How common is it to get an OER overpotential that is <250 mV?

Abstract

The anodic oxygen evolution reaction (OER) in room-temperature water electrolysis is a key bottleneck for achieving green, economical, and efficient hydrogen production. Thermodynamic constraints dictate that liquid water cannot be electrolyzed to gaseous O₂ and H₂ at 1.23 V, with a minimum overpotential of 0.25 V required, increasing the threshold to 1.48 V (the thermoneutral potential at room temperature). While this is true for water electrolysis, the maximum contribution to this 0.25 V overpotential comes from the anodic OER. Alarmingly, many recent studies claim far lower OER overpotentials than 250 mV, an impossibility even under isothermal conditions with a three-electrode setup. Our analysis reveals that, most of the time, these inaccuracies stem from a lack of understanding of thermodynamic constraints, misinterpretation of catalyst redox currents as OER activity, use of uncalibrated reference electrodes, and experiments conducted at non-standard conditions. A review of recent literature shows a consistent OER overpotential plateau of 250 ± 50 mV at 10 mA cm⁻², with onset overpotentials 30–50 mV lower. While minor reductions may result from local heating effects, reports of extremely low OER overpotentials cannot be justified by such factors alone. Instead, they predominantly stem from poor experimental practices and misinterpretations. To ensure reliable OER characterization, we propose corrective measures, including proper reference electrode calibration, isothermal control, and rigorous data validation. Recognizing that OER catalysts can hardly achieve such extremely low overpotentials (<100 mV) at 10 mA cm⁻² is crucial for eliminating errors and fostering progress in electrocatalyst development for efficient green hydrogen production.