Wang Jiong, Wang Huai-Song, Wang Kang, Wang Feng-Bin, Xia Xing-Hua
State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China.
Sci Rep. 2014 Oct 22;4:6723. doi: 10.1038/srep06723.
In recent years, doped carbonaceous materials as alternative catalysts for oxygen reduction reaction (ORR) have received considerable attention due to the low cost and high CO tolerance capability. Different theoretical studies have suggested that oxygen is reduced in a rapid sequence intermediated by diverse oxygen-containing reactive intermediates (ORI). However, due to the short lifetimes of the possible ORI, direct experimental evidence is very difficult to be obtained. Here, we report the synthesis of an ultralight and porous nitrogen-doped graphene (NG) by annealing graphite oxide (GO)-melamine scaffold shaped in ice template. The resultant NG exhibits excellent electrocatalytic activity toward 4e-reduction of oxygen with the onset potential as low as -0.05 V vs. Ag/AgCl in alkaline media. Using this material as model study, sensitive in situ fluorescence spectroelectrochemistry is applied to demonstrate the presence the reactive ORI. The global ORR pathway is unraveled as stepwise electron transfer involving hydroxyl radical as the important intermediate via both inner- and outer-sphere process. This result would likely provide a new insight into the further understanding of ORR mechanism on those intrinsic carbonaceous materials.
近年来，掺杂碳质材料作为氧还原反应（ORR）的替代催化剂，因其低成本和高抗CO能力而受到广泛关注。不同的理论研究表明，氧在多种含氧反应中间体（ORI）介导的快速序列中被还原。然而，由于可能的ORI寿命较短，很难获得直接的实验证据。在此，我们报告了通过对冰模板中成型的氧化石墨（GO）-三聚氰胺支架进行退火来合成超轻且多孔的氮掺杂石墨烯（NG）。所得的NG在碱性介质中对氧的4e还原表现出优异的电催化活性，起始电位低至-0.05 V（相对于Ag/AgCl）。以这种材料作为模型研究，应用灵敏的原位荧光光谱电化学来证明反应性ORI的存在。揭示了整体ORR途径为逐步电子转移，涉及羟基自由基作为通过内球和外球过程的重要中间体。这一结果可能为进一步理解那些本征碳质材料上的ORR机制提供新的见解。
