Academic literature on the topic 'Nanoporous Metallic Foams'

A simple two-step electrochemical method for the fabrication of a new type of hierarchical Sn/SnOx micro/nanostructures is proposed for the very first time. Firstly, porous metallic Sn foams are grown on Sn foil via hydrogen bubble-assisted electrodeposition from an acidulated tin chloride electrolyte. As-obtained metallic foams consist of randomly distributed dendrites grown uniformly on the entire metal surface. The estimated value of pore diameter near the surface is ~35 µm, while voids with a diameter of ~15 µm appear in a deeper part of the deposit. Secondly, a layer of amorphous nanoporous tin oxide (with a pore diameter of ~60 nm) is generated on the metal surface by its anodic oxidation in an alkaline electrolyte (1 M NaOH) at the potential of 4 V for various durations. It is confirmed that if only optimal conditions are applied, the dendritic morphology of the metal foam does not change significantly, and an open-porous structure is still preserved after anodization. Such kinds of hierarchical nanoporous Sn/SnOx systems are superhydrophilic, contrary to those obtained by thermal oxidation of metal foams which are hydrophobic. Finally, the photoelectrochemical activity of the nanostructured metal/metal oxide electrodes is also presented.

During the last decades, significant efforts have been made to directly convert CO2 as a potential feedstock into hydrocarbons as fuels and/or basic chemicals for industrial applications. The electrochemical CO2 reduction reaction (CO2RR) is a promising alternative for a large-scale production of hydrocarbons. However, there are still some challenges including poor product selectivity and highly complex multiple-step reaction mechanisms.[1] In order to convert CO2 on a Cu electrode, high overpotentials up to 1.0 V are required, which make the energy efficiency still rather poor and lead to competition with the H2 evolution.[2] Additionally, the morphology of the Cu materials i.e. structure and ‘chemical state’ (metallic vs oxidized, high vs low coordinated) strongly influence the performance of the CO2RR. Recently, we have shown the critical potential of oxide-metal transition processes for Cu oxide foam annealed at 300°C probed by operando XAS, XRD and Raman spectroscopy.[3,4] All three operando techniques showed an entire reduction of Cu oxide to metallic before the production of hydrocarbons starts. [3,4] In this work, we have investigated the kinetics of both electrochemical oxide-metal reduction and CO2RR on nanoporous Cu foams as catalyst precursor annealed at four different temperatures (100°C, 200°C, 300°C, 450°C) in air using operando Quick X-ray Adsorption Spectroscopy (Quick-XAS). The Quick-XAS measurements were carried out in a custom-made spectro-electrochemical flow cell using 0.5 M KHCO3 as the electrolyte, while the XAS-Spectra were measured in transmission mode. The Quick-XANES data was analyzed by linear combination fit (LCF) and principle component analysis (PCA) to monitor the potential dependent changes of the chemical state and coordination number of the Cu species. Based on the Cu K-edge XANES and EXAFS data, we show that the annealing temperature strongly influences the chemical state of the Cu species. More precisely, the population of the Cu(II) species within the as prepared foams increases with increasing annealing temperature. Starting from the different ratios of Cu(0):Cu(I): Cu(II), the oxide-metal transition processes are shifted in the cathodic direction by applying potential steps of 100 mV. With an increase in annealing temperature, this oxide-metal transition is more rapid and occurs at lower cathodic overpotentials, but still before the production of hydrocarbons begins. In contrast, the potential jump experiments of several hundreds of mV lead to different kinetics of the oxide-metal reduction of Cu species. These transition processes and the resulting structure of porous Cu foams have a huge impact on the product distribution for CO2RR. Altogether, our results provide deeper insights into the oxide-metal transition processes to form the catalytically active Cu species for hydrocarbon formation during CO2RR. Reference: [1] S. Nitopi et al., Chemical Reviews, 2019, 119, 7610. [2] C. W. Li et al., Journal of the American Chemical Society, 2012, 134, 7231. [3] A. Dutta et al., Chimia, 2021, 75, 733. [4] A. Dutta et al., Journal of Catalysis, 2020, 389, 592.

A novel and simple approach for preparing nanoporous binder free Sn : Pb composite metal foam has been demonstrated. The anodized metallic composite block was functionalized and also found a nanoporous structure. A scanning electron microscopy (SEM) result shows that the nanoflake-like arrangement has synthesized. The X-ray diffraction (XRD) results confirm the nanoporous structure of the Sn / Pb foam after etching with 6 M NaOH . The prepared Sn : Pb metal foam is able to be used as a super capacitors electrode to offer large areal capacitance with regards to the synergic integration of Sn and Pb metals and the unique nanoporous structure.

Porous materials have generated a great deal of interest for use in energy storage technologies, as their architectures have high surface areas due to their porous nature. They are promising candidates for use in many fields such as gas storage, metal storage, gas separation, sensing and magnetism. Novel porous materials which are non-toxic, cheap and have high storage capacities are actively considered for the storage of Li ions in Li-ion batteries. In this study, we employed density functional theory simulations to examine the encapsulation of lithium in both stoichiometric and electride forms of C12A7. This study shows that in both forms of C12A7, Li atoms are thermodynamically stable when compared with isolated gas-phase atoms. Lithium encapsulation through the stoichiometric form (C12A7:O2−) turns its insulating nature metallic and introduces Li+ ions in the lattice. The resulting compound may be of interest as an electrode material for use in Li-ion batteries, as it possesses a metallic character and consists of Li+ ions. The electride form (C12A7:e−) retains its metallic character upon encapsulation, but the concentration of electrons increases in the lattice along with the formation of Li+ ions. The promising features of this material can be tested by performing intercalation experiments in order to determine its applicability in Li-ion batteries.

Conversion of CO2 into valuable chemicals and fuels has received widespread attention as a way to tackle the increased CO2 emissions (Gattrell, Gupta and Co, 2006) and this also resulted in a reduction of dependence on fossil fuels . There are different techniques for CO2 conversion to value-added products, where electrochemical reduction (ECR) of carbon dioxide into chemical fuels is identified as a promising way since energy efficiency is high and the products, especially the chemical fuels can be readily stored. Among the variety of metallic electrodes, especially transition metals investigated for activity towards ECR of CO2, tin (Sn), bismuth (Bi), Indium (In) were found to be selective towards formic acid production. However, it was found that these metals show a low catalytic activity. To enhance the performance of CO2 reduction, three dimensional (3D) porous foam structured catalysts can be employed by increasing the active surface area. These 3D porous foam structures of metallic catalyst can be achieved by electrodeposition process by tuning the deposition parameters such that the evolving hydrogen during deposition can act as a dynamic template to fabricate 3D metal deposit structures with high surface areas (Shin, Dong and Liu, 2003). In this work, a 3D foam of copper is electrochemically deposited onto Cu foil (f-Cu) and Cu mesh (f-Cu mesh). Further, the deposition parameters for the electrodeposition of Sn on 3D Cu foam (Sn/f-Cu) were optimized to investigate the activity towards the ECR of CO2. SEM and EDX technique were employed for the physical characterization of the electrodes, while the produced formic acid from the reactions was quantified using ion chromatography. The results indicated that Sn/f-Cu mesh electrode showed better performance for ECR of CO2 to formic acid compared to Sn deposited copper foil (Sn/Cu) and bare copper foam. It was observed that Sn/f-Cu mesh achieved 83 % maximum faradaic efficiency at -1.6 V vs Ag/AgCl. However, a highest rate of formic acid production of 350 µmol/hr.cm2 was achieved at -1.8 V vs Ag/AgCl which is nearly seven times higher than Sn/Cu at the same potential. A similar analysis is going to be performed with the other formic acid selective catalysts like Bi/f-Cu mesh and In/f-Cu mesh. Based on the above analysis on faradaic efficiency against various electrodes, an optimized electrode will be identified and used in scaled-up electrolyser for CO2 reduction. References Gattrell, M., Gupta, N. and Co, A. (2006) ‘A review of the aqueous electrochemical reduction of CO2 to hydrocarbons at copper’, Journal of Electroanalytical Chemistry, pp. 1–19. doi: 10.1016/j.jelechem.2006.05.013. Shin, H. C., Dong, J. and Liu, M. (2003) ‘Nanoporous Structures Prepared by an Electrochemical Deposition Process’, Advanced Materials, 15(19), pp. 1610–1614. doi: 10.1002/adma.200305160.