Electrical conductivity of activated carbon–metal oxide nanocomposites under compression: a comparison study

Abstract

From a granular commercial activated carbon (AC) and six metal oxide (Al2O3, Fe2O3, SnO2, TiO2, WO3 and ZnO) precursors, two series of AC-metal oxide nanocomposites were prepared by wet impregnation, oven-drying at 120 °C, and subsequent heat treatment at 200 or 850 °C in an inert atmosphere. Here, the electrical conductivity of the resulting products was studied under moderate compression. The influence of the applied pressure, sample volume, mechanical work, and density of the hybrid materials was thoroughly investigated. The DC electrical conductivity of the compressed samples was measured at room temperature by the four-probe method. Compaction assays suggest that the mechanical properties of the nanocomposites are largely determined by the carbon matrix. Both the decrease in volume and the increase in density were relatively small and only significant at pressures lower than 100 kPa for AC and most nanocomposites. In contrast, the bulk electrical conductivity of the hybrid materials was strongly influenced by the intrinsic conductivity, mean crystallite size, content and chemical nature of the supported phases, which ultimately depend on the metal oxide precursor and heat treatment temperature. The supported nanoparticles may be considered to act as electrical switches either hindering or favouring the effective electron transport between the AC cores of neighbouring composite particles in contact under compression. Conductivity values as a rule were lower for the nanocomposites than for the raw AC, all of them falling in the range of semiconductor materials. With the increase in heat treatment temperature, the trend is toward the improvement of conductivity due to the increase in the crystallite size and, in some cases, to the formation of metals in the elemental state and even metal carbides. The patterns of variation of the electrical conductivity with pressure and mechanical work were slightly similar, thus suggesting the predominance of the pressure effects rather than the volume ones.

Study of the electrical conductivity of biobased carbonaceous powder materials under moderate pressure for the application as electrode materials in energy storage technologies

“…Nevertheless, amorphous RuO 2 shows much lower EC values than the pure AC (Table 5) and should therefore rather act as an insulating layer which increases resistivity and decreases the EC of the carbon support. Such a behavior has been observed at least for other AC-metal oxide composites (including Al 2 O 3 , Fe 2 O 3 , and ZnO) and as a result, it has been stated that the EC of a hybrid material is mainly determined by the intrinsic EC of the respective metal oxide and not by the altered mechanical properties of the composite compared to the pure AC (Barroso-Bogeat et al, 2014). Concerning the AC-RuO2 nanocomposites, the statement of Barroso-Bogeat et al does not seem to apply as, compared to the raw AC, both the compressibility and the density are significantly higher, which indicates that the mechanical changes are the crucial factors for the increase in EC.…”

“…Regarding the first question, it has been shown that focussing on a constant sample height is reasonable. Previous studies have been conducted by setting a constant mass instead of a constant height (Barroso‐Bogeat et al., ). However, pretests conducted during this work showed that keeping the height constant delivers more reliable and reproducible results.…”

“…Conductivity measurements were conducted using a selfconstructed device based on a procedure described elsewhere (Barroso-Bogeat et al, 2014;Celzard et al, 2002;Sánchez-González, MacÍas-García, Alexandre-Franco, & Gómez-Serrano, 2005). The device consists of two parts: The bottom part is made of a brass bracket with a fixed glass cylinder (inner diameter: 1 cm) and the upper part is a movable brass stamp on which different pressures can exactly be applied using a material testing system of Instron (Instron GmbH) with an integrated altimeter for determining the height of the respective sample after applying different pressures.…”

“…As it was shown that exactly these heterogeneous materials show promising capacitive behavior as electrode materials for EDLCs because of their pseudocapacitive properties (Frackowiak & Béguin, 2001;Hulicova-Jurcakova et al, 2009;Raymundo-Piñero et al, 2009;Su, Wu, Bao, & Yang, 2007;Wang, Zhang, & Zhang, 2012;Zhao, Xia, & Zheng, 2012;Zhi, Xiang, Li, Li, & Wu, 2013), this study focusses on EC measurements of such heterogeneous materials. Past studies on carbon blacks (CB) already showed that conductivity increases with decreasing content of oxygen-and nitrogen-containing surface groups on the carbon surface (Pantea, Darmstadt, Kaliaguine, Sümmchen, & Roy, 2001) and that composites of activated carbon (AC) and certain metal oxides (e.g., Al 2 O 3 , Fe 2 O 3 , SnO 2 ) show lower conductivity values than the pure AC (Barroso-Bogeat, Alexandre-Franco, Fernández-González, Macías-García, & Gómez-Serrano, 2014). Furthermore, the EC of CB is positively correlated with graphitic structures on the surface of the carbon (Pantea, Darmstadt, Kaliaguine, & Roy, 2003).…”

Synergetic Improvement of Stability and Conductivity of Hybrid Composites formed by PEDOT:PSS and SnO Nanoparticles

“…Hybrid composite exhibits improved conductivity as compared with the bare polymer, reaching averaged values of about 6.3 10 2 Ω −1 cm −1 and high charge carrier concentration values around 1.4 10 22 cm −3 , even when the conductivity of SnO nanoparticles shows lower values around 1.8 10 -2 Ω −1 cm −1 . Actually, conductivity values of about 5·10 -6 (Ω −1 cm −1 ) have been reported for bulk SnO at room temperature [38,39]. Some authors reported that, when the surface of the nanoparticles embedded in the polymer is positively charged, the negatively charged PSS chains can be electrostatically attracted, leading to changes in the PEDOT:PSS chains' configuration, which can enhance the electrical conductivity [21].…”