No abstract

Understanding the reactivity of the cathode surface is of key importance to the development of batteries. Here, density functional theory is applied to investigate the oxidative decomposition of the electrolyte component, ethylene carbonate (EC), on layered Li x MO 2 oxide surfaces. We compare adsorption energy trends of atoms and small molecules, on both surface oxygen and metal sites, as a function of the Li content of the surface. The oxygen sites are identified as the reactive site for the electrolyte oxidation reaction (EOR). We report reaction energies and NEBcalculated kinetic barriers for the initial oxidative decomposition of EC, and correlate both with the reaction energy of hydrogen adsorption on oxygen. The hydrogen adsorption energy scales with the distance between the Fermi level and the O-2p band center. We expect this model of the EOR to be valid for other organic electrolytes and other Li metal oxide surfaces, due to its simplicity, and the model leads to simple design principles for protective coatings.

A major contribution to the energy loss in fuel cells originates from poor kinetics of the oxygen reduction reaction (ORR) at the cathode. The ORR mechanism has been understood in descriptor-based approaches, which reveal an activity volcano with a significant overpotential of at least 0.4 V. This energy loss is directly linked to the scaling relation between the binding energy of the ORR intermediates, OH and the OOH. It has become apparent that new catalyst designs are necessary in order to circumvent this scaling relation. One strategy is to stabilize the OOH intermediate in a dissociated state on two active sites, as an O + OH intermediate. Here we demonstrate the feasibility of this strategy in a systematic study of diporphyrin molecular catalysts. This class of catalysts contains two metal sites, whose catalytic chemistry can be influenced by ligands. Using density functional theory (DFT), we study the ORR activity as a function of intermetallic distance, metals, and ligands. Several diporphyrin catalysts are identified with a theoretical overpotenial of less than 0.3 V. The enhanced catalytic activity is understood as a combination of a geometric effect from the diporphyrin structure and an electronic effect from the choice of metal center and ligand. We propose a strategy to reduce the energy loss and climb the 3D volcano by appropriate design of the geometric and the electronic effects.

By combining idealized experiments with realistic quantum mechanical simulations of an interface, we investigate electroreduction reactions of HF, water and methanesulfonic acid on the single crystal (111) facets of Au, Pt, Ir and Cu in a variety of aprotic electrolytes.