Direct methanol fuel cell stack design and testing for application in portable and auxiliary power units

Fuel cells are very promising technologies for efficient electrical energy generation. They can be used for a wide range of applications, such as auxiliary power units (APUs), portable, automotive and stationary devices. The concept of a direct methanol fuel cell (DMFC) is based on the direct feed of a methanol solution to the fuel cell anode, thus simplifying safety, delivery, and fuel distribution issues typical of conventional hydrogen-fed polymer electrolyte fuel cells. In this thesis work, simple and functional stack designs were developed for direct methanol fuel cells (DMFCs) with the aim of reducing capital costs. A simplified planar and monopolar ministack, with a reduced number of components, was designed for portable applications. This planar design facilitated the manufacturing of a compact passive-mode operation ministack. The ministack provided an output power of 1.30 W under air breathing mode operation, at room pressure and temperature without any auxiliary. For application in auxiliary power units (APU), a self-heating and modular bipolar stack, operating up to 90°C without internal cooling, was designed. Bipolar stacks consisted of 5-10 cells (100 cm2 active area), providing an output power of 90 -180 W. The recirculated methanol solution was used as thermostating fluid. The stacks achieved a normalised power density per cell of 180 mW cm-2. Whereas, for the passive mode operation, ministack approached 30 mW cm-2 with 5 M methanol feed. These results favourably compare with the best performance reported in the literature for DMFCs operating under similar conditions. In order to evaluate the feasibility of concrete application of DMFC devices, a cost analysis study was carried out, by considering as model the developed bipolar stack. A scale-down approach, focusing on the model device and projected to a mass production, was used. The data used in this analysis were obtained both from research laboratories and industry suppliers specialising in the manufacturing/production of specific stack components. The study demonstrates that mass production can give a concrete perspective for the large-scale diffusion of DMFCs as APUs. The results show that the cost derived for the DMFC stack is relatively close to that of competing technologies and that the introduction of innovative approaches can result in further cost savings.