X-ray Insights into Formation of −O Functional Groups on MXenes: Two-Step Dehydrogenation of Adsorbed Water
Pengjun Zhang, Hongwei Shou, Yujian Xia, Changda Wang, Shiqiang Wei, Wenjie Xu, Yihong Chen, Zehua Liu, Xin Guo, Kefu Zhu, Yuyang Cao, Xiaojun Wu, Shuangming Chen, Li Song
Abstract
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 Mo 2 CT 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 Mo 2 CT x during electrochemical cycling in an aqueous electrolyte. The obtained Mo 2 CT 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.