A miniature solar device for overall water splitting consisting of series-connected spherical silicon solar cells

A Chloroplast-Localised Fluorescent Protein Enhances the Photosynthetic Action Spectrum in Green Algae

Green microalgae are important sources of natural products and are attractive cell factories for manufacturing high-value products such as recombinant proteins. Increasing scales of production must address the bottleneck of providing sufficient light energy for photosynthesis. Enhancing the photosynthetic action spectrum of green algae to improve the utilisation of yellow light would provide additional light energy for photosynthesis. Here, we evaluated the Katushka fluorescent protein, which converts yellow photons to red photons, to drive photosynthesis and growth when expressed in Chlamydomonas reinhardtii chloroplasts. Transplastomic algae expressing a codon-optimised Katushka gene accumulated the active Katushka protein, which was detected by excitation with yellow light. Removal of chlorophyll from cells, which captures red photons, led to increased Katushka fluorescence. In yellow light, emission of red photons by fluorescent Katushka increased oxygen evolution and photosynthetic growth. Utilisation of yellow photons increased photosynthetic growth of transplastomic cells expressing Katushka in light deficient in red photons. These results showed that Katushka was a simple and effective yellow light-capturing device that enhanced the photosynthetic action spectrum of C. reinhardtii.

Water Electrolysis in Saturated Phosphate Buffer at Neutral pH

Hydrogen production from renewable energy and ubiquitous water has a potential to achieve sustainability, although current water electrolyzers cannot compete economically with the fossil fuel-based technology. Here, we evaluate water electrolysis at pH 7 that is milder than acidic and alkaline pH counterparts and may overcome this issue. The physicochemical properties of concentrated buffer electrolytes were assessed at various temperatures and molalities for quantitative determination of losses associated with mass-transport during the water electrolysis. Subsequently, in saturated K-phosphate solutions at 80 °C and 100 °C that were found to be optimal to minimize the losses originating from mass-transport at the neutral pH, the water electrolysis performance over model electrodes of IrOx and Pt as an anode and a cathode, respectively, was reasonably comparable with those of the extreme pH. Remarkably, this concentrated buffer solution also achieved enhanced stability, adding another merit of this electrolyte for water electrolysis.

A Cocrystal Precursor Strategy for Carbon-Rich Graphitic Carbon Nitride toward High-Efficiency Photocatalytic Overall Water Splitting

Direct and efficient photocatalytic overall water splitting is crucial for the sustainable conversion and storage of renewable solar energy. Herein, we present the design of a carbon-rich graphitic carbon nitride (C_co-C₃N₄), prepared from a layered molecular cocrystal precursor. The cocrystal microsheets were synthesized using a facile hydrothermal process. Following two-step thermal treatment and liquid exfoliation, the product maintains the 2D morphology owing to the toptactic transformation process. The C_co-C₃N₄ exhibits an enhanced photogenerated electron-hole separation, high charge transport capacity, and prolonged lifetime of the carriers, relative to the g-C₃N₄ system. In the absence of any sacrificial reagent or co-catalyst, the C_co-C₃N₄ microsheets exhibit a high photocatalytic activity. The work presented in this report supplies a cocrystal route for the orderly molecular self-assembly of precursor materials to tailor the chemical compositions and electronic structures. Moreover, the generation of a highly efficient water-splitting photocatalyst has larger implications for sustainable energy applications.

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Cocrystal precursor results in high dispersion of active sites at molecular level

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Carbon units drive the separation and transmission of photogenerated electrons

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C_co-C₃N₄ exhibits high catalytic activity without sacrificial reagent or co-catalyst

Toward practical solar hydrogen production - an artificial photosynthetic leaf-to-farm challenge

Solar water splitting is a promising approach to transform sunlight into renewable, sustainable and green hydrogen energy. There are three representative ways of transforming solar radiation into molecular hydrogen, which are the photocatalytic (PC), photoelectrochemical (PEC), and photovoltaic-electrolysis (PV-EC) routes. Having the future perspective of green hydrogen economy in mind, this review article discusses devices and systems for solar-to-hydrogen production including comparison of the above solar water splitting systems. The focus is placed on a critical assessment of the key components needed to scale up PEC water splitting systems such as materials efficiency, cost, elemental abundancy, stability, fuel separation, device operability, cell architecture, and techno-economic aspects of the systems. The review follows a stepwise approach and provides (i) a summary of the basic principles and photocatalytic materials employed for PEC water splitting, (ii) an extensive discussion of technologies, procedures, and system designs, and (iii) an introduction to international demonstration projects, and the development of benchmarked devices and large-scale prototype systems. The task of scaling up of laboratory overall water splitting devices to practical systems may be called "an artificial photosynthetic leaf-to-farm challenge".

Electrolyte Engineering towards Efficient Water Splitting at Mild pH

The development of processes for the conversion of H₂ O and CO₂ driven by electricity generated by renewable means is essential to achieving sustainable energy and chemical cycles, in which the electrocatalytic oxygen evolution reaction (OER) is one of the bottlenecks. In this study, the influences of the electrolyte molarity and identity on the OER at alkaline to neutral pH were investigated at an appreciable current density of around 10 mA cm^-2 , revealing both the clear boundary of reactant switching between H₂ O/OH^- , owing to the diffusion limitation of OH^- , and the substantial contribution of the mass transport of the buffered species in buffered mild-pH conditions. These findings suggest a strategy of electrolyte engineering: tuning the electrolyte properties to maximize the mass-transport flux. The concept is successfully demonstrated for the OER, as well as overall water electrolysis in buffered mild-pH conditions, shedding light on the development of practical solar fuel production systems.

Towards Versatile and Sustainable Hydrogen Production through Electrocatalytic Water Splitting: Electrolyte Engineering

Recent advances in power generation from renewable resources necessitate conversion of electricity to chemicals and fuels in an efficient manner. Electrocatalytic water splitting is one of the most powerful and widespread technologies. The development of highly efficient, inexpensive, flexible, and versatile water electrolysis devices is desired. This review discusses the significance and impact of the electrolyte on electrocatalytic performance. Depending on the circumstances under which the water splitting reaction is conducted, the required solution conditions, such as the identity and molarity of ions, may significantly differ. Quantitative understanding of such electrolyte properties on electrolysis performance is effective to facilitate the development of efficient electrocatalytic systems. The electrolyte can directly participate in reaction schemes (kinetics), affect electrode stability, and/or indirectly impact the performance by influencing the concentration overpotential (mass transport). This review aims to guide fine-tuning of the electrolyte properties, or electrolyte engineering, for (photo)electrochemical water splitting reactions.

Boosting the Performance of the Nickel Anode in the Oxygen Evolution Reaction by Simple Electrochemical Activation

The development of cost-effective and active water-splitting electrocatalysts that work at mild pH is an essential step towards the realization of sustainable energy and material circulation in our society. Its success requires a drastic improvement in the kinetics of the anodic half-reaction of the oxygen evolution reaction (OER), which determines the overall system efficiency to a large extent. A simple electrochemical protocol has been developed to activate Ni electrodes, by which a stable NiOOH phase was formed, which could weakly bind to alkali-metal cations. The electrochemically activated (ECA) Ni electrode reached a current of 10 mA at <1.40 V vs. the reversible hydrogen electrode (RHE) at practical operation temperatures (>75 °C) and a mild pH of ca. 10 with excellent stability (>24 h), greatly surpassing that of the state-of-the-art NiFeO_x electrodes under analogous conditions. Water electrolysis was demonstrated with ECA-Ni and NiMo, which required an iR-free overall voltage of only 1.44 V to reach 10 mA cm_geo^-2 .