Electrical conductivity of metal (hydr)oxide-activated carbon composites under compression. A comparison study

From a granular commercial activated carbon (AC) and six metal (hydr)oxide precursors, including Al(NO3)(3), Fe(NO3)(3), SnCl2, TiO2, Na2WO4 and Zn(NO3)(2), a broadly varied series of metal (hydr)oxide-AC composites were prepared by wet impregnation and subsequent oven-drying at 120 degrees C. 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 show that the mechanical properties of the composites are largely determined by the carbon matrix. Both the decrease in volume and the increase in density under compression were very small and only significant at pressures lower than 100 kPa for AC and most composites. By contrast, the bulk electrical conductivity of the hybrid materials was strongly influenced by the nature, content and intrinsic conductivity of the supported metal phases, which act as insulating thin layers thereby hindering the effective electron transport between AC cores of neighbouring sample particles in contact under compression. Conductivity values for the composites were lower than for the raw AC, all of them falling in the range of typical semiconductor materials. 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. (C) 2014 Elsevier B.V. All rights reserved.