Solar H2 Production Research Articles

Recent advances in titanium carbide MXene-based nanotextures with influential effect of synthesis parameters for solar CO2 reduction and H2 production: A critical review

Photocatalytic solar to energy conversion is considered an attractive approach for overcoming energy crises and environmental concerns. Recently, titanium carbide (Ti3C2) MXenes have been recognized as promising cocatalysts based on their metallic conductivity, excessive active reaction sites, and enlarged surface area. The current review focuses on the properties and applications of Ti3C2 MXenes useful in the field of photocatalysis. More specifically, surface modification of Ti3C2 MXenes by varying synthesis parameters to get pure materials and also composites with the role of functional groups towards solar energy conversion applications is highlighted in this review. The effect of etching and oxidizing pathways to get an efficient cocatalyst has been discussed in detail. Considering the significant effect of parameters, optimum synthesis conditions such as etchant type, concentration, time and type of intercalant in both the Ti3C2 synthesis approaches for improved photoactivity are discussed. Additionally, the surface modification of Ti3C2 through oxidation for TiO2 growth on its surface is deliberated with a detailed discussion on etchant type, concentration, etching time, and environmental factors. The optimum oxidation condition, including temperature, time, and environment for thermal treatment of Ti3C2, were also included. Lastly, the review summarizes the conclusion and future perspectives for solar energy conversion applications.

Synergistic effect of cobalt in hierarchical carbon nitride nanorods (HCNNR) with promising charge transfer rate by hole scavenger for stimulating solar H2 production

One-dimensional (1D) hierarchical carbon nitrides nanorods (HCNNRs) mediated by cobalt was designed and synthesized using a template free hydrothermal approach for improving solar light assisted H2 evolution. The performance of 1D HCNNTs was significantly enhanced compared to bulk g-C3N4 due to larger active surface area, more visible light utilization and superior charge carrier along the unidirectional flow pathways. The 2% Co/HCNNRs (1D) exhibited excellent photocatalytic efficiency and optimal H2 yield reached up to 620 µmol g−1, which is 11.27 and 17.71 folds more than it was attained with pure HCNNR and bulk g-C3N4, respectively. This reveals that 1D structure helps to accelerate charge transport, whereas, Co works as a mediator to trap electrons, thus improving photocatalytic performance. The crucial operating parameters such as sacrificial reagents, feed concentration and catalyst loading were further optimized based on highest H2 evolution. Interestingly, mass transfer, charge transfer and amount of photoinduced charges were greatly dependent on the operating parameters. Higher methanol and lower TEOA concentration were beneficial to yield highest photoactivity and stability. This work provides new approach to construct template free 1D nanorods and would be beneficial to enhance performance in other solar energy related applications.

Z-scheme Ag-NPs-embedded LaCoO3 dispersed pCN heterojunction with higher kinetic rate for stimulating photocatalytic solar H2 production

Well-designed LaCoO3 perovskite anchored pCN Z-scheme heterojunction embedded with Ag NPs was fabricated for photocatalytic H2 evolution under visible irradiation. The pure LaCoO3 phase was obtained having narrow band gap through the combination of coprecipitation and hydrothermal method. The controlled interface heterojunction was produced for the proficient charge’s mobility with the capability of Ag to act as an electron sink. The Ag-LaCoO3/pCN nanocomposite generated H2 yield of 3160 µmol g−1, a 5.5 and 7-folds improved compared to pCN and LaCoO3 samples, respectively. Among the sacrificial agent, TEOA yielded boosted H2 production compared to methanol, linked to strong binding of amine containing pCN with TEOA. Ag-LaCoO3/pCN nanocomposite depicted an excellent stability and reusability over 4 consecutive cycles. Overall, the improved photoactivity was associated with Z-scheme formation of LaCoO3/pCN supported with Ag-NPs, leading to improved absorption of visible light, effective charge separation with more reaction sites. Kinetic model based on the Langmuir-Hinshelwood model was developed for the determining rate of reaction. The model results were fitting well with the experimental data, attributing adsorption process is the rate limiting step and controlled overall reaction kinetics. In conclusion, this study contributes to the development of efficient photo-technology for H2 production towards sustainable solar fuels.

Coupling Red-to-blue Upconversion Organic Microcrystals with Cd0.5 Zn0.5 S for Efficient and Durable Photocatalytic Hydrogen Production.

For semiconductor photocatalysts with excellent performance in solar H2 production, broadening the utilization of solar irradiation is highly necessary to further improve the solar conversion efficiency. Herein, we combined a Cd0.5 Zn0.5 S photocatalyst with DPA/PdTPTBP microcrystals capable of red-to-blue photon upconversion, realizing substantial performance enhancement and an apparent quantum yield of 0.16% for H2 production driven by sub-bandgap photons (600∼650 nm). Meanwhile, this system could smoothly work with H2 production rate of 1.40 mmol g-1 h-1 for as long as 40 hours under 200 mW/cm2 irradiation with only 3% attenuation of photocatalytic activity. Moreover, the O2 -barrier property of DPA/PdTPTBP microcrystals assures that photocatalytic H2 production remains effective in the presence of 10% O2 by volume, which offers an opportunity for the photocatalytic application in O2 -enriched environments. The combination of O2 -resistant upconversion microcrystals and semiconductor catalysts is the most successful solution for the construction of TTA-UC-based photocatalytic H2 production system so far. The present study provides a clear guideline for designing new TTA-UC-based photocatalytic systems.

Critical Optimization of Phosphorus Functionalized Carbon Nanomaterials for Metal‐Free Solar Hydrogen Production and Simultaneous Organic Transformation

AbstractComplete metal‐free P‐functionalized carbon nanomaterials are synthesized from a single molecular precursor, phytic acid, for photocatalytic solar H2 production and simultaneous organic transformation of 4‐methyl benzyl alcohol to 4‐methyl benzaldehyde by managing the complete redox cycle. It is observed that by increasing the carbonization time, P‐functionalized amorphous carbon dots convert to the highly defined 2D sheet‐like nanostructure with optimum P‐functionality, resulting in efficient light absorption, charge separation, and improved active sites for photocatalysis. Finally, the highly defined sheet‐like structure converts to a more defected aggregated form, resulting in the depletion of photocatalytic efficiency. The structural and elemental features are further correlated with the ongoing photophysics by means of steady‐state and time‐resolved fluorescence spectroscopy. Transient photocurrent responses and Mott‐Schottky plots directly support the optimization of P‐functionalized carbon nanostructure for efficient photocatalysis. Finally, the detailed computational studies are carried out to unveil the charge separation mechanism and the crucial role of P‐functionalities as active sites for better charge accumulation as well as H2O adsorption on the surface. Overall, the in‐depth structure–property correlation and critical optimization of the heteroatom functionalized carbon nanomaterials will open up new possibilities for further development of metal‐free photocatalysts for solar‐energy conversion devices.

Solar-Driven Hydrogen Production: Recent Advances, Challenges, and Future Perspectives

Solar H2 production is considered as a potentially promising way to utilize solar energy and tackle climate change stemming from the combustion of fossil fuels. Photocatalytic, photoelectrochemical, photovoltaic–electrochemical, solar thermochemical, photothermal catalytic, and photobiological technologies are the most intensively studied routes for solar H2 production. In this Focus Review, we provide a comprehensive review of these technologies. After a brief introduction of the principles and mechanisms of these technologies, the recent achievements in solar H2 production are summarized, with a particular focus on the high solar-to-H2 (STH) conversion efficiency achieved by each route. We then comparatively analyze and evaluate these technologies based on the metrics of STH efficiency, durability, economic viability, and environmental sustainability, aiming to assess the commercial feasibility of these solar technologies compared with current industrial H2 production processes. Finally, the challenges and prospects of future research on solar H2 production technologies are presented.

A Few Pt Single Atoms Are Responsible for the Overall Co‐Catalytic Activity in Pt/TiO2 Photocatalytic H2 Generation

The use of single atoms (SAs) has become a highly investigated topic in heterogeneous catalysis, electrocatalysis, and most recently also in photocatalysis. In the field of photocatalysis, Pt SAs on TiO2 have been reported to be a highly efficient co‐catalyst in solar H2 production. Herein, the deposition of Pt SAs and nanoparticles on titania nanosheets is investigated. In particular, the Pt species responsible for the high co‐catalytic activity using a cyanide leaching process is elucidated. It is shown that neither Pt0 species nor the majority of Pt SAs do significantly contribute to the co‐catalytic activity of platinum on TiO2. In fact, >90% of the Pt of a standard deposition are non‐active and can be removed by cyanide leaching without activity loss—as a consequence, the remaining Pt SAs amount to a remarkable turnover frequency of 4.87 × 105 h−1 for H2 evolution.

Bacteria‐Triggered Solar Hydrogen Production via Platinum(II)‐Tethered Chalcogenoviologens

AbstractMultifunctional solar energy conversion offers a feasible strategy to solve energy, environmental and water crises. Herein, a series of platinum(II)‐tethered chalcogenoviologens (PtL+‐EV2+, E=S, Se, Te) is reported, which integrate the functions of photosensitizer, electron mediator and catalyst. PtL+‐EV2+(particularly for PtL+‐SeV2+)‐based one‐component solar H2production could be triggered not only by EDTA, but also by facultative anaerobic and aerobic bacteria relying on a simplified mechanism, along with efficient antibacterial activities. In addition, by using real pool water, PtL+‐SeV2+achieved multiple functions, including H2production, antibacterial action and acid removal, which supplied a new strategy to solve various problems in real life via a single system.

Photocatalytic H2 Production on Au/TiO2: Effect of Au Photodeposition on Different TiO2 Crystalline Phases

In this work, we investigated the role of the crystalline phases of titanium dioxide in the solar photocatalytic H2 production by the reforming of glycerol, focusing the attention on the influence of photodeposited gold, as a metal co-catalyst, on TiO2 surface. We correlated the photocatalytic activity of 1 wt% Au/TiO2 in anatase, rutile, and brookite phases with the structural and optical properties determined by Raman spectroscopy, N2 adsorption–desorption measurements, UV–vis Diffuse Reflectance Spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectroscopy (PL), and Dynamic Light scattering (DLS). The best results (2.55 mmol H2 gcat−1 h−1) were obtained with anatase and gold photodeposited after 30 min of solar irradiation. The good performance of Au/TiO2 in anatase form and the key importance of the strong interaction between gold and the peculiar crystalline phase of TiO2 can be a starting point to efficiently improve photocatalysts design and experimental conditions, in order to favor a green hydrogen production through solar photocatalysis.

Bacteria-Triggered Solar Hydrogen Production via Platinum(II)-Tethered Chalcogenoviologens.

Multifunctional solar energy conversion offers a feasible strategy to solve energy, environmental and water crises. Herein, a series of platinum(II)-tethered chalcogenoviologens (PtL+ -EV2+ , E=S, Se, Te) is reported, which integrate the functions of photosensitizer, electron mediator and catalyst. PtL+ -EV2+ (particularly for PtL+ -SeV2+ )-based one-component solar H2 production could be triggered not only by EDTA, but also by facultative anaerobic and aerobic bacteria relying on a simplified mechanism, along with efficient antibacterial activities. In addition, by using real pool water, PtL+ -SeV2+ achieved multiple functions, including H2 production, antibacterial action and acid removal, which supplied a new strategy to solve various problems in real life via a single system.

Water denitration over titania-supported Pt and Cu by combined photocatalytic and catalytic processes: Implications for hydrogen generation properties in a photocatalytic system

The present work provides a new approach to the water denitration process and a facile strategy of catalyst preparation for the efficient hydrogen generation. The main focus of the research reported here was nitrate removal from aqueous solutions and simultaneous hydrogen generation under UV-Vis-light irradiation. This is a very important aspect in case of practical applications, eliminating the external source of hydrogen. Aiming to get a deeper understanding on the role of surface structures (size and shape of nanoparticles) towards the reduction mechanism and to establish basic principles for an efficient process, Pt-Cu/TiO2 and Pt-Cu/TiO2 modified with well-defined Pt nanoparticles were employed. The synthesized materials were characterized using various physicochemical techniques and tested comparatively for: (i) nitrate catalytic reduction by hydrogen (dark reaction) and (ii) nitrate photocatalytic reduction by in-situ generated solar hydrogen. In order to enhance overall denitration reaction by combined photocatalytic and catalytic processes, photo-generated charges and in-situ generated H2 as reducing agent were used. Improvement of catalytic performances of nitrate hydrogenation reaction (~100% NO3¯ conversion) related to intimate contact between Pt and Cu was obtained. The in-situ generated H2 by water splitting over the studied catalysts reduces efficiently NO3¯ ions. Enhanced photocatalytic activity toward solar H2 production by deposited well-defined Pt nanoparticles (~10 nm) was achieved. In order to make possible decontamination of polluted waters using in-situ generated H2 under light exposure, the future optimization of such photo-catalytic systems looks promising.

Coupling of Water-Splitting Mechanism and Doping-Mixture to Design a Novel Cr-Perovskite for Rapid and Efficient Solar Thermochemical H2 Production

Coupling of Water-Splitting Mechanism and Doping-Mixture to Design a Novel Cr-Perovskite for Rapid and Efficient Solar Thermochemical H2 Production

Fabricating Ti3c2tx Mxene Cocatalyst Supported Nial-Ldh/ with G-C3n4 Ternary Nanocomposite for Stimulating Solar Photocatalytic H2 Production

Fabricating Ti3c2tx Mxene Cocatalyst Supported Nial-Ldh/ with G-C3n4 Ternary Nanocomposite for Stimulating Solar Photocatalytic H2 Production

Influential Effect of Etched/Oxidized Ti3c2tx Nanoflowers Integrated Lacoo3/Pc3n4 to Construct Z/S Scheme Heterojunction for Stimulating Solar H2 Production

Influential Effect of Etched/Oxidized Ti3c2tx Nanoflowers Integrated Lacoo3/Pc3n4 to Construct Z/S Scheme Heterojunction for Stimulating Solar H2 Production

Photovoltaic powered solar hydrogen production coupled with waste SO2 valorization enabled by MoP electrocatalysts

In this study, we demonstrated high-rate H2 generation by coupling with the sulfite oxidation reaction (SOR) as an alternative to the oxygen evolution reaction for solar H2 production. The emerging and cost-effective molybdenum phosphide electrocatalyst was appropriately optimized and used as a bifunctional catalyst in an alkaline electrolyte for both SOR and HER. Powered by state-of-the-art perovskite–Si tandem photovoltaics, a remarkable photocurrent density of over 17 mA cm−2 was achieved in the HER coupled with the SOR. In addition to the significantly enhanced photocurrent, the SOR can further reduce the overall cost of solar H2 production owing to the elimination of the expensive membranes required for H2 and O2 gas separation. Considering the high global demand for desulfurization via the SOR, the strategy proposed here will enable practical H2 production from renewable sources while effectively converting the toxic SO2 gas into a value-added product for the chemical industry.

Effect of Defects on Optical, Electronic, and Interface Properties of NiO/SnO2 Heterostructures: Dual-Functional Solar Photocatalytic H2 Production and RhB Degradation.

Photocatalytic H2 evolution and organic pollutant oxidation have witnessed a radical surge in recent times. However, this integration demands spatial charge separation and unique interface properties for a trade-off between oxidation and reduction reactions. In the current work, defect engineering of NiO/SnO2 nanoparticles aided in altering the optoelectronics and interface properties and enhanced photocatalytic activity. After annealing the catalysts in a N2 atmosphere, the hydroxyl groups were replaced by water molecules through surface modification. The photoexcited holes accumulated on SnO2 break the water molecules and facilitate the reduction of protons on NiO; this is known as spatial separation. Meanwhile, direct hole oxidation, an oxygen reduction reaction, ensures the degradation activity in this 2-fold system. By defect engineering, the limitations of SnO2 such as higher H2O adsorption, wide bandgap (reduced from 3.02 to 1.88 eV), and electronic properties were addressed. The H2 production in the current work has attained a value of 3732 μmol/(g h), which is 2.9 times that of the previous best reported under sunlight. Recyclability tests confirmed the stability of vacancies by promoting the reoxidation of defect states during photocatalytic activity. Additionally, efforts were made to study the effect of defect density on the photocurrent, the electrical resistance, and the mechanism of photocatalytic reactions. Electrochemical characterizations, UPS, XPS, UV-DRS, and PL were employed to understand the influence of defects on the bandgap, charge recombination, charge transport, charge carrier lifetime, and the interface properties that are responsible for photocatalytic activity. In this regard, it was understood that maintaining the optimal defect concentration is important for higher photocatalytic efficiencies, as the defect optimality preserves key photocatalytic properties. Apart from characterizations, the photocatalytic results suggest that excess defect density triggers the undesired thermodynamically favored back reactions, which greatly hampered the H2 yield of the process.

Efficient Electronic Modulation of g-C 3 N 4 Photocatalyst by Implanting Atomically Dispersed Ag 1 -N 3 for Extremely High Hydrogen Evolution Rates

Efficient Electronic Modulation of g-C ₃ N ₄ Photocatalyst by Implanting Atomically Dispersed Ag ₁ -N ₃ for Extremely High Hydrogen Evolution Rates

In situ Blue titania via band shape engineering for exceptional solar H2 production in rutile TiO2

Designing an excellent solar photocatalyst based on TiO2 without an external cocatalyst such as Pt remains unresolved despite its exceptional potential for renewable energy production. Here, we report a state-of-the-art solar-driven photocatalytic Cl-doped rutile TiO2, in nanosheet morphology with (110) facets, for H2 production from water splitting in the absence of any external cocatalyst. The Cl-doped rutile TiO2 nanosheets are easily synthesised via a layered titanate’s interconversion through a simple dilute HCl treatment and thermal heating at a convenient temperature. We demonstrate that engineering the band shape can result in long-lasting photogenerated Ti3+, which subsequently can act as an in situ cocatalyst in rutile TiO2. According to our density functional calculations, the Cl dopant has a pivotal role in improving the band shape of TiO2, i.e., significantly reducing the effective mass of the photogenerated electrons and holes, especially when compared to the effect of oxygen vacancy. Consequently, the boosted carrier mobility, resulting from lighter carriers, photogenerates a significant number of prolonged Ti3+ species that enhance photocatalytic activity in situ (i.e., in situ blue titania). Our results show that despite the considerable efforts that have been directed towards narrowing TiO2’s band gap, band shape engineering offers a more facile and robust solution for photocatalysis.

Solar photocatalytic H2 production over CeO2-based catalysts: Influence of chemical and structural modifications

Different CeO2-based materials employed as unconventional photocatalysts for H2 production were here examined. The performances of bare CeO2 prepared by precipitation were compared with those of CeO2-WO3 composites synthetized by co-precipitation and surfactants-mediated precipitation. The bare CeO2 and the best CeO2-WO3 composite were treated with laser irradiation to investigate the modifications of cerium oxide due to this process. Considering the photocatalytic performance, the CeO2-WO3 composite prepared with the HMTA (hexamethylenetetramine) surfactant and irradiated with laser increased the H2 production up to 4 times compared to the bare CeO2, whereas the laser-modified CeO2 and the CeO2-WO3 synthetized by co-precipitation led to a smaller increase of H2 evolution (1.4 and 1.2 times higher than the as-prepared CeO2, respectively). On the basis of the characterization data (Raman, UV–vis Diffuse Reflectance, Photoluminescence, X-ray photoelectron spectroscopies, Transmission electron microscopy and N2 physisorption measurements) it was established that the addition of the HMTA gave higher WO3 dispersion, whereas the subsequent laser treatment facilitated the progressive incorporation of WO3 into CeO2, resulting in a more efficient doping process and a more defective CeO2. All these features were beneficial for the photoproduction of hydrogen. The tuning and the combination of the chemical and the structural modifications of ceria can be a promising route for the solar-driven photocatalysts designed for the green production of H2.

Chemical formula input relied intelligent identification of an inorganic perovskite for solar thermochemical hydrogen production

An efficient prediction procedure based on the random forest method is developed for the intelligent identification of pure and doped perovskites for solar thermochemical H2 production.