Tian, ZihaoKhotseng, LindiwePasupathi, Sivakumar2026-09-092026-09-092026Tian, Z., Liu, H., Zhang, W., Xu, Q., Khotseng, L., Pasupathi, S. and Su, H., 2026. Regulating local phosphoric acid environment via HDTMPA-modified catalyst layers for enhanced high-temperature proton exchange membrane fuel cells. Journal of Power Sources, 692, p.241130.https://doi.org/10.1016/j.jpowsour.2026.241130https://hdl.handle.net/10566/25376Managing phosphoric acid (PA) distribution within the catalyst layers is a critical challenge for the development of high-performance high-temperature proton exchange membrane fuel cells (HT-PEMFCs). This work introduces a novel strategy using hexamethylenediamine tetra(methylenephosphonic acid) (HDTMPA) as a functional additive in the cathode to precisely regulate the local PA environment. HDTMPA performs a dual function: its strong hydrogen-bonding interactions with PA effectively anchor the acid, which prevents the excessive flooding and poisoning of Pt catalyst sites, while its electron-rich nitrogen atoms help establish a robust proton-conduction network. Consequently, a membrane electrode assembly (MEA) with an HDTMPA-modified cathode (0.5 mgPt cm−2) achieves a peak power density of 715 mW cm−2 at 150 °C, a 42% enhancement over the unmodified baseline (503 mW cm−2). Furthermore, the modified MEA demonstrates exceptional durability, exhibiting only a 5.0% performance decay after an accelerated durability test of 10,000 cycles, compared to a 17.5% decay for the control. In-situ electrochemical analysis confirms the enhanced kinetics, validating this molecular design approach as a new avenue for developing highly stable and efficient HT-PEMFCs.enCatalyst layerHDTMPAHigh-temperature proton exchange membrane fuel cellMembrane electrode assemblyPerformanceArticle