Progress in electrocatalytic denitrification using element-doped materials

Abstract

Electrocatalytic denitrification is one of the promising technologies for the treatment of nitrate wastewater. This review comprehensively summarizes the recent advances in electrocatalytic denitrification. Two reaction mechanisms of direct electron transfer and atomic hydrogen (H∗)-mediated indirect reduction in electrocatalytic denitrification are analyzed. It is concluded that the rate-limiting step of electrocatalytic denitrification is the reduction of NO_3- to NO_2- and the key intermediate determining product selectivity is NO. On this basis, the element-doping method and its regulation effects on the catalytic active centers and the electrocatalytic denitrification pathways are summarized, and it is suggested that element doping is an effective method to improve the catalytic activity, product selectivity and long-term stability of electrode materials. In addition, the influence of other factors such as water quality characteristics and operating parameters on the electrocatalytic denitrification performance is discussed. It is confirmed that the coexistence of halogen ions in water, such as Cl^- and Br^-, can significantly improve the N_2 selectivity, and most electrode materials exhibit-the best performance under neutral conditions. Facing the increasing demand of nitrate wastewater treatment, it is pointed out thatthe key bottlenecks limiting the large-scale application of electrocatalytic denitrification are the high electric energy consumption and the complex composition of the actual wastewater which leads to side reactions. Therefore, it is expected that the future research of electrocatalytic denitrification technology needs to conduct long-term pilot-scale tests based on the physicochemical properties of various actual wastewater. In addition to improving the reduction rate and product selectivity, it is also necessary to pay attention to the electric energy consumption and monitor the safety of treated water to facilitate the further development and practical application of electrocatalytic denitrification technology.

Keywords

• electrocatalytic denitrification
• nitrate wastewater
• element doping
• selective reduction
• electric energy consumption