Bypassing Pt(100)-O*OH* deactivation sites via superb ionomer network towards ultra-stable stationary fuel cells

Understanding the voltage degradation under long-term continuous operation is essential for deploying highly stable polymer electrolyte fuel cell (PEFC) in stationary applications, e.g. artificial intelligence (AI) data centers. Here, we identify that Pt(100) surfaces, one of the dominant planes in polycrystalline Pt, are gradually covered by O*OH* species at E=0.708 V RHE , based on chronoamperometry experiments coupled with density functional theory calculations. This coverage elevates the O*OH*→H 2 O barrier and significantly aggravates the oxygen reduction reaction (ORR) kinetics. Guided by this insight, the ORR electrode is constructed with a highly connected network of perfluorinated sulfonic acid ionomer, which is beneficial in bypassing O*OH* sites while maintaining sufficient porosity for O 2 transport. Firstly, the short-side-chain ionomers with different ion exchange capacities (IECs) are mixed with Pt/C to reach the adsorbed ionomer-to-carbon ratios ranging from 0.034 to 0.076, then after the selective isolation of adsorbed ionomers, the desired amount of ionomer with higher IEC is added to create a highly connected network of non-adsorbed ionomers. Electrode slurries are characterized both qualitatively and quantitatively by using rheometer and thermogravimetric analyzer, respectively. The optimized membrane electrode assembly (MEA) results in a cell voltage higher than 0.71 V at 0.5 A·cm -2 , with an unprecedented low decay rate of 10 µV·h -1 over 400 h, that is 4-fold lower than the state-of-the-art commercial MEA. Based on these findings, the rises of both electrode ionomer coverage and connectivity vitalize PEFC to offer a sustainable off-grid solution for ever-growing electricity demands in the current AI challenge.