Graphitic nanostructures in a porous carbon framework significantly enhance electrocatalytic oxygen evolution
Graphitic nanostructures in a porous carbon framework significantly enhance electrocatalytic oxygen evolution
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DOI：
10.1039/c7ta03027d
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发表时间：
2017-12-21
影响因子：
11.9
通讯作者：
Guo, Zhengxiao
中科院分区：
文献类型：
--
作者：
Gadipelli, Srinivas;Li, Zhuangnan;Guo, Zhengxiao
利用双金属分子筛咪唑骨架-8(ZIF-8)作为固体前驱体，同时以多孔碳为模板，以简化的化学气相沉积(CVD)方式生长石墨纳米碳，形成了一种石墨化纳米结构@多孔碳骨架的杂化结构。ZIF-8中的配体2-甲基咪唑(2MIM)在600摄氏度以上分解生成活性碳/碳氢自由基/蒸气。以气相碳为原料，利用镍的高催化活性在化学气相沉积过程中生长石墨纳米结构，用镍部分取代锌金属中心，合成了双金属ZIF-8前驱体。因此，这样的镍中心充当纳米催化剂，从碳化步骤中部分分解的骨架配体产生的碳自由基中生长出石墨纳米结构。这些杂化结构对水裂解析氧反应(OER)表现出极高的电催化活性。此外，随着样品中气孔率的增加和氮掺杂的增加，样品对氧还原和析氢反应(ORR和HER)的催化活性以及对H-2和CO2的气体吸收能力都得到了提高。我们还发现，并不是所有以镍为中心的MOF基前驱体都适合于制备纳米结构。我们的进一步研究表明，样品中的石墨化对提高催化活性起到了关键作用。
A hybrid structure, a graphitic nanostructures@porous carbon framework, is developed by utilizing the bimetallic zeolitic imidazolate framework-8 (ZIF-8) as a solid precursor, simultaneously templating porous carbon and growing graphitic nanocarbon in a simplified chemical vapor deposition (CVD) fashion. A ligand, 2-methylimidazolate (2MIM), in the ZIF-8 decomposes above 600 degrees C to yield active carbon/hydrocarbon radicals/vapour. With the idea of using the high catalytic activity of nickel to grow graphitic nanostructures in a CVD process from gaseous carbon feedstocks, a precursor, bimetallic ZIF-8, is synthesized by partial substitution of zinc metal centres by nickel. Such nickel centres thus act as nanocatalysts to grow graphitic nanostructures from the carbon radicals arising from the partly decomposed ligand of the framework during the carbonization step. These hybrid structures show a highly enhanced electrocatalytic activity for the water splitting oxygen evolution reaction (OER). Furthermore the catalytic activity for the oxygen reduction and hydrogen evolution reactions (ORR and HER), and gas uptake capacities for H-2 and CO2 are enhanced with respect to the increased porosity and nitrogen doping in the samples. We also show that not all the MOF-based precursors with nickel metal centres are suitable for producing nanographitic structures. Our further investigation suggests that the graphitization in the samples plays a critical role in enhancing the catalytic activities.