Synergistically immobilize phosphoric acid on core-shell metal pyrophosphate in the catalytic layer for fuel cells at 240 °C

Abstract

Evaporation and dehydration of phosphoric acid (PA) in the catalytic layer at elevated temperature pose significant challenges to the performance of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) at temperature above 200 °C. In this work, core-shell metal pyrophosphates (c-MP₂O₇, M = Ti, Zr and Sn) have been employed to immobilize PA in the cathode of HT-PEMFCs to improve their performance at temperature up to 240 °C. It reveals that precursors, composition and content of the c-MP₂O₇ play vital roles on the performance of catalytic layers. Compared to the direct addition of metal oxides into the catalytic layer with severe consumption of PA, the incorporation of metal pyrophosphates immobilizes PA on the surface of c-MP₂O₇ as a gel outer layer. This strategy creates an extensive proton diffusion network among the c-MP₂O₇ particles, leading to improved proton conductivity and cell performance. An HT-PEMFC with optimized content of c-SnP₂O₇ (11.6 wt%) in the catalytic layer achieves a remarkable peak power density of 462 mW cm⁻² at 240 °C, accompanied by an increased voltage rate of 0.15 mV h⁻¹ sustained over 35 h at 240 °C and constant load of 0.2 A cm⁻². These results demonstrate a significant milestone in the advancement of HT-PEMFC technology.