[en] We present that microbatteries play a critical role in determining the lifetime of downsized sensors, wearable devices, medical applications, and animal acoustic telemetry transmitters among others. More often, structural batteries are required from the perspective of aesthetics and space utilization, which is however rarely explored. Herein, we discuss the fundamental issues associated with the rational design of practically usable high energy microbatteries. The tubular shape of the cell further allows the flexible integration of microelectronics. A functioning acoustic micro-transmitter continuously powered by this tubular battery has been successfully demonstrated. Finally, multiple design features adopted to accommodate large mechanical stress during the rolling process are discussed providing new insights in designing the structural microbatteries for emerging technologies.

[en] Highlights: • A N,B-codoped carbon nanocage is reported for high efficiency multifunctional electrocatalyst. • DFT calculations reveal the catalytic compatibility of the N,B-codoping for ORR/OER/HER. • A primary zinc-air battery is assembled presenting a maximum power density of 320 mW cm⁻². Nanocarbon materials recognized as effective and inexpensive catalysts for independent electrochemical reactions, are anticipated to possess a broader spectrum of multifunctionality toward oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). A rational design of trifunctional nanocarbon catalyst requires balancing the heteroatoms-doping and defect-engineering to afford desired active centers and satisfied electric conductivity, which however is conceptually challenging while desires in-depth research both experimentally and theoretically. This work reports a N,B-codoped graphitic carbon nanocage (NB-CN) with graphitic yet defect-rich characteristic as a promising trifunctional electrocatalyst through a facile thermal pyrolysis assisted in-situ catalytic graphitization (TPCG) process. Density functional theory (DFT) calculations are conducted, for the first time, to demonstrate that the best performance for ORR/OER and HER can be originated from the configuration with B meta to a pyridinic-N, which presents a minimum theoretical overpotential of 0.34 V for ORR, 0.39 V for OER, and a lowest Gibbs free-energy (ΔG_ads) of 0.013 eV for HER. A primary zinc-air battery is assembled presenting a maximum power density of 320 mW cm⁻² along with excellent operation durability, evidencing great potential in practical applications.

[en] Highlights: • Electric potential in out-of-plane direction across the solid-liquid interface affects the output electric energy. • Correlation between macroscopic droplet motion and the microscopic ion dynamics was investigated. • Dependencies of the operational conditions of the device on output performance were investigated. Energy-conversion devices that generate electric energy from the movement of water have been actively studied. In case where ions play a major role in driving such devices, a clear causal relationship including the effect of ions on the operation of the device has not been clarified. Though, it is assumed that the electric signals generated when the devices are driven by a flowing water droplet or squeezed droplets are associated with the potential profile across the solid-liquid interface, the understanding of the cause and effect is unclear. The unclear understanding of the principle is a critical bottle neck for the enhancement of device performance and device application, such as ion type and concentration sensor. In this study, we investigated the correlation between the contact-area-dependent electric energy generated by ion dynamics and the electric potential across a solid-liquid interface. Further, the dependencies of the operational conditions of the device on output performance were faithfully investigated and the potential for a novel ion type or concentration sensor was introduced.

[en] Highlights: • A micro pseudo-electrochemical polymerization reaction was proposed. • Two end-to-end BaTiO₃ nanocubes can work as a micro electrochemical cell. • The electric potential is derived from the opposite spontaneous polarized charges. • Ultrasonic excitation is introduced to enhance and renew the piezoelectric charges. Conventional electrochemical polymerization is performed on electrodes driven by a direct current power source. It is impossible to realize an electrochemical polymerization reaction on the surfaces of individual nanocrystals in an aqueous system due to the difficulty of connecting all of the nanocrystals to a power source with wires or with the aid of microfabrication, especially in the environment of liquid. In this work, a micro pseudo-electrochemical polymerization reaction was proposed for in situ synthesis of polyaniline (PANI) on the surface of BaTiO₃ nanocubes to form BaTiO₃@PANI core-shell nanocubes. The electric potential of the micro pseudo-electrochemical polymerization originates from the opposite spontaneous polarized charges on the surface of a pair of adjacent BaTiO₃ nanocubes, which form a micro-scale electrochemical cell in reaction solution. Based on the piezotronic effect of the BaTiO₃ nanocubes, ultrasonic excitation was introduced to renew the piezoelectric charges on the surfaces of the BaTiO₃ nanocubes, and enhance the polymerization reaction. The ferroelectric electric potential and piezotronic effect-induced micro pseudo-electrochemical reactions can also be used in other nanomaterials-based electrochemical applications, such as micro-electrochemical water splitting, micro-electrophotocatalysis, and ultrasonic therapy.

[en] Highlights: • Molecular simulation was used to computer structures and properties of NaCl–KCl over operating temperature. • The relationship of molten salt properties and local structure was investigated. • Numercial results showed good accuracy and stability for the proposed strategy. • The BMHTF force field in this study has been proved reasonable to calculate the molten phase properties. Comprehensive molecular simulations have been carried out to compute local structures and transport properties of different components of binary NaCl-KCl over a wide operating temperature range. The partial radial distribution functions, coordination number curves and angular distribution functions were calculated to analyze the influence of temperature and component on local structures of molten Alkali Chlorides. Transport properties were calculated by using reverse non-equilibrium molecular dynamics (RNEMD) simulations including densities, shear viscosity and thermal conductivity. The results show that ion clusters are considered to be formed and the distance of ion clusters become larger with increasing temperature which has great influence on macro-properties. The calculated properties have a good agreement with the experimental data, and similar method could be used to computationally calculate the properties of various molten salts and their mixtures.

[en] Highlights: • High efficiency colloidal quantum dot solar cells were developed using highly polar SAM modified ZnO electron accepting layers. • Synthesized novel self-assembling highly polar molecules for electric dipole layer (EDL). • The solar cell performance was improved by the modification due to enhanced internal electric field and charge collection efficiency. • The power conversion efficiency of 10.89% with energy loss of 0.433 eV was achieved. High performance colloidal quantum dot (CQD) solar cells were developed by modifying ZnO electron accepting layers (EALs) using self-assembled monolayers (SAMs) of highly polar molecules. A high molecular dipole moment of −10.07D was achieved by conjugating a strong electron donor, julolidine, to an electron acceptor, a cyanoacetic acid unit, through a thiophene moiety. The energetic properties of ZnO EALs were manipulated with respect to the dipole moment of the modifying molecules. The built-in potential (V_bi) and internal electric field (E_int) of CQD solar cells could thereby be tuned. The power conversion efficiency (PCE) of the SAM modified devices was improved from 3.7% to 12.9% relative to the unmodified devices as a function of molecular dipole moments (from −5.13D to −10.07D). All figures-of-merit of solar cells were improved simultaneously by SAM modification due to enhanced V_bi, E_int, and charge collection efficiency. The PCE of the highly polar molecule modified devices reached 10.89% with a V_OC of 0.689 V, whereas that of the unmodified devices was 9.65% with a V_OC of 0.659 V. Notably, the remarkably low energy loss of 0.433 eV is achieved in the SAM modified devices.

[en] Highlights: • An ultrathin, lightweight, flexible, and sustainable paper based self-powered system is presented. • A wireless human-machine interaction system is designed for documents management and smart reading with TENG. • The self-powered system could be applied both in sustainable power source and self-powered sensors. Developing lightweight, flexible and sustainable sensor networks with miniaturized integration and functionality for the Internet of Things (IoT) remains a challenge and an urgent demand for the next-generation electronic devices. Paper-based electronics, which represents one of the main green electronics in the future, have been considered as one of the most exciting technologies to meet the consumption of the frequently upgraded electronics. Here, we presented an ultrathin (about 200 µm) and lightweight paper-based self-powered system that consists of a paper-based triboelectric/piezoelectric hybrid nanogenerator and a paper-based supercapacitor. Under human motions such as flipping the page and moving the book/document, the as-fabricated self-powered system built-in the smart book/document was capable of sustaining power for portable devices, such as continuously driving LEDs and the temperature/humidity sensor. With the signal-processing circuit, the paper-based system was further developed into a wireless human-machine interaction system for documents management and smart reading. The ultrathin and highly flexible characteristics of the self-powered system not only endow the device with power generation feature for portable devices, but also build up the wireless human-machine interactions in developing potential applications for the IoT.

[en] Highlights: • Few layer graphene cathodes can achieve stage-one intercalation of AlCl₄^- in Al ion batteries. • Surface defects in few layer graphene adversely influence the intercalation process. • N-doped few layer graphene cathodes inhibit AlCl₄^- intercalation and deteriorate cell performance. Few layer graphene is a promising cathode material for aluminum-ion batteries that use chloroaluminate (AlCl₄^-) ionic liquids as the electrolyte. A fundamental understanding of interactions between the few layer graphene cathode and the ionic liquid electrolyte is key for realizing the full potential of these systems. Through in situ Raman spectroscopy and density functional theory calculations, we show that the cathode is capable of achieving stage-one intercalation within the operating voltage window, leading to improved cell performance. We also show that the presence of structural defects in few layer graphene such as pores induced via plasma exposure or nitrogen dopants can deteriorate the cell performance by either decreasing the electrical connectivity or precluding stage-one intercalation respectively. The cathodes made with highly crystalline few layer graphene display high power and energy densities (~ 200 W h kg⁻¹ at 200 W kg⁻¹ and ~ 160 W h kg⁻¹ at 5000 W kg⁻¹), and are stable with no loss in performance up to 1000 cycles while fully charging to 2.4 V.

[en] Highlights: • An ultralight and flexible self-charging power system has been proposed. • The electrospun PAN papers and carbon papers are basic components of TENGs and SCs. • EP-TENG act as mechanical energy harvester and EP-SC act as energy storage device. • The self-charging power system can sustainably drive electronic devices. To pace with the miniaturization and flexibility tendency of wearable/portable electronics, it is a challenge to develop the lightweight and sustainable power sources with high efficiency. In this work, we proposed an ultralight and flexible self-charging power system via all electrospun paper based triboelectric nanogenerators (EP-TENGs) as energy harvester and all electrospun paper based supercapacitors (EP-SCs) as storage device, respectively. The EP-TENG, made into arch-shape, derived from one nonconductive PAN paper as a triboelectric layer and conductive carbon paper as electrodes. In EP-SC, the conductive carbon paper acted capacitive materials, while the nonconductive PAN paper severed as separator. Therefore, the superiority of the self-charging system is reflected by the properties of these two kinds of papers with lightweight, convenient, low cost, mechanical flexible and tailorable, which were prepared by a simple electrospinning and followed annealing method. When three-parallel EP-TENGs were further integrated with three-series EP-SCs, the all flexible electrospun papers based self-charging power system was constructed. As an effective and innovative power provider, the self-charging system was demonstrated to admirably power an electronic watch and calculator. The proposed self-charging system can be a promising candidate for self-powered wearable electronics and the development of next generation power system in practical applications.

[en] Highlights: • The piezoelectric coefficient of this flexible piezoelectret generator reached ~ 6300 pC/N. • The generator generated peak power of ~ 0.444 mW and worked steadily for ~ 90000 cycles. • The generator worked steadily under extreme moisture and temperature up to 70 °C. Stable and repeatable operation is paramount for practical and extensive applications of all energy harvesters. Herein, we develop a new type of flexible piezoelectret generator, which converts mechanical energy into electricity consistently even under harsh environments. Specifically, the generator, with piezoelectric coefficient (d₃₃) reaching ~ 6300 pC/N, had worked stably for continuous ~ 90000 cycles, and the generator pressed by a human hand produced load peak current and power up to ~ 29.6 μA and ~ 0.444 mW, respectively. Moreover, the capability to steadily produce electrical power under extreme moisture and temperature up to 70 °C had been achieved for possible applications in wearable devices and flexible electronics.