Proton-exchange membrane water electrolyzer (PEMWE) systems currently face challenges due to their high investment costs, primarily stemming from the utilization of platinum group metal (PGM) electrocatalysts to catalyze both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). However, the high price and limited availability of PGM necessitate achieving enhanced electrocatalytic activity and stability. In this study, we present the synthesis and the characterization of porous, interconnected two-dimensional (2D) structures of iridium oxide (IrOx) with tunable Ir oxidation state and crystallography. Our method is based on the synthesis of IrOx/C nanoparticles using a classical polyol method. Upon thermal annealing under air at temperatures ranging from 340◦C to 670◦C, the IrOx nanoparticles merge to form a randomly close-packed aerogel-like structure of IrOx nanocrystallites (1-8 nm) connected by covalent bonds. The textural properties (pore size distribution, specific surface area) and physical properties (Ir oxidation state, IrOx crystallographic structure, conductivity) of the IrOx aerogel-like structures can be adjusted by varying the calcination conditions, enabling control over their OER activity and stability. The best catalytic materials achieve ~10 and ~17-fold enhancements in mass and specific activity for the OER, respectively, compared to standard micrometric IrO2 particles in rotating disk electrode setup tests. Their S-number values were determined using online inductively coupled plasma mass spectrometry, demonstrating an enhanced stability as the annealing temperature increased.