Blaise A. Pinaud

Plasmon Enhanced Solar-to-Fuel Energy Conversion

Future generations of photoelectrodes for solar fuel generation must employ inexpensive, earth-abundant absorber materials in order to provide a large-scale source of clean energy. These materials tend to have poor electrical transport properties and exhibit carrier diffusion lengths which are significantly shorter than the absorption depth of light. As a result, many photoexcited carriers are generated too far from a reactive surface and recombine instead of participating in solar-to-fuel conversion. We demonstrate that plasmonic resonances in metallic nanostructures and multilayer interference effects can be engineered to strongly concentrate sunlight close to the electrode/liquid interface, precisely where the relevant reactions take place. On comparison of spectral features in the enhanced photocurrent spectra to full-field electromagnetic simulations, the contribution of surface plasmon excitations is verified. These results open the door to the optimization of a wide variety of photochemical processes by leveraging the rapid advances in the field of plasmonics.

Technical and economic feasibility of centralized facilities for solar hydrogen production via photocatalysis and photoelectrochemistry

Photoelectrochemical water splitting is a promising route for the renewable production of hydrogen fuel. This work presents the results of a technical and economic feasibility analysis conducted for four hypothetical, centralized, large-scale hydrogen production plants based on this technology. The four reactor types considered were a single bed particle suspension system, a dual bed particle suspension system, a fixed panel array, and a tracking concentrator array. The current performance of semiconductor absorbers and electrocatalysts were considered to compute reasonable solar-to-hydrogen conversion efficiencies for each of the four systems. The U.S. Department of Energy H2A model was employed to calculate the levelized cost of hydrogen output at the plant gate at 300 psi for a 10 tonne per day production scale. All capital expenditures and operating costs for the reactors and auxiliaries (compressors, control systems, etc.) were considered. The final cost varied from

Modeling Practical Performance Limits of Photoelectrochemical Water Splitting Based on the Current State of Materials Research

1.60–

Substrate Selection for Fundamental Studies of Electrocatalysts and Photoelectrodes: Inert Potential Windows in Acidic, Neutral, and Basic Electrolyte

10.40 per kg H2 with the particle bed systems having lower costs than the panel-based systems. However, safety concerns due to the cogeneration of O2 and H2 in a single bed system and long molecular transport lengths in the dual bed system lead to greater uncertainty in their operation. A sensitivity analysis revealed that improvement in the solar-to-hydrogen efficiency of the panel-based systems could substantially drive down their costs. A key finding is that the production costs are consistent with the Department of Energys targeted threshold cost of

Monolithic III–V nanowire PV for photoelectrochemical hydrogen generation

2.00–

Plasmons and rust for solar energy conversion

4.00 per kg H2 for dispensed hydrogen, demonstrating that photoelectrochemical water splitting could be a viable route for hydrogen production in the future if material performance targets can be met.

Thin Films of Sodium Birnessite-Type MnO2: Optical Properties, Electronic Band Structure, and Solar Photoelectrochemistry

Photoelectrochemical (PEC) water splitting is a means to store solar energy in the form of hydrogen. Knowledge of practical limits for this process can help researchers assess their technology and guide future directions. We develop a model to quantify loss mechanisms in PEC water splitting based on the current state of materials research and calculate maximum solar-to-hydrogen (STH) conversion efficiencies along with associated optimal absorber band gaps. Various absorber configurations are modeled considering the major loss mechanisms in PEC devices. Quantitative sensitivity analyses for each loss mechanism and each absorber configuration show a profound impact of both on the resulting STH efficiencies, which can reach upwards of 25 % for the highest performance materials in a dual stacked configuration. Higher efficiencies could be reached as improved materials are developed. The results of the modeling also identify and quantify approaches that can improve system performance when working with imperfect materials.

Effect of Film Morphology and Thickness on Charge Transport in Ta3N5/Ta Photoanodes for Solar Water Splitting

The selection of an appropriate substrate is an important initial step for many studies of electrochemically active materials. In order to help researchers with the substrate selection process, we employ a consistent experimental methodology to evaluate the electrochemical reactivity and stability of seven potential substrate materials for electrocatalyst and photoelectrode evaluation. Using cyclic voltammetry with a progressively increased scan range, we characterize three transparent conducting oxides (indium tin oxide, fluorine-doped tin oxide, and aluminum-doped zinc oxide) and four opaque conductors (gold, stainless steel 304, glassy carbon, and highly oriented pyrolytic graphite) in three different electrolytes (sulfuric acid, sodium acetate, and sodium hydroxide). We determine the inert potential window for each substrate/electrolyte combination and make recommendations about which materials may be most suitable for application under different experimental conditions. Furthermore, the testing methodology provides a framework for other researchers to evaluate and report the baseline activity of other substrates of interest to the broader community.

Tandem Core–Shell Si–Ta3N5 Photoanodes for Photoelectrochemical Water Splitting

Nanowires have attracted a lot of interest for PV applications benefiting from their high aspect ratio geometry. Core-shell structure is ideal for nanowires PVs where the light absorption direction and minority carrier transport direction are decoupled, but the high quality core-shell p-n junction is hard to grow due to the high surface defect density. In this paper, we studied III–V nanowires for photoelectrochemical hydrogen generation where p-n core-shell structure growth is not necessary. A junction is naturally formed between the semiconductor nanowire and liquid electrolyte to extract the photogenerated carriers in nanowires. The wide tunable bandgap of III–V materials are promising for photoelectrochemical hydrogen generation application that requires an energy between 1.7–2.2 eV for reasonable efficiency. GaP nanowires were grown on Si substrates by MOCVD using gold nanoparticles as catalyst. The cathodic and anodic photocurrents were both observed for the GaP nanowires in acidic solution. The stable cathodic photocurrent was believed to be caused by hydrogen evolution while the unstable anodic photocurrent was caused by nanowire degradation.

Controlling the Structural and Optical Properties of Ta3N5 Films through Nitridation Temperature and the Nature of the Ta Metal

We will present progress towards the use of plasmonic metal nanostructures to enhance the efficiency of solar fuel generation [1]. In the past, solar-to-fuel-efficiencies have been limited because of a large mismatch in the length scales for optical absorption and carrier extraction. Future generations of photoelectrodes must employ cheap, earth-abundant absorber materials in order to provide a large-scale source of clean energy. These materials will likely have relatively poor electrical properties, so progress must be made in optimizing their absorption properties [2, 3]. We chose iron oxide (β-Fe2O3; hematite) [4] as a prototype system that shares many features with other candidate materials for future large-scale solar fuel production, and therefore anticipate that the results obtained in this study will be applicable to other materials systems as well. Hematite has relatively weak absorption in the 500–600 nm range (0.1 – 1 µm absorption length), very long compared to its minority carrier diffusion length on the order of 2–4 nm [5] or 20 nm [6].