Protons in Catalytic Architectures: Near (NMR) and Far (Impedance)

Abstract

High performance in the realm of electrochemical energy/catalysis/sensing requires WIRING! —the timely arrival and departure of the electrons, ions, and molecules necessary for reactivity. Architectural design of mesoscale porous nanostructures integrates such multifunctionality to ensure that timely electronic, ionic, and mass transport occurs to electrified reactive interfaces. We probe the nature of proton transport in TiO2 aerogels modified with Au nanoparticles (NPs) as a function of relative humidity using impedance spectroscopy for a long-range assessment and 1H NMR for an environmental assessment of shorter-range proton diffusion and spin–spin relaxation. We synthetically site the Au NPs either between the covalently bonded TiO2 NPs that comprise the oxide aerogel network or by supporting them on the preformed, calcined oxide aerogel; we prepare two Au weight loadings (1 and 4 wt%) using both geometric arrangements of Au∣∣TiO2. A high degree of intimacy between Au nanoparticles and the networked TiO₂ nanoparticles affects the nature of proton transport of the aerogel as a function of equilibration with gas-phase water, decreasing the resistance to proton transport along the oxide network. The presence of even a modest weight loading of Au NPs increases the ionicity of the catalytic platform over that of native, Au-free TiO₂ aerogel.