A series of iridium (Ir) organometallic-based electrocatalysts fused onto high surface-area activated carbon using pyrolysis were prepared for the oxygen evolution reaction (OER) in seawater electrolysis. These catalysts had a low loading of Ir (< 6 wt%), while also inducing atom coordination to the Ir center. The morphology and chemical composition of these electrocatalysts were analyzed by scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy, which all showed a uniform dispersion of Ir and heteroatom-doped moieties. To assess electrocatalytic activity, we used an artificial electrolyte comprising 0.1 M HClO 4 + 3.5 wt % NaCl, and found that these catalysts delivered a low overpotential of 243 mV, a low Tafel slope (92 mV dec À 1), and a high exchange current density (1.4 mA cm À 2). By using a headspace chlorine gas (Cl 2) detector in situ, we discovered that a Cl 2 content of 27 ppm was present. When tested in synthetic seawater, the overpotential exhibited a twofold increase, yet Cl 2 was undetected, thus indicating favorable OER kinetics. This significant finding exemplifies the need for in situ Cl 2 detection for seawater splitting research, since further insight can be derived to help guide the design of novel electrocatalysts.