Study of magnetic field to promote oxygen transfer and its application in zinc-air fuel cells

This study investigates the effects of magnetic field on oxygen transfer and the correlations of electrochemical parameters in different magnetic strengths. The discharge performance of zinc-air fuel cell (ZAFC) was tested under magnetic and nonmagnetic conditions using neodymium-iron-boron/carbon (NdFeB/C) magnetic particles in ZAFC cathode. The results showed that the oxygen diffusion coefficient (D-oi) and transfer coefficient (alpha(i)) increased by 102.14% and 52.38% when the magnetic strength increased from 0 mT to 5.0 mT, respectively. In addition, the electric double-layer capacitance (C-d) increased from 8.16 to 22.46 mu F cm(-2), the charge-transfer resistance (R-ct) decreased from 9.43 Omega cm(2) to 6.02 Omega cm(2), and the oxygen reduction reaction (ORR) current was improved. With the NdFeB/C load density of 2.4 mg cm(-2) in ZAFC cathode, the discharge current of magnetic ZAFC increased by 13.86% compared with the nonmagnetic ZAFC at the 0.80 V discharge voltage. These results indicate that magnetic strength has a positive correlation with D-oi, alpha(i), and the ORR current. Under magnetic attractions, the oxygen transfer process is easier at the Pt/C catalytic surface, and the discharge performance of magnetic ZAFC is superior to the nonmagnetic ZAFC. At lower NdFeB/C load density, increasing the NdFeB/C load density facilitates oxygen transfer and improves the discharge performance of ZAFC. However, the magnetic ZAFC discharge performance decreases at a higher NdFeB/C load density because of the blocked oxygen transfer channel and the magnetic field disorder caused by the magnetic interactions among different magnetic particles. (c) 2012 Elsevier Ltd. All rights reserved.