Display omitted •Defects are strengthened through Gd ions chemisorption onto 2D-gCN electrode.•XPS, SBET, and HR-TEM findings assure the lattice defects of Gd3+/2D-gCN NSs.•Nyquist and Bode plots exhibit the capacitive nature of the electrodes.•Ion’s intercalation leads to enhance the areal capacitance via EDLC mechanism.•Complete retention of Csp (2.59 mF cm−2) over 1000th cycles for Gd3+/2D-gCN NSs. Thiswork reveals a facile synthesis of gadolinium ions adsorbed 2D-graphitic carbon nitride nanosheets (Gd3+/2D-gCN NSs) via a chemical-adsorption method for supercapacitor electrode materials. The structural, microstructural, and electrochemical properties ofGd3+/2D-gCN NSs and pristine 2D-gCN NSs are ascertained.The calculated capacitance for Gd3+/2D-gCN NSs is almost three times higher than the pristine one. The Nyquist and Bode plots exhibit thecapacitancemechanism.Gd+intercalation between the electrical double layers of adjacent 2D-gCN nanosheets increase the Van der Waals gap, which enhances it's specific capacitance. There is almost 100% retention of capacitance for Gd3+/2D-gCN NSs based device over 1000thcycle.