Development of Ion-Pair Membranes for HT-PEM Fuel Cell
Fuel cells are a pivotal technology that convert hydrogen into electricity, heat, and water steam. The conventional low-temperature proton exchange membrane fuel cells (LT-PEMFC) operate within a very narrow temperature range of 70°C to 90°C, which limits this technology for practical applications. In contrast, high-temperature proton exchange membrane fuel cells (HT-PEMFC) operating at temperatures ranging from 160 to 180°C do not require cooling systems or high-purity hydrogen. This makes them particularly well-suited for use in the heavy-duty transport, aviation, and shipping sectors.
However, this technology demands thermally stable and durable materials at elevated temperatures, as well as resistance to phosphoric acid, which is the primary component of the membrane separating the electrodes. Phosphoric acid is a liquid that readily mixes with water, making it susceptible to leaching from the cell. About 10 years ago, Yu Seung Kim and his team at LANL in the USA developed a polymer capable of adsorbing phosphoric acid, thereby significantly reducing acid leaching and the subsequent decline in fuel cell performance.
The MEAsureD project has optimized the polymers and membranes already commercialized by Advent and proposed a new bench of polyelectrolytes for the next generation of PEMs for HT-PEMFC application.
Ion-Pair Membranes – A Breakthrough in HT-PEM Fuel Cells
The recently developed ion-pair membranes are based on polymers bearing permanent charges on its polymer chain. The permanent charges convert the phosphoric acid into a biphosphate ion. This ion is attracted by the counter-charged polymer chain. As a result, the phosphoric acid is ionically adsorbed to the polymer. It has been demonstrated that the adsorption of phosphoric acid is optimized when the ion charges of the polymer are maximized. Therefore, polymer membranes form ion pairs consisting of positively charged polymer chains and negatively charged phosphoric acid and biphosphate. Additionally, the adsorption energy of the uncharged phosphoric acid is found to be higher than in the case of membranes without permanent charges. Consequently, the novel ion-pairs membrane demonstrates enhanced capacity for phosphoric acid adsorption and higher retention.
Effect of phosphoric acid doping degree on the fuel cell performance
Dew to the higher phosphoric acid doping degree of the ion-pair membranes in comparison to the uncharged membranes e.g. polybenzimidazole (PBI), the fuel cell performance is enhanced. The PBI based HT-PEMFC has shown a peak power density of about 400-500 mW/cm2 whereas, the ion-pair based HT-PEMFC has reached about 700-800 mW/cm2 at 160°C and 2 bar back pressure on the electrodes. This is a substantial increase of the performance from 70 to 100%.
Manufacturing Scalability: From Lab to Industry
The viability of a new innovation depends on its capacity for large-scale production. The MEAsureD project focused on the scalability factor, progressing from lab-scale coupons to large-area membranes produced by roll-to-roll manufacturing.
A Step Towards Universal Membrane
Recent research has demonstrated that ion-pair membranes have the capacity to reduce their operational temperature to ambient levels. This capability enables a novel approach known as “cold engine start” for fuel cells, particularly in heavy-duty applications. In addition, these membranes demonstrated potential applications in areas such as water electrolysis, redox flow batteries, and ion batteries.
The development of these polymers and membranes is critical for the MEAsureD project, as it will allow for a wide range of applications. The manufacturing of universal membrane represents a technically sound, cost-efficient model for an indigenous and sustainable hydrogen and clean energy economy.
