Ir Nanoconfined and Doped MnO2 Nanosheets for an Enhanced Electrocatalytic Oxygen Evolution Reaction in Acidic and Basic Medium

One of the promising strategies to generate hydrogen for a future hydrogen economy is via electrocatalytic water splitting, where renewable electricity would be used to convert water into hydrogen and oxygen on an electrocatalyst within an electrolyzer. Oxygen evolution reaction (OER), the anodic half-reaction of water splitting is, however, kinetically sluggish and requires four electron-proton transfers making the overall reaction energy-intensive. For the economical production of hydrogen, improving the reaction kinetics in both low and high pH is of utmost necessity by designing an active and stable OER catalyst. Precious metals like Ir, Ru, and their oxides are known to be excellent OER catalysts but their large-scale application is hindered due to their low earth-abundancy. To address this issue, we have synthesized two types of OER catalysts with varying Ir wt.% to achieve a higher OER-activity per mass of Ir in the catalyst: Ir/MnO 2 , Ir nano-confined in the interlayer of layered MnO 2 nanosheets and Ir-doped MnO 2 nanosheets. In both acidic and basic environments, Ir/MnO 2 exhibited better OER activity than Ir-doped MnO 2 . In 0.5 M H 2 SO 4 , 16.7 wt.% Ir/MnO 2 and 17.5 wt.% Ir-doped MnO 2 exhibited OER overpotentials (η) of 298 mV and 320 mV, respectively, at a current density of 10 mA cm -2 . In 1M KOH electrolyte, 15.4 wt.% Ir/MnO 2 and 17.5 wt.% of Ir-doped MnO 2 exhibited OER η values of 213 mV and 245mV, respectively at 10 mA cm -2 . These overpotentials are ~500 mV lower than the pristine MnO 2 nanosheets and ~60-120 mV lower than commercial reference catalysts (20 wt.% Ir/C and IrO 2 ) at both low and high pH conditions, respectively. These synthesized catalysts were able to outperform the commercial materials by exhibiting four times higher OER-activity per mass of Ir, in both acidic and basic media. Hence, this synthetic approach may be a method to achieve enhanced OER activity using a lower mass of Ir. The physical characterization of the materials was carried out with X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS).