Tailoring Pd content for optimal stability in FeCoNiCu multielement alloy electrocatalysts for oxygen evolution reaction

Multielemental alloys (MEAs) based on Earth-abundant 3d transition metals hold significant promise as low-cost electrocatalysts for the oxygen evolution reaction (OER), but their long-term stability under oxidative conditions remains a major challenge. In this study, we investigate the effect of palladium incorporation on the electrochemical performance and structural durability of FeCoNiCu MEA nanoparticles. Building upon our previous findings that trace Pd addition significantly enhances catalyst durability, an accelerated durability test (ADT) performed at 100 mA cm^-2 reveals that the degradation rate (0.356 mV h^-1) decreased dramatically to approximately 1/350th that of Pd-free FeCoNiCu (125 mV h^-1). In this study, we systematically synthesized a series of Pd-FeCoNiCu alloys with Pd contents ranging from 0.177 to 1.97 at%. Advanced characterization techniques including inductively coupled plasma optical emission spectroscopy (ICP-OES), electron microscopy, synchrotron-based spectroscopy, and electrochemical measurements, were employed to elucidate the correlation between composition, structure, and performance. Our findings reveal a highly non-linear dependence of catalyst performance on Pd content: an optimal range (0.336-0.389 at%) enables long-range d-d/sp orbital hybridization that delocalizes the local density of states (LDOS) of surrounding 3d metals, thereby suppressing oxidative dissolution. In contrast, higher Pd concentrations lead to Pd-Pd interactions, localize electronic perturbation, and accelerate degradation. This volcano-type correlation between Pd content and durability, highlights a general strategy for engineering catalyst longevity <i>via</i> minimal noble-metal doping and spatially cooperative electronic modulation.