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Background With the increasing concerns on the energy shortage and carbon emission issues worldwide, sustainable energy recovery from thermal processes is consistently attracting extensive attention. Nowadays, a significant amount of usable thermal energy is wasted and not recovered worldwide every year. Meanwhile, discharging the wasted thermal energy often causes environmental hazards. Significant social and ecological impacts will be achieved if waste thermal energy can be effectively harnessed and reused. Hence, this study aims to provide a comprehensive review on the sustainable energy recovery from thermal processes, contributing to achieving energy security, environmental sustainability, and a low-carbon future. Main text To better understand the development of waste thermal energy utilization, this paper reviews the sustainable thermal energy sources and current waste energy recovery technologies, considering both waste heat and cold energy. The main waste heat sources are prime movers, renewable heat energy, and various industrial activities. Different waste heat recovery technologies to produce electricity, heating, and cooling are analyzed based on the types and temperatures of the waste heat sources. The typical purposes for waste heat energy utilization are power generation, spacing cooling, domestic heating, dehumidification, and heat storage. In addition, the performance of different waste heat recovery systems in multigeneration systems is introduced. The cold energy from the liquified natural gas (LNG) regasification process is one of the main waste cold sources. The popular LNG cold energy recovery strategies are power generation, combined cooling and power, air separation, cryogenic CO 2 capture, and cold warehouse. Furthermore, the existing challenges on the waste thermal energy utilization technologies are analyzed. Finally, potential prospects are discussed to provide greater insights for future works on waste thermal energy utilization. Conclusions Novel heat utilization materials and advanced heat recovery cycles are the key factors for the development of waste high-temperature energy utilization. Integrated systems with multiply products show significant application potential in waste thermal energy recovery. In addition, thermal energy storage and transportation are essential for the utilization of harnessed waste heat energy. In contrast, the low recovery rate, low utilization efficiency, and inadequate assessment are the main obstacles for the waste cold energy recovery systems. Highlights Industrial waste heat supply technologies and their exhaust features are reviewed. Waste thermal heat recovery technologies are summarized and reviewed. Thermal cold energy recovery technologies are summarized and reviewed. Challenges and prospects of sustainable energy recovery are analyzed.

Low-grade heat accounts for >50% of the total dissipated heat sources in industries. An efficient recovery of low-grade heat into useful electricity not only reduces the consumption of fossil-fuels but also releases the subsequential environmental-crisis. Thermoelectricity offers an ideal solution, yet low-temperature efficient materials have continuously been limited to Bi 2 Te 3 -alloys since the discovery in 1950s. Scarcity of tellurium and the strong property anisotropy cause high-cost in both raw-materials and synthesis/processing. Here we demonstrate cheap polycrystalline antimonides for even more efficient thermoelectric waste-heat recovery within 600 K than conventional tellurides. This is enabled by a design of Ni/Fe/Mg 3 SbBi and Ni/Sb/CdSb contacts for both a prevention of chemical diffusion and a low interfacial resistivity, realizing a record and stable module efficiency at a temperature difference of 270 K. In addition, the raw-material cost  to the output power ratio in this work is reduced to be only 1/15 of that of conventional Bi 2 Te 3 -modules. Thermoelectric materials for low-grade heat recovery applications are limited to Bi 2 Te 3 -based alloys containing expensive Te for decades. Here, the authors demonstrate on a module level, cheap antimonides could enable an efficiency not inferior to that of expensive tellurides.

The integrated waste energy recovery system (IWERS) is a thermal system that recovers waste heat from steam generated in bakeryovens to produce hot water. This reduces energy and water consumption in shopping centers. This article analyzes the technicalimprovement of incorporating renewable solar thermal energy into the system. It introduces the new solar-powered IWERS(SPIWERS) for the first time. The exergetic efficiency of IWERS and SPIWERS was measured over 1 year in real supermarketslocated in different climatic zones to determine their performance variables. This paper presents precise data for future improve-ments in the energy efficiency of waste heat recovery systems, making it an innovative contribution to the field. The exergeticefficiency of IWERS was found to be lower in subtropical climates, but no significant variation was observed in other climatesstudied. Additionally, the exergetic efficiency of IWERS components decreases with ambient temperature, particularly in warmmonths. Regarding SPIWERS, the highest exergetic efficiency values were obtained in oceanic climates. IWERS employs electricboilers, whereas SPIWERS system utilizes solar collectors. Although IWERS exhibited superior overall exergy efficiency, particu-larly in cold climates, SPIWERS distinguished itself with a reduced environmental impact, wholly supplanting electric power withsolar thermal energy and a swift economic return on investment within a period of less than 4 years, a duration that is half that ofIWERS. A detailed examination of the individual components of each system will facilitate the identification of potential avenuesfor enhancement, ensuring the system’s capacity for adaptation to specific climatic conditions and seasonal variations. Thus, theexergy efficiency of the DWH tank in IWERS remains constant across all climatic zones and throughout the year. This exergyefficiency is approximately 65%. In contrast, a notable variation is observed in the case of SPIWERS, which is more pronounced inmore favorable weather conditions. On the other hand, the exergy efficiency of electric water boilers is greater in colder climatesand times of the year, with a range of 30%–40%. Additionally, the exergy efficiency of the solar collector is greater in months andareas with cool ambient temperatures, optimal solar radiation, and moderate fluid temperatures within the collector, with a rangeof 5%–11%.

Crystalline thermoelectrics have been developed to be potential candidates for power generation and electronic cooling, among which SnSe crystals are becoming the most representative. Herein, we realize high-performance SnSe crystals with promising efficiency through a structural modulation strategy. By alloying strontium at Sn sites, we modify the crystal structure and facilitate the multiband synglisis in p-type SnSe, favoring the optimization of interactive parameters μ and m * . Resultantly, we obtain a significantly enhanced PF ~85 μW cm −1 K −2 , with an ultrahigh ZT ~1.4 at 300 K and ZT ave ~2.0 among 300–673 K. Moreover, the excellent properties lead to single-leg device efficiency of ~8.9% under a temperature difference ΔT ~300 K, showing superiority among the current low- to mid-temperature thermoelectrics, with an enhanced cooling Δ T max of ~50.4 K in the 7-pair thermoelectric device. Our study further advances p-type SnSe crystals for practical waste heat recovery and electronic cooling. Thermoelectric technology directly enables both power generation and electronic cooling. Here, the authors realize high-performance SnSe crystals with promising device efficiencies by modulating crystal and band structures.

Thermoelectrics have great potential for use in waste heat recovery to improve energy utilization. Moreover, serving as a solid-state heat pump, they have found practical application in cooling electronic products. Nevertheless, the scarcity of commercial Bi 2 Te 3 raw materials has impeded the sustainable and widespread application of thermoelectric technology. In this study, we developed a low-cost and earth-abundant PbS compound with impressive thermoelectric performance. The optimized n-type PbS material achieved a record-high room temperature ZT of 0.64 in this system. Additionally, the first thermoelectric cooling device based on n-type PbS was fabricated, which exhibits a remarkable cooling temperature difference of ~36.9 K at room temperature. Meanwhile, the power generation efficiency of a single-leg device employing our n-type PbS material reaches ~8%, showing significant potential in harvesting waste heat into valuable electrical power. This study demonstrates the feasibility of sustainable n-type PbS as a viable alternative to commercial Bi 2 Te 3 , thereby extending the application of thermoelectrics. The authors fabricate a thermoelectric cooling device based on n-type PbS based material, which exhibits a remarkable cooling temperature difference of 36.9 K at room temperature, and the single-leg power generation efficiency of 8%.

Thermoelectric materials can realize direct conversion between heat and electricity, showing excellent potential for waste heat recovery. Cu 2 Se is a typical superionic conductor thermoelectric material having extraordinary ZT values, but its superionic feature causes poor service stability and low mobility. Here, we reported a fast preparation method of self-propagating high-temperature synthesis to realize in situ compositing of BiCuSeO and Cu 2 Se to optimize the service stability. Additionally, using the interface design by introducing graphene in these composites, the carrier mobility could be obviously enhanced, and the strong phonon scatterings could lead to lower lattice thermal conductivity. Ultimately, the Cu 2 Se-BiCuSeO-graphene composites presented excellent thermoelectric properties with a ZT max value of ~2.82 at 1000 K and a ZT ave value of ~1.73 from 473 K to 1000 K. This work provides a facile and effective strategy to largely improve the performance of Cu 2 Se-based thermoelectric materials, which could be further adopted in other thermoelectric systems. Here, the authors devise a synthesis strategy to optimize the stability and thermoelectric performance of Cu 2 Se-based materials. They obtain a maximum ZT value of ~2.82 at 1000 K on Cu 2 Se-BiCuSeO-graphene composites.

Conversion of heat to electricity via solid-state devices is of great interest and has led to intense research of thermoelectric materials1,2. Alternative approaches for solid-state heat-to-electricity conversion include thermophotovoltaic (TPV) systems where photons from a hot emitter traverse a vacuum gap and are absorbed by a photovoltaic (PV) cell to generate electrical power. In principle, such systems may also achieve higher efficiencies and offer more versatility in use. However, the typical temperature of the hot emitter remains too low (<1,000 K) to achieve a sufficient photon flux to the PV cell, limiting practical applications. Theoretical proposals3–12 suggest that near-field (NF) effects13–18 that arise in nanoscale gaps may be leveraged to increase the photon flux to the PV cell and significantly enhance the power output. Here, we describe functional NFTPV devices consisting of a microfabricated system and a custom-built nanopositioner and demonstrate an ~40-fold enhancement in the power output at nominally 60 nm gaps relative to the far field. We systematically characterize this enhancement over a range of gap sizes and emitter temperatures, and for PV cells with two different bandgap energies. We anticipate that this technology, once optimized, will be viable for waste heat recovery applications.

This study investigates carbon black (CB) production challenges, including high energy usage and waste of heat sources, by proposing a waste heat energy recovery concept to increase the sustainability of this energy‐intensive and environmentally impactful process. The research involves a novel integration of a steam power plant (STP) with an industrial CB plant (CBP) using Aspen Plus simulation software. Comparative exergetic performance analyses of the system were conducted with this tool, while the Engineering Equation Solver (EES) was used to evaluate the exergoeconomic modelling of the plant. Additionally, environmental sustainability indicators were determined. The integrated plant system delivered CB capacity of 1817 kg/s, converted 98.03% of CB feedstocks with a purification value of 99.25% and produced 195 MW of electricity, significantly improving plant efficiency. The overall energy and exergy efficiencies for the integrated system are computed as 98.75% and 80.40%, respectively, with the STP contributing to the overall plant improvement. About 50% of the produced exergy was destroyed, with the CB combustor accounting for 48% of the combined plant exergetic destruction. Despite a substantial waste–exergy ratio from CBP, the integration of the STP increased the system’s exergetic sustainability index (ESI) by 18%. The exergoeconomic analysis highlighted the highest cost of destruction in the combustor and evaluated the evaporator as the least exergoeconomic factor driver. Components with potential exergetic and cost destruction improvements were identified. In conclusion, integrating power generation units with CB production plants can markedly reduce thermal heat waste in the CBP and enhance integrated plant environmental performance.

The lack of desirable diffusion barrier layers currently prohibits the long-term stable service of bismuth telluride thermoelectric devices in low-grade waste heat recovery. Here we propose a new design principle of barrier layers beyond the thermal expansion matching criterion. A titanium barrier layer with loose structure is optimized, in which the low Young’s modulus and particle sliding synergistically alleviates interfacial stress, while the TiTe 2 reactant enables metallurgical bonding and ohmic contact between the barrier layer and the thermoelectric material, leading to a desirable interface characterized by high-thermostability, high-strength, and low-resistivity. Highly competitive conversion efficiency of 6.2% and power density of 0.51 W cm −2 are achieved for a module with leg length of 2 mm at the hot-side temperature of 523 K, and no degradation is observed following operation for 360 h, a record for stable service at this temperature, paving the way for its application in low-grade waste heat recovery. The lack of desirable barrier layers prohibits the power generation applications of bismuth telluride thermoelectric devices. Here, the authors construct a kind of Ti barrier layer with high strength and low resistivity with a module exhibiting high thermal stability during the service at 523 K.