A highly porous nitrogen-doped carbon sphere (NPC) electrocatalyst was prepared through the carbonization of biomass carbon spheres mixed with urea and zinc chloride in N₂ atmosphere. The sample carbonized at 1000 °C demonstrates a superior oxygen reduction reaction (ORR) performance over the Pt/C electrocatalyst, while its contents of pyridinic nitrogen and graphitic nitrogen are the lowest among samples synthesized at the same or lower carbonization temperatures. This unusual result is explained by a space confinement effect from the microporous and mesoporous structures in the microflakes, which induces the further reduction of peroxide ions or other oxygen species produced in the first step reduction to water to have the preferred overall four electron reduction ORR process. This work demonstrates that in addition to the amount or species of its active sites, the space confinement can be a new approach to enhance the ORR performance of precious-metal-free, nitrogen-doped carbon electrocatalysts.

通过将生物质碳球与尿素和氯化锌混合在N _2中碳化，制备了高度多孔的氮掺杂碳球（NPC）电催化剂。气氛。在1000°C下碳化的样品表现出优于Pt / C电催化剂的氧还原反应（ORR）性能，而在相同或更低的碳化温度下合成的样品中，吡啶氮和石墨氮的含量最低。这种不寻常的结果是由微片中微孔和中孔结构的空间限制效应所解释的，这导致第一步还原过程中产生的过氧化物离子或其他氧物种进一步还原为水，从而具有优选的整体四电子还原ORR工艺。这项工作表明，除了其活性部位的数量或种类以外，空间限制可能是提高不含贵金属，氮掺杂的碳电催化剂的ORR性能的一种新方法。