Progress on electrocatalytic reduction of nitrate on copper-based catalysts

The rapid development of modern industry and agriculture has made serious nitrate pollution in groundwater, which has endangered human health and ecosystems. Electrocatalytic reduction is a new type of water treatment technology developed by combining electrochemistry and catalytic technology. By applying an electric current, an electrochemical reduction reaction of nitrate occurs at the cathode, thereby transforming nitrate into N-2 or economically valuable NH3. Hence, to efficiently convert nitrate in water is alluring from the perspective of environmental protection and energy saving. The key of nitrate electrochemical reduction technology is the cathode material. The optimization of cathode materials is vital to push the development and application of electrocataly tic reduction of nitrate. Good catalytic materials require higher catalytic activity and product selectivity, as well as stability and corrosion resistance in sewage. Copper-based materials have become a research hotspot due to their intrinsic catalytic activity. Currently, researchers have mainly explored metallic copper, single-atom copper, copper alloy and copper based composites. However, it is still a lack of related review to discuss the structure-activity relationship between the structure of copper-based materials and the electrocatalytic nitrate reduction performance. This paper mainly reviews the research progress of electrocatalytic nitrate reduction of copper-based material catalyst, and analyzes the relationship between structure and its selectivity and catalytic activity from the perspective of single matter copper, single atomic copper, copper alloy and copper-based composite materials, respectively. First, the surface defects of the exposed single copper were regulated by changing its surface morphology and then optimized the electrocatalytic nitrate reduction. Because of single copper corrosion resistance and poor catalytic stability, it is not easy to use for nitrate reduction. Secondly, single atomic copper electrode materials exhibit high activity and selectivity in the catalytic reaction. However, how to achieve the high load capacity of a single atom catalyst is an urgent problem for researchers to break through. Then, for the copper alloy, the stability of the catalyst is greatly improved, and because of the synergistic electron effect between metals, the multimetal electrode performance is stable and has corrosion resistance, and the catalytic activity is higher than the ordinary single metals. However, the copper alloy, especially the copper alloy mixed with precious metal, increases the corresponding cost, which is not conducive to the industrial promotion of a large area. Finally, copper and non-metal material carriers form a composite catalyst, which can combine the advantages of low cost, high mechanical strength, strong tunability and good durability of electronic structure. The uniformly dispersed copper nanocatalysts improve the active ratio and surface area of the material, and improve the catalytic activity through the overall cooperation between them. The composite catalyst of copper and its oxides also provides new ideas for the design of the selectivity and activity of high yield ammonia. The future development direction of copper-based materials and the challenges faced by actual industrial applications are discussed.