Asymmetric structural tuning of industrial MnO2 arrays on a hierarchical lead-based anode for manganese metallurgy

Abstract

Manganese dioxide (MnO₂)-modified lead-based anodes (LBAs) are promising candidates to boost the oxygen evolution reaction (OER), but they usually suffer from structural instability and catalytic deactivation upon their irreversible digestion and the insertion of lead (Pb) in the MnO₂ arrays, which consequently restrict their industrial application. Herein, we propose a novel structure tuning strategy to fully exploit the potential of MnO₂ by employing a TiB₂ interlayer that effectively suppresses the in situ electromigration of Pb²⁺ ions across the LBA interface. In situ tests with theoretical calculations indicate that the atomic substitution of Pb in [MnO₆] units alters the electronic states of the host and compresses the length of the adjacent Mn–O space. This is caused by the electronic interaction between Pb and adjacent O atoms in the MnO₂ lattice, finally resulting in a sluggish OER activity. By leveraging the unique pinning effect of TiB₂ on LBA, we synthesized an asymmetric structure of MnO₂ (ASM), which was characterized by axial elongation along the d_z² orbital of [MnO₆], on the LBA/TiB₂ surface. The presence of a high-spin Mn³⁺ cation in octahedral coordination promotes oxygen vacancy formation within ASM lattices, leading to enhanced robustness and low energy barriers for OER. Scaling up the experiments further confirmed the superior advantages of ASM in an Mn electrowinning system. This work provides valuable insights into the industrial applications of structure-controllable MnO₂ materials in electrometallurgy to significantly reduce energy consumption and hazardous by-products.