Electrochemical capacitor in aqueous electrolyte with long lifespan improved by hydrogen bond donor addition

In the electrochemical capacitors (ECs) operating with aqueous electrolytes, corrosion of the current collector is one of critical issues that affects the cycling life, efficiency, and capacitance of the devices. So far, there are no stable metal current collectors in the water-based electrolyte because of its corrosive nature, even if the pH is close to neutral. Here, urea (CH4N2O) is used as an anticorrosive, green additive to 1 M lithium sulfate electrolyte for low-cost electrochemical capacitors based on carbon BP2000 electrodes. In this work, the corrosion study of stainless steel in the presence of such amide demonstrates an effective corrosion-inhibiting character owing to the urea interaction with water in the hydrogen-bonded network. Chemical stability of current collectors owing to a significant 10-fold decrease of the corrosion current and shift of the corrosion potential into negative side has been achieved when 2 M urea, i.e., hydrogen-bond donor (HBD) is added to electrolyte. Furthermore, the addition of this organic compound improves the capacitive performance of the system and prevents the fading of the device with no influence on the electrolyte conductivity. During the floating test of EC at 1.6 V operating in 1 M Li2SO4 with 2 M urea, the capacitance and resistance values keep the end-of-life criteria for over 350 h. Moreover, the galvanostatic investigation of such EC (at 1 A/g) displays performance of more than 60 000 cycles. Furthermore, operando experiments proved that carbon-based electrodes behave differently in lithium sulfate with urea and without additive owing to the formation of strong hydrogen bond network. The molecular structure of electrolyte has been estimated by DFT calculations. Overall, by using lithium sulfate and urea as an electrolytic system, the EC current collector has not only superior corrosion resistance against the aqueous electrolyte but also a high anti-ageing character at 1.6 V, which is favorable to improve the EC electrochemical performance. The use of urea as a stable, cheap electrolyte additive provides an innovative technique to enhance the performance of low-cost aqueous based supercapacitors.