Paracrystalline Ce-Doped IrO <i> _x </i> Nanocatalysts for Superior Acidic Water Oxidation

The acidic oxygen evolution reaction (OER) in proton-exchange membrane water electrolyzers heavily relies on Ir-based catalysts, yet their widespread application is hindered by the trade-off between activity and stability. Recent studies have revealed that the active species formed during OER is not simply amorphous but possesses a distinct paracrystalline structure featuring short-to-medium-range order. However, directly constructing such metastable configurations via simple synthetic routes remains challenging. In this study, we present a rationally designed paracrystalline Ce-doped IrO x catalyst (p-IrO x:Ce), synthesized through a simple one-step pyrolysis method. Physical characterizations reveal that this unique paracrystalline architecture featured moderate Ir oxidation states (+3.5) and a short-range disordered arrangement, together improving the active site exposure and the electronic structure. As a result, the as-prepared p-IrO x:Ce exhibits outstanding acidic OER activity, achieving a low overpotential of 241 mV at 10 mA cm –2 . Mechanistic studies demonstrate that Ce-induced structural distortion activates the lattice-oxygen oxidation mechanism of OER involving decoupled proton–electron transfer, thereby contributing to the enhanced catalytic performance. Notably, p-IrO x:Ce also delivers exceptional long-term durability, sustaining continuous operation at 100 mA cm –2 for over 300 hours with negligible degradation. This work establishes a direct synthetic strategy for constructing metastable paracrystalline Ir-based catalysts and highlights the important role of paracrystalline engineering in overcoming the activity-stability limitations. These findings provide valuable insights into the rational design of high-performance electrocatalysts for sustainable energy conversion processes.