Electrochromic energy storage (EES) devices with high capacity, long-term stability and multicolor display are highly desired for practical applications. Here, we propose a new three-electrode design of an EES device. Two kinds of electrochromic materials (WO₃ and Ti-V₂O₅ respectively) deposited on ITO glass work as electrochromic active layers. Al metal is used as the anodic frame of the device and helps to seal the mixed Li/Al-ion electrolyte. For electrochromic applications, the device shows rapid, self-powered color switching with multicolor display (light yellow, transparent, light red, dark green, dark blue and black). As an energy storage device, the as-assembled device provides open-circuit voltages up to 3.5 V (Al anode/Ti-V₂O₅ cathode) with an areal capacity of up to 933 mA h m⁻² (Al/Ti-V₂O₅ and Al/WO₃), which are the best among those of all reported EES devices. Meanwhile, the utilization of the mixed Li/Al-ion electrolyte and the addition of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) into the films greatly promote the robustness and the cycle stability of the electrochromic layers. Such a new design of the EES device with multicolor display, large charge capacity and high cycle stability can be promising for future color switching/energy storage applications, which may also provide new insights into the design of multifunctional devices.

Metal (Ni, Co or Fe) foams can be in situ converted into metal sulfide (Ni₃S₂, Co₉S₈ or FeS) foams with surface grown N-doped carbon nanotube arrays, and work as efficient superaerophobic electrocatalysts for overall water splitting.

Many previous reports have indicated that the applicable photochromism of WO₃ can only be achieved by combining with metals, semiconductors or organic polymers to improve the coloration efficiency and reversibility, while the investigation of intrinsic WO₃ photochromism has been severely prohibited by its small color change and slow coloration rate. Herein, we report hydrothermally prepared hydrated tungsten oxide nanosheets with fast and reversible intrinsic photochromic response. A gradual yellow-blue color change can be modulated with continuous UV illumination. The following UV/ozone treatment can bleach the nanosheets back to their initial yellowish color within minutes and the reversible process can be continued 20 times without noticeable attenuation, which has never been reported for intrinsic WO₃ photo response. The thin-layered nanostructure of WO₃ indicates a short ionic diffusion length for surface attached species, which promotes fast surface water decomposition upon UV irradiation and accelerates proton intercalation/deintercalation, thus speeding up both the coloration and the bleaching processes. Our research elucidates that hydrated nanostructured WO₃ can present significantly improved photochromic response even without WO₃/metal, WO₃/semiconductor or WO₃/polymer combination, which may lead to technological advances with simple, facilely prepared WO₃ nanosheets in areas such as photolithography, rewritable optical memory devices and nanoinks in inkjet printing.

Nowadays, a variety of multifunctional electrocatalysts are being developed while there is still a lack of suitable design to fully realize their multifunctionalities. Here, we propose a general, simple, two-component design of an electrolyser to replace the traditional three-component design for decoupled water splitting. Trifunctional (OER, HER and ORR) electrocatalysts (such as nickel sulfide foams with surface grown N-doped carbon nanotube arrays) are used as the gas evolution electrode to replace both the cathode and the anode, while materials with suitable redox activities (NaTi₂(PO₄)₃ or commercial Ni(OH)₂) are used as the relay electrode. In such a design, the H₂/O₂ evolution can be switched by reversing the current polarity, and the ORR before the HER consumes the residual O₂ left in the electrolyser, guaranteeing the high purity (∼99.9%) of the as-obtained H₂. With NaTi₂(PO₄)₃ as the relay electrode and the nickel sulfide foam as the gas evolution electrode, owing to the high decoupling efficiency of the NaTi₂(PO₄)₃ relay (97%) and the low HER/OER overpotentials of the trifunctional nickel sulfide foam, an energy conversion efficiency of up to 94.3% can be obtained for the as-assembled electrolyser at a current density of 10 mA cm⁻². When combined with a commercial Si PV module with an efficiency of 14.4%, the as-designed PV-electrolysis system showed a solar-to-hydrogen conversion efficiency of up to 10.4%. Utilization of trifunctional electrocatalysts greatly reduces the complexity of the electrolyser and the overall cost for electrochemical H₂ production, and these electrolysers may potentially be used to construct highly competitive water splitting systems for continuous H₂ production and green energy harvesting. Our research may also bring new insights into the utilization of multifunctional electrocatalysts in other devices, such as metal–air batteries and fuel cells.