David B. Ingram

Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy

Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.

Water Splitting on Composite Plasmonic-Metal/Semiconductor Photoelectrodes: Evidence for Selective Plasmon-Induced Formation of Charge Carriers near the Semiconductor Surface

A critical factor limiting the rates of photocatalytic reactions, including water splitting, on oxide semiconductors is the high rate of charge-carrier recombination. In this contribution, we demonstrate that this issue can be alleviated significantly by combining a semiconductor photocatalyst with tailored plasmonic-metal nanostructures. Plasmonic nanostructures support the formation of resonant surface plasmons in response to a photon flux, localizing electromagnetic energy close to their surfaces. We present evidence that the interaction of localized electric fields with the neighboring semiconductor allows for the selective formation of electron/hole (e(-)/h(+)) pairs in the near-surface region of the semiconductor. The advantage of the formation of e(-)/h(+) pairs near the semiconductor surface is that these charge carriers are readily separated from each other and easily migrate to the surface, where they can perform photocatalytic transformations.

First-Principles Analysis of the Activity of Transition and Noble Metals in the Direct Utilization of Hydrocarbon Fuels at Solid Oxide Fuel Cell Operating Conditions

The direct on-cell use of hydrocarbon fuels in solid oxide fuel cells (SOFCs) involves many thermochemical and electrochemical reactions that occur on anode electrocatalysts, both at and away from the three-phase boundary. We have used first-principles density functional theory calculations and kinetic modeling to investigate relevant reactions associated with the direct utilization of methane on different electrocatalysts at SOFC operating conditions. The investigated reactions are steam and dry reforming of methane, electrochemical oxidation of H 2 and CO, and direct electrochemical oxidation of methane. These studies allowed us to compare the relative activity of different metals and to identify those metals that offer optimal performance. Our analysis shows that under relevant operating conditions, there exists a family of metals (mainly Ni, Co, Rh, Ru, and Ir) that offer maximum activity for all relevant reactions. The findings suggest that a fairly simple anode design including only one material in combination with yttria-stabilized zirconia performing multiple reactions should offer close to optimal performance. While we outline our results for methane in detail, we also comment on the direct utilization of other hydrocarbons.