High surface area MnO2 nanomaterials synthesized by selective cation dissolution for efficient water oxidation

Abstract

Artificial photosynthesis is a promising method that directly transforms solar energy into chemical energy. To achieve artificial photosynthesis, efficient water oxidation catalysts (WOCs) are essential. In nature, the manganese-oxo-calcium cluster (Mn₄CaO₅) in the oxygen-evolving center (OEC) of photosystem II catalyzes water oxidation. Inspired by this process, abundant and inexpensive manganese oxides have been recognized for their high potential as effective and reliable materials for water oxidation reaction. However, in contrast to RuO₂ and IrO₂, manganese oxide catalysts still exhibit less water oxidation efficiency. Herein, we report a simple method for synthesizing high surface area, porous MnO₂ with different crystal structures from the CaMnO₃ precursor by treating with dilute HNO₃ solution followed by heating at different temperatures. These porous MnO₂ nanomaterials have a surface area in the range of 106–272 m² g⁻¹. These nanomaterials exhibit remarkable photochemical water oxidation activity with a maximum turnover frequency (TOF) of 3.29 × 10⁻³ s⁻¹. Our findings suggest a simple way to design and synthesize low-cost, high surface area, porous MnO₂ nanostructures for efficient water oxidation.