Hydrogen production and filling of fuel cell cars

This paper presents a model for a hydrogen production fuel station, which simulates the complete process of hydrogen production under different conditions and demands. This simulation entails the modeling of four main components: an electrochemical hydrogen production cell with a thermal model, electrochemical compression and storage, and optimal car fueling. In the electrochemical cell model, an equivalent circuit for the PEM electrolyzer is built to compute the total electric energy needed for a certain demand of hydrogen. Moreover, the effect of temperature on the efficiency of the electrolyzer is modeled and accounts for the energy exchange process and temperature increase or decrease during electrolysis. Furthermore, a cooling system was developed in order to maintain the cell at optimum operating conditions, and thus operate at maximum efficiency. The hydrogen produced needs to be compressed because of its low volumetric density before it can be used for fuel cell cars. The compression is carried out using an electrochemical compressor. The advantages of this compressor are highlighted and its operation is compared to that of a mechanical compressor regarding efficiency and stability. Furthermore, the issue of back hydrogen diffusion in the compressor is analyzed and its effect on the efficiency of the system assessed; this effect was modeled for different types of membranes of different thicknesses. Finally, a procedure is presented for an automated filling station, and its various control measures are considered in order to maintain an efficient filling operation within the safety limits of the tank.