The electrochemical behavior of rare earth ions (RE3+) doped CaCO3/PEG nanocomposites (RE3+ = 0.08 mol Y, La, and Gd) synthesized via a biomimetic method using dolomite rock as a carbonate source was thoroughly analyzed through XRD, FTIR, UV–Vis-DRS, Band gap, PL, FE-SEM, and HR-TEM analyses. All the prepared products were in rhombohedral structure, and the obtained crystallite size was in the range of 25–23 nm. The average microstrain and dislocation density of the products were also calculated, and the values are 1.33, 1.35, and 1.73 × 10−3 and 12.69, 13.21, and 22.21 × 1014 for Y, La, and Gd-doped CaCO3/PEG nanocomposites. The FTIR results revealed the presence of characteristic peaks (477, 479, and 465 cm−1), which confirmed that the products were Y, La, and Gd-doped CaCO3/PEG nanocomposites. From the UV–Vis-DRS, band gap, and PL analyses, 0.08 mol RE3+ ions doped CaCO3/PEG nanocomposites demonstrate blue shift absorption and emission values with increasing band gap values (4.50, 4.58, and 4.70 eV). The formation of spherical-shaped morphology was affirmed by FE-SEM and HR-TEM analyses, and the calculated particle size was in the range of 32–26 nm. The pseudocapacitive behavior of 0.08 mol Y, La, and Gd-doped CaCO3/PEG nanocomposite electrodes was confirmed via CV, GCD, and EIS. They showed specific capacitances of 261, 270, and 288 F/g, respectively, at 5 mV/s using a CV curve, with 97% cyclic stability over 1000 cycles. Energy and power density were calculated, and the values are 51.6, 52.6, and 53.4 Wh kg−1 and 1416.28, 1229.21, and 1221.347 W kg−1 for Y3+, La3+, and Gd3+ anchored CaCO3/PEG nanocomposites, at 1 A/g respectively. © 2025 Elsevier B.V., All rights reserved.