Ultralow Loading Iridium Doped Hollandite Manganese Oxide Nanowires for Efficient Acidic Oxygen Evolution Reaction.

Abstract

Efficient and durable catalysts for the acidic oxygen evolution reaction (OER) are critical for hydrogen production but remain limited by reliance on scarce iridium (Ir). We present an ultralow-loading Ir catalyst (3 at%, <16 µgIr cm- 2) integrated within a hollandite MnO2 framework, which lowers the overpotential at 10 mA cm- 2 from 580 mV (undoped α-MnO2) to 303 mV and delivers an Ir mass activity an order of magnitude higher than commercial IrOx. Varying pH and potential, we combine ICP-MS dissolution measurements with x-ray absorption spectroscopy, electron energy loss spectroscopy, and 4D scanning transmission electron microscopy. Dissolution is modest, with at least 79% of the Ir and 76% of the Mn remaining after 6 h under applied potential, and Ir remains oxidized and associated with the hollandite framework. Mn, in contrast, undergoes pH- and potential-dependent reduction and local structural disorder. Notably, the strongest Mn reconstruction (pH 0, 1.65 V) coincides with moderate dissolution, whereas the greatest Ir and Mn loss (pH 0, 1.60 V) occurs where the residual material is less reconstructed. Net dissolution therefore does not report on local structural change, highlighting the need to evaluate dissolution, reconstruction, and oxidation state together when designing and assessing Ir-efficient mixed-metal oxide catalysts.

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