(254f) Using Nanoscale Confinement to Improve Oxygen Electrochemistry

Chemical engineers have long specialized in the inter-conversion of latent energy and chemical bonds.  These skills easily lend themselves to optimizing solar energy storage, which helps facilitate a shift towards sustainable and affordable electricity.

            Water splitting is particularly interesting as an energy storage mechanism because water is earth abundant and because the net reduction potential of oxygen gas is near the optimum energy for solar light conversion.  From an electrochemical standpoint, water splitting can be divided into two half-reactions: hydrogen evolution and oxygen evolution.  Currently the oxygen evolution reaction (OER) is the predominant source of overpotential, as the best catalysts available require applied potentials on the order of 300 mV past equilibrium to run at reasonable current densities.

            In this work we use density functional theory calculations to propose a method to increase OER efficiency by creating precisely defined nanostructures.  Traditionally catalysis is thought of as a necessarily two-dimensional surface interaction.  By expanding our understanding to include three-dimensional confinement effects, we capitalize on the fact that OER intermediates (surface bound O, OH, and OOH) have different sizes and respond differently to an oxygenated bonding environment.

            Our study focuses initially on rutile oxide catalysts (RuO_2­ and IrO₂) due to an intricate understanding of these materials provided by previous reports and the agreement they demonstrate between experimentally measured and DFT-predicted OER overpotentials.  We find that previously potential-limiting scaling between intermediate adsorption energies is broken due to confinement effects and hydrogen bond formation, resulting in a reduction in overpotential.  In principle this scheme is capable of improving the efficiency of any OER catalyst on the “left leg” of the previously determined Sabatier-inspired overpotential volcano relation (where ΔG_OH-ΔG_O<1.6 eV), including more economical nickel and manganese oxides.