Designing carbon materials for the electrochemical synthesis of hydrogen peroxide and other advanced applications
Keywords: Chemical Engineering.

It is important to discover inexpensive and high performance materials for energy conversion processes and devices, and environmental protection. Carbon-based materials are of significant interest for this purpose due to their low-cost, earth abundance and versatile multi-functional properties. It is of great importance to design some facile and efficient methods to synthesize new carbon materials for targeted applications. First part of this thesis has focused on design model carbon catalysts for a specific application: electrochemical synthesis of hydrogen peroxide (H2O2) via oxygen reduction reaction. H2O2 is a very versatile and multifunctional chemical that moves an industry of almost 4 billion dollars. However, its industrial synthesis involves a very energy-intensive anthraquinone process. For this reason, electrochemical reduction of O2 provides a simpler and more sustainable method to boost H2O2 applicability. One of the key challenges for this reaction is discovering active, selective and cost-effective electrocatalysts, Few carbon materials have been used for H2O2 production, due to the limited understanding of fundamental mechanisms underlying H2O2-related catalytic reactions, and the lack of the ability to design carbon materials with desired morphology and composition. In this regard, defective carbons with different pore structures were first developed. Then we further prepared a unique type of carbon material containing h-BN domains within the carbon lattice. Both carbon catalysts show high activity and selectivity (> 80%) for O2 reduction to H2O2. Combined with theoretical calculations and advanced characterization techniques, we are able to achieve fundamental insights into the factors underlying the activity enhancements of these materials. It is also found pore structures play a key role in governing the accessibility and stability of catalysts. Both creating a high concentration of active site and providing efficient access to them are important to design high-performance catalysts. Given the importance of advanced structures, the second part of this thesis develops a novel polymer system that can be tailored to produce carbon materials for different energy and environment applications. We have discovered a tunable and simple method for one-pot synthesis of polyacrylonitrile and its copolymer nanostructured particles with various superstructures (flower, pompom, hairy leave, and petal shapes) controlled by employing various solvents or by the incorporation of different co-monomers. The obtained carbon flower particles from this polymer system have demonstrated advantageous properties for potential applications in electrocatalysts, pressure sensors, thermo-switchable safe batteries, and etc. The activated carbon flower is able to produce H2O2 at a record-setting rate of 816 mmmolg-1cath-1 under an electrolyzer set-up at an applied potential of 1.6 V. In addition, these carbon flower particles have also shown promising performance for on-board methane storage. By controlling the synthetic process, the monodisperse carbon flower particles can self-assemble into orderly-packed pellets. They have exhibited a record-setting bulk density of 1.24 g/cm3, and exceptional methane storage capacity of 202 and 227 cm3 (STP) cm-3 at 35 and 65 bar respectively, the highest among all the reported carbon-based materials. This thesis not only develops new synthetic methods to prepare high-performance carbon materials with controlled compositions and structures, but also provides clear understanding and insights to direct the development of future carbon electrocatalysts.