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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]

Solar hydrogen production is one of the ultimate technologies needed to realize a carbon-neutral, sustainable society. However, an energy-intensive water oxidation half-reaction together with the poor performance of conventional inorganic photocatalysts have been big hurdles for practical solar hydrogen production. Here we present a photoelectrochemical cell with a record high photocurrent density of 19.8 mA cm−2 for hydrogen production by utilizing a high-performance organic–inorganic halide perovskite as a panchromatic absorber and lignocellulosic biomass as an alternative source of electrons working at lower potentials. In addition, value-added chemicals such as vanillin and acetovanillone are produced via the selective depolymerization of lignin in lignocellulosic biomass while cellulose remains close to intact for further utilization. This study paves the way to improve solar hydrogen productivity and simultaneously realize the effective use of lignocellulosic biomass. While light-driven water splitting offers a means to produce renewable H2 fuel, water oxidation limits performances and yields low-value products. Here, authors demonstrate a photoelectrochemical cell that converts lignocellulosic biomass into valuable products alongside H2. [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]

Solar‐to‐chemical energy conversion, or so‐called artificial photosynthesis, is a promising technology enabling sustainable production and use of various chemical compounds such as H2, CO, CH4, HCOOH, CH3OH, and NH3. For practical applications, it is necessary to improve the interfacial properties of light‐harvesting semiconductors through modification with proper electrocatalysts, by trying to overcome their intrinsic limitations such as rapid recombination, sluggish reaction kinetics, and photocorrosion. Compared to their heterogeneous counterparts, molecular electrocatalysts have a higher catalytic activity and more flexibility in their design/synthesis and integration with semiconducting materials. In this article, we review recent efforts on the tailored assembly of molecular electrocatalysts to address the above issues for artificial photosynthesis, especially those for oxygen evolution reactions on semiconductor photoelectrodes for photoelectrochemical water oxidation. One can expect that the strategies and methods developed for the tailored assembly and integration of molecular electrocatalysts on water oxidation photoanodes can provide insights for the design and fabrication of various forms of photosynthetic devices due to the similarity between their underlying principles. [ABSTRACT FROM AUTHOR]

We report the development of semiconducting melanin‐based organic/inorganic hybrid photoanodes for solar water oxidation. Synthetic melanin thin‐film incorporating polyoxometalate (POM) water oxidation catalysts (WOCs) are readily deposited on the surface of various n‐type inorganic semiconductors (e.g. Fe2O3, BiVO4, and TiO2) by electropolymerization. The deposition of melanin and POM hybrid (MP) thin‐film results in the remarkably improved performance of an underlying semiconductor photoanode for solar water oxidation with a significantly increased photocurrent density and decreased onset potential for water oxidation through the formation of a melanin‐based p–n heterojunction structure. We believe that this study can provide insights into the design and fabrication of various melanin‐based optoelectronic devices by utilizing its unique physicochemical properties. Artificial photosynthesis: Semiconducting synthetic melanin‐based organic/inorganic hybrid photoanodes were fabricated for solar water oxidation. Detailed analysis revealed that electrochemical deposition of melanin on an n‐type inorganic semiconductor leads to the formation of a p–n heterojunction structure and can be utilized for the fabrication of efficient photoanodes for solar water oxidation (see figure). [ABSTRACT FROM AUTHOR]

Charge Separation Efficiency: Modulating Charge Separation Efficiency of Water Oxidation Photoanodes with Polyelectrolyte-Assembled Interfacial Dipole Layers (Adv. Funct. Keywords: charge separation; interfacial dipole; layer-by-layer assembly; photoelectrodes; polyelectrolyte multilayers Charge separation, interfacial dipole, layer-by-layer assembly, photoelectrodes, polyelectrolyte multilayers. [Extracted from the article]

The design and fabrication of solar‐to‐chemical energy conversion devices are enabled through interweaving multiple components with various morphologies and unique functions using a versatile layer‐by‐layer assembly method. Cationic and anionic polyelectrolytes are used as an electrostatic adhesive to assemble the following functional materials: plasmonic Ag nanoparticles for improved light harvesting, upconversion nanoparticles for utilization of near‐infrared light, and polyoxometalate water oxidation catalysts for enhanced catalytic activity. Polyelectrolytes also have an additional function of passivating the surface recombination centers of the underlying photoelectrode. These functional components are precisely assembled on a model photoanode (e.g., Fe2O3 and BiVO4) in a desired order and various combinations without degradation of their intrinsic properties. As a result, the performance of water oxidation photoanodes is synergistically enhanced. This study can enable the design and fabrication of novel solar‐to‐chemical energy conversion devices. [ABSTRACT FROM AUTHOR]