Recent experiments at BESSY II with tender X-rays have revealed that the interactions between phosphorous acid and platinum catalysts in high-temperature PEM fuel cells are more intricate than previously thought. These findings indicate that variations in humidity can have a significant impact on the oxidation processes at the platinum-electrolyte interface.

High-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) are favored for micro-stationary electricity sources due to their efficiency. However, one of the drawbacks of these fuel cells is the leaching of phosphoric acid from the membrane, which can poison the platinum catalyst and reduce performance.

Studies have shown that during the operation of HT-PEMFCs, phosphoric acid may be reduced to phosphorous acid, further exacerbating the poisoning of platinum catalysts. The complex interactions between platinum and phosphorous/phosphoric acid involve both poisoning and oxidation processes.

A recent study by Prof. Dr. Marcus Bär’s team investigated the oxidation behavior of aqueous phosphorous acid under conditions similar to HT-PEMFC operation. Using in-house designed electrochemical cells and tender X-ray spectroscopy, they uncovered multiple oxidation pathways, including platinum-catalyzed chemical oxidation, electrochemical oxidation, and heat-promoted oxidation.

The study found that all oxidation pathways of phosphorous acid involve reactions with water, highlighting the significant influence of humidity within fuel cells. By controlling humidification levels, it may be possible to prevent catalyst poisoning by phosphorous acid and enhance the efficiency of HT-PEM fuel cells.

The results of the study suggest that adjustments to the operating conditions of HT-PEMFCs could prevent catalyst poisoning and improve overall efficiency. Understanding the degradation pathways of fuel cells is crucial for the development of hydrogen-based energy systems.

Overall, the study sheds light on the complex interactions between phosphorous acid and platinum catalysts in fuel cells, providing valuable insights for the optimization of HT-PEMFC operation. By unraveling the oxidation processes at the platinum-electrolyte interface, researchers may be able to enhance the performance and longevity of high-temperature polymer electrolyte membrane fuel cells.

Chemistry

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