A rapid start-up strategy for polymer electrolyte fuel cells at subzero temperatures based on control of the operating current density

Abstract

In a previous study, we numerically described the three distinct stages of ice evolution during the cold start of a polymer electrolyte fuel cell (PEFC), namely, the freezing, undersaturated, and melting stages. Based on our numerical observations, we propose an efficient start-up strategy for achieving a rapid cell temperature rise while simultaneously mitigating the rate of ice accumulation within a cell. The key to this cold-start strategy involves raising the operating current of the PEFC in the undersaturated stage, which accelerates the cell temperature rise without any further ice accumulation. Using a three-dimensional, transient cold-start model, we numerically demonstrate that raising the cell current in the undersaturated stage is very effective and significantly improves the cold-start behavior of a PEFC. In contrast, increasing the cell current in the freezing stage has a negative impact on the PEFC cold start in that the oxygen reduction reaction causes the water production rate to increase, leading to more rapid ice growth. This ultimately results in cold-start failure and the deterioration of the porous electrode structure. This study clearly illustrates that optimization of the cold-start operation is key to improving the cold-start performance, while also pointing to the importance of the roles played by PEFC cold-start modeling and the simulations used to search for an optimum cold-start strategy.