A review on biomass-derived N-doped carbons as electrocatalysts in electrochemical energy applications

The development of biomass-derived N-doped carbonaceous materials as electrocatalysts is of great importance considering their resource abundance in the earth, low price, ease synthesis process, and their electro/chemical compatibility as reaction medium for a wide range of electrochemical energy applications. In the current review, various types of biomass-derived N-doped carbon materials with the combination of heteroatoms (H), transition metals, and conducting polymers are reviewed according to their roles in each application that includes fuel cells, water splitting, batteries, and supercapacitors. The electrocatalytic activity of biomass-derived N-doped carbon materials is discussed based on the key reactions of each application, such as oxygen redox reaction, hydrogen generation reaction, sulfur/vanadium redox reactions and so on. For example, oxygen reduction reaction electrocatalysts can be categorized into five types, that is, i) metal-free N doping, ii) metal-free N, H co-doping, iii) metal-free N, H multiple doping, iv) metal-N doping, and v) metal-N, H co-doping. Further, their electrochemical performance is compared with state-of-the-art noble metal-based catalysts including Pt/C and IrO2. The key roles of the biomass-derived N-doped carbonaceous electrocatalysts in various types of rechargeable batteries, meanwhile, are first summarized including metal-air, lithium-sulfur, metal-carbon dioxide, and vanadium redox flow batteries. It is anticipated that this review could not only contribute to the rational design of biomassderived catalyst synthesis but also boost scientific research efforts in the valorization of biomass-derived resources for the electrochemical energy applications.