Facile General Route toward Tunable Magnéli Nanostructures and Their Use As Thermoelectric Metal Oxide/Carbon Nanocomposites

Abstract

Engineering nanoscale interfaces is a requisite for harnessing electrical and thermal transports within nanostructured materials, especially those destined for thermoelectric applications requiring an unusual combination of low thermal conductivity and electrical resistivity. Nanocomposites open up possibilities in this area, but are still bound to a very narrow range of materials. Here, we report a new approach combining the sol-gel process toward hybrid materials with spark plasma sintering (SPS) to yield functional nanocomposites based on substoichiometric titanium oxides Ti(n)O(2n-1), so-called Magnéli phases. The potential of this new approach is demonstrated by three results. First, multiple Ti(n)O(2n-1) compounds (n = 3, 4, 5, 6, 8) are obtained for the first time as sole nano-Magnéli crystalline phases with controlled specific surface areas from 55 to 300 m(2)·g(-1), classified as potential thermoelectric n-type metal oxides and paving the way toward advanced systems for energy-harvesting devices and optoelectronics. Second, this work combines the use of sol-gel and SPS processes to yield percolated nanocomposites based on metal oxide nanoparticles embedded in a carbon matrix with low electrical resistivity (2 × 10(-4) Ω·m for a Ti(4)O(7) compound) and reduced thermal conductivity (1 W·m(-1)·K(-1)) with respect to bulk phases. Finally, the discovered materials are reliable with thermoelectric figures of merit (ZT = 0.08) relatively high for n-type Ti-O-based systems and metal oxides. Thereby this study represents a proof of concept for the development of promising, cheaper, and more efficient thermoelectric conversion devices.

Enhanced Electrocatalytic N2 Reduction via Partial Anion Substitution in Titanium Oxide–Carbon Composites

“…[21] It is worth to note that the latter bands almost disappear in M-1100, as more free carbon reacts with TiO 2 to form TiCa th igher temperature. [22] Theh igher increase in weight for M-1100 than for M-1000 indicates the higher carbide content in the former which is in line with the XRD results.Inaddition, the temperature of substitution of carbon shifts to higher values for M-1100 indicating the higher thermodynamic barrier for re-oxidation in TiCt han in C-Ti x O y .N 2 (À196 8 8C) physisorption curves ( Figure S6) show that M-Ts still have ap orous structure with high SSA. Besides, TGA under air was carried out to investigate the structures of M-Ts ( Figure 2b).…”

Highly conductive nano-sized Magnéli phases titanium oxide (TiOx)

“…Another synthesis approach carried out by Portehault et al . was a sol-gel method to synthesize monoliths consisting of TiO x clusters in a carbon matrix, resulting in a surface area as high as 400 m 2  g −1  14 . Although the carbon matrix contributed to a high surface area, the proportion of carbon was very high whereas TiO x NPs, with their absence or minimum presence of a carbon matrix, are favorable for improved durability.…”

Synthesis of Ti4O7 Nanoparticles by Carbothermal Reduction Using Microwave Rapid Heating

“…Carbothermal reduction is an efficient method for producing reduced titanium oxides because carbon is safe and inexpensive. This method has been used for producing nano-sized reduced titanium oxides by using organotitanium compounds as the raw material [6,7]. Very fine TiO 2 is produced by the decomposition of organotitanium compounds.…”