Electrochemical and Structural Studies of Nanodiamond Composites

The method of detonation synthesis is used to obtain nanodiamond composites (NDCs), and electrochemical and porosimetric studies are carried out for some NDC samples containing both a nanodiamond powder fraction and a nondiamond carbon fraction. Samples of untreated detonation soot (NDC-1) and products of its gas-phase purification (NDC-2 and NDC-3) with different ratio of nanodiamond and nondiamond carbon are studied. The content of the latter in the NDC-1, NDC-2, and NDC-3 samples is 48, 24, and 1 wt %, respectively. It is shown that the intensity of Raman bands of crystalline graphite (1580 cm^–1) and disordered graphite phase (1360 cm^–1) is higher in the initial detonation soot, as compared to samples partially or completely purified from nondiamond carbon. Here, the specific resistance of the samples increases in the series NDC-1 < NDC-2 < NDC-3, i.e., at an increase in the share of the nanodiamond fraction. The method of standard contact porosimetry shows that samples are characterized by high values of both overall specific (1040–1290 m² g^–1) and hydrophilic specific surface area and that the degree of NDC hydrophilicity decreases at an increase in the nanodiamond concentration. The CV curves of NDC samples have a shape typical for double electric layer charging complicated by ohmic losses growing at an increase in the nanodiamond fraction. Nanodiamond boration results in a decrease in its specific resistance and in its significant hydrophilization. The data of impedance measurements for NDC-1 and NDC-2 samples show that a decrease in the fraction of conducting carbon is accompanied by a significant decrease in capacitance. Studies of oxygen electroreduction on the Pt/NDC-1 catalytic system demonstrate its stability in time, which is probably related to a decrease in the aggregation degree of platinum particles due to the lower corrosion rate of the nanodiamond powder support as compared to standard carbon blacks. Thus, some of the studied NDC samples are promising as supports of oxygen reduction catalysts.