Understanding the effects of transition metal intercalation on electronic and electrochemical properties of Ti3C2Tx MXene

MXenes are 2D transition metal carbides, nitrides, and/or carbonitrides, capable of intercalation by various cations through chemical or electrochemical means. Previous research has primarily focused on intercalating alkaline and alkaline earth cations, such as Li+, K+, Na+, Mg2+ or alkylammonium cations, into Ti3C2Tx MXenes. However, the impact of intercalated transition metal (TM) ions on the electronic and electrochemical properties of MXenes remains largely unexplored. In this study, we investigated the effects of pre-intercalated Cu ions on Ti3C2Tx MXenes and vice versa to gain a comprehensive understanding of how the electronic and electrochemical properties of both intercalated TM ion and MXene host are altered. Using in-situ X-ray absorption spectroscopy (XAS), we reveal changes in the oxidation states of intercalated Cu ions and Ti atoms during charging and their corresponding role in charge storage mechanisms. Our findings show that electronic coupling between Ti3C2Tx and Cu ions results in modified electrochemical and electronic properties compared to pristine Ti3C2Tx. These insights lay the foundation for the rational design and utilization of TM ion intercalants to tailor the properties of MXenes for various electrochemical systems and beyond.