Efficient industrial hydrogen production via water splitting hinges on the development of highly effective oxygen evolution catalysts and a clear understanding of their catalytic mechanisms. Among various strategies, exploiting the synergistic effects of transition metals has shown great promise, although the underlying mechanisms remain elusive. Here, we investigate bi-transition metal borides, Mo₂MB₂ (M = Co and Ni), as a model system to unravel these synergistic effects and the evolution of active species during the oxygen evolution reaction (OER). Using combined in-situ and ex-situ characterization techniques, we monitor the structural and valence changes of constituent elements in real time. We find that Mo and B undergo oxidation and dissolution at the anode, initiating distinct evolutionary pathways. In Mo₂CoB₂, rapid structural collapse leads to the formation of γ-CoOOH as the active species. In contrast, Mo₂NiB₂ exhibits a more gradual surface-driven transformation, producing γ-NiOOH and Ni–O–Mo species. Chronopotentiometry testing reveals continued Mo and B dissolution, culminating in the transition of γ-phases to amorphous states, followed by recrystallization into β-phases. This study provides critical insights into dissolution-induced structural evolution, active species dynamics, and the synergistic interactions between Mo/B and Co/Ni during OER catalysis.

Understanding the dynamic structural and chemical evolutions at the catalyst–electrolyte interfaces is crucial for the development of active and stable electrocatalysts. In this work, β-Li₂IrO₃ is employed as a model catalyst for the oxygen evolution reaction (OER). Its elastic three-dimensional Ir-O framework enables us to investigate the Li⁺ cation dissolution-induced structure evolutions and the formation mechanism of amorphous IrO_x species. Electrochemical measurements by rotating ring disk electrode (RRDE) reveal that up to 60% of the measured OER current can be ascribed to catalyst degradation. A series of in-situ X-ray diffraction spectroscopy (XRD), X-ray absorption spectroscopy (XAS), and Raman spectroscopy are conducted. Structure vibration is observed with oxidation states of Ir being reduced abnormally during OER at high potentials. It’s hypothesized that the reversible proton intercalations are responsible for the Ir turn-over mechanism. Results of this work demonstrate a stable and elastic iridate structure and reveal the initial catalyst degradation behaviors during OER in acid media.