The polymer electrolyte membrane fuel cell (PEMFC) utilizes a polymer membrane as an electrolyte, possibly needing filler or functionalization for improved cell effectiveness. In this study, carbon nanodots (CDs) were functionalized by polydopamine (PD) to enhance the properties of CDs as potential filler for fuel cell applications. The functionalized carbon nanodots (PD-CDs) were subjected to characterization of Structural groups, building properties, elemental evaluation, thermal properties, and morphological features of the resulting functionalized carbon nanodots (PD-CDs) using FTIR, XRD, thermogravimetric analysis, SEM-EDX, as well as TEM. Ion exchange capacity (IEC) was also conducted to quantify ions transfer to have more insight on the potential use of PD-CDs as filler. The infrared spectra of PD-CDs reveal a broader band at 3400 cm−1 compared to CDs. This peak is attributed to the presence of N-H and O-H groups formed in the PD functionalization process. The diffractogram of PD-CDs exhibits a wide peak at 2θ = 26°, which is a result of the creation of a PD covering on outerly of CDs. However, thermal analysis shows that PD-CDs have lower thermal stability than CDs. Filler morphology does not alter by the coating as shown by microscopy images except increasing in its size across. Micrographs of the filler confirmed size growth after dopamine alteration, crediting a positive PDA layer decoration on CDs. IEC value of the PD-CDs increases from 0.56 to 1.22 mmol g−1 with the increasing temperature. These PD-CDs have great potential as fillers for PEMFC construction.