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Abstract Thermoelectric (TE) materials that directly convert heat to electricity are of great significance for sustainable development. However, TE generators (TEGs) made from electronic TE materials suffer from low Seebeck coefficient (10−2–100 mV K−1). While ionic TE capacitors based on ionic conductors exhibit high thermovoltage (100–102 mV K−1), ionic TE capacitors provide power discontinuously only under variation of temperature gradient as ions cannot transport across electrodes to external circuits. Herein, an ionic/electronic hybrid nanocomposite TE converter (NCTEC) by integrating carbon nanotube/polylactic acid nanofibrous fabrics (CPNF) with gelatin ionogel is reported. The resulting NCTEC exhibits a record‐high output power density normalized by squared temperature gradient (Pave/ΔT2) of 1.72 mW m−2 K−2 and realizes continuous power output (over 12 h) at a constant temperature gradient, which is among the highest reported power output for TE converters and can be attributed to the combination of substantial increase in interfacial capacitive effect between ionogel and CPNF and an optimized electrical property of the CPNF. The work provides an effective strategy to overcome the limitations of both TEGs and ionic TE capacitors.

Electricity generation through photovoltaic panel (PV) has gained momentum and is considered as the best option. Some of the issues which need immediate attention include i) maintaining the top surface temperature in the operating range, ii) utilization of the dissipated heat from the panel, and iii) heating from unused infrared (IR) photons. Cooling with heat harvesting devices based on the Peltier effect requires comparatively less maintenance and is emerged as a cost-effective option. This study highlighted the potential application of heat harvesting devices (HHDs) to enhance electricity generation and thereby increasing the performance efficiency of the PV panel. Different approaches to photovoltaic cooling to maintain the surface temperature were also evaluated. It is observed that the electrical efficiency is almost 1.2–1.5 times higher in the case of functional PV panel in comparison to commercial (Blank) PV panels. Laboratory investigations using the solar simulator for comparing the different systems by illumination of similar solar light intensity revealed a significant impact on electrical efficiency. It was observed that blocking IR components at a time using cut-off filters enhances the efficiency by 0.8 times. This study has also shown that cooling techniques for PV maintain a low and stable operating surface temperature by extracting the thermal heat to improve the overall conversion efficiency of the commercially available photovoltaic panel. Engineers and stakeholders working on the photovoltaic system theory, design, scale-up, and/or application for providing cleaner energy might benefit from the reported study. [Display omitted] • Efficiency of Functional photovoltaic panel (commercial panel integrated with cooling system) is higher than commercial panel. • Heat harvesting device along with fins improves the efficiency significantly. • Experiments in controlled conditions at lab scale and at higher scale shows efficiency enhancement. • Lower Levelised cost of electricity for functional panel suggests large energy application with high business potential. [ABSTRACT FROM AUTHOR]

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Here, we present our current attempt to intrinsically dope Ni0, Co0, and Fe0 nanoparticles within NiII‐, CoII‐, and FeII‐borate glassy matrices, respectively. The system was prepared by one‐pot reaction of the desired MTII salt with excess NaBH4 through an in‐situ reduction and hydrolysis processes to afford metallic MT0 nanoparticles dispersed into the MT‐BO3 matrix. The composition and structural characteristics of these MT0:MT‐BO3 materials were identified by thermal oxidation, ATR‐IR, X‐ray powder diffraction, and magnetic techniques as glassy/amorphous borate matrices containing magnetic nanoparticles. The electrical conductivity (σ) of cold‐pressed discs of these metal‐doped composites shows that they behave as nonohmic semiconductors within the temperature range of 303 ≤ T ≤ 373 K suggesting a mixed electronic‐ionic conduction. However, their thermal conductivity (κ) occurs through phonon lattice vibration dynamics rather than electronic. The σ/κ ratio shows a steep non‐linear increase from 9.4 to 270 KV−2 in Ni0:Ni‐BO3. In contrast, a moderate‐weak increase is observed for Co0:Co‐BO3 and Fe0:Fe‐BO3 analogs. The obtained materials are examined for thermoelectric (TE) applications by determining their Seebeck coefficient (S) power factor (PF), figure of merit (ZT), and conversion efficiency (η%). All the TE data shows that Ni0:Ni‐BO3 (S, 80 μVK−1; PF, 97.7 mWm−1 K−1; ZT 0.54; η, 2.15%) is a better TE semiconductor than the other two MT0:MT‐BO3. This finding shows that Ni0:Ni‐BO3 is a promising candidate to exploit low‐temperature waste heat from body heat, sunshine, and small domestic devices for small‐scale TE applications. [ABSTRACT FROM AUTHOR]

Solar energy offers various advantages, including ease of access and improved predictability compared to other renewable energy sources in vogue. This energy source is used for a variety of applications, including power generation, desalination, and heating. PV panels are commonly used to generate direct electricity. The acquired solar thermal energy, on the other hand, it can be used to generate electricity indirectly via a medium like a solar tower. PV panels are being utilised for small-scale and off-grid energy generation, and their efficiency is affected by a number of factors such as operating temperature, the material used in their construction and solar irradiation. Also the conversion efficiency of the PV panels reduces as the temperature increases. This paper discusses various cooling approaches that can be used to lower the operating temperature of PV cells. The goal of this review study is to improve the performance of small household PV systems by keeping cell temperatures as low as possible and uniform. The influence of the operating temperature of the cells using various cooling strategies are also discussed along with the electrical efficiency. This study looks at the benefits and drawbacks of passive and active cooling on the operating performance of PV panel.Article Highlights: Efficiency is affected by solar radiation, dust, shading, temperature and humidity. Liquid spraying improves the electrical performance by reducing the temperature. Fins harvest the dissipated heat of panel and increases its conversion efficiency. Phase change material and heat pipes are effective passive heat control technologies. For greater energy transmission and faster cooling, active methods are preferable. [ABSTRACT FROM AUTHOR]

The reduced electrical efficiency of PV modules caused by the increase of cell temperature, is a crucial issue for photovoltaic applications in buildings. Traditional solutions focus on passive cooling techniques to achieve heat regulation of PV modules, but cannot use effectively solar radiation not absorbed by solar cells. Therefore, in the current study a spectral splitting PV/T system is developed, which targets to filter part energy with Ag nanofluid and balance the effective heat and electricity harvesting for buildings. For this purpose, an indoor experimental investigation using a solar simulator is carried out to evaluate the performance of spectral-splitting PV/T system with optimal Ag nanofluid. The effects of solar radiation, optical thickness and mass fraction on the heat/electricity yield are discussed to illustrate the potential utilization in buildings. Results indicate that increased solar radiation would have a negligible effect on the electrical efficiency with a cell temperature of 25 °C. Due to the reduced transmittance of the Ag nanofluid caused by the increased optical thickness or mass fraction, electricity yield is decreased but harvest of heat is increased. In addition, adding Ag/water nanofluid above PV modules, would have a positive effect on the heat regulation of cell temperature. • Experimental investigation of PV/T system using solar simulator is presented. • The effect of solar radiation on the performance of PV/T systems is investigated. • The correlation between optical thickness/mass fraction and yield is reported. [ABSTRACT FROM AUTHOR]

[Display omitted] • Neutralization flow battery with H 2 electrodes has positive temperature coefficient. • TREC for intermittent and continuous heat harvesting was proposed. • Power up to 10–24 μW cm−2 and efficiency of 1.4–2.9 % w/o recuperation. • Power output can be enhanced to 140 or even 220 μW cm−2 using higher ΔT. • NFB energy efficiency at 20 mA cm−2 was increased by 3.7 % via heat harnessing. An enormous amount of energy is wasted annually in the form of low-grade heat with a temperature below 100 °C. Recently, studies on heat harvesting have focused on semiconductor-based devices, but nowadays, electrochemical devices based on a thermally regenerative cycle (TREC) are growing in importance due to their superior thermoelectric power. Among them, TRECs based on flow batteries (TREC-FB) are especially attractive since they offer more flexibility for heat harvesting and an opportunity for continuous heat-to-power (HTP) conversion. However, this technology struggles due to the high cost of the flow batteries they are based on, particularly the costly electrolyte solutions. We offer a novel approach for continuous heat harvesting based on the emerging technology of the neutralization flow battery (NFB) with low-cost and highly soluble electrolytes, which consists of two hydrogen electrodes immersed in acid and base solutions. Since values of both electrodes' temperature coefficient differ, NFB can be used for heat harvesting: the cell temperature coefficient varies in the range of 0.64–1.1 mV K−1. Here, we present both intermittent and continuous TREC based on NFB, with a focus on the latter due to its convenience. Our study on continuous heat harvesting shows that for a temperature difference between the heat source and heat sink of 25 °C, one can achieve power of 10–24 μW cm−2, and efficiency of 1.4–2.9 % even without any recuperation. Alternatively, increasing the temperature difference to 55 °C results in a 6-fold increase in power at 1.6–3.5 % efficiency. We found that due to the low freezing point of the electrolytes, one can obtain even higher HTP performance if the heat sink temperature is about 0 °C. Additionally, we examined NFB performance under various temperatures and proposed low-grade heat harnessing using intermittent NFB heating/cooling to enhance its cycling performance. We believe that the proposed approaches facilitate further development of high-performance TREC-FB and thereby extend the possibilities for heat harvesting. [ABSTRACT FROM AUTHOR]

We focus on the growth of p-type CuAlO2 thin films and its thermoelectric properties. Thin films are deposited by pulsed laser deposition technique on single-crystal sapphire substrates varying the oxygen partial pressure. Thin film deposited at oxygen partial pressure of 200 mTorr presents bigger grains (about 10 μm in size) and shows Seebeck coefficient as high as 270 µV/K with a conductivity of about 0.8 S/cm so that its power factor is about 5.7 µW/mK2 at 800 K, twice than observed in the film deposited at 60 mTorr of oxygen. [ABSTRACT FROM AUTHOR]

[Display omitted] • Robust and flexible thermogalvanic cells were constructed with bacterial cellulose. • By adding LiBr, the TGC possess excellent anti-drying and anti-freezing properties. • The TGCs had a high toughness and good thermoelectric performance in wide temperature range. • Multifunctional application scenarios of TGC were demonstrated at various temperature. Harvesting the ubiquitous low-grade heat based on thermoelectric materials is an effective approach to ensure sustainable development. Quasi-solid thermogalvanic cell based on hydrogel has attracted considerable attention. However, challenge arise from the limited working temperature range and poor mechanical properties, thus severely restrict their long-term stability and application scenarios, especially under harsh environment. Herein, a robust, flexible and eco-friendly quasi-solid thermogalvanic cell is reported based on natural polymer bacterial cellulose confined with Fe(CN) 6 3−/4− redox couple and hygroscopic salts. The as-fabricated bacterial cellulose-based thermogalvanic cell (BC-TGC) possesses excellent mechanical properties, exhibiting a tension strength of 3.4 MPa, a Young's modulus of 2.58 MPa and a high toughness of 644.6 KJ m−3. The introduction of hygroscopic salts (LiBr) endows the BC-TGC with excellent anti-drying and anti-freezing properties. The thermoelectric performance of BC-TGCs was investigated thoroughly, which could generate steady electricity under a small temperature gradient in a wide working range of −50 to 50 °C. The multifunctional applications of the BC-TGC were demonstrated, indicating that they could adapt to different temperatures and harsh environments, which greatly expanded the application scenarios of TGC. We expect that this study will provide an effective solution for portable, flexible and robust power supplies fabrication for low-grade heat harvesting. [ABSTRACT FROM AUTHOR]

[Display omitted] • A hybrid device made of both electronic and ionic materials. • Harvest heat from both temperature gradient and temperature fluctuation. • Both materials contribute to heat harvesting. • Heat harvesting depends on the temperature fluctuation. Thermoelectric materials based on the Seebeck effect can harvest heat only from temperature gradient, while waste heat can induce both temperature gradient and temperature fluctuation. Here, we demonstrate the high performance in heat-to-electricity harvesting by integrating the thin film of an inorganic thermoelectric material, Bi 0.4 Sb 1.6 Te 3 , with an ionogel that has a high ionic thermovoltage due to the Soret effect. The hybrid inorganic-ionic thermoelectric converter composed of a Bi 0.4 Sb 1.6 Te 3 layer and an ionogel layer can generate power from both the temperature gradient via the Seebeck effect of Bi 0.4 Sb 1.6 Te 3 and the temperature fluctuation via the Soret effect of the ionogel. The overall performance of devices is related to the properties of the two layers, the interface between them, and the temperature gradient and fluctuation. Because of the additional heat harvesting from temperature fluctuation, this hybrid device can exhibit much higher performance in heat harvesting than the control thermoelectric generator (TEG) with the Bi 0.4 Sb 1.6 Te 3 layer alone, depending on the temperature fluctuation and humidity. The power performance of the hybrid converters can be higher than the TEG film by about 1/3 under temperature fluctuation at the relative humidity of 90%. [ABSTRACT FROM AUTHOR]

Silicon is the most widely used functional material, as it is geo-abundant and atoxic. Unfortunately, its efficiency as a thermoelectric material is very poor. In this paper, we present and discuss advances of research on silicon and related materials for thermoelectric applications, mostly focusing on the comparison between the two strategies deployed to increase its performance, namely either reducing its thermal conductivity or, in polycrystalline materials, increasing its power factor. Special attention will be paid to recent results concerning silicon thin films. The enhancement of Si performances has motivated efforts to develop integrated heat microharvesters operating around room temperature, which will be reviewed also in view of their applications to power wireless sensors for the Internet of Things. [ABSTRACT FROM AUTHOR]

Various electrochemical approaches for low-grade heat harvesting have been investigated in recent years. However, most current studies are based on electrochemistry methods, while thermodynamic methods that focus on the general energy conversion mechanism are relatively rare. In this study, to quantify the chemical energy of electrochemical systems, Gibbs free energy is introduced as the third dimension in the conventional T-S diagram from a perspective of thermodynamic cycles, and a graphic analysis method is proposed consequently. Then the ideal cycle, which could identify the conversion relationship among heat, work and chemical energy, is presented guided by the graphic analysis method. A discussion is presented as well to explain the non-ideality of actual cycles. Finally, as a representative case, the energy conversion mechanism and the efficiency expression of thermally regenerative electrochemical cycle are restated, to valid the graphic analysis method. The graphic analysis method polishes the thermodynamic theoretical system of electrochemical systems for heat harvesting where chemical energy matters, and leads to an in-depth understanding on the intrinsic energy conversion mechanism. Furthermore, the graphic analysis method would provide a theoretical guidance for integration of chemical energy into the construction of thermodynamic cycles, and even enlighten the boundary extension of thermodynamic cycles. • A novel graphic analysis method for ESHH is proposed. • The ideal cycle of conversion among heat, work and chemical energy is presented. • The efficiency expression of TREC considering irreversibility is restated. [ABSTRACT FROM AUTHOR]