Nitrogen and phosphorus Co-doped porous carbon: Dopant, synthesis, performance enhancement mechanism and versatile applications

Porous carbon is widely used in energy storage and environmental protection due to its well-developed pore structure, large specific surface area, low cost and excellent chemical/thermal stability. However, the hydrophobic surface of pure carbon materials can limit the performance of carbon materials. Non-metallic heteroatom doping is an effective strategy to improve the performance of carbon materials efficiently. In particular, nitrogen-phosphorus co-doped porous carbon (N/P–C) has received much attention in the past few years. When N/P–C is applied in the field of energy storage and adsorption, its internal micropores are the main part contributing to the active sites, mesopores and macropores mainly play the role of transport channels and storage reservoirs, respectively; therefore, the hierarchical pore structure combining both micropores, mesopores and macropores can significantly enhance the electrochemical and adsorption properties of N/P–C. In addition, the hydrophobic surface of pure carbon materials can limit the performance of carbon materials. In contrast, the doping of N and P heteroatoms introduces a large number of functional groups on the surface of the carbon material and improves the surface wettability of the carbon material, in addition to enhancing the electrical conductivity and providing more active sites, thus further improving the performance of the N/P–C. In this review, dopants and preparation methods for synthesis N/P–C are summarized in recent years. And the mechanism of nitrogen (N)-phosphorus (P) co-doping for performance enhancement is also discussed. Then, we discuss in detail the applications of N/P–C in the fields of supercapacitors (SCs), metal-ion hybrid capacitors (HC), metal-ion batteries, fuel cells, adsorption, etc. Finally, the potential and challenges of N/P–C for applications in energy storage/conversion and adsorption are discussed.