No abstract

No abstract

No abstract

No abstract

No abstract

Activated carbons (ACs) have been prepared from chemical treatment of walnut shells (WS) precursor at various temperatures (400‒800 °C) by using phosphoric acid (H3PO4) as activating agent. Influence of activation temperature on the porosity development and capacitive properties of resulting carbons was investigated. Thermal post-treatment of carbons previously activated at moderate temperature, e.g. 400 °C allowed further structural and porosity modification. Then, these carbons were investigated by scanning electron microscopy, Raman spectroscopy, energy-dispersive X-ray spectroscopy, electrochemical techniques and low temperature nitrogen adsorption exhibiting high BET specific surface area of approximately 2100 m2 g-1 and a total pore volume up to 1.3 cm3 g-1. Carbon material obtained through activation by H3PO4 at 400 °C and post-treated at 800 °C was used to make electrodes which were implemented to realize AC/AC capacitor using 1 mol L-1 Li2SO4. The electrochemical capacitor demonstrated high capacitance of 123 F g-1 per mass of one electrode, reduced cell resistance and stable capacitance for 5000 galvanostatic charge/discharge cycles at 1.0 A g-1.

Enhancing the operating voltage of supercapacitors (SCs), hence their specific energy,isimportant. However,longterm hold at high voltage entails loss of capacitance,increase of resistance and internal pressure.Suchdetrimental effects could be reduced by obtaining quantitative information on the relative impact of the various mechanisms leading to the worsening of the SCs performance.Now,for acarbon/carbon supercapacitor in aqueous Li 2 SO 4 ,aself-consistent approach is used to assign leaking charge during high voltage hold to the charge:1 )distributed throughout the electrochemical cell (steady-state leakage current measurements), 2) spent at each electrode for gases production (operando electrochemical mass spectrometry (EMS) analysis and pressure records), 3) utilized to oxidizet he electrodes surface (from post-mortem surface functionality determination by temperature programmed desorption (TPD)), and 4) used for other parasitic reactions.

Enhancing the operating voltage of supercapacitors (SCs), hence their specific energy, is important. However, long‐term hold at high voltage entails loss of capacitance, increase of resistance and internal pressure. Such detrimental effects could be reduced by obtaining quantitative information on the relative impact of the various mechanisms leading to the worsening of the SCs performance. Now, for a carbon/carbon supercapacitor in aqueous Li2SO4, a self‐consistent approach is used to assign leaking charge during high voltage hold to the charge: 1) distributed throughout the electrochemical cell (steady‐state leakage current measurements), 2) spent at each electrode for gases production (operando electrochemical mass spectrometry (EMS) analysis and pressure records), 3) utilized to oxidize the electrodes surface (from post‐mortem surface functionality determination by temperature programmed desorption (TPD)), and 4) used for other parasitic reactions.