【作者】 黄裕熙；

【导师】 俞汉青；

【作者基本信息】 中国科学技术大学 ， 应用化学， 2014， 博士

【摘要】 生物电化学系统(BES)和CO2电化学还原反应具有从废弃物中回收、利用和合成有用资源的潜力,属于新型的电化学能源转化过程。如何设计和合成性能优异的催化剂是废弃物电化学转化中的一个共性问题,也是废弃物资源化过程中面临的一个重大挑战。本论文针对上述新型电化学能源转化反应过程中催化剂效率低的问题,以纳米材料设计合成为核心,通过电极材料制备、反应过程解析和实际应用效果评价等手段,研发新型的BES和C02电化学转化纳米催化剂,提高转化效率,为它们的实际应用提供理论指导和技术支持。论文主要研究内容和成果如下：1.以多壁碳纳米管为原材料制备了氧化石墨烯纳米带(GONRs),并通过电泳方法制成GONRs修饰碳纸用作BES阳极材料。电化学实验证实了GONRs能够加速Shewanella oneidensis MR-1表面细胞色素c的电子传递；同时,由于GONRs具备较大的电化学活性面积,电子媒介的电子传递作用也得到了增强。微生物燃料电池(MFC)试验进一步验证了GONRs修饰电极的应用潜力,在GONRs的帮助下,不管是使用纯菌还是混合菌的MFC的功率密度都有了较大提升。这种增强效果得益于GONRs极大的长径比,可以作为纳米线进行电子传递,同时其良好的电化学活性也增强了电子媒介的电子传递能力。2.利用电化学沉积法在碳纸表面沉积修饰了Pd纳米颗粒。电化学测试结果表明,所制备的纳米Pd电极在中性的电解液环境中具有较低的产氢过电位,并且具备良好的稳定性。在微生物电解池(MEC)阴极产氢反应中,纳米Pd电极表现出很好的催化活性,与商品化的铂黑催化剂相比,其单位质量的催化效果是铂黑的50多倍,而负载量则远远低于铂黑,展现了应用于MEC电极材料的良好潜力。3.用柠檬酸钠辅助光化学还原PdCl422-和GO的方法一步制得分散性良好的rGO载Pd纳米颗粒材料。由于未使用表面活性剂,所制得的纳米复合材料可以直接使用而无需额外的表面处理或退火。ORR测试表明用该方法制备得到的rGO-Pd具有卓越的催化活性和稳定性。这种活性的提高是石墨烯和纳米Pd相互作用的结果。这种新型的催化剂具有应用于BES阴极的前景。同时,这种合成方法也提供了一种在温和条件下无需精细调控即可获得具有优异催化性能的rGO载金属纳米颗粒材料的合成新策略。4.合成了Au-Fe3O4纳米颗粒,并通过电化学还原使之还原为Au-Fe哑铃状纳米颗粒。所得到的Au-Fe在电化学C02还原反应过程中表现出产烃的催化活性。产物分析表明其主要催化产物为C2H4、C2H6、C3H6和C3H8,此外还有微量的CH4和HCOOH生成。电化学测试表明,Au和Fe的耦合产生协同效应,使CO在催化剂表面的吸附强度发生改变,从而使CO2被还原为吸附态的CO之后,能够发生进一步质子化作用。基于电化学实验结果,我们推测了CO2在Au-Fe还原为烃类的可能途径。该研究结果表明异质结纳米材料有望成为催化CO2电化学还原产生烃类的一类新型催化剂。更多还原

【Abstract】 Bio-electrochemical systems (BES) and electrochemical CO2reduction reaction are two novel energy conversion processes, which offer the opportunities of resource recycling from wastes. A common challenge in these reactions is to design and synthesize powerful catalysts to enhance catalytic efficiencies. In this dissertation, efforts are focused on the syntheses and applications of novel catalysts for BES and CO2electrochemical reduction. Various characterization techniques, including microscopic, chromatographic and electrochemical approaches, are employed to evaluate the performance of the catalysts. The main contents and achievements are as follows:1. Graphene oxide nanoribbons (GONRs) network was assembled on carbon paper for preparing an anode to serve as efficient electron collector in BESs. It was demonstrated that the GONRs made the EET process of Shewanella oneidensis MR-1more effective. The substantial improvement was attributed to the advantages of the GONRs, which acted as nanowires and had a large electrochemical active surface area. Since GONRs can be readily modified onto electrode substrates through an electrophoretic deposition, the GONRs could be a promising material for constructing highly efficient electrodes for BESs.2. Carbon paper coated with Pd nanoparticles was prepared using electrochemical deposition method and used as the cathodic catalyst in an MEC to facilitate hydrogen production. The electrode coated with Pd nanoparticles showed a lower overpotential than the carbon paper cathode coated with Pt black. The coulombic efficiency, cathodic and hydrogen recoveries of the MEC with the Pd nanoparticles as catalyst were slightly higher than those with a Pt cathode, while the Pd loading was one order of magnitude less than Pt. Thus, the catalytic efficiency normalized by mass of the Pd nanoparticles was about fifty times higher than that of the Pt black catalyst.3. Reduced GO supported Pd nanoparticles were synthesized using one-pot photochemical citrate reduction of PdCl42-and GO. Owing to the surfactant-free synthesis process, the resulting materials did not need further surface washing or annealing. ORR tests revealed that the prepared rGO-Pd nanoparticles had an excellent catalytic activity and stability, showing a great potential in BES applications. Control experiments showed that the nanoparticles should be assembled on the rGO surface properly to achieve the improved electrochemical activity. This synthetic approach is effective to prepare rGO supported Pd nanoparticles under mild conditions without sophisticated reaction control, and may also be readily applied to synthesize other rGO-metal nano-composites like rGO-Pt and rGO-Au.4. The synthesis of Au-Fe dumbbell nanoparticles and application for the electrochemical hydrocarbon production from CO2were explored. Product analysis revealed that C2H4, C2H6, C3H6and C3H8, with trace amount of CH4and HCOOH were produced with the catalysis of Au-Fe dumbbell nanoparticles. Electrochemical analyses demonstrated that the CO adsorption strength was tuned due to this synergetic effect, and resulted in further protonation of the adsorbed CO. On the basis of the experimental results, it was prorposed that such a synergetic effect may lead to stable C1species adsorption and lower the activation barrier for the subsequent C-C bond formation. Our work demonstrates that heterogeneous hybrid NPs can be a new family of catalyst to catalyze CO2to hydrocarbons electrochemically.更多还原