With the advancement of portable technology, suitable power sources must be developed. In comparison to standard battery technology, microscale fuel cells demonstrate higher energy densities and the potential for nearly instantaneous recharging [1]. However, fuel cells are commonly less efficient than batteries, and thusly, produce more waste heat. Waste heat is generated in methanol polymer electrolyte membrane fuel cells via the oxygen reduction reaction, the methanol oxidation reaction, and ohmic heating in the membrane. The oxygen reduction reaction accounts for the vast majority of the total heat generated [2]. Consequently, heat generation and removal in conventional fuel cell architectures has been carefully investigated in order to achieve effective thermal management [3]. Here we present a novel microscale fuel cell design that utilizes a half-membrane electrode assembly (MEA). In this design, a single fuel/electrolyte stream provides an additional pathway for heat removal that is not present in traditional fuel cell architectures. There are three streams in this fuel cell design: methanol fuel, oxygen, and nitrogen. Previously a simplified model neglecting the heat transfer through the anode side and nitrogen stream has been investigated [4]. The simplified model only has one heat generation source in the cathode catalyst.

The ANSYS Fluent model presented here investigates heat removal of inlet fuel temperatures of 22°C, 40°C, 50°C, 60°C, and 70°C. This new model simulates the complete fuel cell including the anode side and nitrogen stream. There are three heat generation sources in the new model: oxygen reduction in the cathode catalyst, methanol oxidation in the anode catalyst, and ohmic heating in the membrane. Continuity, momentum, and energy equations were solved simultaneously by ANSYS Fluent to obtain the results. Heat generation densities are determined experimentally for all inlet fuel temperatures. The simulations predict thermal profiles throughout this microscale fuel cell design. The exit temperature of the fuel stream, oxygen stream, and nitrogen stream were obtained to determine the rate of heat removal. Simulation results show that the fuel stream dominates heat removal at room temperature. As inlet fuel temperature increases, the majority of heat removal occurs via convection with the ambient air by the exposed current collector surfaces. The top and bottom current collector removes nearly the same amount of heat. The model also shows that heat transfer through the oxygen channel and nitrogen channel is minimal over the range of inlet fuel temperatures. Ultimately, these simulations can be used to determine design points for best performance and durability in a single-channel microscale fuel cell.

[1] M.A. Goulet, E. Kjeang, Journal of Power Sources, 260 (2014) 186-196.

[2] A.Z. Weber, J. Newman, Journal of the Electrochemical Society, 153 (2006) A2205-A2214.

[3] H. Ju, H. Meng, C-Y. Wang, International Journal of Heat and Mass Transfer, 48 (2005) 1303-1315.

[4] L. Sun, A.S. Hollinger, ASME 2017 15th International Conference on Fuel Cell Science, Engineering and Technology, V001T03A001-V001T03A001.