Effect of the Pore Structure of the Gas Diffusion Electrode on the Power Generation and Mass Transport Properties of Direct Formic Acid Fuel Cell

Abstract

Direct Formic Acid Fuel Cell has been attracted match attention due to its higher power density and lower crossover. In order to improve their performance, we have tried to improve the mass transport in the anode electrode since a large amount of carbon dioxide is emitted by the electrochemical reaction. For the anode electrode, diffusion layer, such as carbon cloth and carbon paper used in the polymer electrolyte fuel cell, is commonly used in direct formic acid fuel cell. These diffusion layers were suitable for the gas supplying; however, it is not clear that these diffusion layers were also suitable for direct liquid fuel cell using liquid fuel. Moreover, the suitable pore structure of diffusion layer for the direct liquid fuel cell is also unknown. In this context, we fabricated the gas diffusion layer having different pore diameter, thickness and porosity using same manner and material in order to evaluate the effect of the pore structure of diffusion layers on the power generation characteristics and mass transport properties in direct formic acid fuel cell. The diffusion layers having 0.03-0.1 mm in average pore diameter, 60-90% in porosity, and 0.1-0.3 mm in thickness could be successfully fabricated using the purchased carbon fiber. The direct formic acid fuel cells using different diffusion layers for anode were fabricated and evaluated the i-V performance and crossover flux. It was found that the big pore can enhance the fuel feed rate to the anode catalyst layer under low current density (low CO2 emission), on the other hands, it did not contribute to the improvement of the fuel feed rate to the catalyst layer under higher current regions (high CO2 emissions). Small pore showed the counter trend. These results implies that the liquid feed and CO2 emissions is closely related the pore properties of diffusion layers, therefore, it is suggested that diffusion layer having suitable pore properties for direct liquid fuel cell is desired.