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

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 dz(2) 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.