Microelectrode-enabled Electrocrystallization of Cobalt TCNQ Complex for Gas Sensing

Abstract

Electrocrystallization is a promising method for controlled charge-transfer complex (CTC) deposition on microfabricated electrodes for gas sensing applications. However, there remains a gap in our understanding of CTC electrodeposition. In this study, we focus on investigating the electrocrystallization of cobalt tetracyanoquinodimethane (Co-TCNQ) on a microdisk electrode to elucidate and control the process. Leveraging the microelectrode technique, we conduct steady-state measurements to observe nucleation and crystal growth dynamics, particularly in the early stages of electrocrystallization. We use cyclic voltammetry and chronoamperometry to examine Co-TCNQ electrocrystallization under various electrolytic conditions. We identify electrocrystallization kinetics, ranging from electrokinetic to diffusion-limited growth, governing the nucleation and growth of Co-TCNQ crystals. Notably, we pinpoint the applied overpotential and precursor concentration range necessary for a single nucleation site on the microelectrode. Moreover, we demonstrate control over crystal orientation and morphology. Our findings reveal a nonclassical growth pathway for Co-TCNQ crystals characterized by oriented attachment of small crystallites along the conductive long axis. Importantly, electrodeposited Co-TCNQ on patterned microelectrodes exhibits selective sensing capabilities for nitrogen dioxide gas. Overall, this study sheds light on CTC electrodeposition through a proof-of-concept demonstration involving Co-TCNQ electrodeposition on microelectrodes, presenting potential applications across diverse materials.