Performance Enhancement of Polymer Electrolyte Membrane with Nano-Calcium Carbonate Prepared by Mechanochemical for Direct Methanol Fuel Cell Applications

Direct methanol fuel cells (DMFCs) have great potential for use in portable electronics. However, obstacles such as methanol crossover, insufficient proton conductivity, and the high cost of Nafion hinder the broad commercialization of this technology. In line with the prevailing “waste-to-wealth” movement, eggshell powder was chosen as the filler for the Nafion matrix (rN-ES). Nano-calcium carbonate (nano-CaCO₃) was first produced from eggshell waste by a mechanochemical process before inclusion in the Nafion polymer matrix by the solution casting process. Cyclic voltammetry and electrochemical impedance spectroscopy were used to measure methanol permeability and proton conductivity. The composite membrane showed the highest value for ion exchange capacity of 1.25 mmol g⁻¹ and water uptake of 46.54%. Remarkably, the through-plane method showed better proton conductivity (4.87 mS cm⁻¹) compared to N117. The methanol permeability of the rN-ES composite membranes decreased to 3.3 times the permeability of N117. In the passive single-cell test of the DMFC, the use of a composite membrane with 5 wt.% nano-CaCO₃ resulted in a rise in the maximum power density from 9.5 to 12.37 mW cm⁻². These results prove that the incorporation of nano-CaCO₃ as a filler in a Nafion matrix is practicable for DMFC applications.