Thermochromic smart windows switch between transmitting and blocking solar infrared radiation (IR) based on temperature. These properties enable passive modulation of solar heat gain, which significantly lowers energy consumption in buildings and increases comfort levels for occupants via a balanced indoor climate. In this study, we set up a tailored test building in Eindhoven (The Netherlands) to monitor the real-life performance of a thermochromic smart window. We produced full sized double-glazed windows comprising a laminated outboard made from thermochromic interlayers, installed them in the test building and monitored their light transmission, solar heat gain and glass surface temperature over a full year. This enabled us to study the thermochromic phase transition of a smart window under real-life conditions for the first time. We demonstrated that the temperature of the smart window's outer glass pane regulated the phase transition and that the overall performance matched well with lab data. A glass surface temperature of 30 degrees C, influenced by the outdoor temperature and solar irradiance (photothermal heating), led to phase transition to the IR blocking state. During summer the smart window transitioned to its IR blocking state around 13:00, whereas in winter glass surface temperatures remained below 30 degrees C, retaining an IR transparent state of the smart window. In spring and autumn photo-thermal heating on cold, but sunny days led to undesired transitions to the IR blocking state, where glass surface temperatures exceeded outdoor temperatures by up to 20 degrees C. We studied the effect of photothermal heating in detail to conclude that optimized behavior of the smart window can be achieved with a phase transition temperature around 35-40 degrees C.

Building-integrated photovoltaics (BIPV) have achieved a high level of technical maturity. In spite of that, the installed capacity remains limited. To stimulate the integration of solar panels in the built environment, aesthetical features like color and freedom in size and shape are of key importance for architects and building owners. Multilayer interference coatings are an attractive coloring technique for solar panels, as they are known for their high solar transmission and tuneable reflection peak. The latter gives rise to an intense metallic reflection color. In this study, the outdoor performance of colored versus non-colored BIPV panels was investigated, and a method has been developed to measure the color variation of the solar panels with respect to outdoor conditions, viewing angles and tilt angles of the setup. A limited performance loss of 15% was measured for colored solar panels compared to their black counterparts, caused by a reduction in generated photocurrent due to light loss. Outdoor color measurements showed that the cloudiness of the sky and the tilt angle of the setup are key parameters causing a color variation from yellow-green to blue-green. In addition, the developed method and tailored measurement setup have proven their value in quantifying color appearance of colored BIPV in realistic and varying outdoor conditions.

Copper niobate metal oxides have gained significant attention in the field of CO2 reduction because of their great potential to address current energy and environmental challenges. Conventional solid-state synthesis methods generally suffer from poor cation homogeneity, whereas sol-gel processes facilitate molecular-scale mixing of precursors and enhanced compositional uniformity. However, many conventional sol-gel routes employ harmful or nonsustainable complexing agents, limiting their sustainability and scalability. Here, we report a facile citrate-complex aqueous solution-gel route for the controlled synthesis of CuNb2O6 and Cu3Nb2O8 phases. Citric acid functions as a chelating and polymerizing agent, facilitating the homogeneous complexation of Cu and Nb cations in aqueous solution while simultaneously promoting molecular-level mixing prior to gelation. The used precursor solution chemistry enables thermal decomposition and crystallization, leading to the reproducible formation of well-defined copper-niobate phases. The phase formation and purity of the target phases were confirmed using in situ high-temperature X-ray diffraction (HT-XRD), Raman spectroscopy, scanning electron microscopy (SEM), and UV-vis spectroscopy. The synthesized materials were further evaluated as precatalysts for photothermal CO2 hydrogenation, where CO was identified as the sole reaction product.

Abstract Vanadium is a transition metal widely used in steel production, batteries, and catalysis. It is a critical material and its disposal poses significant environmental challenges, making recovery and reuse a necessity. This study presents an innovative approach for the recovery and reuse of vanadium from spent catalysts, transforming it into high-purity V2O5 as the precursor for advanced VO2-based thermochromic coatings for smart windows. A multistep process comprising reductive acid leaching, oxidation, and selective precipitation was employed to develop two recovery pathways, resulting either in high-purity vanadium pentoxide (total metallic impurities of 2.14 ppm; extraction yield = 26%) or in a high extraction yield of 72% (total metallic impurities = 1.78%). The material was subsequently converted to monoclinic VO2 and applied for the production of a thermochromic solar control coating for smart windows. Optical measurements revealed a visible transmittance of 55% and a solar modulation of 4.4%, consistent with values for state-of-the-art VO2 coatings prepared by chemical reduction of virgin V2O5. This process demonstrates the technical feasibility of recovering vanadium from spent catalysts and reuse it in functional materials for smart windows, contributing to resource efficiency and environmental sustainability.

Fiber Bragg based - fiber optic sensors were applied in operando to monitor the temperature of illuminated plasmonic catalysts at various depths inside the catalyst bed during light-driven CO2 hydrogenation. Multipoint temperature measurements showed that single-sided illumination induced a pronounced vertical temperature gradient, which remained stable throughout the reaction. This behaviour was observed in two light driven reactions: the exothermic Sabatier reaction catalysed by Ru/Al2O3 and the endothermic reverse water gas shift reaction catalysed by Au/TiO2. The temperature gradient, attributed to a combination of limited light penetration depth and poor thermal conductivity of the catalyst bed, must be taken into account in kinetic studies. Metal loading and gas composition had a strong influence on the temperature gradient, while gas flow rate and reaction heat had a negligible effect. For catalyst temperatures up to 250 & ring;C, radiative heat loss accounted for approximately 15 % of the incident light power. Our study demonstrates that accurate in operando temperature monitoring at multiple positions inside the catalyst bed is essential to distinguish between thermal and nonthermal contributors in plasmon catalysis.

The transition to a sustainable energy system is crucial to meet climate targets and reduce fossil fuel dependence. Solar hydrogen systems offer a promising route for renewable hydrogen production. This study presents a techno-economic assessment of hydrogen production using integrated solar hydrogen panels combined with balance-of-plant equipment such as compressors. The analysis combines detailed Aspen Plus process design with an hourly solar model to capture the impact of system scale and hydrogen storage under intermittent operation. Results show that large-scale integrated systems can achieve costs comparable to photovoltaic–electrolyzer setups, suggesting a feasible and streamlined alternative. System scale is the dominant factor influencing the levelized cost of hydrogen (LCOH). At a small scale (1000 panels), the LCOH is about 49 €/kg. Including hydrogen storage reduces costs by up to 40% through better utilization of capital-intensive components. At larger scales, costs decrease substantially: 100,000 panels yield an LCOH of 9.1 €/kg, and 10 million panels reach 7.3 €/kg. In these large systems, storage slightly increases costs because added capital expenditures outweigh operational gains. If solar-to-hydrogen efficiency improves to 23% and panel costs drop to 120 €/m2, hydrogen could be produced at around 3.8 €/kg. These findings emphasize the importance of scale, efficiency gains, and cost reduction to enable affordable renewable hydrogen directly from sunlight and water.

This study reports the conversion of CO2 and H2 to CO and H2O at low temperature and low pressure (up to 203 degrees C, p = 3.5 bar) using plasmonic Au/CeO2-x photocatalysts, with mildly concentrated sunlight as the sole energy source (up to 9 kW m-2). Systematic catalytic studies were carried out by varying the CeO2-x particle size, Au particle size and loading, and the concentration of oxygen vacancies. Upon illumination, all Au/CeO2-x catalysts showed a CO production of up to 2.6 +/- 0.2 mmol CO per gAu per h (104 +/- 8 mu mol CO per gcat per h), while the supports without Au did not show any activity. We determined that both photothermal and non-thermal effects contribute to the light-driven reverse water-gas shift reaction catalysed by plasmonic Au/CeO2-x. A photothermal contribution was found from the exponential relationship between the CO production and the solar irradiance. In the dark, all Au/CeO2-x photocatalysts and supports without Au produced CH4 instead of CO with >= 97% selectivity, indicating a significant non-thermal contribution in light. A linear dependence of catalytic activity on the accessible interface area between CeO2-x and Au was found, which is in line with an associative formate-mediated reaction mechanism occurring at the metal-support interface. Tuning the VO content through thermal treatments yielded decreased photocatalytic activity for oxidised samples, identifying them as pre-catalysts. The stability of the Au/CeO2-x photocatalysts was evaluated, demonstrating that the catalytic performance was affected by adsorption of H2O as a reaction product, which could be fully restored upon heating in vacuo.

Monoclinic vanadium dioxide (VO2 (M)) is a promising material for various applications ranging from sensing to signature management and smart windows. Most applications rely on its reversible structural phase transition to rutile VO2 (VO2 (R)), which is accompanied by a metal-to-insulator transition. Bottom-up hydrothermal synthesis has proven to yield high quality monoclinic VO(2)but requires toxic and highly reactive reducing agents that cannot be used outside of a research lab. Here, we present a new hydrothermal synthesis method using nontoxic and safe-to-use oxalic acid as a reducing agent for V2O5 to produce VO2 (M). In early stages of the process, polymorphs VO2 (A) and VO2 (B) were formed, which subsequently recrystallized to VO2 (M). Without the presence of W6+, this recrystallization did not occur. After a reaction time of 96 h at 230 C-degrees in the presence of (NH4)(6)H(2)W(12)O(40 )in Teflon-lined rotated autoclaves, we realized highly crystalline, phase pure W-doped VO2 (M) microparticles of uniform size and asterisk shape (Delta H = 28.30 J center dot g(-1), arm length = 6.7 +/- 0.4 mu m, arm width = 0.46 +/- 0.06 mu m). We extensively investigated the role of W6+ in the kinetics of formation of VO2 (M) and the thermodynamics of its structural phase transition.

Continuous-flow methodologies offer promising avenues for sustainable processing due to their precise process control, scalability, and efficient heat and mass transfer. The small dimensions of continuous-flow reactors render them highly suitable for light-assisted reactions, as can be encountered in carbon dioxide hydrogenations. In this study, we present a reactor system emphasizing reproducibility, modularity, and automation, facilitating streamlined screening of conditions and catalysts for these processes. The proposed commercially available photoreactor, in which carbon dioxide hydrogenation was conducted, features narrow channels with a high-surface area catalyst deposition. Meticulous control over temperature, light intensity, pressure, residence time, and reagent stoichiometry yielded the selective formation of carbon monoxide and methane using heterogeneous catalysts, including a novel variant of ruthenium nanoparticles on titania catalyst. All details on the automation are made available, enabling its use by researchers worldwide. Furthermore, we demonstrated the direct utilization of on-demand generated carbon monoxide in the production of fine chemicals via various carbonylative cross-coupling reactions.

The deployment of renewable chemicals and fuels production is directly connected to technical developments, political incentives and investments. The route towards market competitiveness of such chemicals and fuels requires significant cost reduction from state-of-the-art production and operation. In this manuscript, we estimate to what extent the expected technical improvements of the sunlight-powered reverse water gas shift process catalysed by a Au/TiO2 photocatalyst can improve its economic performance. Multiple factors and different scenarios are explored to identify the main dependencies that drive price reductions for this technology. Our projections indicate that the total capital investments required to deploy this green CO production route have the potential to decline from 325 million euros down to 51 million euros for an annual CO production of 100 kton based on the technical improvements. The levelized cost of CO could decrease from around 205 €/GJ CO to 53 €/GJ CO. These results indicate that sunlight-powered chemistry can become competitive when higher carbon taxes are applied to the production of fossil CO (75-200€/ton CO2).

In this article we analyze how syngas produced in a renewable way can replace fossil-fuel based syngas production and thereby play an essential role in the decarbonization of industry. We show that in essentially all industrial applications renewable H2 and/or CO can replace syngas from fossil fuel feedstocks, and quantify the flows of these chemical building blocks required for the transformation of industry towards a net-zero emitting sector. We also undertake a techno-economic analysis, in which we demonstrate that under specific assumptions for the learning rates of some of the key process components, renewable syngas can become cost-competitive with that produced from fossil fuels. Cost competitiveness, however, only materializes for four of the five routes when natural gas prices are at least around 3 €/GJ and carbon taxes increase from 90 €/tCO2 today to 300 €/tCO2 in 2050.

A new benign aqueous route toward bismuth‐containing photoelectrodes is proposed to eliminate the need for harmful organic solvents and/or acids. A CuBi 2 O 4 photocathode is prepared by stabilizing the metal ions through complexation in pH neutral aqueous solutions. Merits of the proposed approach are elemental homogeneity (with unique doping possibilities) and ease of fabrication (e.g., high scalability). The prepared aqueous CuBi 2 O 4 precursor forms a nearly phase‐pure kusachiite crystalline phase free of organics residuals and capable of water reduction due to its sufficiently negatively positioned conduction band at −0.4 V versus RHE. Deposition on fluorine doped tin oxide coated glass (FTO/glass) substrates and thermal treatment leads to uniform but granular films of CuBi 2 O 4 with excellent control over stoichiometry and thickness, owing to the facile and non‐destructive synthesis conditions. Ultimately, the optimized CuBi 2 O 4 photocathodes produce AM1.5G photocurrent densities of up to −1.02 mA cm −2 at 0.4 V versus RHE with H 2 O 2 as an electron scavenger, competing with bare CuBi 2 O 4 prepared through less benign non‐aqueous organic synthesis routes.

The switching performance of W/VO2 nanoparticles in thermochromic glass laminates was investigated. W/VO2 powder was prepared, and displayed a phase transition temperature and switching enthalpy of 20.9 degrees C and 37.5 +/- 0.2 J g- 1, respectively. Using wet bead milling, the particle size was reduced from 24 +/- 2 mu m to 120 +/- 10 nm. In the same process, the switching enthalpy decreased to 18.2 +/- 0.6 J g-1 due to partial loss of crystallinity. The kinetics of the structural phase transition were studied using Friedman's differential isoconversional method. This demonstrated that the activation energy |E alpha| was inversely proportional to the square of the difference between the material's temperature and the critical switching temperature T0, pointing out that nucleation kinetics were determining the rate. Furthermore, |E alpha| decreased upon milling, and kinetic asymmetry was induced. The milled nanoparticles were compounded with PVB to produce thermo-chromic films, which were applied for laminating glass plates. The impact of nanoparticle size and concentration on the resulting optical properties of the laminate, viz. solar transmission and solar modulation, was studied in detail. The highest solar modulation obtained was 9.4%. The results obtained in this study are of direct importance for the application in smart windows, showing that (i) the W/VO2 particle size needs to be <= 100 nm to avoid excessive haze, (ii) both powder production and bead milling require further process optimization to minimize functional performance losses, and (iii) T0 should be set about 3 degrees C lower to ensure a sufficiently fast switch at the temperature of choice.

Thermochromic window coatings represent a promising technology to improve the energy efficiency of buildings in intermediate climates. With the technology approaching market introduction it is important to investigate its performance limits within smart windows and to identify existing development challenges. Here we analyze the theoretical maximum performance of thermochromic window coatings that modulate IR transmission whilst retaining high visible transparency. The set limitations lead to a theoretical maximum solar modulation of 39.1%. Within an insulated glazing unit (IGU), where at least 2 glass panes and a conventional low-e coating are required, this value is further reduced to 12.9%. We show that by carefully selecting a low-e coating with the highest compatibility to a thermochromic coated glass and by allowing 10% of modulation in the visible spectral range, the theoretical maximum can be increased to 23.1%, illustrating the importance to codesign and match both coatings within a smart window to reach optimum performance. Furthermore, we compared our current best-performing VO2:SiO2 composite coating within an IGU to the theoretical maximum. The analysis shows that with a solar modulation of 13.4%, the coating is currently at 59% of the theoretical maximum. Finally, we propose and discuss several strategies to proceed further toward the theoretical maximum.

The urgent need to reduce the carbon dioxide level in the atmosphere and keep the effects of climate change manageable has brought the concept of carbon capture and utilization to the forefront of scientific research. Amongst the promising pathways for this conversion, sunlight-powered photothermal processes, synergistically using both thermal and non-thermal effects of light, have gained significant attention. Research in this field focuses both on the development of catalysts and continuous-flow photoreactors, which offer significant advantages over batch reactors, particularly for scale-up. Here, we focus on sunlight-driven photothermal conversion of CO2 to chemical feedstock CO and CH4 as synthetic fuel. This review provides an overview of the recent progress in the development of photothermal catalysts and continuous-flow photoreactors and outlines the remaining challenges in these areas. Furthermore, it provides insight in additional components required to complete photothermal reaction systems for continuous production (e. g., solar concentrators, sensors and artificial light sources). In addition, our review emphasizes the necessity of integrated collaboration between different research areas, like chemistry, material science, chemical engineering, and optics, to establish optimized systems and reach the full potential of this technology.

Distinguishing between photothermal and non-thermal contributions is essential in light-driven chemical processes. Use of a tailored optical temperature sensor based on fiber Bragg gratings enabled us to obtain an accurate temperature map of an illuminated plasmonic catalyst bed with high spatiotemporal resolution. This demonstrates that accurate multi-point temperature measurements are a prerequisite for a correct interpretation of catalysis results of light-powered chemical reactions.

The continuous flow reverse water gas shift (rWGS) process was efficiently catalyzed by a plasmonic Au/TiO2 nanocatalyst using sunlight as sole and sustainable energy source. The influence of the catalyst bed thickness on the CO production rate was studied, and three different catalytic regimes were identified as direct plasmon catalysis (DPC), shielded plasmon catalysis (SPC) and unused plasmon catalysis (UPC). The CO2  : H2 ratio was optimized to 4 : 1 and a maximum CO production rate of 7420 mmol ⋅ m-2  ⋅ h-1 was achieved under mild reaction conditions (p=3.5 bar, no external heating, Ee =14.0 kW ⋅ m-2 ), corresponding to an aparent quantum efficiency of 4.15%. The stability of the Au/TiO2 catalyst was studied for 110 h continuous operation, maintaining more than 82% of the initial CO production rate. On/off experiments mimicking discontinuous sunlight powered processing furthermore showed that the Au/TiO2 catalyst was stable for 8 consecutive runs.

Plasmonic CO2 methanation using γ-Al2O3-supported Ru nanorods was carried out under continuous-flow conditions without conventional heating, using mildly concentrated sunlight as the sole and sustainable energy source (AM 1.5, irradiance 5.5–14.4 kW·m−2 = 5.5–14.4 suns). Under 12.5 suns, a CO2 conversion exceeding 97% was achieved with complete selectivity towards CH4 and a stable production rate (261.9 mmol·gRu−1·h−1) for at least 12 h. The CH4 production rate showed an exponential increase with increasing light intensity, suggesting that the process was mainly promoted by photothermal heating. This was confirmed by the apparent activation energy of 64.3 kJ·mol−1, which is very similar to the activation energy obtained for reference experiments in dark (67.3 kJ·mol−1). The flow rate influence was studied under 14.4 suns, achieving a CH4 production plateau of 264 µmol min−1 (792 mmol·gRu−1·h−1) with a constant catalyst bed temperature of approximately 204 °C.

Reducing energy consumption and CO2 emissions becomes more and more important. Not only because of climate change related issues, but also to realize our ambition to become energy independent. To increase the energy-efficiency in buildings, we developed a thermochromic coating for smart windows which is optimized for climates with seasonal changes. Here we present the first results of our smart window performing in real environment. We show that measured solar transmission and thermochromic performance is comparable to measurements in the lab. Furthermore, we present a further optimized thermochromic coating with record optical properties of Tvis = 70% and ΔTsol = 20.1%. Via a building energy simulation study using data from this high performing coating, we show that energy savings between 17-37% can be achieved in the Netherlands, depending on the building type. Furthermore we show that by the use of our new smart window annual energy cost savings between 266 – 553 EUR/a for a single household can be achieved. The thermochromic coating usually accounts for 60 – 70% of these cost savings equaling between 8 – 10 EUR/a per m2 glass. Due to the low material and processing costs for the thermochromic coating, an attractive return on invest with market conform profit margin is possible.

Natural gas is a potent greenhouse gas but remains an attractive energy resource for a good number of reasons. Because complementing the use of natural gas with carbon dioxide capture and storage yields several drawbacks, producing synthetic natural gas instead could be an interesting alternative. Methanation is an established and well-known process, and with atmospheric carbon dioxide as input it could deliver a climate-neutral energy carrier, which we refer to as renewable natural gas. At present, however, methanation is exceedingly costly. In this paper we try to answer two main questions: (I) can innovative methanation such as based on sunlightpowered plasmon catalysis compete with more conventional methanation options using the Sabatier reaction in e.g. adiabatic fixed-bed processes; (II) can these two alternatives ever compete with abundantly available natural gas? Under realistic assumptions for technology learning, we find that innovative methanation technology could compete with conventional methanation systems sometime between 2032 and 2039 in our base case scenario. The required learning investments for the innovative option would amount to about 80 M(sic), spent on an installed capacity of around 750 MW. We also conclude that the levelized cost of methane remains dominated by the cost of hydrogen until at least the middle of the century. Methanation could in principle compete with natural gas by 2050, but only if a carbon tax is levied of at least 270 (sic)/tCO(2).