ABSTRACT
The expansion of the Internet of Things market and the proliferation of wearable technologies have generated a significant demand for textile-based energy storage systems. This work reports the engineered design of hybrid electrode nanomaterials of N-doped carbon nanotubes (CNT-N) functionalized with two types of manganese oxides (MOs)-birnessite (MnO2) and hausmannite (Mn3O4)-and their application in solid-state textile-based hybrid supercapacitors (SCs). A versatile citric acid-mediated eco-friendly one-pot aqueous precipitation process is proposed for the fabrication of the hybrids. Remarkably, different types of MOs were obtained by simply changing the reaction temperature from room temperature to 100 °C, without any post-thermal treatment. Asymmetric textile SCs were developed using cotton fabrics coated with CNT-N and the hybrids as textile electrodes, and poly(vinyl) alcohol/orthophosphoric acid as the solid-gel electrolyte. The asymmetric devices presented enhanced energy storage performance relative to the symmetric device based on CNT-N and excellent cycling stability (>96%) after 8000 charge/discharge cycles owing to synergistic effects between CNT-N and the MOs, which endowed nonfaradaic and pseudocapacitive features to the SCs. The asymmetric SC based on CNT-N@MnO2 featured 47% higher energy density and comparable power density to the symmetric CNT-N-based device (8.70 W h cm-2 at 309.01 µW cm-2 vs. 5.93 W h cm-2 at 346.58 µW cm-2). The engineered hybrid CNT-N@MO nanomaterials and the eco-friendly citric acid-assisted one-pot precipitation route open promising prospects not only for energy storage, but also for (photo)(electro)catalysis, wastewater treatment, and (bio)sensing.
ABSTRACT
The worldwide energy scarcity arising from the massive consumption of nonrenewable energy sources raised a global awareness of the need for cleaner and affordable energy solutions to mitigate climate change and ensure the world sustainable development. The rise of the Internet of Things and the fast growth of the groundbreaking market of wearable electronics boosted a major quest for self-powered technologies merging energy harvesting and energy storage functionalities to meet the demands of a myriad of market segments, such as healthcare, transportation, defense and sports. Thermoelectric devices are a green energy harvesting solution for wearable electronics since they harness the low-grade waste heat from ubiquitous thermal energy sources and convert it into electrical energy. However, these systems generate electrical energy in an intermittent manner, depend on the local heat release availability and require an additional unit to store energy. Flexible and wearable supercapacitors are a safe and eco-friendly energy storage solution to power wearables, offering advantages of security, longer cycle life, higher power density and faster charging over batteries. However, an additional unit that generates energy or that is able to charge the storage device is required. More recently, a new class of all-in-one thermally-chargeable supercapacitors blossomed to meet the requirements of the next generation of autonomous wearable electronics and ensure an endurable energy supply. This self-chargeable hybrid technology combines the functionalities of thermal energy harvesting and supercapacitive energy storage in a single multitasking device. In this Perspective, the advances in the burgeoning field of all-in-one thermally-chargeable supercapacitors for flexible/wearable applications will be critically examined, ranging from their structure and working principle to the rational design of the composing materials and of tailor-made architectures. It will start by introducing the foundations of single flexible/wearable thermoelectric generators and supercapacitors and will evolve into the pioneering venture of fully-integrated thermal energy harvesting/storage systems. It will end by highlighting the current bottlenecks and future pathways for advancing the development of this sophisticated smart technology.
Subject(s)
Energy-Generating Resources , Wearable Electronic Devices , Electric Power Supplies , Electrodes , Hot TemperatureABSTRACT
Correction for 'Multifunctional mixed valence N-doped CNT@MFe2O4 hybrid nanomaterials: from engineered one-pot coprecipitation to application in energy storage paper supercapacitors' by Clara Pereira et al., Nanoscale, 2018, 10, 12820-12840.
ABSTRACT
This work reports on the design of novel mixed valence hybrid N-doped carbon nanotubes/metal ferrite nanomaterials (MFe2O4, M(ii) = Mn, Fe, Co) with tailored composition, and magnetic and electrical properties through a straightforward eco-sustainable and less time consuming one-pot in situ coprecipitation process. The potentialities of this strategy rely on the lack of oxidative treatments to the support and thermal annealing, besides the use of aqueous conditions, a chelating base (isopropanolamine) and low temperatures. The process afforded the controlled nucleation/growth of the MFe2O4 nanoparticles (NPs), with sizes of 3.2-5.4 nm and superparamagnetic properties, on the surface of the N-doped carbon nanotubes (CNT-N) and their immobilization by covalent bonding. The nitrogen-based functionalities of CNT-N allied with the use of a coprecipitation agent with coordinating properties towards M(ii)/Fe(iii) cations were responsible for these achievements. To unravel the potentialities of the novel nanohybrids (CNT-N@M), they were tested as electrode active nanomaterials in the fabrication of all-solid-state asymmetric paper supercapacitors (SCs). All asymmetric SCs presented significantly higher performance than the symmetric CNT-N based one, with an enhancement of the energy density to up to 6.0× and of the power density to up to 4.3× due to the occurrence of both non-faradaic and faradaic charge storage mechanisms. Moreover, they led to enhanced volumetric energy density (up to 11.1×) and power density (up to 5.2×) compared with other solid-state hybrid paper SCs based on carbon materials recently reported in the literature. These results highlight the importance of conjugating a conductive support bearing N-based functionalities with MFe2O4 NPs featuring redox properties towards synergistically enhanced energy storage.
