Design, Synthesis And Application Of Nanocatalysts For Novel Electrochemical Energy Conversion Reactions

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.