A Thermally Decomposable Template Route to Synthesize Nitrogen-Doped Wrinkled Carbon Nanosheets as Highly Efficient and Stable Electrocatalysts for the Oxygen Reduction Reaction

We successfully developed a thermally decomposable template route to prepare wrinkled carbon nanosheets with a high level of nitrogen functional moieties by direct carbonization of biomass glucose and dicyandiamide as the renewable feedstocks. Confined pyrolysis of glucose within the interlayers of dicyandiamide-derived g-C₃N₄ as a thermally removable template results in the formation of two-dimensional (2D) wrinkled carbon nanosheets as well as simultaneous high-level nitrogen doping. The textural properties and nitrogen contents could be controlled by adjusting the mass ratio of glucose/dicyandiamide. Among various samples, the sample prepared with the dicyandiamide/glucose mass ratio of 7/1 has optimal activity for the electrocatalytic oxygen reduction (onset potential −0.12 V vs saturated calomel electrode (SCE); limiting current density 4.73 mA/cm²) in 0.1 M KOH solution, the half-wave potential of which is only 67 mV larger than that for 20 wt % Pt/C. Moreover, it demonstrates a highly efficient four-electron reaction process, as well as superior durability and tolerance to MeOH crossover to Pt/C. The excellent activity is mainly attributed to the high content of pyridinic and graphitic-N groups, highly graphitized structures, and wrinkled 2D nanostructures, efficiently promoting the increased exposure of actives sites and fast mass/electron transfer

Synthesis of Nitrogen-Doped Porous Carbon Spheres with Improved Porosity toward the Electrocatalytic Oxygen Reduction

In this study, a series of activated N-doped porous carbon spheres (ANCSs) have been prepared from biomass as the carbon source to be used as highly active and stable electrocatalysts toward the electrocatalytic oxygen reduction reaction (ORR). Hydrothermal carbonization of biomass glucose, which obtains uniform carbon nanopsheres, is followed by doping N atoms by treatment in ammonia and subsequent activation treatment to form ANCSs. The resultant ANCSs possess a large specific surface area of up to 2813 m²/g and pore volume of up to 1.384 cm³/g, and adjustable N contents (2.38–4.53 atom %) with increasing activation temperature. The graphitic and pyridinic-N groups dominate in various N functional groups in the ANCSs. Remarkably, the 1000 °C-activated sample demonstrates competitive activity and outstanding stability and methanol crossover toward the ORR with a four-electron transfer pathway in alkaline media compared to commercial Pt/C catalyst. This excellent performance should be mainly due to effective N-doping and high porosity which can boost the mass transfer and charge transfer and provide a larger number of active sites for the ORR. The unique spherical morphologies with improved porosity as well as excellent stability and recyclability make these ANCSs among the most promising ORR electrocatalysts in practical applications