Substrate-driven optimization of microfluidic aluminum–air fuel cells: a comparative study of glass fiber vs. cellulose paper

Microfluidic aluminium-air fuel cells (µA-aFCs) offer attractive low-cost, compact, and environmentally benign power sources for portable and off-grid electronics. Their performance is strongly governed by electrolyte transport within the paper-based microfluidic channel. Here we demonstrate that the performance of µAl-aFCs can be significantly improved by replacing conventional cellulose (Whatman #1) electrolyte substrates with glass fiber (GF) paper. Owing to its more open fibrous network, accelerated capillary flow, and improved chemical stability under alkaline conditions, GF paper enables more efficient electrolyte replenishment to the cathode and facilitates ionic transport within the device. Using KOH and NaOH electrolytes ranging from 0.5 to 5 M, electrochemical polarization, impedance, and discharge characteristics were evaluated as a function of substrate type and electrolyte concentration. The optimal configuration, consisting of GF paper and 3.5 M KOH, produced a peak power density of 72.89 ± 1.66 mW/cm² and a maximum current density of 143.76 ± 1.14 mA/cm², nearly double that obtained with Whatman #1 substrates. Impedance analysis indicates reduced ohmic and diffusion-related losses at intermediate electrolyte concentrations, while galvanostatic discharge tests demonstrate stable operation under constant load. These findings highlight substrate engineering using GF paper as a simple materials-based strategy for enhancing the performance of microfluidic Al-air fuel cells.