High entropy oxides (HEOs) are of great interest for heat conversion due to their promising electrical and thermal properties. In this research, we aim to obtain single-phase HEO with the chemical composition Co-Cr-Fe-Mn-Ni-O, with the unequal at. % of metals, via Solid-State Reaction (SSR), and substitute Ni with Cu. The samples were sintered at 1000 °C for 20 – 35 h. For the samples with Ni, two main phases were formed: rock salt-structured Fm-3m and spinel-structured Fd-3m. As for the material with Cu, single-phase material was formed with the spinel-crystal structure Fd-3m. Obtained samples exhibit high values of the Seebeck coefficient (330 μV/K at 573 K for the sample with Ni that was synthesized for 35 h and 120 μV/K at 573 K for the sample with Cu) and electrical conductivity (4.58 S/cm at 1073 K for the single-phased sample with Cu). These results indicate that these materials can be used as highly efficient semiconductor high-entropy alloys. Further optimization of the SSR is needed to produce a single-phase material with Ni.

Carbon nanotube/polymer composites have recently received considerable attention for thermoelectric (TE) applications. The TE power factor can be significantly improved by forming composites with carbon nanotubes. However, the formation of a uniform and well-ordered nanocomposite film is still challenging because of the creation of agglomerates and the uneven distribution of nanotubes. Here, we developed a facile, efficient, and easy-processable route to produce uniform and aligned nanocomposite films of P3HT and carbon nanotube forest (CNTF). The electrical conductivity of a pristine P3HT film was improved from ∼10^–7 to 160 S/cm thanks to the presence of CNTF. Also, a further boost in TE performance was achieved using two additives, lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and tert-butylpyridine. By adding the additives to P3HT, the degree of interchain order increased, which facilitated the charge transport through the composite. Under the optimal conditions, the incorporation of CNTF and additives led to values of the Seebeck coefficient, electrical conductivity, and power factor up to rising 92 μV/K, 130 S/cm, and 110 μW/m K², respectively, at a temperature of 344.15 K. The excellent TE performance of the hybrid films originates from the dramatically increased electrical conductivity and the improved Seebeck coefficient by CNTF and additives, respectively.

Thermoelectric materials convert waste heat into electric energy. Oxyselenide-based materials, specifically, p-type BiCuSeO is one of the most promising materials for these applications. There are numerous approaches to improve the heat-to-electricity conversion performance. Usually, these approaches are applied individually, starting from the pure intrinsic material. Higher performance could, however, be reached by combining a few strategies simultaneously. In the current work, yttrium, niobium, and phosphorous substitutions on the bismuth sites in already bismuth deficient Bi_1-xCuSeO systems were investigated via density functional theory. The bismuth-deficient system was used as the reference system for further introduction of substitutional defects. The substitution with phosphorous showed a up to 40 meV (11 %) decrease in the energy gap between conduction and valence bands at the highest substitution concentration. Doping with niobium led to the system changing from a p-type to an n-type conductor, which provides a possible route to obtain n-type BiCuSeO systems.

Water splitting is considered one of the most promising approaches to power the globe without the risk of environmental pollution. The oxygen evolution reaction (OER) is even more challenging because the generation of only one oxygen molecule involves the transfer of four e^– and removal of four H⁺ ions from water. Thus, developing highly efficient catalysts to meet industrial requirements remains a focus of attention. Herein, the prominent role of Sn in accelerating the electron transfer kinetics of Ni₅P₄ nanosheets in OER is reported. The post catalytic survey elucidates that the electrochemically induced Ni–Sn oxides at the vicinity of phosphides are responsible for the observed catalytic activity, delivering current densities of 10, 30, and 100 mA cm^–2 at overpotentials of only 173 ± 5.2, 200 ±7.4, and 310 ± 5.5 mV, respectively. The density functional theory calculation also supports the experimental findings from the basis of the difference observed in density of states at the Fermi level in the presence/absence of Sn. This work underscores the role of Sn in OER and opens a promising avenue toward practical implementation of hydrogen production through water splitting and other catalytic reactions. 

Direct stacking of n‐type and p‐type metal oxide (MOx) semiconductors is one of the appealing directions toward low cost and environmentally friendly photovoltaics (PVs). However, the main shortcoming, hindering the PV performance of MOx heterojunction devices is attributed to the tradeoff between light absorption and maximized carrier extraction in p‐type MOx. In this work, we demonstrate that the nanorod (NR) geometry of Co₃O₄ light absorber with a nearly ideal bandgap of ∼1.48 eV, can remove this hurdle through strong internal light trapping of adjacent one‐dimensional (1D) structure and enhanced carrier mobility. The inverted n‐on‐p configuration of the core‐shell 1D heterojunction, obtained by depositing a thin TiO₂ n‐type layer, resulted in enlarged charge generation compared to the typical p‐on‐n counterpart device. Fine‐tuning of Co₃O₄ NRs length, permits PV investigation of the heterojunctions with respect to absorber layers thickness. The optimized Co₃O₄ NRs/TiO₂ heterojunction (30 nm Co₃O₄ NR length) presented a record high open circuit photovoltage (V_oc) of (0.52 ± 0.03) V under 1 sun irradiation. Impedance analysis of the heterojunctions, indicates formation of the p⁺‐p depletion. The presented work can highlight some vital venues to enhance photoconversion efficiency of the all‐oxide heterojunctions while introducing a pioneer contender as inverted (n‐on‐p) MOx heterojunction.

Harnessing energy lost in the form of heat is an important challenge today. Organic thermoelectric materials (TE) can convert lost heat into electricity at relatively low temperature. Single-walled carbon nanotubes (SWCNTs) are known to boost the TE properties of organic-based materials at room temperature (TR). However, the TE performance decreases with the increasing temperature, which restricts the working temperature region of the devices. Here, we present a three steps investigation: initially, the influence of the net of SWCNTs on TE properties of polymer matrix; secondly, creation of hybrid fillers via SWCNTs treatment with gold chloride; lastly, chemical post-treatment of obtained systems in the temperature range 325–410 K. In the process of HAuCl4 aerosolization (gold chloride treatment) on the surface of nanotubes, different ionic conformations (Au and AuCl4−) can be formed. For this reason, we performed a theoretical investigation on the influence of ionic conformations on SWCNTs on the electronic structure. Implementation of SWCNTs net into polymer matrix alongside gold chloride doping and chemical post-treatment successfully increased the power factor of the system in the temperature interval from 300 to 410 K. These results demonstrate the potential of combined approach in creation of hybrid fillers based on organic/inorganic materials with chemical post-treatment in boosting the thermoelectric performance within the whole operating temperature of polymer-based composite alongside the importance of theoretical modeling in tuning the electronic structure of composite systems through a material-by-design approach.

Graphene (G) and metal-decorated G nanocomposites are among the most promising materials for a wide variety of practical applications, and, therefore, the development of fast and reliable methods for nanocomposite synthesis is an important task. Herein we report the new fast approach for solution combustion synthesis (SCS) of large-area G–metallic nanocomposites in an air atmosphere. The G-based nanocomposites were obtained by a SCS using copper and nickel nitrates, as well as their stoichiometric mixture as the metal source and citric acid as a fuel and carbon source. The G structures started on the catalytic surface of freshly synthesized metallic nanograins during the combustion process and formed large-area free-standing films due to the high-energy and fast synthesis process. We proposed a mechanism of formation of the G-based nanocomposites. The phase compositions, structural features, and magnetization behavior of G@Cu, G@Ni, and G@CuNi nanocomposites are carefully studied and described. G@metal nanocomposites were studied as a material for the creation of a highly effective sensing element of semiconductor gas sensors.

Thermoelectric materials allow direct conversion of waste heat energy into electrical energy, thus contributing to solving energy related issues. Polymer‐based materials have been considered for use in heat conversion in the temperature range from 20 to 200 °C, within which conventional materials are not efficient enough, whereas polymers due to their good electronic transport properties, easy processability, non‐toxicity, flexibility, abundance, and simplicity of adjustment, are considered as promising materials. Due to the large variety of available polymers and the almost unlimited combinations of possible modifications, the field of polymer‐based thermoelectrics is very rapidly developing, already reaching efficiency values close to those of inorganic systems. In the current progress report, the most recent advances in the field are discussed. New approaches to improve thermoelectric performance are described, with a focus on revising the mechanisms to improve the thermoelectric properties of the three most investigated polymer matrixes: poly(3,4‐ethylenedioxythiophene) polystyrene sulfonat, poly(3‐hexylthiophene‐2,5‐diyl), and polyaniline, alongside the three main paths of optimizing properties: incorporation of carbon‐based material and inorganic substances, and treatment with chemical agents. The most promising research in the field is highlighted and thoroughly analyzed. The path toward a lab‐to‐fab transition for thermoelectric polymers is suggested in perspective.

Polymer-based composites are of high interest in the field of thermoelectric (TE) materials because of their properties: abundance, low thermal conductivity, and nontoxicity. In applications, like TE for wearable energy harvesting, where low operating temperatures are required, polymer composites demonstrate compatible with the targeted specifications. The main challenge is reaching high TE efficiency. Fillers and chemical treatments can be used to enhance TE performance of the polymer matrix. The combined application of vertically aligned carbon nanotubes forest (VA-CNTF) is demonstrated as fillers and chemical post-treatment to obtain high-efficiency TE composites, by dispersing VA-CNTF into a poly (3,4-ethylenedioxythiophene) polystyrene sulfonate matrix. The VA-CNTF keeps the functional properties even in flexible substrates. The morphology, structure, composition, and functional features of the composites are thoroughly investigated. A dramatic increase of power factor is observed at the lowest operating temperature difference ever reported. The highest Seebeck coefficient and electrical conductivity are 58.7 μV K^-1 and 1131 S cm^-1, respectively. The highest power factor after treatment is twice as high in untreated samples. The results demonstrate the potential for the combined application of VA-CNTF and chemical post-treatment, in boosting the TE properties of composite polymers toward the development of high efficiency, low-temperature, flexible TEs.