No abstract

Supercapacitors (SCs), including the most established electrochemical double layer capacitors (EDLCs), are energy storage systems that can be charged in the second timescale, while sustaining a great number of re-charge cycles without losing efficiency. Undoubtedly, their major drawback is their insufficient energy density compared to batteries. Meanwhile, the reduction of the SC costs using cheap and sustainable electrolytes is also a trivial criterion to be considered in the competition race of the energy storage technologies. In this work, we report an extended characterization of aqueous SCs, screening acidic, neutral and alkaline electrolytes, as well as the addition of KI as a prototypical redox additive, and performing both two- and three-electrode configuration measurements. By using near-neutral electrolytes, our aqueous EDLCs can reach a maximum cell voltage superior to 2 V, enabling energy densities higher than 18 W h kg−1 (comparable or approaching those of lead acid and Ni–Cd batteries) at a power density up to almost 7 kW kg−1 (significantly superior to those of competing battery technologies). The introduction of redox additives can significantly increase the capacity of the SCs. However, compared to EDLCs, both the cell voltage and the energy efficiency of the SCs decrease because of partially irreversible faradaic redox reactions and overpotentials of kinetically limited redox reactions. While debunking the myth that aqueous SCs exhibit low energy density, our study also remarks the importance of adequately assessing aqueous SCs, showing the current challenges of advanced SC architectures alternative to EDLCs.

Edible electronics is a growing field that aims to produce digestible devices using only food ingredients and additives, thus addressing many of the shortcomings of ingestible electronic devices. Edible electronic devices will have major implications for gastrointestinal tract monitoring, therapeutics, as well as rapid food quality monitoring. Recent research has demonstrated the feasibility of edible circuits and sensors, but to realize fully edible electronic devices edible power sources are required, of which there have been very few examples. Drawing inspiration from living organisms, which use redox cofactors to power biochemical machines, a rechargeable edible battery formed from materials eaten in everyday life is developed. The battery is realized by immobilizing riboflavin and quercetin, common food ingredients and dietary supplements, on activated carbon, a widespread food additive. Riboflavin is used as the anode, while quercetin is used as the cathode. By encapsulating the electrodes in beeswax, a fully edible battery is fabricated capable of supplying power to small electronic devices. The proof‐of‐concept battery cell operated at 0.65 V, sustaining a current of 48 µA for 12 min. The presented proof‐of‐concept will open the doors to new edible electronic applications, enabling safer and easier medical diagnostics, treatments, and unexplored ways to monitor food quality.

2D metal monochalcogenides have recently attracted interest for photoelectrochemical (PEC) applications in aqueous electrolytes. Their optical bandgap in the visible and near‐infrared spectral region is adequate for energy conversion and photodetection/sensing. Their large surface‐to‐volume ratio guarantees that the charge carriers are photogenerated at the material/electrolyte interface, where redox reactions occur, minimizing recombination processes. However, solution‐processed photoelectrodes based on these materials exhibit energy conversion efficiencies that are far from the current state of the art expressed by established technologies. This work reports a systematic morphological, spectroscopic, and PEC characterization of solution‐processed films of photoactive InSe flakes for PEC‐type photodetectors. By optimizing the thickness and hybridizing InSe flakes with electrically conductive Sn:In2O3 (ITO) nanocrystals, photoanodes with a significant photoanodic response in both acidic and alkaline media are designed, reaching responsivity up to 60.0 mA W−1 (external quantum efficiency = 16.4%) at +0.4 V versus RHE under visible illumination. In addition, a strategy based on the use of sacrificial agents (i.e., 2‐propanol and Na2SO3) is proposed to improve the stability of the InSe and ITO/InSe photodetectors. Our data confirm the potential of 2D InSe for PEC energy conversion and sensing applications, remarking the challenges related to InSe stability during anodic operation.

The development of edible electronics and robotics represents a novel opportunity in several application scenarios, from food monitoring and healthcare to search and rescue. In this context, the EU-funded ROBOFOOD project aims to merge food science, robotics, and engineering to study the possible application of food-derived materials in traditional electronic and robotic components. Besides the possible out-of-body applications, the use of food-derived materials holds great potential for gastrointestinal (GI) monitoring. Avoiding the use of toxic materials, digestible sensorsi.e. diagnostic food -can reduce the risk of poisoning and retention in case of device malfunctioning, limiting the need for surgical extractions.Here we present an edible pressure-induced contact-resistance pressure sensor made of a gelatin-based body, an activated carbon conductive coating, printed gold electrodes and an ethyl cellulose substrate. Preliminary results show that the sensor is successful in detecting pressure changes above a certain threshold depending on the diaphragm height. For a device with a height of 500 µm, the pressure threshold was between 20.3 and 25.3 g/cm 2 . While further developments are required to enable the use of the sensor in real-case scenarios, this work represents a first proof-of-concept of diagnostic food.

Edible electronics and robotics are emerging areas intimately bridging food science and engineering to deliver technology using food‐derived materials. Edible devices offer unprecedented opportunities thanks to features such as bioresorbability, nutritional value, associated taste, minimal toxicity, and sustainability. However, several challenges need to be addressed to bring edible devices closer to reality. Although prototypal edible sensors are available, rotation sensors—an essential component for orientation perception—are still missing. Integrating sensors, actuators, and structural components into an edible system also remains a challenge due to the lack of processes and standardization. Here the first edible tilt sensor is presented. Starting from a commercial nonedible bistable tilt sensor, each material is replaced with edible equivalents using simple and straightforward fabrication approaches. Its functionality is validated in the first implementation of an autonomous and partly edible rolling robot, which has a nutritional value of 807.5 kcal and integrates gelatin actuators, an array of tilt sensors, and an edible wheeled frame. The robot works in closed loop, perceiving its orientation and input for actuation from the sensors. These findings may pave the way to novel edible technologies, from drug delivery for wild animals to health applications.

In this work, we report the synthesis of an active material for supercapacitors (SCs), namely α-Fe2O3/carbon composite (C-Fe2O3) made of elongated nanoparticles linearly connected into a worm-like morphology, by means of electrospinning followed by a calcination/carbonization process. The resulting active material powder can be directly processed in the form of slurry to produce SC electrodes with mass loadings higher than 1 mg cm−2 on practical flat current collectors, avoiding the need for bulky porous substrate, as often reported in the literature. In aqueous electrolyte (6 M KOH), the so-produced C-Fe2O3 electrodes display capacity as high as ~140 mAh g−1 at a scan rate of 2 mV s−1, while showing an optimal rate capability (capacity of 32.4 mAh g−1 at a scan rate of 400 mV s−1). Thanks to their poor catalytic activity towards water splitting reactions, the electrode can operate in a wide potential range (−1.6 V–0.3 V vs. Hg/HgO), enabling the realization of performant quasi-symmetric SCs based on electrodes with the same chemical composition (but different active material mass loadings), achieving energy density approaching 10 Wh kg−1 in aqueous electrolytes.