insight into complex electrodeposition processes.⁷ In addition to deconvolving distinct charge-storing processes, we also use 3D Bode analysis to understand the positive effects of carbothermal shock on improving the double-layer response of graphene oxide–carbon nanotube composites.⁶ Analyzing impedance in the form of 2D color-mapped surface plots reveals that the characteristic relaxation time of these electrodes is 70% faster than activated carbon. These studies highlight an exciting direction to garner key mechanistic information regarding the complex electrochemical response of advanced electrochemical materials.

References

[1] L. Bai and B. E. Conway, AC impedance of faradaic reactions involving electrosorbed intermediates: Examination of conditions leading to pseudoinductive behavior represented in three-dimensional impedance spectroscopy diagrams. J. Electrochem. Soc., 138, 2897–2907 (2019).

[2] L. Bai and B. E. Conway, Three-dimensional impedance spectroscopy diagrams for processes involving electrosorbed intermediates, introducing the third electrode-potential variable—Examination of conditions leading to pseudo-inductive behavior. Electrochim. Acta, 38, 1803–1815 (1993).

[3] J. S. Ko, M. B. Sassin, J. F. Parker, D. R. Rolison, and J. W. Long, Combining battery-like and pseudocapacitive charge storage in 3D MnOx@carbon electrode architectures for zinc-ion cells. Sustain. Energy Fuels 2, 626–636 (2018).

[4] J. S. Ko, M. B. Sassin, D. R. Rolison, and J. W. Long, Deconvolving double-layer, pseudocapacitance, and battery-like charge-storage mechanisms in nanoscale LiMn₂O₄ at 3D carbon architectures. Electrochim. Acta, 275,225–235 (2018).

[5] J. S. Ko, C.-H. Lai, J. W. Long, D. R. Rolison, B. Dunn, and J. Nelson Weker, Differentiating double-layer, pseudocapacitance, and battery-like mechanisms by analyzing impedance measurements in three dimensions. ACS Appl. Mater. Interfaces, 12, 14071–14078 (2020).

[6] J. S. Ko, P. Y. Meng, H. Elazar-Mittelman, J. K. Johnson, Z. Xia, and S. Holdren, Rapid carbothermal shock enhances the double-layer response of graphene oxide–carbon nanotube electrodes. Energy Fuels, 35, 17919–17929 (2021).

[7] J. S. Ko, M. D. Donakowski, M. B. Sassin, J. F. Parker, D. R. Rolison, and J. W. Long, Deciphering charge-storage mechanisms in 3D MnOx@carbon electrode nanoarchitectures for rechargeable zinc-ion cells. MRS Commun., 9, 99–106 (2019).