A Flexible Vertical-Section Wood/MXene Electrode with Excellent Performance Fabricated by Building a Highly Accessible Bonding Interface.

Cross-section wood (CW) is generally used as a host for free-standing electrodes, as the abundant opened pores can provide large space for loading guest materials with high electrical conductivity and electrochemical activity. However, there is still a challenge for CW to be used in flexible supercapacitors (SCs) because of its low mechanical strength. Herein, as an alternative to CW, vertical-section wood (VW) with excellent mechanical strength and good flexibility is developed and used as a free-standing and flexible electrode by using Ti 3 C 2 T x (MXene) with ultrahigh conductivity and good electrochemical activity as a guest material. In particular, the highly accessible bonding interface for Ti 3 C 2 T x is first built by delignification on VW to generate abundant pores for continuously absorbing Ti 3 C 2 T x and to expose cellulose with abundant oxygen-containing groups for stable combination with Ti 3 C 2 T x . Then, cyclic pressing is used to form negative pressure to pump the Ti 3 C 2 T x suspension into VW, combining with a preheating process to trigger layer-by-layer self-assembly of Ti 3 C 2 T x nanosheets onto a wood cell wall by evaporating water in the suspension. As a result, the free-standing electrode has a large Ti 3 C 2 T x loading mass proportion of 33 wt %, a high conductivity of 3.14 S cm -1 , and good flexibility with much higher mechanical strength of 15.1 MPa than 0.4 MPa of CW. The symmetric SC delivers a good specific capacitance of 805 mF cm -2 at 0.5 mA cm -2 , a remarkably high rate capability of 84% to 10 mA cm -2 , and an energy density of 13.85 μW h cm -2 at 87.5 μW cm -2 . Additionally, this SC shows a long lifespan of 90.5% after 10,000th charge and discharge cycles even at a constant bending angle of 90°, suggesting promising potential in flexible devices.