First-principles investigation of heterogeneous electrocatalysis at the solid-liquid interface



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Carbon-based metal-free electrocatalysts are promising alternatives to precious metals in energy storage and conversion applications providing comparable performance at much lower costs. Conventional studies in to their performance assume that these carbon electrodes are ideal non-polarizable electrodes, following the methodology used to describe metallic electrodes, to simplify the theoretical description of reaction overpotentials. This method has not provided a clear description of the active sites or the principles underlying this activity. This suggests that the conventional approach may not be adequate to distinguish the true catalytic performance of these materials. Graphene-like materials are to possesses a very small quantum, or electrode, capacitance, implying the chemical potential may vary substantially with charge in the system. This can, in turn, influence all the interactions occurring at the electrode/electrolyte interface. By introducing this concept to first-principles methodologies for studying interfacial reactions we can gain valuable insights in to the activity, identifying indicators of performance and design principles to optimize these carbon-based materials for catalysis. In this dissertation, we explore the catalytic performance of carbon-based metalfree electrodes in two parts. In Part I, we evaluate first-principles techniques used to describe the interface between graphene electrodes and aqueous solution, motivated by the inconclusive results of conventional approaches. Analysis demonstrates the influence of electrode capacitance over the predicted overpotentials. Additionally charge transfer is identified as key to the activation and adsorption of oxygen. Being a function of the substrate-intermediate-solvent interactions, we demonstrate that the solvent models must be carefully selected to provide the correct description of the Coulombic interactions. Part II focuses on describing the oxygen reduction performance of different types of activated graphene materials, motivated by the active sites identified in the previous section. The method outlined above is used to demonstrate a reaction mechanism for the oxygen reduction reaction occurring on topological defects. Important details governing the catalyst performance, including the role of pH and the high selectivity for the most efficient pathway, can be explained using this method. The work presented herein provides new insight into the electrochemical activity of graphene-like materials and future directions for catalyst development. We anticipate that the established methodology and analysis can be broadly applicable to other nanostructured materials and reaction chemistries for metal-free heterogeneous catalysis.


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