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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.

We outline a systematic approach to develop active catalyst materials for an electrochemical reaction. The strategy allows one to tune binding energies of oxygen reaction intermediates on a catalyst surface by taking advantage of two effects: weakening oxygen binding energies by means of thin-film overlayers, and strengthening oxygen binding energies through nanoscale effects. By engineering a core–shell nanoparticle morphology with the appropriate dimensions, that is, the thickness of the overlayer and the size of the nanoparticle, bonding properties can be modified to improve the catalytic activity of the core–shell system. We demonstrate the application of this strategy for oxygen reduction by identifying Ru@Pt as a candidate material using density functional theory calculations, and then use these calculations to guide the synthesis of active Ru@Pt core–shell catalysts. The Ru@Pt particles, synthesized using a wet chemical method, exhibit ∼2 times higher specific activity (based on electrochemical active surface area) than state-of-the-art Pt/C from TKK.

Irreversible, thermally induced sintering of heterogeneous catalysts is one of the most deleterious causes of activity loss during catalytic reaction and/or regeneration. Silica-coated Pd catalysts (Pd@SiO2) were prepared by a simple one-pot, water-in-oil microemulsion method and investigated as models for a general synthesis to encapsulate active nanoparticle catalysts to provide stability during extended periods of cycling and regeneration under harsh experimental conditions. An idealized stability test would involve both a catalyst whose activity changes significantly as particles sinter and test conditions that could readily induce sintering. Acetylene hydrogenation was chosen as the test reaction because its catalytic and regenerative (oxidative coke removal) cycling induce the destructive sintering conditions desired for such a test. When compared with Pd particles deposited on the outside of an identical silica support (Pd/SiO2 catalyst), the silica-encapsulated catalyst Pd@SiO2 deactivates at a much slower rate and is readily regenerated without sintering over multiple reaction and regeneration cycles. It is also found that silica encapsulation suppresses coking and insitu formation of PdC. TEM, XRD, BET, XPS, and TGA, before and after reaction and regeneration, were used to characterize the encapsulated Pd@SiO2 catalysts and compare them to conventionally supported Pd/SiO2.

Herein, a high surface area electrode (HSE) consisting of indium tin oxide (ITO) as a scaffold and ultrathin Ti-doped hematite (α-Fe2O3) as the absorber material is developed. The HSE exhibits sixfold improvement in photoactivity over an analogous photoelectrode with a flat morphology. Interfacial recombination due to dopant impurities and shunting resulting from a high pinhole density in the hematite layer limit the device performance. These limitations are mitigated by introducing a tin oxide barrier layer, which reduces recombination at the solid–solid interface and mitigates shunting. Employing the HSE with an appropriate barrier layer improves charge separation efficiency and catalytic activity compared to conventional planar devices. This strategy can potentially be extended to other light absorber materials whose performance is affected by charge transport limitations.

Screening of different sources of Pd/C shows reagents of highly variable nanoparticle sizes and oxidation states of the metal. Typically, catalysts with higher surface area are viewed as likely to be the more reactive. In this paper a new form of Pd/C, "UC Pd" is described that is shown to contain larger nanoparticles yet it is the most reactive catalyst of those sold commercially for Sonogashira coupling reactions. UC Pd functions efficiently in the absence of a copper co-catalyst, under very mild and "green" conditions using inexpensive 95% EtOH at 50 degrees C. It is also the only form of Pd/C that can be recycled. In side-by-side reactions with several commercially available forms of Pd/C, none compete successfully with UC Pd under standardized conditions. Physical data obtained from extensive surface analysis using TEM, XRD, XPS, and CO-TPD measurements lead to an explanation behind the unique reactivity of this new recyclable form of Pd/C.

In an attempt to improve photoelectrochemical (PEC) processes that is important in solar-to-chemical energy conversion, various materials have been proposed that have the potential for hydrogen production. For instance, hematite has many advantages for hydrogen production since it is somehow stable, has a relatively narrow bandgap, inexpensive, abundant and environmentally responsible. However, their use in PEC devices have been limited by several factors like poor conductivity and high electron-hole pair recombination rates. Strategies to overcome this limitation have been produced such as designing the hematite structure to permit more efficient transport and collection of photogenerated charge carriers. Others include the addition of surface electrocatalysts on iron oxide photoelectrodes, and doping the iron oxide with heteroatoms. Dopant species have also been introduced in the literature. However, there have been few reports on the synthesis of hematite films by electrodeposition and virtually no reports of electrodeposition of doped hematite. As such, an electrochemical route to prepare thin film photoanodes of nanocrystalline Pt-doped iron oxide has been proposed. It showed improvements in the performance of PEC when compared to pure iron oxide thin films.