Synergistic effect of anion and cation in oxalic acid for graphene surface engineering and its enhanced pseudocapacitance performance

Highlights: • Utilized oxalic acid as a green reducing agent to prepare the reduced graphene oxide modified with rich CO and COH. • The synergistic effect of carboxylation and decarboxylation of GO edge by oxalic acid can achieve more retention of C=O. • Rapid reduction reaction, oxygen groups conversion and equilibrium of reactions are the three stages of rGO-oxalic formation. • The rGO-oxalic showed good electrochemical properties (301.1 F/g at 1 A/g and 89.5% capacitance retention after 10,000 cycles). -- Abstract: The reduced graphene oxide (rGO-oxalic) with rich carbonyl and hydroxyl groups was prepared by using oxalic acid as reducing agent, and the structure of rGO-oxalic was characterized by XRD, Raman, TEM, AFM, XPS and BET. The anion and cation in oxalic acid play an important role in the removal of oxygen groups on GO surface, but the chemical reaction and mechanism are different. The further study indicated that the GO was reduced rapidly and effectively in the initial stage of reaction, and it is selective reduction in the middle and final stage of the reaction, showing that more carbonyl and hydroxyl groups were retained. The supercapacitor with rGO-oxalic as electrode material exhibited the superior specific capacitance (301.1 F·g⁻¹ and 217.0 F·g⁻¹ at 1 A·g⁻¹ in three- and two-electrode systems, respectively). Meanwhile, the capacitance retention was as high as 89.5% after 10,000 cycles at 5 A·g⁻¹ for the symmetric supercapacitor. The research on the reduction mechanism of rGO-oxalic is beneficial to its potential application in energy storage and other fields.