New insights into the electrochemical behaviour of porous carbon electrodes for supercapacitors

Activated carbons, with different surface chemistry and porous textures, were used to study the mechanism of electrochemical hydrogen and oxygen evolution in supercapacitor devices. Cellulose precursor materials were activated with different potassium hydroxide (KOH) ratios, and the electrochemical behaviour was studied in 6 M KOH electrolyte. In situ Raman spectra were collected to obtain the structural changes of the activated carbons under severe electrochemical oxidation and reduction conditions, and the obtained data were correlated to the cyclic voltammograms obtained at high anodic and cathodic potentials. Carbon-hydrogen bonds were detected for the materials activated at high KOH ratios, which form reversibly under cathodic conditions. The influence of the specific surface area, narrow microporosity and functional groups in the carbon electrodes on their chemical stability and hydrogen capture mechanism in supercapacitor applications has been revealed.The authors would like to thank the Engineering and Physical Sciences Research (EPSRC) for financial support of electrochemical energy conversion and storage research in the Electrochemical Innovation Lab (EP/R023581/1; EP/P009050/1; EP/N032888/1; EP/K014706/2; EP/M014371/1; EP/M023508/1; EP/M009394/1; EP/K038656/1), the Royal Academy of Engineering, Generalitat Valenciana and FEDER (PROMETEOII/2014/010), projects CTQ2015-66080-R (MINECO/FEDER). M.M.T and D.I.A. are grateful to UPM-Kymmene Corporation that provided the cellulose materials used throughout the experiments. M.J.M.L. acknowledges Generalitat Valenciana for the financial support through a VALi+d contract (ACIF/2015/374). I.P.P and G.H. thank the China Scholarship Council (CSC) and EPSRC for their financial support (EP/L015862/1)