Novel Two-Dimensional Materials: From Synthesis to Electrocatalysis and Energy Storage

Advanced energy conversion and storage systems are essential to meet the global energy demand and to replace the fossil fuels. Researchers around the world have devoted a significant amount of effort on developing novel, cost-efficient and environment-friendly energy solutions. However, the progress of this effort has been hindered by many obstacles and one of them is the lack of advanced materials to serve as highly active catalysts in core electrochemical reactions. Here, we report the synthesis, characterization, and evaluation of less studied and rarely studied members of transition metal dichalcogenide (TMDCs) and show their superior performance in core electrochemical reactions towards Li-O2 battery applications. In addition to the interesting electronic properties of TMDCS, their performance was enhanced when paired with a suitable electrolyte combination, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) and dimethyl sulfoxide (DMSO). In particular, the synergy between the ionic liquid (IL) and the TMDC catalyst facilitates the electrochemical performance at the TMDC edge atoms where the IL plays multiple roles to enhance catalytic reaction. We report the synthesis, characterization and electrochemical performance of 24 members of TMDC family for oxygen reduction and evolution reactions in aprotic electrolyte to mimic the operation of Li-air batteries. These studies not only exhibit significant enhancement in electrochemical activity compared to the state-of-the-art electrocatalysts, but also provide a comprehensive library of new materials, method for their synthesis and various in-depth characterization of their compositional and structural features. Chapter 2 and 3 cover the synthesis, characterization and study of less studied and rarely studied TMDCs in oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in aprotic medium with Li salts. In these two chapters, chemical vapor transport (CVT) has been employed to synthesize crystalline bulk of 24 TMDCs. A liquid-phase exfoliation technique was used to synthesize the two-dimensional (2D) structure of these materials and a complete suite of characterization experiments along with density functional theory calculations and molecular dynamics simulations were performed to study the chemical composition, electronic properties and atomic structure of these catalysts. All of these catalysts were tested in ORR and OER with aprotic electrolyte and their outstanding catalytic activity was demonstrated. In chapter 4, a 2D copper (Cu)-based conductive metal organic framework (c-MOF) is studied in CO2RR with low overpotentials using a hybrid electrolyte of choline chloride and potassium hydroxide (KOH). The 2D nano-flakes (NFs) of copper tetrahydroxyquinone (Cu-THQ) with three different reduced particle size are first obtained by liquid-phase exfoliation and their performance was evaluated accompanied by product characterization and in-situ measurements and DFT calculations to get insight on the role of active sites and favorable reaction pathways. Our results reveal a selective conversion of CO2 to CO in low overpotentials, a record catalytic activity and CO formation turnover frequency much higher than the state-of-the-art MOF-based catalysts with CO selectivity and a negligible overpotential for this reaction. In chapter 5, the Cu-THQ catalyst is used in a Li-air battery chemistry with a hybrid electrolyte combination which includes LiNO3 salt and InBr3 redox mediator (RM) in TEGDME solvent. The paired Cu-THQ cathode and electrolyte combination achieve an efficient Li-air battery operation with a significantly reduced charge-discharge potential gap and an extended cycle life under significantly high current rates and increased capacity. Chapter 6 summarizes the findings and results and future objectives.