Stimuli-responsive reversible coloration-change materials represent a highly demanded type of smart systems useful for a wide variety of applications, with a significant growing interest in multicolor abilities. In particular, electrochromic materials have received a great deal of attention due to their versatility and broad range of industrial uses. However, most of the existing electrochromic technologies provide a single coloration, while achieving multiple colors based on simple approaches remains a challenge. The present article reports on PVA gel-based electrochromic devices, containing a single viologen, providing a colorless and two different well-defined colored states. The successful fabrication of a device, based on two viologens (multi-EC gel) with a simple architecture (glass/TCO/multi-EC gel/TCO/glass), with five different multiswitchable colors based on four-zoned electrodes (rainbow-like ECD) is also demonstrated. This novel easy-to-make multichromic system represents a significant breakthrough toward the generation of full-color devices, expanding the potential of electrochromic technology.

Reduced graphene oxide (RGO) films have been electrodeposited on indium tin oxide-coated polyethylene terephthalate (ITO-PET) substrates from graphene oxide (GO) solutions, and the resulting flexible transparent electrodes have been used in electrochromic devices of ethyl viologen (EtV(2+)). The electrochromic performance of devices with bare ITO-PET electrodes and ITO-PET coated with RGO has been compared. Under continuous cycling tests up to large voltages, the RGO film was oxidized and dispersed in the electrochromic mixture. The resulting devices, which contained GO and RGO in the electrochromic mixture, showed lower switching voltages between the colored and bleached states. This electrocatalytic activity of the solution-phase GO/RGO pair toward the electrochemical reaction of the electrochromic redox couple (the dication EtV(2+) and the radical cation EtV(+•)) allowed devices with an optical contrast higher than the contrast of those free of GO at the same applied voltage.

A novel slime‐type electrochromic system based on polyvinyl alcohol (PVA) and borax, in combination with a viologen and a redox pair has been developed. On top of overcoming the limitations of both liquid electrolytes, such as the risk of leakage and difficulty of assembly and of solid electrolytes, such as limited transparency and slow response time, this easy‐to‐make slime electrochromic system offers an excellent wettability and transparency and achieves high‐performance in terms of optical contrast (>65 % at 550 nm), switching time (<5 s as estimated for 90 % of the total transmittance change at 550 nm) and cyclability (8 000–10 000). For the electrochromic devices shown here, the CIELAB 1976 color space coordinates at the “on” state were L*=7.12, a*=18.08, and b*=−21.02, corresponding to a purple color. The color efficiencies were 75.5 cm2 C−1 and 149.3 cm2 C−1 for coloration and bleaching processes respectively.

In order to reduce food waste and meet the needs of the demanding modern consumer regarding the quality of food items, it is crucial to monitor the supply chain and storage conditions of perishable food products. Considering this scenario, temperature plays an important role on food safety and quality during storage and supply. In this work, a critical temperature indicator (CTI) based on a solvent melting point is developed. Furthermore, the present CTI working principle is improved by the use of microfluidics technology. As final result, a novel and functional CTI-smart sensor which combines irreversible visual color changes and radio frequency identification (RFID) technologies is achieved. Such CTI integrated to a RFID tag provides a unique advantage to monitor the supply chain in real time by the simple use of a RFID reader in strategic points.

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