Molten‐Salt Etching Activates Cr‐Doped Al ₂ O ₃ on Graphene for Alkaline Oxygen Evolution

ABSTRACT

Aluminum oxide is an earth‐abundant yet catalytically inert p‐block oxide, as its lack of accessible d orbitals limits oxygen‐intermediate binding in the conventional adsorbate evolution mechanism (AEM). Herein, we activate the intrinsic oxygen evolution reaction (OER) activity of Al ₂ O ₃ by incorporating high‐valence Cr species through a one‐step molten‐salt electrochemical strategy. Using Cr ₂ AlC MAX phase as an integrated Cr, Al, and C precursor, selective Al extraction, Cr incorporation, and in situ carbon reconstruction are coupled to form Cr‐doped Al ₂ O ₃ nanoparticles anchored on a conductive graphene scaffold (Cr‐Al ₂ O ₃ @G). The integrated route mitigates nanoparticle agglomeration and weak interfacial contact typical of multi‐step syntheses. Cr‐Al ₂ O ₃ @G delivers an overpotential of 310 mV at 10 mA cm ⁻² , markedly lower than bare Al ₂ O ₃ and comparable to commercial IrO ₂ , while offering an estimated ∼70,000‐fold lower metal cost. It also achieves a metal‐mass‐normalized activity of 112 A g ⁻¹ . Mechanistic studies involving pH‐dependent kinetics, tetramethylammonium cation inhibition, and in situ ¹⁸ O‐isotope differential electrochemical mass spectrometry (DEMS) reveal that Cr incorporation reconstructs the Al‐O electronic environment and promotes a lattice‐oxygen‐mediated (LOM) pathway. This work provides a MAX‐phase‐derived strategy for cost‐effective activation of p‐block oxides.