Abstract Microfluidic fuel cells (MFCs) exploit the two fluids to form the parallel flow in the microchannel, naturally separating the fuel and oxidant, and eliminate the proton exchange membranes in the traditional fuel cells. These membrane-free fuel cells not only have outstanding advantages such as wide selections of the reactants and simple configurations, but also tackle issues related to the membranes including membrane deformation and degradation and so on. To gain the all-alkaline MFC in the anode and cathode, we constructed the direct sodium formate/potassium ferricyanide microfluidic fuel cell with the catalyst-free cathode. Sodium formate was used as the fuel, potassium ferricyanide was adopted as the oxidant, and the electrolytes in the anode and cathode were both sodium hydroxide solutions. We investigated the effects of the flow rates, oxidant concentrations, fuel concentrations on the performance of the MFC. The performance of the MFC was gained by the linear sweep voltammetry from the open circuit voltage to 0.0 V with the sweep rate of 10 mV•s^-1. Experimental results showed that the performance of the MFC achieved the optimum, with the peak power density of 123.93 mW•cm^-2 and the limiting current density of 220.93 mA•cm^-2 under the conditions of 200 μL•min^-1 flow rate, 1 mol•L^-1 potassium ferricyanide and 1.5 mol•L^-1 sodium formate. The discharge test and electrochemical impedance spectroscopy (EIS) measurement were carried out under the conditions of the optimal cell performance. To evaluate the stability of this MFC, the discharge performance of the MFC under the constant voltage (0.78 V) was measured. The result showed that the MFC could stably discharge for about 2.25 h. Moreover, the internal resistance of the fuel cell was gained by the EIS measurement in the frequency range from 1 MHz to 50 mHz with the amplitude of 10 mV. After fitting the EIS result, the internal resistance of the MFC under the open-circuit voltage was 18.4 Ω.

Key words: microfluidic fuel cell, sodium formate, potassium ferricyanide, liquid oxidant, alkaline media, performance research