Nitrogen-doped graphene quantum dots (GQDs) and graphitic carbon nitride (g-C₃N₄) quantum dots are synthesized via a solid-phase microwave-assisted (SPMA) technique. The resulting GQDs are deposited on graphite felt (GF) and are employed as high-performance electrodes for all-vanadium redox flow batteries (VRFBs). The SPMA method is capable of synthesizing highly oxidized and amidized GQDs using citric acid and urea as the precursor. The as-prepared GQDs contain an ultrahigh O/C (56–61%) and N/C (34–66%) atomic ratio, much higher than the values reported for other carbon-based nano-materials (e.g. oxidized activated carbon, carbon nanotubes, and graphene oxide). Three types of quantum dots, having an average particle size of 2.8–4.2 nm, are homogeneously dispersed onto GF electrodes, forming GQD/GF composite electrodes. Through deposition of GQDs onto the electrode structure, the catalytic activity, equivalent series resistance, durability, and voltage efficiency are improved. The capacity utilization using GQD/GF electrode is substantially enhanced (∼69% increase within 40 cycles). The improved performance is attributed to the synergistic effect of GQDs containing oxygen functionalities (epoxy, phenolic and carboxylic groups) and lattice N atoms (quaternary, pyrrolic and pyridinic N) which result in enhanced wettability and increased electrochemical surface area providing increased reaction sites.

中文翻译：

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钒氧还原液流电池中储能的石墨烯量子点修饰碳电极

通过固相微波辅助（SPMA）技术合成了氮掺杂石墨烯量子点（GQDs）和石墨氮化碳（gC ₃ N ₄）量子点。生成的GQD沉积在石墨毡（GF）上，并用作全钒氧化还原液流电池（VRFB）的高性能电极。SPMA方法能够使用柠檬酸和尿素作为前体来合成高度氧化和酰胺化的GQD。制备的GQD包含超高的O / C（56-61％）和N / C（34-66％）原子比，远远高于其他碳基纳米材料（例如氧化的活性炭，碳纳米管和氧化石墨烯）。平均粒径为2.8-4.2 nm的三种类型的量子点均匀地分散在GF电极上，形成GQD / GF复合电极。通过将GQD沉积到电极结构上，可提高催化活性，等效串联电阻，耐久性和电压效率。使用GQD / GF电极的容量利用率得到了显着提高（在40个循环内增加了约69％）。性能的提高归因于含有氧官能团（环氧基，酚基和羧基）和晶格N原子（季，吡咯基和吡啶基N）的GQD的协同作用，从而提高了润湿性并增加了电化学表面积，从而增加了反应部位。