Hierarchically structured electrochemical materials
The optimization of materials for photoelectrochemical applications requires the rational balancing of properties on multiple length scales. These properties include light absorption, electron/reactant/product transport, relaxed quality constraints, and efficient use of expensive components. To develop strategies for the simultaneous optimization of these complex systems, we use self-assembled colloidal solids to create precisely-controlled hierarchical structures. These structures can be used to template the chemical synthesis of materials like structured surfaces for catalysis, three dimensional optical and photonic materials, and 'patchy' colloids with asymmetric pairwise interactions.
Advantageously disordered materials
In some cases, precisely-engineered structures are not necessary. Allowing for disorder in materials has obvious advantages in synthesis by permitting the use of low fidelity, but low cost synthetic processes. In optical and photonic materials more interesting phenomena may emerge when the characteristic length scale of disorder approaches the wavelength of light. The apparent path length of light can increase due to increased scattering at interfaces in the material, improving the absorption properties of inexpensive semiconductors for photovoltaics. Light can also be trapped in small volumes by waveguiding, optical cavities, or emergent modes of localization. We use mixed colloidal systems as templates for chemically synthesized disordered materials. Through simulations, optical characterization, and photoelectrochemical experiments we can explore how controlled disorder can be used to improve the performance of these materials for applications that require efficient light utilization.
Methods for real-space characterization of electrochemical processes
Structured electrocatalysts and photoelectrochemical materials offer a number of advantages over planar ones. These include increased surface area and catalyst loading; high densities of favorably reactive crystallite facets, grain boundaries, and defects; the diffusive trapping of intermediates; and strategic separation of light absorbers and electrocatalysts in photoelectrochemical systems. To understand how these structures can be used in advantageous ways, we are interested in developing methods to characterize electrochemical processes like electrodeposition and catalysis using optical and x-ray microscopy techniques.