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Solar reforming (SR) is a promising green‐energy technology that can use sunlight to mitigate biomass and plastic waste while producing hydrogen gas at ambient pressure and temperature. However, practical challenges, including photocatalyst lifetime, recyclability, and low production rates in turbid waste suspensions, limit SR's industrial potential. By immobilizing SR catalyst materials (carbon nitride/platinum; CNx|Pt and carbon nitride/nickel phosphide; CNx|Ni2P) on hollow glass microspheres (HGM), which act as floating supports enabling practical composite recycling, such limitations can be overcome. Substrates derived from plastic and biomass, including poly(ethylene terephthalate) (PET) and cellulose, are reformed by floating SR composites, which are reused for up to ten consecutive cycles under realistic, vertical simulated solar irradiation (AM1.5G), reaching activities of 1333 ± 240 µmolH2 m−2 h−1 on pre‐treated PET. Floating SR composites are also advantageous in realistic waste where turbidity prevents light absorption by non‐floating catalyst powders, achieving 338.1 ± 1.1 µmolH2 m−2 h−1 using floating CNx versus non‐detectable H2 production with non‐floating CNx and a pre‐treated PET bottle as substrate. Low Pt loadings (0.033 ± 0.0013% m/m) demonstrate consistent performance and recyclability, allowing efficient use of precious metals for SR hydrogen production from waste substrates at large areal scale (217 cm2), taking an important step toward practical SR implementation. Reusable floating composites of carbon nitride containing hollow glass microspheres separate to the air‐water interface where they catalyze solar reforming (SR) reactions, transforming waste streams to hydrogen gas. Driven by sunlight, the floating composite produces hydrogen gas from plastic and biomass substrates over consecutive cycles and enables SR in turbid waste suspensions, addressing some key concerns for potential application.

The reforming of natural gas with steam and CO2 is commonly referred to as mixed reforming and considered a promising route to utilize CO2 in the production of synthetic fuels and base chemicals such as methanol. In the present study, the mixed reforming reaction is assessed regarding its potential to effectively utilize CO2 in such processes based on simple thermodynamic models. Requirements for the mixed reforming reactions based on process considerations are defined. These are the avoidance of carbon formation in the reactor, high conversion of the valuable inlet streams CH4 and CO2 as well as a suitable syngas composition for subsequent synthesis. The syngas composition is evaluated based on the module M = ( z H 2 − z CO 2 ) / ( z CO 2 + z CO ) ,   which should assume a value close to 2. A large number of different configurations regarding CO2/H2O/CH4 at the reactor inlet, operating pressure and outlet temperature are simulated and evaluated according to the defined requirements. The results show that the actual potential of the mixed reforming reaction to utilize CO2 as feedstock for fuels and methanol is limited to approximately 0.35 CO2/CH4, which is significantly lower than suggested in literature. At 900 °C and 7 bar at the reactor outlet, which is seen suitable for solar reforming, a ratio of H2O/CH4 of 1.4 can be set and the resulting value of M is 1.92 (CO2/CO/H2 = 0.07/0.4/1).

Green hydrogen from photocatalytic water-splitting and photocatalytic lignocellulosic reforming is a significant proposition for renewable energy storage in global net-zero policies and strategies. Although photocatalytic water-splitting and photocatalytic lignocellulosic reforming have been investigated, their integration is novel. Furthermore, biosynthesis can store the evolved hydrogen and fix the atmospheric carbon dioxide in a biocathode chamber. The biocathode chamber is coupled to the combined photocatalytic water-splitting and lignocellulose oxidation in an anode chamber. This integrated system of anode and biocathode mimics a (bio)electrosynthesis system. A visible solar radiation-driven novel hybrid system comprising photocatalytic water-splitting, lignocellulose oxidation, and atmospheric CO2 fixation is, thus, investigated. It must be noted that there is no technology for reducing atmospheric CO2 concentration. Thus, our novel intensified technology enables renewable and sustainable hydrogen economy and direct CO2 capture from air to confront climate change impact. The photocatalytic anode considered is CdS nanocomposites that give a low absorption onset (200 nm), high absorbance range (200–800 nm), and narrow bandgap (1.58–2.4 V). The biocathode considered is Ralstonia eutropha H16 interfaced with photocatalytic lignocellulosic oxidation and a water-splitting anode. The biocathode undergoes autotrophic metabolism fixing atmospheric CO2 and hydrogen to poly(3-hydroxybutyrate) biosynthesis. As the hydrogen evolved can be readily stored, the electron–hole pair can be separated, increasing the hydrogen evolution efficiency. Although there are many experimental studies, this study for the first time sets the maximum theoretical efficiency target from mechanistic deductions of practical insights. Compared to physical/physicochemical absorption with solvent recovery to capture CO2, the photosynthetic CO2 capture efficiency is 51%. The maximum solar-to-hydrogen generation efficiency is 33%. Lignocelluloses participate in hydrogen evolution by (1–4)-glycosidic bond decomposition, releasing accessible sugar monomers or monosaccharides forming a Cd–O–R bond with the CdS/CdOx nanocomposite surface used as a photocatalyst/semiconductor, leading to CO32− in oxidised carboxylic acid products. Lignocellulose dosing as an oxidising agent can increase the extent of water-splitting. The mechanistic analyses affirm the criticality of lignocellulose oxidation in photocatalytic hydrogen evolution. The critical conditions for success are increasing the alcohol neutralising agent’s strength, increasing the selective (ligno)cellulose dosing, broadening the hybrid nanostructure of the photocatalyst/semiconductor, enhancing the visible-light range absorbance, and increasing the solar energy utilisation efficiency.

The energy supply characteristic of a proton‐exchange membrane fuel cell for houses is strongly influenced in a hydrogen supply unit. Therefore, a bioethanol reforming system (FBSR) with a sunlight heat source is developed as a potential fuel supply system for distributed fuel cells. However, the temperature distribution of a catalyst layer in the reactor is not stable under conditions of unstable solar radiation and unstable outside air temperature; as a result, it is thought that the inversion ratio (the percentage of hydrogen obtained from ethanol) of a reforming reaction will decrease. In this paper, heat transmission analysis was used in the catalyst layer of the reformer of FBSR, and the fundamental performance of FBSR was investigated. Fluctuations of the solar insolation over a short period of time affect the hydrogen‐generating rate of FBSR. Moreover, the amount of hydrogen production of FBSR was simulated using meteorological data from a day in March and a day in August in a cold region (Sapporo in Japan). In this research, the relation between the collected area of a solar collector and the energy supply to an individual house was obtained. The reactor has the geometry of a cylinder and it is filled up with the spherical reforming catalysts that are several millimeters in diameter. The heat collected with solar collector B is transferred to the heat‐supply surface of the reactor, thus heating the catalyst layer.

The main advantage of concentrated solar power (CSP) is the production of carbon free energy. However, the problem is that the energy produced must be directly consumed. This could be dealt with by the chemical storage of solar energy in the form of an energy carrier such as hydrogen (H2), which is transportable and can be used upon request. The available routes to produce solar hydrogen as well as different kinds of solar reactors known from the literature are presented. If solar thermochemical processes are used to decompose hydrocarbons (either biomass or fossil), the resulting mixture of hydrogen and carbon monoxide (CO) can be used as the feedstock for ‘Fischer Tropsch’-based liquid fuel production, for diesel and gasoline replacements. In addition, the idea of combining solar H2 with an actual waste such as carbon dioxide (CO2) to produce renewable solar HC fuels is discussed. This is an attractive way to manage the problem of CO2 storage and, at the same time, to create an intermediate step which is essential for the development of the appropriate infrastructure that could support the H2 economy. Finally, some potential industrial applications of solar fuels and solar energy are described.

Steam natural gas reforming is the preferred technique presently used to produce hydrogen. Proposed in 1932, the technique is very well established but still subjected to perfections. Herein, first, the improvements being sought in catalysts and processes are reviewed, and then the advantage of replacing the energy supply from burning fuels with concentrated solar energy is discussed. It is especially this advance that may drastically reduce the economic and environmental cost of hydrogen production. Steam reforming can be easily integrated into concentrated solar with thermal storage for continuous hydrogen production. Steam methane reforming (SMR) is the favored technique to produce hydrogen, well established but subjected to perfections in catalysts and processes. Herein, the decomposition of CH4 in the presence of Ni on TiO2 support is shown. Especially replacing energy supply from burning fuels with concentrated solar energy is avenue to drastically reduce economic and environmental cost of hydrogen production by SMR.

Solar-heating catalysis has the potential to realize zero artificial energy consumption, which is restricted by the low ambient solar heating temperatures of photothermal materials. Here, we propose the concept of using heterostructures of black photothermal materials (such as Bi 2 Te 3 ) and infrared insulating materials (Cu) to elevate solar heating temperatures. Consequently, the heterostructure of Bi 2 Te 3 and Cu (Bi 2 Te 3 /Cu) increases the 1 sun-heating temperature of Bi 2 Te 3 from 93 °C to 317 °C by achieving the synergy of 89% solar absorption and 5% infrared radiation. This strategy is applicable for various black photothermal materials to raise the 1 sun-heating temperatures of Ti 2 O 3 , Cu 2 Se, and Cu 2 S to 295 °C, 271 °C, and 248 °C, respectively. The Bi 2 Te 3 /Cu-based device is able to heat CuO x /ZnO/Al 2 O 3 nanosheets to 305 °C under 1 sun irradiation, and this system shows a 1 sun-driven hydrogen production rate of 310 mmol g −1 h −1 from methanol and water, at least 6 times greater than that of all solar-driven systems to date, with 30.1% solar-to-hydrogen efficiency and 20-day operating stability. Furthermore, this system is enlarged to 6 m 2 to generate 23.27 m 3 /day of hydrogen under outdoor sunlight irradiation in the spring, revealing its potential for industrial manufacture. The 1 sun-heating temperatures of photothermal materials can be generally elevated from ~90 °C to ~300 °C by hybridizing with infrared insulating materials, capable of driving methanol reforming to 310 mmol g −1 h −1 over CuO x /ZnO/Al 2 O 3 nanosheets.

The chemical looping reforming of methane using an SrFeO3 oxygen carrier to produce synthesis gas from solar energy was experimentally investigated and validated. High-temperature solar heat was used to provide the reaction enthalpy, and therefore the methane feedstock was entirely dedicated to producing syngas. The two-step isothermal process encompassed partial perovskite reduction with methane (partial oxidation of CH4) and exothermic oxidation of SrFeO3-δ with CO2 or H2O splitting under the same operating temperature. The oxygen carrier material was shaped in the form of a reticulated porous foam structure for enhancing heat and mass transfer, and it was cycled in a solar-heated tubular reactor under different operating parameters (temperature: 950–1050 °C, methane mole fraction: 5–30%, and type of oxidant gas: H2O vs. CO2). This study aimed to assess the fuel production capacity of the two-step process and to demonstrate the potential of using strontium ferrite perovskite during solar cycling for the first time. The maximum H2 and CO production rates during CH4-induced reduction were 70 and 25 mL/min at 1000 °C and 15% CH4 mole fraction. The increase in both the cycle temperature and the methane mole fraction promoted the reduction step, thereby enhancing syngas yields up to 569 mL/g during reduction at 1000 °C under 30% CH4 (778 mL/g including both cycle steps), and thus outperforming the performance of the benchmark ceria material. In contrast, the oxidation step was not significantly affected by the experimental conditions and the material’s redox performance was weakly dependent on the nature of the oxidizing gas. The syngas yield remained above 200 mL/g during the oxidation step either with H2O or CO2. Twelve successive redox cycles with stable patterns in the syngas production yields validated material stability. Combining concentrated solar energy and chemical looping reforming was shown to be a promising and sustainable pathway toward carbon-neutral solar fuels.

Hydrogen is considered to be an ideal energy carrier to achieve low-carbon economy and sustainable energy supply. Production of hydrogen by catalytic reforming of organic compounds is one of the most important commercial processes. With the rapid development of photocatalysis in recent years, the applications of photocatalysis have been extended to the area of reforming hydrogen evolution. This research area has attracted extensive attention and exhibited potential for wide application in practice. Photocatalytic reforming for hydrogen evolution is a sustainable process to convert the solar energy stored in hydrogen into chemical energy. This review comprehensively summarized the reported works in relevant areas, categorized by the reforming precursor (organic compound) such as methanol, ethanol and biomass. Mechanisms and characteristics for each category were deeply discussed. In addition, recommendations for future work were suggested.

Solar fuels can be cost-effectively produced using solar-driven thermochemical processes. Hybridizing thermochemical processes can not only effectively utilize solar energy but also achieve clean conversion of fossil fuels. With this method, the solar energy level can be upgraded, and the irradiation fluctuation can be solved. It is worth noting that solar reactors play an important role in this technology. In this study, we demonstrated a 10-kW parabolic trough solar-driven reactor prototype for methane reforming and solar fuel production. The primary setup of the experimental platform consisted of a trough concentrating solar collector, chemical looping reforming reactors with indirect heat transfer, and associated auxiliary equipment. Experiments on the chemical looping redox cycle were conducted using nickel-based NiO/NiAl 2 O 4 as the OC under different direct normal irradiation (DNI) from 740 to 920 W/m 2 . Under irradiation at approximately 920 W/m 2 , the methane conversion initially increased to 92% before declining to 75% from 0 to 900 s and then to 2500 s. Under these conditions, the syngas concentration increased from 30% to 57% and the solar-to-fuel efficiency reached 59%. The oxygen transfer rate during the chemical looping redox cycle was also experimentally investigated. Cyclic redox cycle experiments were conducted for 540 min of long-term operation to assess the duration and adaptability performance. The fractional oxidation can consistently return to almost 1.0 after each redox cycle, indicating strong reactivity and regenerability when exposed to different levels of DNI. The reactivity of the chemical looping redox cycle during typical autumn and winter days was also investigated and discussed. This study aimed to prove that this 10-kW parabolic trough reactor prototype can harness 500°C solar heat to drive efficient methane reforming, offering a promising avenue for solar fuel production.