|Place of Conferral||北京
以溶剂热法合成了具有纳米笼状的Cu-MOF化合物，并采用溶剂-置换法对该MOF的纳米笼进行活化。通过循环伏安法分别对活化前后的Cu-MOF样品进行了电化学性质测定。结果发现，由于活性中心Cu2+的存在，活化前后的样品均呈现了一对Cu2+/Cu+氧化还原峰。虽然两种MOFs都具有电化学活性，但只有活化后的MOF能够催化氧还原反应，且氧还原的起始电位（vs. Ag/AgCl）较其他MOFs正移100 mV。这是因为样品经过活化处理后，溶解O2可以扩散进入纳米笼中，进而被Cu+催化还原，而未活化的样品中纳米笼被溶剂分子占据，O2无法接触到催化活性中心。为了避免活化后的MOF在扫描过程中从玻碳电极表面脱落，将还原态的氧化石墨烯修饰在玻碳电极与MOF之间，充当两者间的电子传输介质，增强了Cu-MOF催化层的稳定性。
以2,2'-联吡啶-5,5'-二羧酸（bpdc）为配体，Zn(NO3)•6H2O为金属盐在水热条件下合成了一种新型的吡啶基MOF（[Zn(bpdc)DMA]·DMF），并以这种MOF作前驱体，通过在800 ℃直接碳化制备了氮掺杂的多孔碳（NPC800）。将NPC800修饰在玻碳电极表面，通过循环伏安法和线性扫描伏安法研究其对氧还原反应的电催化性能。结果发现，NPC800的氧还原起始电位与商业Pt/C接近（-0.14 V vs. SCE），且氧还原电流远大于商业Pt/C。然后，以NPC800作催化剂载体，通过电沉积技术制备碳载Pt催化剂（Pt/NPC800）。结果证实，Pt/NPC800对甲醇氧化具有催化作用，且其催化稳定性高于具有相同Pt负载量的商业Vulcan XC-72碳材料。
以上述合成的吡啶基MOF为前驱体，改变碳化温度，制备了两种氮掺杂的多孔碳（NPC800和NPC1000），通过循环伏安法和恒流充放电法研究了两种多孔碳的电容性能。结果发现，NPC800表现出了较大的比电容（在1 A g-1的比电容为226.6 F g-1）、很好的倍率性能（电流密度高达10 A g-1时，比电容仍保持在178.0 F g-1）以及循环稳定性（充放电1200个循环内其比电容都保持其初始电容的92%以上）。|
|Other Abstract||Energy crisis is one of the biggest challenges faced by the mankind in twenty-first century. It’s urgent for us to explore the alternative energy for the traditional fossil energy. An effective method to solve this problem is to realize the storage and conversion of the renewable energy sources using the clean energy techniques such as fuel cells. Metal-organic frameworks (MOFs) as a class of crystalline porous materials with high surface area and redox-active sites have been paid much attention in electrocatalytic field. In addition, MOFs can serve as a template/precursor to prepare porous carbons with high surface area, which have potential application prospects in oxygen reduction reaction and supercapacitor. In this thesis, I studied the electrocatalytic property of a highly porous Cu-MOF compound containing nanocages towards oxygen reduction reaction, and employed a novel bipyridine-based MOF to prepare the nitrogen-doped porous carbons, which was further used for oxygen reduction reaction, methanol oxidation reaction and supercapacitor. Details are listed as followed.
A highly porous MOF containing nanocages was synthesized through solvothermal reaction and fully activated by the solvent-exchange method. Cyclic voltammetry was utilized to study the electrochemical activity of the as-prepared and activated MOF samples. Although both the MOF samples showed electrochemical activity of Cu2+/Cu+ redox pairs owing to the existence of Cu2+ active sites, only the activated MOF could catalyze oxygen reduction reaction, and the occurrence potential of oxygen reduction (vs. Ag/AgCl) shifted to the positive near 100 mV in comparison with other MOF catalysts. This was because the dissolved O2 can enter into the nanocage and was electrocatalytically reduced by Cu+ after the activation of MOF, while the occupancy of nanocages by solvent molecules can hinder the diffusion of dissolved O2 into the nanocage of the as-prepared MOF. In order to avoid detachment of the activated MOF from the glassy carbon electrode surface during electrochemical scanning in aqueous solution, reduced graphene oxide was immobilized onto a glassy carbon electrode surface as a binder and electron transfer mediator under MOF active layer.
A novel pyridine-containing MOF ([Zn(bpdc)DMA]·DMF) was first constructed by solvothermal reaction of 2,2'-bipyridine-5,5'-dicarboxylate (bpdc) with zinc nitrate, and then it was converted to the nitrogen-doped porous carbons (NPC800) by direct carbonization at 800 ℃. NPC800 was modified onto the glassy carbon electrode surface to investigate its electrocatalytic property towards oxygen reduction reaction in alkaline solution through cyclic voltammetry and linear sweep voltammetry. The onset potential of NPC800 for oxygen reduction was 0.14 V (vs. SCE), which was similar to commercial Pt/C. Notably, its catalytic current was higher than Pt/C. Pt-catalyst supported on the nitrogen-doped porous carbons (Pt/NPC800) was prepared by means of electrodeposition. Pt/NPC800 showed catalytic role for methanol oxidation reaction, and also had better stability than Pt-catalyst supported on commercial Vulcan XC-72 with the same Pt loading.
Two different nitrogen-doped porous carbons (NPC800 and NPC1000) were prepared through direct carbonization of the above-mentioned pyridine-based MOF by changing the carbonization temperature. Cyclic voltammetry and galvanostatic charge-discharge were employed to investigate their capacitive properties. NPC800 showed higher specific capacitance (226.6 F g-1 at 1 A g-1) than NPC1000, possessed good rate capability (retaining 178.0 F g-1 even at a high current density up to 10 A g-1), and displayed good cycling stability (retaining more than 92% of the initial capacitance after 1200 cycles).|
朱丹丹. 金属有机框架基多孔材料的制备及电化学性能研究[D]. 北京. 中国科学院研究生院,2015.
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