Wax from Pyrolysis of Waste Plastics as a Potential Source of Phase Change Material for Thermal Energy Storage

Over the past half-century, plastic consumption has grown rapidly due to its versatility, low cost, and unrivaled functional properties. Among the diff erent implemented strategies for recycling waste plastics, pyrolysis is deemed the most economical option. Currently, the wax obtained from the pyrolysis of waste plastics is mainly used as a feedstock to manufacture chemicals and fuels or added to asphalt for pavement construction, with no other applications of wax being reported. Herein, the thermal pyrolysis of three common waste polyolefin plastics: high-density polyethylene(HDPE), low-density polyethylene(LDPE), and polypropylene(PP), was conducted at 450 ℃. The waste plastics-derived waxes were characterized and studied for a potential new application: phase change materials(PCMs) for thermal energy storage(TES). Gas chromatography–mass spectrometry analysis showed that paraffin makes up most of the composition of HDPE and LDPE waxes, whereas PP wax contains a mixture of naphthene, isoparaffin, olefin, and paraffin. Diff erential scanning calorimetry(DSC) analysis indicated that HDPE and LDPE waxes have a peak melting temperature of 33.8 ℃ and 40.3 ℃, with a relatively high latent heat of 103.2 J/g and 88.3 J/g, respectively, whereas the PP wax was found to have almost negligible latent heat. Fourier transform infrared spectroscopy and DSC results revealed good chemical and thermal stability of HDPE and LDPE waxes after 100 cycles of thermal cycling. Performance evaluation of the waxes was also conducted using a thermal storage pad to understand their thermoregulation characteristics for TES applications.

Thermal and Electrical Properties of Liquid Metal Gallium During Phase Transition

Liquid metal gallium has been widely used in numerous fields, from nuclear engineering, catalysts, and energy storage to electronics owing to its remarkable thermal and electrical properties along with low viscosity and nontoxicity. Compared with high-temperature liquid metals, room-temperature liquid metals, such as gallium(Ga), are emerging as promising alternatives for fabricating advanced energy storage devices, such as phase change materials, by harvesting the advantageous properties of their liquid state maintained without external energy input. However, the thermal and electrical properties of liquid metals at the phase transition are rather poorly studied, limiting their practical applications. In this study, we reported on the physical properties of the solid–liquid phase transition of Ga using a custom-designed, solid–liquid electrical and thermal measurement system. We observed that the electrical conductivity of Ga progressively decreases with an increase in temperature. However, the Seebeck coefficient of Ga increases from 0.2 to 2.1 μV/K, and thermal conductivity from 7.6 to 33 W/(K·m). These electrical and thermal properties of Ga at solid–liquid phase transition would be useful for practical applications.

Bottom-Up Engineering Strategies for High-Performance Thermoelectric Materials

The recent advancements in thermoelectric materials are largely credited to two factors,namely established physical theories and advanced materials engineering methods.The developments in the physical theories have come a long way from the“phonon glass electron crystal”paradigm to the more recent band convergence and nanostructuring,which consequently results in drastic improvement in the thermoelectric figure of merit value.On the other hand,the progresses in materials fabrication methods and processing technologies have enabled the discovery of new physical mechanisms,hence further facilitating the emergence of high-performance thermoelectric materials.In recent years,many comprehensive review articles are focused on various aspects of thermoelectrics ranging from thermoelectric materials,physical mechanisms and materials process techniques in particular with emphasis on solid state reactions.While bottom-up approaches to obtain thermoelectric materials have widely been employed in thermoelectrics,comprehensive reviews on summarizing such methods are still rare.In this review,we will outline a variety of bottom-up strategies for preparing high-performance thermoelectric materials.In addition,state-of-art,challenges and future opportunities in this domain will be commented.

Two quasi-interfacial p-n junctions observed by a dual-irradiation system in perovskite solar cells

In general,perovskite solar cells(PSC)with a sensitized or thin-film architecture absorb light from a single-side illumination,and carrier separation and transport only take place inside the active layer of the perovskite film.Herein,we demonstrated a dualirradiation PSC system in which light passes through both the fluorinated tin oxide(FTO)side and the Au electrode side,resulting in much faster interfacial charge carrier extraction and transportation than that in a single-irradiation system,in which light passes through from either the FTO or semitransparent Au electrode side.This dual-irradiation PSC system with a configuration of FTO/Cl-TiO_(2)/Mp-TiO_(2)/mixed perovskite/spiro-OMeTAD/Au/ITO can form two quasi-interfacial p-n junctions,which occur separately at the interfaces of TiO_(2)/perovskite and perovskite/spiro-OMeTAD.When the PSC device was illuminated simultaneously from both the FTO and Au/ITO sides,the PSC achieved a total power conversion efficiency(PCE)as high as 20.1%under high light intensity(1.4 sun),which is higher than PCE(18.4%)of a single-irradiation system.The time of flight(TOF)photoconductivity,small perturbation transient photovoltaic(TPV),finite-difference time-domain(FDTD)optical simulations,and dual illumination-sidedependent impedance spectroscopy(ISD-IS)were used to authenticate the presence of two quasi-interfacial p-n junctions in the PSC,creating more charge carriers than only one quasi p-n junction,and thus leading to a fast recombination process.

Transparent flexible thin-film p-n junction thermoelectric module

Transparent and flexible thermoelectrics has been highly sought after for future wearable devices.However,the main stumbling block to prevent its widespread adoption is the lack of p-type transparent thermoelectrics and the stringent criteria of electrical and thermal properties matching appropriately between p-legs and n-legs.This work demonstrates the fabrication of p-type PEDOT:PSS films whose optical properties,electrical conductivity,thermal conductivity,and Seebeck coefficient were engineered to perfectly match the n-type indium tin oxide(ITO)counterparts.The dense p-type PEDOT:PSS and n-type ITO thin films show a thermoelectric figure of merit of zT=0.30 and 0.29 at 450 K,and a thermal conductivity of 0.22 and 0.32 W m^(−1) K^(−1),respectively.A flexible thermoelectric generator(TEG)module with a high transmittance of>81%in the visible wavelength range of 400-800 nm is fabricated using 10 pairs of p-type PEDOT:PSS and n-type ITO thin film legs.An ultra-high power density of 22.2 W m^(−2) at a temperature gradient of 80 K was observed,which is the highest power density reported for organic/hybrid-based flexible TEGs so far.Our transparent flexible thin-film p-n junction thermoelectric module with exceptionally high power generation may take a tremendous step forward towards multi-functional wearable devices.

Coupling Degree Evaluation of China’s Internet Financial Ecosystem Based on Entropy Method and Principal Component Analysis

This paper attempts to evaluate the coordinated development state of the subsystems within the internet financial ecosystem in China from 2011 to 2016.Focusing on the main business modes,technological innovation,and the external environment,we select 29 indicators to construct an index system and adopt a coupling coordination degree model for evaluation.Furthermore,we use two weight calculation methods,entropy weight and principal component analysis,to ensure the robustness of the results.The empirical results show that China’s internet financial ecosystem experienced five development stages from 2011 to 2016,which are moderate disorder,near disorder,weak coordination,intermediate coordination,and good coordination.Different methods of obtaining weights have little effect on the empirical results.These findings suggest that at the beginning,the coordinated development of China’s internet financial ecosystem was hindered by factors including the scarcity of main business modes and the defect of technological innovation;then,with the rapid development of China’s internet industry,the external environment became another drawback in coordinated development.Finally,based on the findings,we give some policy recommendations from a global perspective to achieve a sustainable internet financial ecosystem.