Correlation of sp2 carbon bonds content in magnetron-sputtered amorphous carbon films to their electrochemical H2O2 production for water decontamination applications

The radio frequency (RF)-magnetron sputtering technique was used to deposit amorphous carbon (a-C) films onto different substrates at different deposition substrate temperatures (T-d) ranging from room temperature (RT) to 750 degrees C. The carbon bonding states of the a-C films were systematically investigated by means of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) as a function of T-d. The Raman analyses clearly show that an increase of T-d leads to significant microstructural changes of the initially mixed sp(2)/sp(3) carbon bonds, for the films deposited at RT into a more graphitic like sp(2) bonding at higher T-d. This increase of [sp(2)]-bonded fraction of carbon atoms to the detriment of the sp(3) bonded ones has been quantitatively confirmed by the XPS carbon C 1s core level spectra analyses. Indeed, the sp(3)-bonds content of the a-C films is found to diminish from 44% at RT to a minimum value of 16% around T-d = 450 degrees C and then stabilizes around 26% at T-d = 750 degrees C. On the other hand, the hydrogen peroxide (H2O2) production capacity of these a-C films was systematically evaluated, and found to reach its maximum of 11.2 lg/L/cm(2) at T-d = 450 degrees C, at which the highest C sp(2)-bonds content was also observed. We were thus able to point up, for the first time, a fairly linear correlation between the produced amount of H2O2 of the a-C films and their relative [sp(2)] bonding content, over an [sp(2)] relative content range as wide as (0-84%). These results clearly demonstrate the relevance of a-C films with a pronounced graphitic like character for H2O2 production. Such a-C cathodes with an enhanced H2O2 production capacity are highly sought for in electrochemical decontamination of water from persistent organic pollutants. (C) 2015 Elsevier Ltd. All rights reserved.