Electrochemical Actuators with Multicolor Changes and Multidirectional Actuation.

Electrochemical (EC) actuators have garnered significant attention in recent years, yet there are still some critical challenges to limit their application range, such as responsive time, multifunctionality, and actuating direction. Herein, an EC actuator with a back-to-back structure is fabricated by stacking two membranes with bilayer V2 O5 nanowires/single-walled carbon nanotubes (V2 O5 NWs/SWCNTs) networks, and shows a synchronous high actuation amplitude (about ±9.7 mm, ±28.4°) and multiple color changes. In this back-to-back structure, the inactive SWCNTs layer is used as a conductive current collector, and the bilayer network is attached to a porous polymer membrane. The dual-responsive processes of V2 O5 nanowires (V2 O5 NWs) actuation films and actuators are also deeply investigated through in situ EC X-ray diffraction and Raman spectroscopy. The results show that the EC actuation of the V2 O5 NWs/SWCNTs film is highly related to the redox behavior of the pseudocapacitive V2 O5 NWs layer. At last, both V2 O5 NWs and W18 O49 nanowires (W18 O49 NWs)-based EC actuators are constructed to demonstrate the multicolor changes and multidirectional actuation induced by the opposite lattice changes of V2 O5 NWs and W18 O49 NWs during ionic de-/intercalation, guiding the design of multifunctional EC actuators in the future.

Ultrafast, Stable Electrochromics Enabled by Hierarchical Assembly of V2O5@C Microrod Network.

Vanadium pentoxide (V2O5) with multicolor transition is widely studied in the electrochromic (EC) field to enrich color species of transition-metal oxides; yet, it always suffers from slow switching speed caused by poor electron conductivity and slow ion diffusion, poor cycling stability induced by large volume change during the EC reaction process. Herein, hierarchical network assembly of V2O5@C microrods is introduced to develop an ultrafast, stable, multicolor EC film. Using a two-step pyrolysis that involves metal-organic framework templates, porous microrods with a well-preserved one-dimensional structure are prepared through the assembly of V2O5@C nanocrystals at nanoscale, providing more active sites for ionic insertion and accessible pathways for electron transport. After spray-coating the V2O5@C microrods on conductive substrates, interconnected networks composed of V2O5@C microrods at microscale ensures the infiltration of electrolyte and provide ion transport channels. In addition, the nanoscale porous structure and coated carbon layer can accommodate volumetric changes during ion insertion/extraction process, ensuring high electrochemical stability. As a result, EC electrode with V2O5@C microrods network performed rapid switching speed (1.1/1.0 s) and stable cycle ability (96% after 2000 cycles). At last, flexible large-scale devices and multicolor digital displays were assembled to demonstrate potential application in next-generation wearable electronics.