Complex Impedance Spectroscopy Study of the Thermolysis Products of Metal-Organic Frameworks

The products of thermal transformation of MOF-253 (Al-containing MOF) and its Pt-based derivative, into carbon-black-based electrocatalyst were studied using ac impedance spectroscopy. The thermolysis was carried out at 700-1050 degrees C under an inert atmosphere. The resulting products were found to possess diverse electrical properties, revealed through very different impedance responses. Assynthesized MOF material was an insulator with a conductivity of sigma = 1.3 X 10(-11) S cm(-1). Products obtained at 700-800 degrees C behaved as semiconductors with low room temperature conductivity of ca. sigma approximate to 10(-6)-10(-5) S cm(-1) and strong thermal dependence (sigma approximate to 10(-3) S cm(-1) at 200 degrees C). They exhibited complex impedance responses, which may be interpreted as mixed conduction, where semiconducting behavior was accompanied by ionic charge transfer. The final product obtained at 1050 C exhibited a particular metal-like conductance with positive but weak temperature dependence and ambiance conductivity of sigma = 9.0 X 10(-2) S cm(-1). The properties of Pt/carbon-based material obtained at 950 degrees C seem to be transient between the latter two conduction states. Thermolysis of initial MOF-253 is less hindered and occurs at lower temperatures. The conductivity of the final product of pyrolysis at 1050 degrees C of initial MOF-253 was inferior to that of Pt-MOF with sigma(25) (degrees)c = 1.0 x 10(-2) S cm(-1). A tentative interpretation of the results is presented.