Bubble residence during water splitting reactions at structured semiconductor-electrocatalyst interfaces.

by Coridan, Robert

Integrated semiconductor-electrocatalyst systems are attractive materials for driving water electrolysis to store solar energy in chem. bonds. Structured semiconductor-electrocatalyst interfaces offer many design advantages over continuous thin-film layers of state-of-the-art electrocatalysts, such as increased mass loading of sub-optimal materials, reduced reflection from metals blocking light-absorbing semiconductors, and maintaining high photovoltages at the semiconductor-liq. junction. Contrarily, distributing electrocatalysts on interfaces can also impair the overall energy conversion efficiency of these reactions occurring at these interfaces by introducing mass transport overpotentials to the kinetics of the reaction. For gas-evolving reactions like water splitting, the energy conversion efficiency can be reduced by bubbles blocking electrocatalyst areas or by increasing the reflection of incident light. Here, we explore the dynamics of bubbles evolved at structured semiconductor-electrocatalyst interfaces and their effects on the kinetics of electrolysis. We describe the use of synchrotron-based, high-speed x-ray imaging for in situ studies of gas-evolving hydrogen evolution and water oxidn. reactions under conditions relevant to solar fuels applications. Imaging the dynamics of electrolytic bubble evolution allows us to measure the effects of electrostatic surface interactions, hierarchical organization of catalysts, and the collective behavior of bubbles. We are able to show that rational hierarchical structuring of the electrocatalysts can be used to improve catalytic performance by controlling the evolution of the gas-liq.-solid interface.