Strategies for stable water splitting via protected photoelectrodes

Abstract

Photoelectrochemical (PEC) solar-fuel conversion is a promising approach to provide clean and storable fuel (e.g., hydrogen and methanol) directly from sunlight, water and CO. However, major challenges still have to be overcome before commercialization can be achieved. One of the largest barriers to overcome is to achieve a stable PEC reaction in either strongly basic or acidic electrolytes without degradation of the semiconductor photoelectrodes. In this work, we discuss fundamental aspects of protection strategies for achieving stable solid/liquid interfaces. We then analyse the charge transfer mechanism through the protection layers for both photoanodes and photocathodes. In addition, we review protection layer approaches and their stabilities for a wide variety of experimental photoelectrodes for water reduction. Finally, we discuss key aspects which should be addressed in continued work on realizing stable and practical PEC solar water splitting systems.

Current perspectives in engineering of viable hybrid photocathodes for solar hydrogen generation

“…To be used, the metal, e.g. Ti, should have lower work function compared with the conduction band edge potential of the light harvester (figure 8) [22,53,85]. For example a thin layer of Ti metal, 5 nm in thickness, successfully protected and activated a p-Si photocathode [53].…”

“…In this article, we review the current trenches being developed in engineering of viable hybrid photocathodes for the hydrogen generation. The current development of photoanodes could be referred to several articles published elsewhere [7,[19][20][21][22][23]. We first describe the principal operation of a hybrid photocathode composed of a light harvester and a H 2 -evolving catalyst.…”

Polymorphism and Structural Distortions of Mixed-Metal Oxide Photocatalysts Constructed with α-U3O8 Types of Layers

“…The illustration in Figure 9 shows a photocatalyst particulate and the four basic steps, where (d) also includes the competing volume and surface recombination processes. An efficient photocatalyst must have band gap energies capable of the absorption of visible light energies and possess energetic band positions suitable for driving water reduction and oxidation reactions (i.e., E g ≥ 1.23 eV) [90]. The valence and conduction band energies of several semiconductors are plotted in Figure 10, and shown relative to the water redox couples for water splitting.…”

“…In addition perovskite-based photocatalysts have been extensively studied and various strategies have been employed for enhancing photocatalytic performance [90,114,115]. The use of mixed-metal compositions is critical to lowering the bandgap sizes of simpler metal oxides into the visible region [116].…”

Fuel Production from Seawater and Fuel Cells Using Seawater

“…[9,10] Water is also needed to produce hydrogen as a clean and sustainable alternative energy source to fossil fuels by water splitting to prevent global warming stemmingf rom large-scale CO 2 emissions from the combustion of fossil fuels. [11][12][13][14][15][16][17][18][19][20] Therefore, water and clean energy are inextricably linked with each other.A bout 97 %o ft he water on our planet is seawater (3.0-5.0 %s alts) with 1.0 %b eing brackish ground water (0.05-3.0 %s alts), indicatingt hat the vast amounts of seawater would provide an early unlimited water supply if saline water could be used directly as ac lean and nearly infinite energy source. Microorganisms living in seawater can also be used in sediment microbial fuel cells to generate electric power from variouss ubstrates (electron sources) containing in seawater,w hich reduce dioxygen to water.…”