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1 Understanding the role and immobilization of molecular catalysts on photoelectrodes is essential to use their full potential for efficient solar fuel generation. Here, a CoII4O4 cubane with proven catalytic performance and an active H2O--Co2(OR)2 --OH2 edge-site moiety is immobilized on BiVO4 photoanodes through a versatile layer-by-layer assembly strategy. This delivers a photocurrent of3.3 mA cm-2 at 1.23 VRHE and prolonged stability. Tuning the thickness of the Co4O4 layer has remarkable effects on photocurrents, dynamic open circuit potentials, and charge carrier behavior. Comprehensive-time and frequency-dependent perturbation techniques are employed to investigate carrier kinetics in transient and pseudo-steady-state operando conditions. It is revealed that the Co4O4 layer can prolong carrier lifetime, unblock kinetic limitations at the interface by suppressing recombination, and enhance charge transfer. Additionally, its flexible roles are identified as passivation/hole trapping/catalytic layer at respective lower/moderate/higher potentials. These competing functions are under dynamic equilibrium, which fundamentally defines the observed photocurrent trends. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) water oxidation is a highly challenging task that acts as a bottleneck for efficient solar hydrogen production. It is because each cycle of water oxidation is composed of four proton‐coupled electron transfer (PCET) processes and conventional photoanodes and cocatalysts have limited roles in enhancing the charge separation and storage rather than in enhancing catalytic activity. In this study, a simple and generally applicable strategy to improve the PEC performance of water oxidation photoanodes through their modification with polyethyleneimine (PEI) hydrogel is reported. The rich amine groups of PEI not only allow the facile and stable modification of photoanodes by crosslinking but also contribute to improving the kinetics of PEC water oxidation by boosting the PCET. Consequently, the PEC performance of various photoanodes, such as BiVO4, Fe2O3, and TiO2, is significantly enhanced in terms of photocurrent densities and onset potentials even in the presence of notable cocatalyst, cobalt phosphate. The present study provides new insights into and strategies for the design of efficient photoelectrodes and PEC devices. [ABSTRACT FROM AUTHOR]

A series of new quaternary group 4 metal palladium sulfides, A2MPd3S6 (A = Rb, M = Hf; A = Cs, M = Zr, Hf) have been prepared from elements with the use of alkali metal halide fluxes and they are structurally characterized by single crystal x‐ray diffraction methods. They are isostructural and the structure of the title compounds consists of anionic ∞2[MPd3S62−] slabs and alkali metal ions. In the slab, the group 4 metals are surrounded by six S atoms in a trigonal prismatic fashion and the Pd atoms are coordinated with four S atoms in square planar fashion. Two hexagons made of six edge‐sharing square planar PdS4 are interconnected by two trigonal prismatic MS6 to form the basic repeating unit, M2Pd12S28. These are linked together to form the infinite two‐dimensional ∞2[MPd3S62−] slabs. These slabs stack on top of each other and they are separated by alkali metal cations. There is no strong SS bonding interaction in this phase and the charge valence of the title compounds could be expressed as [A+]2[M4+][Pd2+]3[S2−]6 (A = Rb, M = Hf; A = Cs, M = Zr, Hf). [ABSTRACT FROM AUTHOR]

The charge separation efficiency of water oxidation photoanodes is modulated by depositing polyelectrolyte multilayers on their surface using layer‐by‐layer (LbL) assembly. The deposition of the polyelectrolyte multilayers of cationic poly(diallyldimethylammonium chloride) and anionic poly(styrene sulfonate) induces the formation of interfacial dipole layers on the surface of Fe2O3 and TiO2 photoanodes. The charge separation efficiency is modulated by tuning their magnitude and direction, which in turn can be achieved by controlling the number of bilayers and type of terminal polyelectrolytes, respectively. Specifically, the multilayers terminated with anionic poly(styrene sulfonate) exhibit a higher charge separation efficiency than those with cationic counterparts. Furthermore, the deposition of water oxidation molecular catalysts on top of interfacial dipole layers enables more efficient photoelectrochemical water oxidation. The approach exploiting the polyelectrolyte multilayers for improving the charge separation efficiency is effective regardless of pH and types of photoelectrodes. Considering the versatility of the LbL assembly, it is anticipated that this study will provide insights for the design and fabrication of efficient photoelectrodes. [ABSTRACT FROM AUTHOR]

We report a fully solution processable bias-free photoelectrochemical (PEC) cell for overall solar water splitting using a Cu2O photocathode and a BiVO4 photoanode. They were modified with catalytic multilayers (CMs) for hydrogen and oxygen evolution reactions (HER and OER), respectively, using simple and versatile layer-by-layer (LBL) assembly. The deposition of the respective CMs composed of cationic polyelectrolyte and anionic molecular polyoxometalate (POM) electrocatalysts resulted in remarkably improved performance in terms of both photocatalytic activity and stability. Detailed PEC analysis revealed that the CMs not only facilitated (1) charge transport to and (2) catalytic charge transfer at the photoelectrode/electrolyte interface, but also suppressed the deactivation of photoelectrodes, especially a labile Cu2O photocathode, by the formation of a protective coating layer. As a result, we could successfully fabricate an efficient and stable PEC cell for unassisted solar water splitting without the use of toxic/hazardous chemicals and energetic processes, which have been inevitably employed. We believe that this study provides a simple and versatile platform for the design and fabrication of various forms of electrochemical PEC devices in an environmentally friendly manner. [ABSTRACT FROM AUTHOR]