Lamellar structured Ce-S-NC heterogeneous electrocatalyst as the highly durable cathode for passive direct liquid fuel cells

Abstract

Passive direct liquid fuel cells are promising power generation devices with the advantages of convenient transportation, storage for liquid fuel and high power density. This paper focuses on improving the intrinsic electrocatalytic performance and durability of nitrogen-doped carbon (N-C) cathodic electrocatalysts. Then, lamellar structured Ce-S-NC heterogeneous electrocatalyst was synthesized and used as a highly durable cathode for two types of passive direct liquid fuel cells, i.e., direct methanol fuel cells (DMFCs) and direct borohydride fuel cells (DBFCs). In this work, the effect of the S/C molar ratio on the microstructure and electrocatalytic performance of the Ce-S-NC electrocatalysts was investigated, and excellent intrinsic oxygen reduction reaction activity was obtained at an S/C molar ratio of 0.15. The peak power densities of Ce-S-NC based DMFCs reached up to 12.5, 23.6 and 41.9 mW·cm−2 at 20, 40 and 60 °C, respectively. The peak power densities of 59.3, 84.6 and 132.6 mW·cm−2 were obtained in Ce-S-NC based DBFCs at 20, 40 and 60 °C, respectively. In the durability tests, both the Ce-S-NC based air-breathing DBFCs and passive DBFCs showed the stable operation than that of N-C and Ce-NC. When the current density increased from 50 to 150 mA·cm−2, the Ce-S-NC based DBFC can be operated for 882 h, and only 34 and 91 h for that of N-C and Ce-NC. The electrochemical impedance spectroscopy tests proved Ce-S-NC based DBFC showed the faster mass transfer efficiency. The outstanding durability of Ce-S-NC is mainly attributed to the improved defect density and mass transfer.