Bismuth-Tin Core-Shell Particles From Liquid Metals: A Novel, Highly Efficient Photothermal Material that Combines Broadband Light Absorption with Effective Light-to-Heat Conversion.

This study presents a pioneering investigation of hybrid bismuth-tin (BiSn) liquid metal particles for photothermal applications. It is shown that the intrinsic core-shell structure of liquid metal particles can be instrumentalized to combine the broadband absorption characteristics of defect-rich nano-oxides and the high light-to-heat conversion efficiency of metallic particles. Even though bismuth or tin does not show any photothermal characteristics alone, optimization of the core-shell structure of BiSn particles leads to the discovery of novel, highly efficient photothermal materials. Particles with optimized structures can absorb 85% of broadband light and achieve over 90% photothermal conversion efficiency. It is demonstrated that these particles can be used as a solar absorber for solar water evaporation systems owing to their broadband absorption capability and become a non-carbon alternative enabling scalable applications. We also showcased their use in polymer actuators in which a near-infrared (NIR) response stems from their oxide shell, and fast heating/cooling rates achieved by the metal core enable rapid response and local movement. These findings underscore the potential of BiSn liquid metal-derived core-shell particles for diverse applications, capitalizing on their outstanding photothermal properties as well as their facile and scalable synthesis conditions.

Solar energy powered electrochemical reduction of CO2 on In2O3 nanosheets with high energy conversion efficiency at a large current density.

Electrochemical CO2 reduction (ECO2R) to value-added chemicals offers a promising approach to both mitigate CO2 emission and facilitate renewable energy conversion. We demonstrate a solar energy powered ECO2R system operating at a relatively large current density (57 mA cm-2) using In2O3 nanosheets (NSs) as the cathode and a commercial perovskite solar cell as the electricity generator, which achieves the high solar to formate energy conversion efficiency of 6.6 %. The significantly enhanced operative current density with a fair solar energy conversion efficiency on In2O3 NSs can be ascribed to their high activity and selectivity for formate production, as well as the fast kinetics for ECO2R. The Faradic efficiencies (FEs) of formate In2O3 NSs are all above 93 %, with the partial current density of formate ranging from 2.3 to 342 mA cm-2 in a gas diffusion flow cell, which is among the widest for formate production on In-based catalysts. In-situ Raman spectroscopy and density functional theory simulations reveal that the exceptional performances of formate production on In2O3 NSs originates from the presence of abundant low coordinated edge sites, which effectively promote the selective adsorption of *OCHO while inhibiting *H adsorption.

Triplet-Sensitized Switching of High-Energy-Density Norbornadienes for Molecular Solar Thermal Energy Storage with Visible Light.

Norbornadiene-based photoswitches have emerged as promising candidates for harnessing and storing solar energy, holding great promise as a viable solution to meet the growing energy demands. Despite their potential, the effectiveness of their direct photochemical conversion into the resulting quadricyclanes has room for improvement owing to (i) moderate quantum yields, (ii) poor overlap with the solar spectrum and (iii) photochemical back reactions. Herein, we present an approach to enhance the performance of such molecular solar thermal energy storage (MOST) systems through the triplet-sensitized conversion of aryl-substituted norbornadienes. Our study combines deep spectroscopic analyses, irradiation experiments, and quantum mechanical calculations to elucidate the energy transfer mechanism and inherent advantages of the resulting MOST systems. We demonstrate remarkable quantum yields using readily available sensitizers under both LED and solar light irradiation, significantly surpassing those achieved through direct excitation with photons of higher energy. In contrast to the conventional approach, light-induced back reactions of the high-energy products do not play any role, allowing quantitative switching within minutes. These results not only underscore the potential of triplet-sensitized MOST systems to leverage the high energy storage capabilities of multistate photoswitches but they might also stimulate the broader usage of sensitization strategies in photochemical energy conversion.

CO2-to-CO conversion with over 10% efficiency using earth abundant system in a single-compartment reactor with oxygen tolerant Mn complex catalyst.

The direct conversion of CO2 in flue gas to value-added chemicals is a potentially important cost-effective solar-driven CO2 reduction technology. The present work demonstrates the solar-powered conversion of CO2 to CO with greater than 10% efficiency using a Mn complex cathode and an Fe-Ni anode in a single-compartment reactor without an ion exchange membrane in conjunction with a Si solar cell. Reactors separated by ion exchange membranes are typically used to prevent any effects of oxygen generated by the counter electrode. However, the present Mn complex catalyst maintained its activity even in the presence of 15% O2. Operando surface-enhanced Raman spectroscopy established that the present Mn catalyst preferentially reacted with CO2 without adsorbing O2. This unique characteristic enabled solar-driven CO2 reduction using a single-compartment reactor. In contrast, catalytic metals such as Ag tend to lose activity in such systems as a consequence of reaction with oxygen produced at the anode.

Continuous Solar Energy Conversion Windows Integrating Zinc Anode-Based Electrochromic Device and IoT System.

Integration of solar cells and electrochromic windows offers crucial contributions to green buildings. Solar-charging zinc anode-based electrochromic devices (ZECDs) present opportunities for addressing the solar intermittency issue. However, the limited energy storage capacity of ZECDs results in wasted harnessing of solar energy as well as overcharging. Herein, spectral-selective dual-band ZECDs that continuously transport solar energy to indoor appliances by remotely controlling the repeated bleached-tinted cycles during the daytime, are reported. Hexagonal phase cesium-doped tungsten bronze (h-Cs0.32WO3, CWO) nanocrystals are adopted for dual-band ZECDs due to their independent control ability of near-infrared (NIR) and visible (VIS) light transmittance (∆T = 73.0%, 700 nm; ∆T = 83.7%, 1200 nm) and excellent cycling stability (0.8% optical contrast decay at 1200 nm after 10 000 cycles). The prototype device (i.e., CWO//Zn//CWO) delivers extraordinary thermal insulation capability, displaying a 10 °C difference between "bright" and "dark" modes. Furthermore, an Internet of Things (IoT) controller to control the NIR and VIS lights of the CWO//Zn//CWO window wirelessly with a smartphone, empowering the continuous discharging of the solar-charged window during the daytime remotely, is developed. Such windows represent an intriguing potential technology whose future impact on green buildings may be substantial.

A Comprehensive Review of Solar Photocatalysis & Photothermal Catalysis for Hydrogen Production from Biomass: from Material Characteristics to Engineering Application.

Biomass photoreforming is a promising way of producing sustainable hydrogen thanks to the abundant sources of biomass feedstocks. Solar energy provides the heat and driven force to initial biomass oxidation coupled with H2 evolution. Currently, biomass photoreforming is still far from plant-scale applications due to the lower solar energy utilization efficiencies, the low H2 yield, and the lack of appropriate photoreactors. The production of H2 from photoreforming of native biomass and platform molecules was summarized and discussed with particular attention to the prospects of scaling up the catalysis technology for mass hydrogen production. The types of photoreforming, including photocatalysis and photothermal catalysis, were discussed, consequently considering the different requirements for photoreactors. We also reviewed the photoreactors that support biomass photoreforming. Numerical simulation methods were implemented for the solid-liquid two-phase flow and inter-particle radiative transfer involved in the reaction process. Developing concentrated photothermal catalytic flowed reactors is beneficial to scale-up catalytic hydrogen production from biomass.

Perfluorinated Zinc Porphyrin Sensitized Photoelectrosynthetic Cells for Enhanced TEMPO-Mediated Benzyl Alcohol Oxidation.

This research introduces a novel series of perfluorinated Zn(II) porphyrins with positive oxidation potentials designed as sensitizers for photoelectrosynthetic cells, with a focus on promoting the oxidation of benzyl alcohol (BzOH) mediated by the 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) organocatalyst. Three dyes, CLICK-3, CLICK-4, and BETA-4, are meticulously designed to explore the impact of substituents and their positions on the perfluorinated porphyrin ring in terms of redox potentials and energy level alignment when coupled with SnO2/TiO2-based photoanodes and TEMPO mediator. A comprehensive analysis utilizing spectroscopy, electrochemistry, photophysics, and computational techniques of the dyes in solution and sensitized thin films unveils an enhanced charge-separation character in the 4D-π-1A type BETA-4. Incorporating four dimethylamino donor groups at the periphery of the porphyrin ring and a BTD-accepting linker at the ß-pyrrolic position equips the structure with a more efficient donor-acceptor system. This enhancement ensures improved light-harvesting capacity, resulting in a doubled incident photon-to-current conversion efficiency (IPCE% ≃30%) in the presence of LiI compared to meso-substituted dyes CLICK-3 and CLICK-4. Sensitizing SnO2/TiO2 thin films with BETA-4 successfully promotes the photooxidation of benzyl alcohol (BzOH) in the presence of the rapid TEMPO radical catalyst, yielding photocurrents of approximately 125 µA/cm2 in an optimized TBPy/LiClO4/ACN electrolyte. Notably, when lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) replaces TBPy as the base for TEMPO-catalyzed BzOH oxidation, a remarkable photocurrent of around 800 µA/cm2 is achieved, marking one of the highest values reported for this photoelectrochemical reaction to date. This study underscores that the proper functionalization of perfluorinated zinc porphyrins positions these dyes as ideal candidates for sensitizing SnO2/TiO2 in the photodriven oxidation of BzOH. It also highlights the crucial role of carefully tuning electrolyte composition based on the electronic properties of molecular sensitizers.

Direct solar energy conversion on zinc-air battery.

A concept of solar energy convertible zinc-air battery (SZAB) is demonstrated through rational design of an electrode coupled with multifunction. The multifunctional electrode is fabricated using nitrogen-substituted graphdiyne (N-GDY) with large π-conjugated carbonous network, which can work as photoresponsive bifunctional electrocatalyst, enabling a sunlight-promoted process through efficient injection of photoelectrons into the conduction band of N-GDY. SZAB enables direct conversion and storage of solar energy during the charging process. Such a battery exhibits a lowered charge voltage under illumination, corresponding to a high energy efficiency of 90.4% and electric energy saving of 30.3%. The battery can display a power conversion efficiency as high as 1.02%. Density functional theory calculations reveal that the photopromoted oxygen evolution reaction kinetics originates from the transition from the alkyne bonds to double bonds caused by the transfer of excited electrons, which changes the position of highest occupied molecular orbital and lowest unoccupied molecular orbital, thus greatly promoting the formation of intermediates to the conversion process. Our findings provide conceptual and experimental confirmation that batteries are charged directly from solar energy without the external solar cells, providing a way to manufacture future energy devices.

Transient-State Self-Bipolarized Organic Frameworks of Single Aromatic Units for Natural Sunlight-Driven Photosynthesis of H2O2.

Constructing π-conjugated polymer structures through covalent bonds dominates the design of organic framework photocatalysts, which significantly depends on the selection of multiple donor-acceptor building blocks to narrow the optical gap and increase the lifetimes of charge carriers. In this work, self-bipolarized organic frameworks of single aromatic units are demonstrated as novel broad-spectrum-responsive photocatalysts for H2O2 production. The preparation of such photocatalysts is only to fix the aromatic units (such as 1,3,5-triphenylbenzene) with alkane linkers in 3D space. Self-bipolarized aromatic units can drive the H2O2 production from H2O and O2 under natural sunlight, wide pH ranges (3.0-10.0) and natural water sources. Moreover, it can be extended to catalyze the oxidative coupling of amines. Experimental and theoretical investigation demonstrate that such a strategy obeys the mechanism of through-space π-conjugation, where the closely face-to-face overlapped aromatic rings permit the electron and energy transfer through the large-area delocalization of the electron cloud under visible light irradiation. This work introduces a novel design concept for the development of organic photocatalysts, which will break the restriction of conventional through-band π-conjugation structure and will open a new way in the synthesis of organic photocatalysts.

Enhanced Power Generation Using a Dual-Surface-Modified Hematite Photoanode in a Direct Glyphosate Photo Fuel Cell.

Given the current and escalating global energy and environmental concerns, this work explores an innovative approach to mitigate a widely employed commercial herbicide using a direct glyphosate (Gly) photocatalytic fuel cell (PFC). The device generates power continuously by converting solar radiation, degrading and mineralizing commercial glyphosate-based fuel, and reducing sodium persulfate at the cathode. Pristine and modified hematite photoanodes were coupled to Pt/C nanoparticles dispersed in a carbon paper (CP) support (Pt/C/CP) dark cathode by using an H-type cell. The Gly/persulfate PFC shows a remarkable current and power generation enhancement after dual-surface modification of pristine hematite with segregated Hf and FeNiOx cocatalysts. The optimized photoanode elevates maximum current density (Jmax) from 0.35 to 0.71 mA cm-2 and maximum power generation (Pmax) from 0.04 to 0.065 mW cm-2, representing 102.85 and 62.50% increase in Jmax and Pmax, respectively, as compared to pristine hematite. The system demonstrated stability over a studied period of 4 h; remarkably, the photodegradation of Gly proved substantial, achieving ∼98% degradation and ∼6% mineralization. Our findings may significantly contribute to reducing Gly's environmental impact in agribusiness since it may convert the pollutant into energy at zero bias. The proposed device offers a sustainable solution to counteract Gly pollution while concurrently harnessing solar energy for power generation.

Surface Reconstruction on Metal Nitride during Photo-oxidation.

The efficient conversion and storage of solar energy for chemical fuel production presents a challenge in sustainable energy technologies. Metal nitrides (MNs) possess unique structures that make them multi-functional catalysts for water splitting. However, the thermodynamic instability of MNs often results in the formation of surface oxide layers and ambiguous reaction mechanisms. Herein, we present on the photo-induced reconstruction of a Mo-rich@Co-rich bi-layer on ternary cobalt-molybdenum nitride (Co3 Mo3 N) surfaces, resulting in improved effectiveness for solar water splitting. During a photo-oxidation process, the uniform initial surface oxide layer is reconstructed into an amorphous Co-rich oxide surface layer and a subsurface Mo-N layer. The Co-rich outer layer provides active sites for photocatalytic oxygen evolution reaction (POER), while the Mo-rich sublayer promotes charge transfer and enhances the oxidation resistance of Co3 Mo3 N. Additionally, the surface reconstruction yields a shortened Co-Mo bond length, weakening the adsorption of hydrogen and resulting in improved performance for both photocatalytic hydrogen evolution reaction (PHER) and POER. This work provides insight into the surface structure-to-activity relationships of MNs in solar energy conversion, and is expected to have significant implications for the design of metal nitride-based catalysts in sustainable energy technologies.

Stable Photoelectrochemical Reactions at Solid/Solid Interfaces toward Solar Energy Conversion and Storage.

Electrochemistry has extended from reactions at solid/liquid interfaces to those at solid/solid interfaces. However, photoelectrochemistry at solid/solid interfaces has been hardly reported. In this study, we achieve a stable photoelectrochemical reaction at the semiconductor-electrode/solid-electrolyte interface in a Nb-doped anatase-TiO2 (a-TiO2:Nb)/Li3PO4 (LPO)/Li all-solid-state cell. The oxidative currents of a-TiO2:Nb/LPO/Li increase upon light irradiation when a-TiO2:Nb is located at a potential that is more positive than its flat-band potential. This is because the photoexcited electrons migrate to the current collector due to the bending of the conduction band minimum toward the negative potential. The photoelectrochemical reaction at the semiconductor/solid-electrolyte interface is driven by the same principle as those at semiconductor/liquid-electrolyte interfaces. Moreover, oxidation under light irradiation exhibits reversibility with reduction in the dark. Thus, we extend photoelectrochemistry to all-solid-state systems composed of solid/solid interfaces. This extension would enable us to investigate photoelectrochemical phenomena uncleared at solid/liquid interfaces because of low stability and durability.

Perovskite/silicon tandem solar cells-compositions for improved stability and power conversion efficiency.

Perovskite/Silicon Tandem Solar Cells (PSTSCs) represent an emerging opportunity to compete with industry-standard single junction crystalline silicon (c-Si) solar cells. The maximum power conversion efficiency (PCE) of single junction cells is set by the Shockley-Queisser (SQ) limit (33.7%). However, tandem cells can expand this value to ~ 45% by utilising two stacked solar cells to harvest the solar spectrum more efficiently. 33.9% PCE has already been achieved with PSTSCs. This perspective analyses recent advances in PSTSC technology, with an emphasis on optimal perovskite composition, the problem and mitigation of light-induced halide phase segregation, self-assembled hole transporting monolayers and additives that can improve and stabilise the perovskite. Top-performing compositions show three cationic components (Cs+, FA+, Pb2+) and three anionic (I-, Br-, Cl-) with a bandgap between 1.55 and 1.77 eV and a theoretical maximum of 1.73 eV (717 nm). Anionic additives such as (Br3)- and SCN- reduce trap states and segregation. 2D-perovskite grain boundary interfaces are created with cationic alkylammonium additives such as methyl-phenethylammonium (MPEA) and result in improved performance. 2-, 3- or 4-terminal devices with a (partly) textured silicon heterojunction (SHJ) bottom cell are ideal. An ultra-thin interfacial recombination layer (~ 5 nm) of indium tin oxide (ITO) or indium zinc oxide (IZO) containing a carbazole-based hole transporting self-assembled monolayer (Me-4PACz) is used for optimal 2-terminal tandem devices.

Enabling Direct Photoelectrochemical H2 Production using Alternative Oxidation Reactions on WO3.

The efficient and inexpensive conversion of solar energy into chemical bonds, such as in H2 via the photoelectrochemical splitting of H2O, is a promising route to produce green industrial feedstocks and renewable fuels, which is a key goal of the NCCR Catalysis. However, the oxidation product of the water splitting reaction, O2, has little economic or industrial value. Thus, upgrading key chemical species using alternative oxidation reactions is an emerging trend. WO3 has been identified as a unique photoanode material for this purpose since it performs poorly in the oxygen evolution reaction in H2O. Herein we highlight a collaboration in the NCCR Catalysis that has gained insights at the atomic level of the WO3 surface with ab initio computational methods that help to explain its unique catalytic activity. These computational efforts give new context to experimental results employing WO3 photoanodes for the direct photoelectrochemical oxidation of biomass-derived 5-(hydroxymethyl) furfural. While yield for the desired product, 2,5-furandicarboxylic acid is low, insights into the reaction rate constants using kinetic modelling and an electrochemical technique called derivative voltammetry, give indications on how to improve the system.

Water-Soluble Azobenzene-Based Solar Thermal Fuels with Improved Long-Term Energy Storage and Energy Density.

Azobenzene (azo)-based solar thermal fuels (STFs) have been developed to harvest and store solar energy. However, due to the lipophilicity and low energy density of azo-based STFs, the derived devices demand a large amount of toxic organic solvents for continuous and scalable energy storage. Herein, we report an ionic strategy to prepare water-soluble azo-based STFs (WASTFs) with improved energy storage performance, which can be realized through a facile quaternization reaction using commercial reagents. A family of WASTFs were synthesized, and all of them showed good water solubility, long-term thermal half-life (>30 days), and high energy storage density (a highest energy density of ∼143.6 J g-1 corresponding to an energy storage enthalpy of ∼111.8 kJ mol-1). Compared to the electrically neutral azo-based STFs with similar chemical structures, ΔH and thermal half-life (τ1/2) of the WASTFs are 2.5 times higher and 7.3 times longer, respectively. Cation-π interactions between the quaternized moieties [N+(CHx)4] and benzene moieties of azo were confirmed, which could account for their improvement of the energy storage performance. Macroscale heat release with an average temperature difference of ∼2 °C was achieved for the WASTFs prepared in this work. Generally, a novel family of WASTFs are synthesized and show great applicable prospects in fabricating advanced solar energy storage devices.

Unlocking the Potential of Nanoribbon-Based Sb2S3/Sb2Se3 van-der-Waals Heterostructure for Solar-Energy-Conversion and Optoelectronics Applications.

High-performance nanosized optoelectronic devices based on van der Waals (vdW) heterostructures have significant potential for use in a variety of applications. However, the investigation of nanoribbon-based vdW heterostructures are still mostly unexplored. In this study, based on first-principles calculations, we demonstrate that a Sb2S3/Sb2Se3 vdW heterostructure, which is formed by isostructural nanoribbons of stibnite (Sb2S3) and antimonselite (Sb2Se3), possesses a direct band gap with a typical type-II band alignment, which is suitable for optoelectronics and solar energy conversion. Optical absorption spectra show broad profiles in the visible and UV ranges for all of the studied configurations, indicating their suitability for photodevices. Additionally, in 1D nanoribbons, we see sharp peaks corresponding to strongly bound excitons in a fashion similar to that of other quasi-1D systems. The Sb2S3/Sb2Se3 heterostructure is predicted to exhibit a remarkable power conversion efficiency (PCE) of 28.2%, positioning it competitively alongside other extensively studied two-dimensional (2D) heterostructures.

Highly Efficient Nitrogen-Fixing Microbial Hydrogel Device for Sustainable Solar Hydrogen Production.

Conversion of sunlight and organic carbon substrates to sustainable energy sources through microbial metabolism has great potential for the renewable energy industry. Despite recent progress in microbial photosynthesis, the development of microbial platforms that warrant efficient and scalable fuel production remains in its infancy. Efficient transfer and retrieval of gaseous reactants and products to and from microbes are particular hurdles. Here, inspired by water lily leaves floating on water, a microbial device designed to operate at the air-water interface and facilitate concomitant supply of gaseous reactants, smooth capture of gaseous products, and efficient sunlight delivery is presented. The floatable device carrying Rhodopseudomonas parapalustris, of which nitrogen fixation activity is first determined through this study, exhibits a hydrogen production rate of 104 mmol h-1  m-2 , which is 53 times higher than that of a conventional device placed at a depth of 2 cm in the medium. Furthermore, a scaled-up device with an area of 144 cm2 generates hydrogen at a high rate of 1.52 L h-1  m-2 . Efficient nitrogen fixation and hydrogen generation, low fabrication cost, and mechanical durability corroborate the potential of the floatable microbial device toward practical and sustainable solar energy conversion.

Non-Lignin Constructing the Gas-Solid Interface for Enhancing the Photothermal Catalytic Water Vapor Splitting.

The progress of solar-driven water-splitting technology has been impeded by the limited light response capability of semiconductor materials. Despite attempts to leverage nearly 50% of infrared radiation for photothermal synergy and catalytic reaction enhancement, heat loss during liquid phase reactions results in low energy conversion efficiency. Here, the photothermally driven catalytic water-splitting system, which designs K-SrTiO3 -loaded TiN silica wool at the water-air interface. Photocatalytic tests and density functional theory calculations demonstrate that the thermal effect transforms liquid water into water vapor, thereby reducing the reaction free energy of catalysts and improving the transmission rate of catalytic products. Hence, the hydrogen evolution rate reaches 275.46 mmol m-2  h-1 , and the solar-to-hydrogen (STH) efficiency is 1.81% under 1 sun irradiation in this gas-solid system, which is more than twice that of liquid water splitting. This novel photothermal catalytic pathway, which involves a coupled reaction of water evaporation and water splitting, is anticipated to broaden the utilization range of the solar spectrum and significantly enhance the conversion efficiency of STH.

Surface Oxygen Species in Metal Oxide Photoanodes for Solar Energy Conversion.

Converting and storing solar energy directly as chemical energy through photoelectrochemical devices are promising strategies to replace fossil fuels. Metal oxides are commonly used as photoanode materials, but they still encounter challenges such as limited light absorption, inefficient charge separation, sluggish surface reactions, and insufficient stability. The regulation of surface oxygen species on metal oxide photoanodes has emerged as a critical strategy to modulate molecular and charge dynamics at the reaction interface. However, the precise role of surface oxygen species in metal oxide photoanodes remains ambiguous. The review focuses on elucidating the formation and regulation mechanisms of various surface oxygen species in metal oxides, their advantages and disadvantages in photoelectrochemical reactions, and the characterization methods employed to investigate them. Additionally, the article discusses emerging opportunities and potential hurdles in the regulation of surface oxygen species. By shedding light on the significance of surface oxygen species, this review aims to advance our understanding of their impact on metal oxide photoanodes, paving the way for the design of more efficient and stable photoelectrochemical devices.

Bis- and Tris-norbornadienes with High Energy Densities for Efficient Molecular Solar Thermal Energy Storage.

Molecular solar thermal energy storage (MOST) systems can convert, store and release solar energy in chemical bonds, i.e., as chemical energy. In this work, phenyl- and naphthyl-linked bis- and tris-norbornadienes are presented as promising MOST systems with very high energy densities. The substrates were synthesized by Suzuki-Miyaura coupling reactions and their absorption properties and characteristic parameters for MOST applications were investigated. The norbornadiene derivatives showed absorption onsets of up to 386 nm and photoisomerization quantum yields of 56 % per photoisomerization event. The resulting quadricyclane products have half-lifes up to 14 d and very high energy densities of up to 734 kJ/kg. Overall, these norbornadienes fulfill necessary criteria for an optimal MOST system and are, therefore, a highly promising basis for the development of materials for efficient solar energy conversion and storage.