Combined Modeling and Experimental Analysis of Direct Methanol Microscale Fuel Cells

Abstract

With the advancement of portable technology, suitable power sources must be developed. Alternatives to standard battery technology, such as fuel cells, have shown promise; however such fuel cells are in their infancy with regards to industrial and consumer adoption [1-3]. In order for fuel cells to become a feasible alternative to traditional dry-cell alkaline and lithium-ion batteries, their performance must be optimized for their intended application via manipulation of parameters such as fuel molarity, flow rate, temperature, and electrode geometry. Here, we present a mathematical model of a microscale direct methanol fuel cell (DMFC), validated with experimental data. In the past, an iterative fabrication approach was undertaken to optimize DMFC performance, involving the fabrication and testing of many individual components to assess the effects of individual parameters. This model provides a means to automate the design process and remove the fabrication requirement. Prior parametric studies by Thorson et al. [4] show that shorter and wider electrodes yield higher current densities, however a recent review by Goulet et al. [5] highlights the need for a combined modeling and experimental approach to evaluating electrode design in a microscale fuel cell. Here we present a mathematical model to analyze the fuel flow pattern and performance of a direct methanol microscale fuel cell as a function of electrode geometry. Localized current densities are calculated over the electrode surface to elucidate the differences between electrode geometries. In the present work, the dimensions of the fuel channel are constant (0.5 cm (L) x 1.0 cm (W) x 0.125 cm (H)), while the length and width of the catalyst deposition region are varied. The model is validated with experimental data taken as a function of electrode geometry, fuel concentration, fuel temperature, and fuel flow rate. The performance of our experimental fuel cell is consistent with our modeling studies, achieving a maximum power density greater than 25 mW/cm2 at room temperature with 1 M methanol. The model presented here, in conjunction with the supporting experimental data, expands prior parametric studies [4] to predict optimal electrode design with regard to methanol concentration, temperature, and flow rate. [1] C.K. Dyer, Fuel Cells Bulletin, 2002 (2002) 8-9. [2] E. Kjeang, N. Djilali, D. Sinton, Journal of Power Sources, 186 (2009) 353-369. [3] A.S. Hollinger, P.J.A. Kenis, Journal of Power Sources, 240 (2013) 486-493. [4] M.R. Thorson, F.R. Brushett, C.J. Timberg, P.J.A. Kenis, Journal of Power Sources, 218 (2012) 28-33. [5] M.A. Goulet, E. Kjeang, Journal of Power Sources, 260 (2014) 186-196. Figure 1