Porous Alloys and Chalcogenides for Energy Storage and Conservation

Abstract

The increase in energy demand, continuous depletion of energy resources, and generation of greenhouse gases significantly need to be answered. Therefore, there is a need to find alternative sustainable energy technologies for their storage system. The key objective of this work is centered on the facile synthesis of porous metal alloys and doped chalcogenides for energy storage and conservation purposes. Research interest in porous metal alloys and doped chalcogenides has been increased due to the distinguished characteristics associated with them. Primarily, transition metal-based supercapacitors have attracted wide consideration as supercapacitor applications owing to their higher electrical conductivity, rich redox chemistry, and cost-effectiveness. However electrochemical energy storage capability of bimetallic alloys can be further improved by generating porosity in their structure. Herein, the low-cost, benign, and scalable inverse Leidenfrost method is employed for the synthesis of porous Cu64Ni36 alloy. The powder X-ray diffraction results verify the formation of single-phase Cu, Ni, and Cu64Ni36 alloy having face-centered cubic structure. Scanning electron microscopy and the Brunauer-Emmett-Teller (BET) method determine the porosity and surface area, respectively. The surface area of Cu64Ni36 alloy is calculated to be 16 m² g-1 , BET also confirming the mesoporous nature of prepared Cu, Ni, and Cu64Ni36 alloy. Further, Temperature Programmed Reduction (TPR) and Temperature Programmed Oxidation (TPO) analysis describe that the prepared porous Cu64Ni36 alloy is stable towards oxidation up to 568 °C (841.15 K). The prepared porous were evaluated electrochemically as electrode materials for supercapacitor application. The cyclic voltammetry (CV) measurements show that all the prepared porous materials show a pseudocapacitive mechanism for electrochemical energy storage. The porous Cu64Ni36 alloy electrode exhibits a desirable specific capacitance (SC) value of 610 F g-1 (101 mAh g -1 ) at 1 A g-1 with 70.2% retention after 5000 cycles at 20 A g-1 for application as an electrode material for supercapacitor. The solution and charge transfer resistance is measured to be 3.38 Ω and 0.16118 Ω, respectively using electrochemical impedance spectroscopy. The improved electrochemical energy storage behavior is attributed to the porosity and high conductivities of Cu64Ni36 alloy. Additionally, this work also offers a new direction for porous bimetallic alloys to study as supercapacitors. This demonstrates the promising behavior of mesoporous Cu64Ni36 alloy as an electrode material for supercapacitor application. In addition to studying the supercapacitor response of Cu64Ni36, this alloy has also been tested theoretically and experimentally for hydrogen storage and carbon dioxide capture. Expediently, it gave promising results for gas storage material. Cu64Ni36 mesoporous alloy has exhibited good sorption capacity for CO2 of about 0.19 mmol/g (0.85 wt. %) at 30 °C (303.15 K) and 30 bar of pressure. Further, theoretical studies for hydrogen storage have been carried out using density functional theory and have shown favorable results. The theoretical data shows that Cu64Ni36 mesoporous alloy has a maximum of 3.48 wt. % storage capacity for hydrogen which is exceptionally good. The obtained results are preferably comparable to reported results for mesoporous materials, as alloy has never been investigated earlier for CO2 sequestration and H2 storage. Therefore, current studies open new dimensions in the remediation of environmental changes as well as for the experimental implementation of bimetallic porous alloys for hydrogen storage. Further, doped Sb2Te3 narrow band gap semiconductor is attracting considerable attention for different electronic and thermoelectric applications. Trivalent Samarium (Sm) and Indium (In) doped Sb2Te3 microstructures have been synthesized by the economical solvothermal method. Powder X-ray Diffraction (PXRD) was used to verify the synthesis of single-phase doped and undoped Sb2Te3 and the doping of Sm and In within the crystal lattice of Sb2Te3. Further, morphology, structure elucidation, and stability have been investigated systematically by Scanning Electron Microscopy (SEM), Raman analysis, and Thermogravimetric Analysis (TGA). These analyses verified the successful synthesis of hexagonal undoped Sb2Te3 (AT) and (Sm or In) doped Sb2Te3 (SAT, IAT) microstructures. Moreover, the comparison of dielectric parameters, including dielectric constant, dielectric loss, and tan loss of AT, SAT, and IAT was studied in detail. An increment in the electrical conductivities, both; AC and DC from 1.92 × 10-4 to 4.9 × 10-3 (Ωm) -1, and a decrease in thermal conductivity (0.68-0.60 W m-1K -1 ) was observed due to doping of trivalent (Sm, In) dopants which produced defects in structure and consequently leads toward lower thermal conductivity. To the best of our knowledge, the synthesis, and dielectric properties of (Sm, In) doped and undoped Sb2Te3 in comparison with electrical properties and thermal conductivity have not been reported earlier. This implies that appropriate doping of Sm and In in Sb2Te3 is promising to enhance the electronic and thermoelectric behavior. Additionally, Au-doped Sb2Te3 microstructures have also been prepared and tested for both magnetic and thermoelectric (TE) properties, as Au-doped Sb2Te3 microstructures have shown exceptionally improved electrical conductivity (σDC) and lowest thermal conductivity (κ) as a function of temperature. The obtained values of σDC were 0.029- 0.106 (Ωm) -1 from a temperature range of 298-493 K while κ was (0.59-0.49 W m-1K -1 ). Higher electrical conductivity and lower κ are the characteristic features for the deployment of any material for TE application. Furthermore, the maximum calculated value of Seebeck coefficient (S) of Au-doped Sb2Te3 microstructures was 129 μV K-1 which seems suitable for thermoelectric application. The obtained parameters show that the prepared Au doped Sb2Te3 microstructures can be utilized efficiently for TE applications, strategically improved further by varying dopant concentration and addition of co-dopants.