Understanding ageing mechanisms of porous carbons in non-aqueous electrolytes for supercapacitors applications

International audience; Two activated porous carbon powders with different surface functional groups content have been electrochemically polarized in tetraethylammonium tetrafluoborate (Et4NBF4) in acetonitrile electrolyte to study their ageing mechanism as supercapacitor electrodes. Temperature-programmed desorption coupled with mass spectrometry technique (TPD-MS) is used to track the change of carbon surface chemistry – surface functional groups and/or adsorption of degradation products occurring upon polarizations. A potentiostatic study of the carbons in a two-compartment cell unveil the catalytic role of water in the ageing mechanism. Combining these results with our previous work, we propose different scenarios to depict the ageing mechanisms of the two carbons. For carbon A, hydrolysis of BF4− at the positive electrode leads to carbon oxidation together with soluble poly-acetonitrile oligomer occurred from reaction between BF4• radicals and acetonitrile. Ageing mechanism is also assumed to set off with the hydrolysis of BF4− for carbon B; but, in here the formed oligomers react with acid functional groups present at the carbon surface to form a protective, passive-like layer at both positive and negative electrodes which hampers a further electrode ageing.