Ligand assisted electrochemical process switching

Abstract

Electrochemical processes at the electrode–electrolyte interface are broadly divided into charge-transfer and charge-storage phenomena. Charge-transfer reactions, controlled by electrocatalysts, constitute the core of electrocatalysis and are essential for energy conversion and storage technologies. In contrast, charge-storage processes originate from electrical double-layer formation, giving rise to capacitive currents whose relevance depends on the application. Suppression of double-layer currents is critical for enhancing analyte detection in electrochemical sensing, whereas their amplification is desirable for improving charge-storage performance in supercapacitor systems. Accordingly, precise modulation of both charge-transfer and charge-storage processes is central to efficient electrochemical process control. Molecular electrocatalysts such as phthalocyanines and porphyrins have emerged as versatile platforms for modulating electrochemical processes due to their excellent chemical and thermal stability and highly tunable optoelectronic properties. [1-2] In these systems, electrochemical behavior is commonly attributed to the nature of the central metal ion, while the influence of the ligand remains comparatively underexplored. [3-5] The primary objective of this thesis is to elucidate the role of ligand architecture in regulating charge-transfer processes and modulating the electrical double layer. To this end, the thesis first examines ligand-assisted tuning of electrochemical reaction kinetics relevant to energy conversion, revealing that ligand modification significantly affects reaction rates without altering the underlying reaction mechanism. The influence of ligand structure on reaction pathways is subsequently explored in the electrochemical oxygen reduction reaction, where a ligand-isomerization strategy enables controlled switching from a two-electron to a four-electron pathway. Further, ligand-induced modulation of the electrical double layer at the electrode–electrolyte interface is investigated, and the resulting proton charge assembly is exploited for actuation applications. Finally, the same ligand-isomerization approach is applied to regulate the electrical double-layer current for the development of low-noise electrochemical sensors, where suppression of background capacitive currents enhances sensitivity and lowers detection limits for analytes of clinical and environmental importance. 1. Yang, S.; Yu, Y.; Gao, X.; Zhang, Z.; Wang, F., Chem. Soc. Rev. 2021, 50 (23), 12985–13011. 2. Lee, B. H.; Shin, H.; Rasouli, A. S.; Choubisa, H.; Ou, P.; Dorakhan, R.; Grigioni, I.; Lee, G.; Shirzadi, E.; Miao, R. K.; Wicks, J.; Park, S.; Lee, H. S.; Zhang, J.; Chen, Y.; Chen, Z.; Sinton, D.; Hyeon, T.; Sung, Y. E.; Sargent, E. H., Nat. Catal. 2023, 6, 234–243. 3. Chen, K.; Cao, M.; Lin, Y.; Fu, J.; Liao, H.; Zhou, Y.; Li, H.; Qiu, X.; Hu, J.; Zheng, X.; Shakouri, M.; Xiao, Q.; Hu, Y.; Li, J.; Liu, J.; Cortés, E.; Liu, M., Adv. Funct. Mater. 2022, 32 (10), 2111322. https://doi.org/https://doi.org/10.1002/adfm.202111322. 4. Madhuri, K. P.; John, N. S., Appl. Surf. Sci. 2018, 449, 528–536. 5. Chen, K.; Liu, K.; An, P.; Li, H.; Lin, Y.; Hu, J.; Jia, C.; Fu, J.; Li, H.; Liu, H.; Lin, Z.; Li, W.; Li, J.; Lu, Y.-R.; Chan, T.-S.; Zhang, N.; Liu, M., Nat. Commun. 2020, 11 (1), 4173. https://doi.org/10.1038/s41467-020-18062-y.