Phase change heat storage can solve some new energy intermittent and waste heat recovery problems, but heat storage is needed to act as this energy hub. Since the direct contact heat accumulator has the advantages of simple structure, large heat transfer area, and small heat transfer resistance, it is a good choice for improving energy storage rate. Although a great deal of research has been done on phase change materials and heat accumulators over the years, a systematic review of direct-contact heat accumulators is lacking. This paper reviews the related research on direct contact heat storage, aiming to summarize the research work on direct contact phase change heat storage systems. Various phase change materials (PCMs) for direct contact systems are analyzed, and the study of PCM melting crystallization behavior, heat transfer coefficients and system performance in direct contact systems is summarized, as well as the improvement methods for direct contact vessels and PCMs. It provides a useful reference for future research on direct-contact heat storage systems.

This study aims to investigate the effect of NaOH immersion time and concentration on the activation of carbon from Oil Palm Frond (OPF), specifically focusing on the surface morphology and characteristics as the electrodes to biobattery application. The method employed involves carbonization and activation with NaOH at various concentrations: 0.5 M, 1 M, 1.5 M, 2 M, and 2.5 M, along with different immersion times of 12, 18, 24, 30, and 36 hours. Subsequently, the activated carbon is analyzed using a Scanning Electron Microscope (SEM) to observe its morphology, and the Brunauer Emmett Teller (BET) method is utilized to determine the carbon surface area. Furthermore, a voltage test uses a multimeter to assess the electric potential properties. Another outcome of this study is developing a prototype bio-battery POWER. Activated carbon from oil palm frond (OPF) testing resulted in 1 M NaOH, giving the highest surface area of 336.493 m 2g -1, and immersion time at 30 hours gave the optimum result of 396,808 m 2g -1. At the same time, the biobattery electrical test voltage of 0,653 V at a concentration of 1 M and 0,902 V at 30 hours of immersion.

This study aims to green synthesize and full characterize CdO nanoparticles by means of an environmentally friendly synthesis using Crocus sativus in its reaction with cadmium ions. The CdO nanoparticles were characterized and their purity was confirmed by XRD and UV.-Vis. spectroscopy. Moreover, scanning electron microscopy (SEM) showed that the prepared cadmium oxide nanoparticles were polymorphic. Furthermore, cadmium oxide nanoparticles were cast in the gas storage (H 2) study. The hydrogen storage results prove that the maximum H 2 uptake was equal to 2.85 Wt.%H 2 at a pressure of 69 bar at 77 K with ∆H=0.62607 KJ/mol H 2 and ∆S=3.35697 J/mol H 2. K. Moreover, the thermodynamic studies under four different temperatures proves that the maximum H 2 uptake could be recorded at a pressure limit of 69-86.2 bar.

The electrochemical and charge storage performance of a fluorine-free structurally flexible pyrrolidinium-based ionic liquid hybrid electrolyte (HILE) in a symmetric graphite-based supercapacitor is thoroughly investigated. The HILE revealed thermal decomposition at 270 ºC, a glass transition (T g) temperature of −73 ºC, and ionic conductivity of 0.16 mS cm −1 at 30 ºC. A systematic variable temperature 1H and 31P NMR spectroscopy and diffusometry, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge-discharge (GCD) are employed. HILE-based supercapacitor demonstrated a notable specific capacitance of 186 Fg −1 at a scan rate of 1 mVs −1 and a specific capacitance of 122 Fg −1 at a current density of 0.5 Ag −1. The maximum energy density of 49 Wh kg −1, a power density of 370 W kg −1 at a current density of 0.5 A g −1 and a potential window of 4V were obtained. HILE displayed a promising electrochemical performance over a wide potential window of 4V and temperature range (−20 ºC to 90 ºC) in a symmetric graphite supercapacitor.

The electrochemical performance of Polyaniline (PANI) can be significantly improved due to the incorporation of spinel-type transition metal oxide, i.e., 1 wt. % of Nickel Ferrite (NiFe 2O 4) into the PANI matrix. In this report, we have synthesised NiFe 2O 4 (NF), PANI1:1 ratio, PANI1:2 ratio, and PANI/NiFe 2O 4 nanocomposites, i.e., PANI1:1/NF1 and PANI1:2/NF2 nanocomposites by in-situ oxidative polymerization method. The conducting network formed in the nanocomposite significantly increases the multiple valence states of the metal for the electrolytic ions. The PANI/NiFe 2O 4 nanocomposite shows good interaction and was confirmed by Fourier Transform Infra-red Spectroscopy (FTIR) and Raman analysis. The SEM analysis reveals a uniformly porous and agglomerated globular morphology of the nanocomposite. Also, the PANI/NiFe 2O 4 composite (PANI1:1/NF1) exhibits enhanced supercapacitive properties due to improve strong conducting path of PANI, which helps to provide the delocalization of the electrons in the polymeric chain. The highest specific capacitance ~ 758 Fg -1 is achieved for PANI 1:1/NF1 sample as compared to bare PANI1:1 (677 Fg -1), PANI1:2 (500 Fg -1), NF (253 Fg -1) and other PANI1:2/NF2 (686 Fg -1) samples at 10 mV/s scan rate in a two-electrode system due to NF nanoparticles filling the vacant places in the polymeric matrix. The energy density (54 Whkg -1), power density (1705 Wkg -1) and good cycling stability approx. 97 % after 10000 GCD cycles of the device is found for PANI1:1/NF1. The EIS studies further confirm that the PANI 1:1/NF1 device has a lower charge transfer resistance (R ct) ~ 0.35 Ohm in comparison to other fabricated devices. It seems that NiFe 2O 4 acts as a “superhighway” for charge transportation between PANI which is beneficial for supercapacitors.

Microfibrillated cellulose (MFC) with reinforcing effects is a useful building block in the fabrication of flexible and thin supercapacitors. Herein, a hybrid tin oxide-cellulose nanocomposite was hydrothermally produced and coated on MFC thin films to form a supercapacitor. The hybrid tin oxide-cellulose thin films were structurally analyzed using scanning electrode microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The cellulose thin film with the highest loading of hybrid tin oxide-cellulose nanocomposite exhibited a specific capacitance of 225.88 F/g at 100 mV/s and 486.38 F/g at 20 mV/s in the three-electrode electrochemical system. In addition, it revealed good cyclic stability up to 40 cycles run continuously with 95% cyclic retention. The high specific capacitance and superior cyclic stability could be related to the enhanced charge mobility and ion diffusion between the solid and electrolyte interface. The cellulose thin film coated with flower-like hybrid nanocomposite showed great potential in energy storage.