International Journal of Energy Research

Electric double-layer capacitors have attracted considerable attention for energy storage because of their excellent power capability, high stability, and long cycle life. Activated carbon is the most widely employed electrode material for electric double-layer capacitors owing to its high specific surface area, hierarchical porous structure, and high electrical conductivity. However, to increase the energy density of the devices, new synthetic methods for enhancing their specific capacitances are required. We developed a facile preparation method for petroleum pitch-based activated carbon and investigated the optimal conditions to improve its electrochemical performance in terms of rate capability, specific capacitance, and cycle life. The obtained activated carbon exhibited a high specific capacitance (163.67 F/g at 0.1 A/g), which can be attributed to the efficient charge transport due to the micropores developed in the open macroporous walls of the carbon structure and the high electrical conductivity. Our approach provides an efficient strategy for synthesizing activated carbon with excellent properties. The results reveal a correlation between the physicochemical and electrochemical properties of activated carbon.

Achieving excellent electrochemical performance at high charging rate has been a long-cherished dream in the field of lithium-ion batteries (LIBs). As a part of the efforts to meet the goal, an innovative strategy for the synthesis of 3D porous highly graphitic carbon microspheres, to which numerous hollow metal oxide nanospheres are anchored, for use as anode in LIBs is introduced. Hollow carbon nanosphere-aggregated microspheres prepared from the spray drying process are graphitized with the aid of metal catalysts, and subsequent oxidation selectively removed amorphous carbon, leading to the formation of highly conductive graphitic carbon matrix. Numerous hollow metal oxide nanospheres formed simultaneously during the oxidation process via nanoscale Kirkendall diffusion are anchored onto the carbonaceous matrix, effectively reinforcing the structural integrity by alleviating volume changes and reducing lithium-ion diffusion lengths. The synergistic effect of combining hollow metal oxide nanospheres with high theoretical capacity with conductive carbon matrix led to accelerated electrochemical kinetics, resulting in high capacity at high charging rate. In addition, trapping the hollow metal oxide nanospheres inside hollow carbon nanospheres could effectively alleviate the volume changes, which led to high structural stability. When applied as LIB anodes, the microspheres exhibit a capacity of 411 mA h g⁻¹ after 2500 cycles at 10.0 A g⁻¹, with ~80% capacity retention. The anode exhibits a high capacity of 274 mA h g⁻¹ at an extremely high current density of 50.0 A g⁻¹, thus demonstrating the structural merits of the microspheres.

Despite widespread recognition of the serious risk of battery thermal runaway (BTR) in lithium-ion batteries, the process and associated external ignition mechanism remain poorly understood. In this study, BTR was measured using thermodynamics and visualization techniques in 10 lithium-ion batteries under thermal abuse conditions. The venting speed was measured by particle image velocimetry and boundary detection. The external ignition mechanism was characterized in terms of flame area. The average BTR onset temperature across the 10 test batteries was 215.6°C. The average maximum temperature was 831.1°C, and the variation between experiments was high compared with the BTR onset temperature due to swelling, repairing, and venting. BTR occurred in four stages (ejection of vent gas with flame, extinction of flame, random and simultaneous ignition, and flame propagation and flame jet formation). The initial average venting speed was approximately 123.8 m/s. The structural and venting speeds of vent gas were similar after a stable flame jet formed. The speed of the core of the gas jet peaked at 20 to 40 m/s. The venting speed decreased as the distance from the jet core increased.

Wearable or patchable biosensors have attracted tremendous attention due to their continuous health-monitoring capabilities. In particular, self-powered passive biosensors based on a piezoelectric nanogenerator (PENG) have demonstrated measurements of physiological signals from which cardiovascular information can be analyzed such as heart rate and blood pressure. However, challenges still remain with regard to both material and device aspects. For the effective and accurate measurement of extremely weak physiological signals, various methods have been introduced, including employment of inorganic lead-based piezoelectric materials and design of a complex material or device structure. In spite of their effectiveness in enhancing the piezoelectric output response, the introduced methods brought concomitant issues, such as toxicity and complexity. We present unique methods to produce a transparent standalone piezoelectric polymer film which can be directly transferred to any surface such as the human skin. Through a room temperature solvent vapor annealing process, we further enhance the crystallinity and a portion of the ferroelectric β-phase of the transparent standalone polymer film, resulting in an improved piezoelectric output response. Based on these two new methods introduced, we demonstrate a simple sandwich-structured, transparent, and patchable biosensor based on PENG for radial artery detection with significantly reduced complex manufacturing processes, providing great practical value.

Triboelectric nanogenerators (TENGs) have been considered a promising energy harvester. However, the wear-induced limited lifetime of the surface structure on fluoropolymeric contact layers of the TENG has been a critical issue in its commercialization because surface structures on soft engineering materials play a key role in enhancing the generation of electricity in TENGs. After the surface structure on the polymeric contact layer is worn out, the layer is required to be replaced with a new one with intact surface structures to reenhance the degraded output performance of the TENG. Herein, injection molding-assisted mass production is applied to manufacture micro/nanoscale surface-structured perfluoroalkoxy alkane (PFA) contact layers, which exhibit easily replaceable but fully recyclable characteristics. The optimized production time is shorter than 1 min, and the unit cost under $1 of manufacturing surface-structured PFA contact layers is achieved. TENG with the fabricated PFA contact layer can generate over 620 V of voltage and up to 12.4 mW of power from solid-solid contact and separation when the contact area is and the contact frequency is 10 Hz. The manufactured PFA contact layer can be facilely replaced with a new one before the end of its lifetime to maintain the electrical output of the TENG, and the postused one can be fully recycled via reprocessing as the material for injection molding. Consequently, a tile-floor-based TENG is proposed as a proof-of-concept demonstration to show environmentally friendly and closed-loop production of TENGs.

The necessity of transitioning from the fossil fuels era to a green economy based on renewable energy resources has become increasingly urgent. This is in order to minimize the impact of energy supply fluctuations and combat global warming, especially in the wake of the recent oil price shock due to the Russian invasion of Ukraine. The present study is aimed at identifying and analyzing the most influential variables affecting renewable energy consumption (REC) among the G-7 countries using a log-linear dynamic panel model that covers the data period from 1996 to 2018. The results indicated that foreign direct investment (FDI) and regulatory quality index (RQI) have negative impacts on REC, while urbanization and GDP per capita have positive influences. Furthermore, urbanization has the highest absolute value coefficient, which is equal to 1.26. This means that a one percent increase in urban population will lead to about a 1.26 percent increase in REC. This finding highlights the importance of planned urbanization and converting buildings and houses into environmentally friendly structures to promote REC. Also, the positive effect of GDP per capita on REC suggests that stable economic growth will enhance the share of REC in total energy consumption. Thus, the countries should robust their economies against exogenous shocks like energy price jumps. Finally, a two-stage Granger-type cointegration test showed that the variables are in a long-run and stable relationship, which implies the reliability of the research findings.