The hydrophilicity of carbon for the performance enhancement of direct ascorbic acid fuel cells

As a representative of low-temperature direct biomass fuel cells, direct ascorbic acid fuel cells (DAAFCs) carry many advantages, including renewable fuel, easy transportation and storage, and high safety. However, a major challenge of DAAFCs confronting us is relatively low power density. Herein, to deal with this challenge, we treat carbon black (BP 2000) with nitric acid at an optimal concentration (4 M), which is further employed as anodic electrocatalyst for AA oxidation with improved hydrophilicity. Consequently, hydrophilic AA molecules can more readily access the surface of the carbon electrocatalyst and donate electrons. Furthermore, the electrocatalytic effect of acid-treated carbon for AA oxidation reaction is quantitatively evaluated by the determination of activation energy, which has not been assessed prior to this study. In a similar way, nitric acid treatment is also applied to gas diffusion layer (GDL) at the anode side. In addition, Nafion content in anodic electrocatalyst layer, single cell operating temperature, and hot pressing conditions for the fabrication of membrane electrode assembly (MEA) as well as membrane thickness are also optimized. A maximum power density of 31 mW cm(-2) is eventually attained at 80 degrees C with anode ionomer content of 9.2% and hot pressing at 130 degrees C and 6 MPa for 2 min. This power density is 1.72 times of that reported previously with carbon black as the anode electrocatalyst. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.