developed to achieve dual-responsive devices with color change and actuation, such as thermoelectric actuators, magnetochromic actuators, and photochromic actuators, to facilitate their application in military camouflage, robotics, healthcare, etc. [3][4][5][6] However, the stimulus sources of dual-responsive devices are affected by the surrounding environmental conditions, thereby hindering the development of highly controllable and precise dualresponsive behaviors.Compared with the stimuli mentioned above, electricity is highly controllable and hence provides a potential pathway for achieving high-frequency, stable, and accurate dual-responsive devices. [7][8][9] Among various electricity-induced strategies, the electrochemical (EC) method has garnered significant attention owing to its low driving voltage and large actuation amplitude, and is generally classified into two categories: a method based on electric dual-layer capacitance (EDLC) and one based on pseudocapacitance. [10][11][12] In the EDLC-based method, the surface electro-sorption/-desorption of electrolyte ions will cause reversible expansion and recovery of micro-/nanopores, thereby inducing reversible actuation. [13][14][15] However, it is difficult to simultaneously trigger optical color changes (bandgap structure) for the EDCL process based on only the adsorption and the desorption of ions.Pseudocapacitive EC actuators primarily rely on the Faradic redox reaction and involve ion intercalation into the active materials to achieve volumetric expansion and contraction. [10,[16][17][18][19] Hence, it is particularly important to introduce changes in the optical bandgap based on the EC actuator to achieve the dual-responsive of color/shape changes. For instance, Detsi et al. coated a nanolayer of electrochromic polymer onto the ligaments of nanoporous gold, which caused reversible dimensional and color changes during EC actuation. [20] Our team fabricated an electrochromic actuator based on W 18 O 49 nanowires (W 18 O 49 NWs) and demonstrated the color change/actuation dual-responsive phenomenon. [21] Macroscopic actuation was systemically investigated and derived from the lattice contraction/recovery of W 18 O 49 NWs during Li ion (Li + ) de-/intercalation. Nevertheless, a few challenges remain to be addressed. 1) The dual-responsive actuators in the air cannot present the color changes, owing to the inconspicuous color contrast 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 V 2 O 5 nanowires/single-walled carbon nanotubes (V 2 O 5 NWs/SWCNTs) networks, and shows a synchronous high actuation amplitude (about ±9.7 mm, ±28.4°) and multiple color changes. In this backto-back structure, the inactive SWCNTs layer is used as a conductive current collector, and the bil...

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Vanadium pentoxide (V 2 O 5 ) 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 V 2 O 5 @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 V 2 O 5 @C nanocrystals at nanoscale, providing more active sites for ionic insertion and accessible pathways for electron transport. After spray-coating the V 2 O 5 @C microrods on conductive substrates, interconnected networks composed of V 2 O 5 @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 V 2 O 5 @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.

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Metal–organic frameworks (MOFs) are highly desired for electrochromic (EC) applications because of their designable porous structures for fast ionic transport. However, the intrinsic low electronic conductivity of traditional MOF-based EC materials leads to a slow switching speed, poor coloration efficiency, and unfavorable cyclability. Conductive MOFs, with a tunable porous crystal structure and highly improved electronic conductivity, are proposed as promising candidates to achieve synchronous high-speed transport of electrons and ions in the EC process. Here we demonstrate fast and high-coloration-efficiency EC electrodes based on interfacially assembled conductive MOF Ni3(HITP)2 films. The reversible EC behavior of Ni3(HITP)2 is systematically explored and elaborated as the redox of Ni nodes in the crystal. Finally, we demonstrate MOFs-based devices that could potentially be used in fields such as digital displays and optical modulation.