Achieving multifunctional lignin-based carbonized polymer dots (CPDs) with controlled structures lie at the forefront of energy-environmental materials, yet tackling the structure-activity relationship is needed to optimize the assembling design in diverse applications. Here we report a bifunctional dot-sheet heterostructure of intercalating lignin-CPDs into layered double hydroxides (CoNi-LDH) to link Fenton-like water purification and zinc-ion hybrid capacitors (ZIHCs). The amino-functionalized CPDs hold the binding abilities of metal-ions over a wide concentration, posing the potentials to coordinate bimetallic hydroxides. Benefiting from high graphitization and conductivity, the green-emitting CPDs are paired with CoNi-LDH to enhance the interlayer spacing, rapid ionic-inserting transfer, and reversible chemical adsorption. In a three-electrode system, the CoNi-LDH@CPDs exhibit an ultrahigh specific capacitance of 1553.2 F g−1 at 1 A g−1 with excellent rate performance (70.82% capacitance retention at 10 A g−1). Thanks to the optimized geometric and electronic structure, intensified active sites and specific surface area, the CoNi-LDH@CPDs can activate percarbonate to eliminate antibiotic (∼94.44%) via reactive oxygen species and direct electron transfer paths over the entire pH of 3−11, with a robust stability of up to 82.16% even after ten consecutive cycles. After a low-temperature functionalization, the phase transition of layered metallic oxides (CoNi-LMO) is taken place onto the CPDs, which expedites high conductivity and abundant redox active sites to serve as the cathode of ZIHCs. It delivers a superior energy density of 122.97 Wh kg−1 at 1050 W kg−1 with a potential window of 2.1 V, and a long-term cycling durability of 98.89% even at a current rate of 20 A g−1. Our work not only advances the synthesis of CPDs from renewable lignin but also provides the insights into optimizing CPDs-intercalated LDH materials for multifunctional pollutant dissociation and energy storage.

Bismuth sulfide (Bi2S3) exhibits potentials in thermoelectric field, due to their environmental friendliness, high Seebeck coefficients, and low thermal conductivity. However, the peak ZT for binary Bi2S3 does not exceed 1.0, inhibiting its practical applications. Starting from the precipitation smelting of bismuth concentrate process, this study constructs multi-type, multi-scale in-situ secondary phases and porous structures through FeCoNi (FCN) medium-entropy alloy addition, significantly enhancing the ZT value of Bi2S3-based thermoelectric materials. The introduced FCN reacts with pre-synthesized Bi2S3 nanorod matrix during spark plasma sintering and forms precipitate complex with FCN-S core and Bi shell microstructures. FCN doping improves the carrier concentration of Bi2S3 and the reduced Bi from Bi2S3 acts as carrier transport channels for mobility optimization. Due to the stacking effect of Bi2S3 nanorods and the volatile nature of metallic Bi, porous Bi2S3 structure is formed, characterized by randomly-distributed and micro-to-nanoscale pores. The coexistence of various lattice defects effectively scatter phonons and suppress the lattice thermal conductivity, thus an excellent peak ZT of 1.1 is achieved at 773 K in a 0.25 wt.% FCN-doped Bi2S3 sample. This study, drawing on the process of ore smelting, proposes a convenient method for preparing high-performance chalcogenide thermoelectric materials with porous structures.

Emerging carbonized polymer dots (CPDs) from natural aromatic-like lignin biopolymer have ignited the renaissance of sustainable nanoscale biomass valorization but are hindered by structural instability and functionality barriers. Herein, we report an interfacial heterostructure engineering that immobilizes lignin-based dual-emissive CPDs onto Fe, Co layered double hydroxides (LDHs), with the function of a recyclable electrode. The CPDs deliver a stable metal-ion binding behavior via rapid light-quenching with a low limit-of-detection, which are fixed into FeCo-LDH to improve the electrical conductivity, available reactive site, structural stability, and charge storage. The reconstructed FeCo-LDH@CPDs electrode outputs an ultrahigh specific capacitance of 1842.0 F g− 1 at 1 A g− 1. When assembled into a symmetrical supercapacitor (SSCs), it also achieves a superior energy density of 33.79 Wh kg− 1 at 375 W kg− 1, excellent rate performance and long-term cycling lifespan (100

Efficient lithium extraction from salt lakes is critical for lithium development. Lithium/aluminum layered double hydroxides (Li/Al-LDHs) exhibit high selectivity and are considered effective adsorbents for lithium recovery from salt lake brines. However, designing excellent Li/Al-LDH adsorbents with both high adsorption selectivity and cycle stability has remained highly challenging. Here, we demonstrate an adsorption resin composed of porous natural kaolinite and Li/Al-LDHs that enables efficient and stable Li+ adsorption. The Li/Al-LDHs and kaolinite are mixed and plasticized into spherical porous granules. This adsorbent offers high Li+ adsorption capacity for efficient lithium extraction and excellent mechanical strength for long-term use. The adsorbent was then evaluated for lithium recovery from authentic salt lake brines. Consequently, the Li/Al-LDHs-Kln adsorbent achieved a Li+ adsorption capacity of 7.5 mg & centerdot;g-1 at 200 mg & centerdot;L-1 brines from the Qinghai Yiliping Salt Lake, which ranks among the highest values of Mg2+/Li+ ratio at ambient temperature reported to date. After 100 adsorption-desorption cycles, the adsorbent retained a capacity above 7.0 mg & centerdot;g-1. This demonstrates strong stability in both adsorption performance and crystal structure, underscoring its potential for industrial lithium extraction. Thus, the effective application of Li/Al-LDHs adsorbent has the potential to fundamentally transform the lithium supply chain especially for lithium-ion batteries.

Developing carbonized polymer dots (CPDs) from naturally aromatic lignin represents a sustainable blueprint to maneuver the diversified structure of quantum state carbon-cores and polymer-hybrid shell layers. To break the imprison of pure CPDs, a highly compatible system with high-entropy layered hydroxides (HELHs) is acceptable yet challenging direction to modify their surface structure and functionality of CPDs for water remediation. Herein, we report the heteroatom-doped lignin CPDs that exhibit a strongly sensitive and selective binding ability with Fe3+ and Cu2+ ions, thereby expediting a rapid and stable coordination with HELHs. Due to their tunable charge transfer properties, the intercalation of CPDs into HELHs can improve the layer-spacing, electron conductivity, exposed reactive sites and mass-transfer, posing a high-performance peroxymonosulfate (PMS) activator to dissociate antibiotics. The CPDs-HELHs composite delivers a decomposition of over 95% chloroquine phosphate (CQP), tetracycline (TC), oxytetracycline (OTC) and carbamazepine (CBZ), with the superior reaction kinetics, ionic anti-interfering, robust durability and practical water adaptability. Mechanistic studies infer that the CPDs are conducive to interfacial direct electron shuttling and singlet oxygen generation for guiding the non-radical-dominated reaction paths, thereby enhancing both the stability and efficiencies of Fenton-like reactions with broad-spectrum antibiotic removal. This work establishes a feasible heterointerface-engineered lignin-first principle to advance sustainable water purification, bridging biomass-environment insights into carbon-neutral future.

Developing on-demand biomass valorization represents an ideal path to alleviate the double burden of a sustainable energy-environment future, yet exploring tunable lignin-first chemistry to accomplish multifunctional water purification remains elusive. Herein, we report a versatile solvent-fractionation to construct heteroatom-doped multicolor lignin carbon quantum dots (CQDs) with the functions of bimodal pollutant sensing, metal-ionic visualization, and photocatalytic antibiotic dissociation. With the aid of oxidation cleavage and biphasic extraction, the underlying lignin features of molecular weight and functional linkages influence the quantum size and core-surface state of CQDs conferring the unique optical-structure-performance. The N, S co-doped blue-emitting CQDs via light-quenching offer the selective identification of Fe3+-ions in a broad response range with an acceptable limit of detection. The addition of L-cysteine can efficiently restore the fluorescence of CQDs by forming a stable Fe3+-L-cys complex. The green-emissive CQDs are facilely embedded into cellulose hydrogel to directly visualize the presence of metal-ions. A red-CQDs modified ternary ZnIn2S4 (ZIS) composite is fabricated to achieve photocatalytic antibiotic removal with an efficiency of similar to 85%. The excellent photo-generated electron and storage capabilities of CQDs improve the light-capturing, electron conduction, and charge carrier separation of ZIS. The reactive species are of importance to photocatalytic tetracycline oxidation, wherein the electron holes (h(+)) function as the main contributor followed by & sdot;O-2(-), O-1(2) and & sdot;OH. The directly interfacial electron escaping-shuttling with the help of optimized electronic and energy-band structures is confirmed via electrochemical test and theoretical computation. We anticipate that the present work not only sheds substantial light to manipulate polychromatic lignin-based CQDs via a tailored solvent-engineering, but also presents an emerging green route of emphasizing biomass-water nexus. (c) 2025 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license

Tin-based perovskite solar cells are promising lead-free photovoltaic devices, but their performance is limited by severe defect-assisted recombination and inefficient interfacial charge transport. Herein, phenethylammonium iodide (PEAI) was introduced as a buried-interface modification layer between NiOx and the tin-based perovskite absorber, and its concentration-dependent effects were systematically investigated. PEAI modification improved film quality and facilitated charge extraction, while deep-level transient spectroscopy (DLTS) revealed a significant reduction in deep-level defect density and trap capture cross section, confirming effective defect passivation at the NiOx/perovskite interface. Among the investigated concentrations, 1 mg mL- 1 PEAI provided the optimal balance between defect passivation and charge transport, resulting in a champion power conversion efficiency of 7.58%. In addition, the optimized unencapsulated device retained 94% of its initial efficiency after 850 h of storage in nitrogen. This work highlights the importance of concentration-dependent buried-interface engineering and provides insights into defect regulation and charge-transport optimization in NiOx-based tin perovskite solar cells.

The multifunctional waste-free valorization of biomass is urgently needed to shape the carbon-neutral future of sustainable energy storage and water purification, yet it is still suffering from the dilemma of its complex structures and molecular heterogeneities. This work integrates alkaline sulfite fractionation with deep eutectic solvent neutralization to achieve a stepwise conversion of bamboo into bifunctional energy-environment materials. As an electrode of zinc-ion hybrid capacitors, the hierarchically-porous lignin-based cathode with defect-rich architecture delivers an exceptional energy density of 136.1 Wh kg-1 at 900 W kg-1 with outstanding rate capability and long-term cycling stability (84.4% over 10 000 cycles), owing to the enhanced affinity of Zn2+ by Fe, N, and S co-doping. Beyond that, the carbonized pulp-fiber catalysts featuring alkali-etched mass-transfer channels and cobalt-incorporated active-centers demonstrate efficient Fenton-like water remediation, including superior antibiotic adsorption and percarbonate activation (over 85% removal of tetracycline, oxytetracycline, and chloroquine-phosphate at 100 mg L-1), robust anions anti-interference, and durability. Mechanistic and theoretical investigations reveal that the synergistic degradation involves surface-binding radical generation, 1O2, interfacial electron transfer, and adsorption-intensified oxidation, varying with the pollutant physicochemical properties of half-wave potential and molecular orbital energy. This work expands a practical closed-loop lignocellulose platform of bringing advanced functions into biomass-energy-water nexus fields.

Solar-powered seawater desalination offers a promising solution to the urgent issue of water scarcity by utilizing the endless energy of sunlight, yet attaining high-performance wood-structured interfacial evaporation remains elusive. We report a facile approach that combines lignin-based carbon quantum dots (CQDs) and perforated bulk wood to improve the evaporation rate and photothermal conversion, wherein the as-prepared CQDs in the evaporator functions as a intensifier to light adsorption and solar-to-heat conversion. Owing to the photoelectric transition of lignin CQDs, adding lignin CQDs alters the natural structure and properties of wood interface with punched holes, thereby heightening the ratio of intermediate water in the device to lower the enthalpy of water evaporation with salt-tolerance and long-term serviceability. Fluidic simulation reveals that the punched large channels with high water flux provokes the salt concentration gradient in hierarchical pores. In the meantime, the concentrated water at the top layer transports downward by diffusion and convection, thus making the spontaneous horizontal and vertical salt exchange. Through the depositing CQDs onto the surface-carbonized wood, the optimum evaporation performance of 3.722 -4.003 kg m- 2 h- 1 with over 86 % solar-to-vapor efficiency under one sun irradiation is achieved in 0.05 wt% saline water. Owing to the 3D-interconnected porous channels and CQDs photothermal interfaces, the evaporator could operate stably in highly saline water and practical outdoor scene. This work sketch a blueprint of all-wood-based interfacial evaporators with excellent seawater desalination performance, pointing to a broader future for the coordination of sustainable biomass conversion and water purification.

Thick electrodes can reduce the ratio of inactive constituents (e.g., conductive and binder agents) in the overall cell to boost energy and power densities, yet suffering from longer ion diffusion paths has overlooked. Tailoring sustainable wood-structured ultrathick electrode with low-tortuosity hierarchical structure is a promising alternative to achieve energy-dense and stable supercapacitors (SCs). The present work reports a facile vertical-hole engineering that perforates artificial small orifices (similar to 0.5 mm diameter) across the bulk wood in the perpendicular direction to connect the parallel channels, constructing the well-aligned freeway of self-standing wood monolithic electrode with a thickness of 1.3-4.2 mm. Ions and electrons thereby acquire less time travelling to abundant active spots throughout the holistic wood thick electrode, which results in low cell resistance, high rate capability and energy density. Benefitting from the holey structure, the optimum wood thick electrode (with a thickness of 2.5 mm) exhibits a remarkable areal capacitance of 27.2 F cm(-2) at 1 mA cm(-2) and long-term cycling stability, allowing its aqueous symmetric SCs with a maximum areal energy density of 3.16 mWh cm(-2) at 1280 mW cm(-2). The assembled quasi-solid-state device delivers a high areal capacitance (2.9 F cm(-2) at 1 mA cm(-2)) and energy density (1.1 mWh cm(-2)), also indicating the excellent lifespan and structural integrity. The fluidic simulation confirms that the drilled holes enhance the mass transfer of electrolyte, thereby enabling ion exchange and reducing the concentration polarization in the cell. The superior structure of wood-structured ultrathick electrode not only exploits the feasibility in SCs, but also illumines a bright direction to develop renewable electrodes via pore engineering of earth-abundant biomass.

Sustainable carbonized lignin microspheres (CLMs), with their size-tunable electrochemical properties and scalable synthesis, enable the breakthroughs in which inexpensive state-of-the-art electrodes are needed. In the quest for high-capacity battery cathodes, vanadium oxynitride (VNO) have stimulated the intense interest in zinc-ion storage owing to their unprecedented electroactive and physical properties. It is highly desired yet very challenging to boost the high-performance zinc-ion hybrid supercapacitors (ZIHSCs) of carbon-stabilized VNO composite. Inspired by the nature ability to immobilize VNO, we demonstrate the uniform growth of VNO nanoparticles onto the surface of CLMs using a functional-chelation strategy. Owing to the inherent functional species (e.g., hydroxyl, phenolic and carboxyl groups), lignin can provide electron pairs to coordinate with vanadium ions for embedding VNO in amorphous carbon framework. The cross-linking network of CLMs-fixed VNO nanoparticles forms a hierarchical structure, providing an ordered channel to rapidly transport electrolyte ions and electron flow with redox abilities. In a typical three-electrode setup, it exhibits an ultrahigh specific capacitance of 1948 F g(-1) at 1 A g(-1) with an excellent rate performance. As a cathode of ZIHSCs with the tunable compressed densities, the VNO@CLMs delivers a high energy density of 163.6 Wh kg(-1) and superior retention of similar to 66 %, as well as, the long-term stability (over 5,000 charging-discharging cycles) even at 20 A g(-1). Additional theoretical simulations demonstrate that the close-packed VNO lattice plane and stable carbon-layer can enhance interfacial Zn2+ diffusion and storage. The current work navigates a direction not only to improve the highperformance, durable ZIHSCs via rational cathode design, but also to push forward the carbon-neutral technologies of lignin-biomass valorization.

Harnessing renewable low-cost, bulk wood-structured materials with highly porous, anisotropic and compressible properties that fulfills sustainable water purification is imperative yet still challenging to push forward a circular bioeconomy. In this work, a bimetallic Fe-Co implanted, N-doped wood carbon aerogel (Fe-Co/NWCA) is constructed to guarantee the facile regeneration in high-performance catalytic antibiotic decomposition via activating peroxymonosulfate (PMS). A rapid, reversible and excellent tetracycline (TC) elimination performance (similar to 90% in 12 min) within a wide pH range of 3-11 is achieved by Fe-Co/NWCA-mediated system. Importantly, the as-prepared hydrophilic Fe-Co/NWCA not only delivers a favorable robustness to interfering anions (e.g., Cl-, H2PO4- and HCO3-), but also presents a superior recyclability with over 90% retention after the fourth cycling operation via a convenient squeezing behavior. Integration of radical quenching experiments and electron paramagnetic resonance demonstrates the participation of reactive oxygen species (ROS) into catalytic TC oxidation, wherein the dominant contributor is O-1(2) followed by O-2(center dot)-, SO4 center dot- and center dot OH. As an important non-radical route, the directly interfacial electron transfer is confirmed by electrochemical measurements and density-functional-theory computations. In the context of activating PMS, the multi-valent Fe, Co-coordinated species function as the redox reactive site to trigger diversiform ROS with accelerated kinetics, while N, O-associated surface defects and unsaturated functional groups (e.g., -COOH and ketonic C=O) contribute to the O-1(2) formation and electron shuttling. This universal approach paves a critical avenue to manufacture the reactive wood-based aerogels with hierarchical microchannels in the practical pollutant remediation, shedding the valuable insights on multifunctional biomass-water nexus.

NiFe LDH exhibits excellent OER performance due to its unique layered structure. However, the limited density of active sites in NiFe LDH hinders further enhancement of OER performance. By introducing surface oxygen defects to modulate the surface functional groups and interfacial active sites of LDHs, the electrocatalytic reaction kinetics are effectively optimized. The introduced oxygen vacancies increase the interface active sites of the NiFe LDH catalysts, thereby improving the interfacial reaction rate and optimizing the catalytic performance. In this work, sulfate-intercalated NiFe0.3 LDH with abundant oxygen vacancies was synthesized by a co-precipitation method. The abundant oxygen vacancy defects resulted in a reduction in long-range atomic order and crystallinity, leading to the formation of a crystal/amorphous structure. This structural modification optimized the mass transport process during OER, enhanced the electronic configurations of Ni and Fe, and improved their synergistic interactions, thereby increasing the catalytic activity. At a current density of 10 mA cm-2, a low overpotential of 230 mV and a Tafel slope of 50.7 mV dec-1 were achieved. Furthermore, after 40 h of continuous cycling, the overpotential of the NiFe0.3 LDH sample exhibited minimal change. This work provides new insights into the rational synthesis of high-performance OER catalysts with vacancy defects using the co-precipitation method.

Recently, Bi2S3 has garnered significant interest in the thermoelectric field due to its abundant and low-toxicity constituents. Nevertheless, pure Bi2S3 material has not been utilized in thermoelectric applications because of its low electrical conductivity. This study presents the fabrication of the Bi-0.33(Bi6S9)Br-doped Bi2S3 bulk samples with high electrical conductivity and mechanical performance via the melting method in conjunction with spark plasma sintering technology. The increased electron concentration is attributed to the replacement of S2- by Br- and the introduction of extra Bi in the lattice. At 323 K, the electrical conductivity of the Bi2S3 + 3 wt% Bi-0.33(Bi6S9)Br sample increased to 208 Scm(-1), signifying a 3-order-of-magnitude enhancement compared to the pure sample. The enhanced electrical conductivity led to the optimization of the electrical transport properties. At 573 K, the Bi2S3 + 2 wt% Bi-0.33(Bi6S9)Br bulk sample achieved a peak power factor value of 481 mu Wm(-1)K(-2), which is four times higher than that of the pure sample. Notably, the low lattice thermal conductivity of the Bi2S3 + 5 wt% Bi-0.33(Bi6S9)Br sample was 0.56 W-1 m(-1)K(-1) at 673 K. Given the significantly enhanced electrical transport properties and suppressed thermal conductivity, the Bi2S3 + 2 wt% Bi-0.33(Bi6S9)Br sample achieved a peak ZT value of 0.45 at 673 K and a high ZT(ave) value of 0.33 from 373 to 673 K. Compared to the pure Bi2S3 sample, these values are 5 times and 3 times higher, respectively. Such advancements can be implemented in the domain of power generation. Additionally, the mechanical properties of the sample exhibited substantial enhancement, and the average hardness of the 2 wt% Bi-0.33(Bi6S9)Br-doped sample increased from 2.73 GPa of the pure sample to 3.03 GPa. This novel strategy of dual point defects modulation provides a new pathway to enhance the thermoelectric performance of Bi2S3 and other material systems.

Achieving a waste-treats-pollutant vision, rationally designed lignin valorization that encompasses a shining story of multicolor carbon dots is proposed to promote selective metal-ion sensing and photocatalytic antibiotic removal.

The notion of biomass valorization has been widely adopted to alleviate low-carbon-emission anxieties with the attributes in energy-environmental sustainability via groping multiscale-structured composite, yet still suffering from the dilemma of lignin upcycling. In this context, we propose a novel dot-sheet-assembled heterostructure featuring all lignin-derived bifunctional carbon composites (Co-N-C@CDs) that includes porous Co, N co-modified nanosheets and solvent-extracted carbon quantum dots. The photo-physical properties of lignin-based CDs are refined into multicolor green- and red-emissive fractions (GCDs and RCDs) via a facile biphasic fractionation. Owing to the high-graphite and conductivity, the red-emitting RCDs are installed with lamellar Co-N-C to favor the enlarged interlayer spacing, fast ionic intercalation-transfer and reversible chemical adsorption, thereby resulting in high-performance capacitive deionization (CDI) and zinc-ion hybrid capacitors (ZIHCs). While assembling the CDI device, the Co-N-C@CDs possess a maximum adsorption capacity of 33.64 mg g(-1) NaCl in water desalination with stable restorable behavior. As the cathode of ZIHCs, it delivers an operating voltage of 2.0 V and superior energy density of 209.72 Wh kg(-1), posing a long-term cycling durability at high current rates. Detailed hierarchical structure readily enables the large specific surface area, excellent percolating porosity, intercalated hydrogen bonds and redox active sites, which are conducive to not only expedite ionic infiltration and charge reaction kinetics but also reduce the energy barriers of aqueous ion adsorption. The multiscale 0D-2D supramolecular assembly breaks the frontier of lignin valorization to connecting energy-environment functions, thereby meeting the needs of carbon-neutral society.

State-of-the art biomass valorization represents a classic yet fast-growing area in striding the threshold of sustainable energy-environmental research. How to explore a waste-free route is of great concern to maneuver lignocellulose potentials with multifunctional water purification. As a proof-of-concept, we proposed a tandem manufacture with the aid of acidic hydrothermal fractionation for the multi-scale wheat straw valorization into green-emitting carbon quantum dots (GCQDs), as well as, the Co, N co-doped biochar (Co-N-C). By means of xylan-based oligomers and m-phenylenediamine (m-PDA), the GCQDs emit stable green luminescence in a broad excitation span, which can be adopted to selectively sense metal-ions (e.g., Ag+ and Fe3+) within an ultra-wide concentration. Through a facile confinement of Co-MOFs, the hierarchically porous Co-N-C with lamellar edge structure and redox active sites are achieved to exert high-performance catalytic antibiotic dissociation (an optimal rate of degrading similar to 97 % tetracycline, TC) and capacitive deionization (CDI, salt adsorption capacities of 23.5 mg g(-1) NaCl and 44.07 mg g(-1) CdCl2) with excellent cycling stability. Taking advantages of theoretical models, radicals trapping and direct charge-transfer, a synergistic benefit from reactive oxygen species and interface electron shuttling is exerted to efficient antibiotic decomposition. The salt-ionic diffusion and capture mechanisms of Co-N-C are plotted via layered conductive framework, ion intercalation/electro-sorption, and faradaic redox conversion. We believe that the present work paves a new avenue to waste-free lignocellulose conversion that involves matching the sustainable water purification with maximum biorefining revenue and feasibility.

Bismuth sulfide is a promising thermoelectric material because of its low cost and toxicity; however, its low electrical conductivity limits its thermoelectric properties. In this study, Bi2S3+x wt% HfCl4 (x = 0, 0.25, 0.5, 0.75, and 1.0) bulk samples are fabricated using a combination of melting and spark plasma sintering. The microstructures, electronic structures, and thermoelectric properties of the composites are characterized. The results of electronic structure calculations show that doping with HfCl4 produces an impurity energy level that narrows the bandgap and allows the Fermi energy level to enter the conduction band, leading to a favorable increase in carrier concentration. By regulating the HfCl4 doping concentration, the electrical conductivity of the 0.75 wt% doped sample reaches 253 Scm-1 at 423 K and its maximum ZT value is 0.47 at 673 K. Moreover, the sample is compounded with Bi2S3 nanorods prepared by the hydrothermal method, reducing thermal conductivity by 30% due to the introduction of additional interfaces and pores. This resulted in a final ZT value of 0.61 at 673 K, which is approximately eight times higher than that of pure Bi2S3. This step-by-step optimization approach provides a valuable methodology for enhancing the performance of other thermoelectric material systems.

Bi2S3 is composed of inexpensive and environmental friendliness elements, which has received extensive interests and been investigated as a promising mid-temperature thermoelectric material for years. Even pure Bi2S3 possesses a high Seebeck coefficient and low thermal conductivity, its low electrical conductivity leads to a low figure of merit (ZT) value. In this work, Bi2S3 fabricated by solid-state melting combined with spark plasma sintering can significantly enhance the thermoelectric performance via introducing small amounts of Cu and BiCl3. Cu interstitial doping and Cl substitution on S site result in a large increase in electrical conductivity. Additionally, the enhanced phonon scattering is derived from the point defects caused by element doping, the grain boundaries, and the small amount of secondary phase, which leads to the low thermal conductivity. Finally, a high ZT value of 0.7 is obtained at 773 K and reaches a large average ZT of 0.36 in the temperature range from room temperature (RT) to 773 K for the Cu-interstitial-doped and BiCl3-alloyed (Cu0.01Bi2S3 + 0.175 mol% BiCl3) sample. Furthermore, the mechanical properties of the Cu0.01Bi2S3 + 0.175 mol% BiCl3 sample are lower than those of other Bi2S3 samples, which stem from the weak chemical bonding strength.

Nanostructuring is a conventional approach to decrease thermal conductivity, nevertheless, the effect of grain boundaries on scattering phonon is limited. Herein, a new concept of complex nanostructuring is proposed. The copper sulfides-based nanocomposites with high thermoelectric properties and phase stability were fabricated by combining with solid-state reaction and spark plasma sintering techniques. The main phase of Cu12Sb4S13 and Cu1.96S with complex nanostructures is obtained by introducing CoSb3 additive to Cu1.8S matrix. Hole concentration in p-type composites is tailored by Co3+ doping in Cu+ site, resulting in the significantly enhanced Seebeck coefficient. Furthermore, an ultralow thermal conductivity of 0.47 W m-1 K-1 at 773 K is achieved due to the enhanced phonons scattering by continuous nanopores, extra phase interfaces and nanoprecipitates. The record high ZT of 1.6 is achieved at 773 K in Cu-S based thermoelectric material system for the composite specimen, namely Cu1.8S-5 wt.% CoSb3. Our result provides a new strategy to construct complex nanostructures in reducing thermal conductivity of composite materials.