Contradictory role of reactive oxygen species in dissolution-dependent activity of Pb-based anodes in acidic electrooxidation

Abstract

The dilemma of activity and stability limits the application of metal-based anodes in electrooxidation, especially in concentrated acid media, and thus causes the emission of hazardous wastewater and waste. Herein, a strong correlation is first reported between activity and Pb²⁺ dissolution of Pb-based anodes in acidic-electrooxidation. This complex relationship lies in the contradictory role of reactive oxygen species (ROS, SO₄⁻* and OH*). Although the evolution of ROS is a crucial step for Pb passivation and oxygen evolution, the elimination of ROS results in exposure and dissolution of Pb²⁺. Moreover, oxygen evolution is hindered due to the mismatch of ROS energy bonding. Based on these discoveries, a simple, competitive and sustainable strategy is proposed for changing the ROS evolution environment by precoating MnO₂ on Pb-based anodes. Pb-based MnO₂ anodes (PMAs) with different ROS evolution environments present ultra-low Pb²⁺ dissolution (reduced by ∼95%) and enhanced oxygen evolution performance because of the uniform energy bonding distribution. These findings have conclusively confirmed ROS behaviour control as the criterion for alleviating dissolution-dependent activity of metal-based anodes for extensive electrooxidation.