X‑ray Insights into Formation of −O Functional Groups on MXenes: Two-Step Dehydrogenation of Adsorbed Water

• Published in: Nano letters 2023-02, Vol.23 (4), p.1401-1408
• Main Authors: Zhang, Pengjun, Shou, Hongwei, Xia, Yujian, Wang, Changda, Wei, Shiqiang, Xu, Wenjie, Chen, Yihong, Liu, Zehua, Guo, Xin, Zhu, Kefu, Cao, Yuyang, Wu, Xiaojun, Chen, Shuangming, Song, Li
• Format: Article
• Language: English
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.2c04712

Engineered MXene surfaces with more −O functional groups are feasible for realizing higher energy density due to their higher theoretical capacitance. However, there have been only a few explorations of this regulation mechanism. Investigating the formation source and mechanism is conducive to expanding the adjustment method from the top-down perspective. Herein, for the first time, the formation dynamics of −O functional groups on Mo2CT x are discovered as a two-step dehydrogenation of adsorbed water through in situ near-ambient-pressure X-ray photoelectron spectroscopy, further confirmed by ab initio molecular dynamics simulations. From this, the controllable substitution of −F functional groups with −O functional groups is achieved on Mo2CT x during electrochemical cycling in an aqueous electrolyte. The obtained Mo2CT x with rich −O groups exhibits a high capacitance of 163.2 F g –1 at 50 mV s –1, together with excellent stability. These results offer new insights toward engineering surface functional groups of MXenes for many specific applications.