Reaction Of Hydrogen Research Articles

Isoreticular Squaraine-Linked Titanium-Organic Frameworks for Photocatalytic Water Splitting to Hydrogen Under Visible Light.

Inspired by the excellent photocatalytic activity of TiO2, titanium metal-organic frameworks (Ti-MOFs) with broad absorption of visible light are regarded as promising photocatalysts, but carboxylate-linkers used in them are mainly limited to the large extended π-electron systems. Developing Ti-MOFs using organic linkers with a donor-acceptor-donor (D-A-D) structure is expected to improve their charge separation but is still challenging. Herein the design of two new isoreticular Ti-MOFs, Ti6-SQ1 and Ti6-SQ2 are reported, by using squaraines bearing different electron donors as organic linkers. Discrete fourier transform (DFT) calculations demonstrate that ligand-to-metal charge transfer (LMCT) from the acceptor units of squaraines to the Ti6-oxo secondary building units (SBUs) drives the photocatalytic water splitting to hydrogen reaction. Compared with Ti6-SQ2, the shorter distance between the squaraine centers and the Ti6-oxo SBUs in Ti6-SQ1 makes stronger LMCT, showing higher photocatalytic hydrogen evolution efficiency of 11.5mmol g-1h-1 under visible light (λ > 420nm), which is ≈8 times that of Ti-based MOF photocatalysts reported so far. This work provides a new strategy to design Ti-MOF photocatalysts and understand their structure-property relationship.

Control of hydrogen concentrations by microbial sulfate reduction in two contrasting anoxic coastal sediments

IntroductionMolecular hydrogen is produced by the fermentation of organic matter and consumed by organisms including hydrogenotrophic methanogens and sulfate reducers in anoxic marine sediment. The thermodynamic feasibility of these metabolisms depends strongly on organic matter reactivity and hydrogen concentrations; low organic matter reactivity and high hydrogen concentrations can inhibit fermentation so when organic matter is poor, fermenters might form syntrophies with methanogens and/or sulfate reducers who alleviate thermodynamic stress by keeping hydrogen concentrations low and tightly controlled. However, it is unclear how these metabolisms effect porewater hydrogen concentrations in natural marine sediments of different organic matter reactivities.MethodsWe measured aqueous concentrations of hydrogen, sulfate, methane, dissolved inorganic carbon, and sulfide with high-depth-resolution and 16S rRNA gene assays in sediment cores with low carbon reactivity in White Oak River (WOR) estuary, North Carolina, and those with high carbon reactivity in Cape Lookout Bight (CLB), North Carolina. We calculated the Gibbs energies of sulfate reduction and hydrogenotrophic methanogenesis.ResultsHydrogen concentrations were significantly higher in the sulfate reduction zone at CLB than WOR (mean: 0.716 vs. 0.437 nM H2) with highly contrasting hydrogen profiles. At WOR, hydrogen was extremely low and invariant (range: 0.41–0.52 nM H2) in the upper 15 cm. Deeper than 15 cm, hydrogen became more variable (range: 0.312–2.56 nM H2) and increased until methane production began at ~30 cm. At CLB, hydrogen was highly variable in the upper 15 cm (range: 0.08–2.18 nM H2). Ratios of inorganic carbon production to sulfate consumption show AOM drives sulfate reduction in WOR while degradation of organics drive sulfate reduction in CLB.DiscussionWe conclude more reactive organic matter increases hydrogen concentrations and their variability in anoxic marine sediments. In our AOM-dominated site, WOR, sulfate reducers have tight control on hydrogen via consortia with fermenters which leads to the lower observed variance due to interspecies hydrogen transfer. After sulfate depletion, hydrogen accumulates and becomes variable, supporting methanogenesis. This suggests that CLB’s more reactive organic matter allows fermentation to occur without tight metabolic coupling of fermenters to sulfate reducers, resulting in high and variable porewater hydrogen concentrations that prevent AOM from occurring through reverse hydrogenotrophic methanogenesis.

Hydrogen Oxidation and Evolution Reaction on Platinum in Alkaline Electrolyte: Fixed Reference vs. Overpotential and the Effect of H2 Concentration

Abstract Understanding the kinetics of the hydrogen oxidation and evolution reaction (HOR/HER) in alkaline media is of great interest, but the underlying mechanism and the dependency on the hydrogen pressure are still debated. Herein, we investigated the HOR/HER on polycrystalline platinum in alkaline electrolyte using a rotating disk electrode (RDE). Unlike typically done, we performed the data analysis on a fixed potential scale, which has implications for the assessment of RDE mass-transport corrections and the definition of reaction orders. Analyzing the kinetic currents on a fixed potential, we find hydrogen reaction orders of essentially one and zero for the HOR and HER, respectively, at larger overpotentials. In contrast, fitting the kinetic currents in a potential around equilibrium with a Butler-Volmer model yields differing kinetic parameters and fractional reaction orders. Our findings can be explained with a potential-dependent transition in the HOR mechanism from Tafel–Volmer at small overpotentials to Heyrovsky–Volmer at higher overpotentials, with a concomitant change in the H2 reaction order from fractional to unity, thus reconciling previous propositions on the alkaline HOR/HER mechanism. Our results demonstrate the strength of using a fixed potential scale, and we expect this approach to be beneficial for studies of other electrocatalytic reactions.

Coupling Photocatalytic Hydrogen Production with Key Oxidation Reactions.

Hydrogen represents a clean and sustainable energy source with wide applications in fuel cells and hydrogen energy storage systems. Photocatalytic strategies emerge as a green and promising solution for hydrogen production, which still reveals several critical challenges in enhancing the efficiency and stability and improving the whole value. This review systematically elaborates on various coupling approaches for photocatalytic hydrogen production, aiming to improve both efficiency and value through different oxidation half-reactions. Firstly, the fundamental mechanism is discussed for photocatalytic hydrogen production. Then, the advances, challenges, and opportunities are expanded for the coupling of photocatalytic hydrogen production, which focuses on the integration of value-added reactions including O2 production, H2O2 production, biomass conversion, alcohol oxidation, and pollutants treatment. Finally, the challenges and outlook of photocatalytic H2 production technology are analyzed from the aspects of coupling hydrogen production value, photocatalyst design and reaction system construction. This work presents a holistic view of the field, emphasizing the synergistic benefits of coupled reactions and their practical application potential, rather than focusing on catalysts or single reaction systems. This review provides valuable references for the development and application of photocatalytic hydrogen production in energy conversion and environmental conservation through sustainable, eco-friendly and economic pathways.

Coupling Photocatalytic Hydrogen Production with Key Oxidation Reactions

AbstractHydrogen represents a clean and sustainable energy source with wide applications in fuel cells and hydrogen energy storage systems. Photocatalytic strategies emerge as a green and promising solution for hydrogen production, which still reveals several critical challenges in enhancing the efficiency and stability and improving the whole value. This review systematically elaborates on various coupling approaches for photocatalytic hydrogen production, aiming to improve both efficiency and value through different oxidation half‐reactions. Firstly, the fundamental mechanism is discussed for photocatalytic hydrogen production. Then, the advances, challenges, and opportunities are expanded for the coupling of photocatalytic hydrogen production, which focuses on the integration of value‐added reactions including O2 production, H2O2 production, biomass conversion, alcohol oxidation, and pollutants treatment. Finally, the challenges and outlook of photocatalytic H2 production technology are analyzed from the aspects of coupling hydrogen production value, photocatalyst design and reaction system construction. This work presents a holistic view of the field, emphasizing the synergistic benefits of coupled reactions and their practical application potential, rather than focusing on catalysts or single reaction systems. This review provides valuable references for the development and application of photocatalytic hydrogen production in energy conversion and environmental conservation through sustainable, eco‐friendly and economic pathways.

Photooxidation of Polyolefins to Produce Materials with In-chain Ketones and Improved Materials Properties.

Herein, we report a selective photooxidation of commodity postconsumer polyolefins to produce polymers with in-chain ketones. The reaction does not involve the use of catalyst, metals, or expensive oxidants, and selectively introduces ketone functional groups. Under mild and operationally simple conditions, yields up to 1.23 mol% of in-chain ketones were achieved. Installation of in-chain ketones resulted in materials with improved adhesion of the materials and miscibility of mixed plastics relative to the unfunctionalized plastics. The introduction of ketone groups into the polymer backbone allows these materials to react with diamines, forming dynamic covalent polyolefin networks. This strategy allows for the upcycling of mixed plastic waste into reprocessable materials with enhanced performance properties compared to polyolefin blends. Mechanistic studies support the involvement of photoexcited nitroaromatics in consecutive hydrogen and oxygen atom transfer reactions.

Regulating metal-oxygen covalency of TiO2 by Ru doping and phase transition for boosted hydrogen evolution

Titanium dioxide, with excellent stability, high catalytic activity and abundant reserves, is an ideal substitute for noble metals in hydrogen reaction reactions (HER). However, the strong *H adsorption makes it only a substrate. Tuning metal-oxygen covalency can effectively optimize the adsorption energy. Herein, Ru-modified TiO2 with different phases (rutile, anatase and their mixed-phase) is synthesized, where metal-oxygen covalency and phase transition synergistically boost HER. The target m-Ru@TiO2-x exhibits high HER activity under large current density in wide pH, requiring low overpotential of 87/284 mV (acidic), and 47/366 mV (alkaline) to deliver 10 and 1000 mA·cm−2, respectively, superior to benchmark Pt/C. Theoretical calculation shows that Ru incorporation and mixed rutile-anatase endow m-Ru@TiO2-x with a more negative O p band and decreased overlap between Ti d and O p states, ultimately expediting the desorption of hydrogen during HER. This work enlightens an efficient pathway for tuning the metal-oxygen covalency in HER catalysts.

High Response and ppb-Level Detection toward Hydrogen Sensing by Palladium-Doped α-Fe2O3 Nanotubes.

Developing hydrogen sensors with parts per billion-level detection limits, high response, and high stability is crucial for ensuring safety across various industries (e.g., hydrogen fuel cells, chemical manufacturing, and aerospace). Despite extensive research on parts per billion-level detection, it still struggles to meet stringent requirements. Here, high performance and ppb-level H2 sensing have been developed with palladium-doped iron oxide nanotubes (Pd@Fe2O3 NTs), which have been prepared by FeCl3·6H2O, PdCl2, and PVP electrospinning and air calcination techniques. Various characterization techniques (FESEM, TEM, XRD, and so forth) were used to prove that the nanotube structure was successfully prepared, and the doping of Pd nanoparticles was realized. The experiments show that palladium doping can significantly improve the gas response of iron oxide nanotubes. Specifically, 0.59 wt % Pd@Fe2O3 NTs have high response (Ra/Rg = 41,000), high selectivity, and excellent repeatability for 200 ppm hydrogen at 300 °C. Notably, there was still a significant response at a low detection limit (LOD) of 50 ppb (Ra/Rg = 16.8). This excellent hydrogen sensing performance may be attributed to the high surface area of the nanotubes, the p-n heterojunction of PdO/Fe2O3, which allows more oxygen to be adsorbed on the surface, and the catalytic action of Pd nanoparticles, which promotes the reaction of hydrogen with surface-adsorbed oxygen.

Electron Transfer Capability in Atomic Hydrogen Reactions for Imidazole Groups Bound to the Insulating Alkanethiolate Layer on Au(111).

The charge transfer capability associated with chemical reactions at metal-organic interfaces was studied via the atomic H addition reaction for an imidazole-terminated alkanethiolate self-assembled monolayer (Im-SAM) film on Au(111) at room temperature, using near-edge X-ray absorption fine structure spectroscopy, infrared reflection absorption spectroscopy, work function measurements, and density functional theory calculations. The imidazolium cation is a stable species in liquids; therefore, it is pertinent to determine whether the hydrogenation reactions of the imidazole groups produce imidazolium cations accompanied by electron transfer to the Au substrate, even in the absence of solvate and/or counterions on the insulating alkanethiolate layer. The experiments made it clear that the imidazolium moieties were formed during the irradiation of Im-SAM with atomic H. Theoretical model calculations also revealed that the total energies and molecular orbital levels satisfied the imidazolium cation formation associated with electron transfer. In a detailed analysis of the work function change depending on H irradiation, we confirmed that some of the imidazolium radicals became cations in Im-SAM.

Optimizing propylene production via acetone hydrodeoxygenation: Insights from catalytic studies with Cu/γ-Al2O3 and Hβ zeolite

Propylene is a crucial light olefin in the petrochemical industry and can be produced via acetone hydrodeoxygenation, which involves two sequential reactions: first, acetone undergoes hydrogenation catalyzed by metallic sites, followed by the dehydration of the resulting isopropanol catalyzed by acidic sites. In this study, propylene production through acetone hydrodeoxygenation was investigated using a physical mixture of 35 wt% Cu/γ-Al2O3 and Hβ zeolite to investigate how various reaction parameters affect acetone conversion and propylene yield. Using the experimental design methodology, empirical models were developed to correlate acetone conversion (Xacet) and propylene yield (Yprop) with the ratio of 35 wt% Cu/γ-Al2O3 to Hβ (CR), total catalyst weight (Cw), hydrogen volumetric flow rate (FH2) and reaction temperature (T). The maximum propylene yield achieved in the catalytic tests was 73.46 %. A long-term test demonstrated the catalyst's reusability, remaining active even after 22 hours of reaction with only a slight decrease in propylene yield. Analysis of the experimental data revealed that increasing T and Cw positively affected propylene yield, whereas higher CR and FH2 had negative effects. According to the Pareto chart, reaction temperature was the most influential variable for propylene yield, followed by CR, FH2 and Cw. For acetone conversion, the order of significance among the variables was T >CR >Cw >FH2.

First-principles thermodynamical modeling of molecular reactions on α-U(001) and α-UH3(001) surfaces and their influence on hydrogen activation

Density functional theory calculations coupled with thermodynamic analysis have been performed to investigate the reactions of hydrogen and impurity gases including O2, CO2, CO, N2 on α-U(001) and α-UH3(001) surfaces. Binding strength of adsorbates on α-UH3 is calculated to be weaker than α-U, suggesting enhanced poisoning-resistant properties of U-hydride compared to its metallic state. Surface phase diagrams of U under binary H2-O2, H2-N2 and H2-CO gaseous environments show that while N and C elements prefer to stay in their hydrogenated states on the hydride surface, isolated O atoms favorably interact with both α-U(001) and α-UH3(001), indicating the heavily poisoning effect of impurities containing oxygen. Global optimization of partially oxidized α-U(001) slabs induces surface geometry reconstruction and the activity of oxidized surfaces toward hydrogen adsorption can be linearly correlated with local electronic and atomic properties of the adsorption site.

Synergy effect of nozzle structure and pre-chamber reactivity on the combustion characteristics of ammonia engines

Ammonia (NH3) offers an attractive opportunity for internal combustion engines (ICE) to be carbon–neutral. An active pre-chamber fueled with hydrogen might be suitable to overcome the poor combustion characteristics of ammonia engines. The primary goal of this work is to numerically study the combustion characteristics of ammonia engines with a hydrogen-fueled pre-chamber, and the synergy effect of nozzle structure and pre-chamber reactivity (hydrogen quantity) are also considered. The results show that the hydrogen fraction is reduced to a low degree in the pre-chamber because of the scavenging process. Thus, it is better to inject hydrogen into the pre-chamber during the compression stroke. Although high pre-chamber reactivity is effective in improving the main chamber combustion, a multi-hole pre-chamber is needed to get the maximum promoting effect of the high reactivity when compared to the single-nozzle pre-chamber. For multi-hole pre-chamber, 2 mm is the recommended nozzle diameter when considering the promoting effect, and the recommended area-volume ratio (nozzle number) is increased with the pre-chamber reactivity. For nitrogen-based emissions, the distribution strongly depends on the flame characteristics. High pre-chamber reactivity can significantly reduce the NH3 emissions, while NO emissions will increase with the pre-chamber reactivity. The current study can give some insights and be a preface for the development of ammonia engines.

Investigation on the effects of swirl-strength on flashback phenomenon of premixed CH[formula omitted]/H[formula omitted]/air flame in a bluff-body swirl burner

Blending a low ratio of hydrogen into traditional hydrocarbon fuels can reduce the modification in structure of existing combustors. However, even a low hydrogen ratio can increase the propensity of flashback due to the extremely high reactivity of hydrogen. Swirl number is a key parameter of swirl combustors which determines the flow structure. To design reliable gas turbine combustors for hydrogen-blended fuels, the study in the effect of swirl strength on flashback characteristic and the underlying mechanism is necessary. In this study, the flashback characteristics of premixed 30% H2/70% CH4/air flame in a bluff-body swirl burner is investigated via both experiment and large-eddy simulations with the flamelet-generated-manifold method (FGM-LES). The flashback mode and flame-flow interaction are analyzed based on the LES results. It is found that the increase in swirl strength will increase the propensity of flashback and promote the flashback speed of premixed 30% H2/70% CH4/air flame in the bluff-body swirl burner. The turns from Mode II (small-scale flame bulges leading flashback) to Mode I (large-scale swirling flame tongue leading flashback) during flashback of hydrogen-blended flames due to the production of stronger reversed flow by swirling flow. It is also found that stronger swirl strength will result in a smoother flame front and narrower strain rate distribution range which suppresses the local hydrogen enrichment due to preferential diffusion of hydrogen, thus suppressing the flame propagating speed. However, this effect is not dominant in flashback process compared to the promotion of reversed flow by increased swirl strength.

Direct mechanochemical synthesis of nano-LiAlH4 promoted by 0.696 wt% TiCl4 catalyst surface-modified Al powder

LiAlH4, known for its high hydrogen capacity and metastable nature, is a promising hydrogen source under mild conditions. However, its reversible regeneration from stable binary dehydrogenation phases (LiH/Al) is thermodynamically and kinetically hindered. By constructing a homogeneous and highly dispersed molecular layer of TiCl4 on the surface of the Al reactant to enhance the kinetics of the multiphase interfacial reaction, we achieved the direct mechanochemical synthesis of nano-LiAlH4, bypassing the intermediate phase Li3AlH6. Using the strong Lewis acidity of Ti4+, TiCl4 was chemically adsorbed onto the surface of the Al powder through Ti-O-Al bonds, with a loading capacity of only 0.696 wt%. The obtained TiCl4 surface-modified Al powder and LiH were hydrogenated by ball milling for 10 h under hydrogen pressure to synthesize nano-LiAlH4, which was then dehydrogenated at room temperature. This indicates that the crucial effects of the catalytic sites were dispersed on the reactant surface to ensure the local environment of the multiphase absorption/desorption hydrogen reaction interface and promote the reaction kinetics.

Enhance hydrogen storage in lightweight solid-state systems based on Poly(vinylnaphthalene)

This article highlights the potential of poly(2-vinylnaphthalene) (PVN) as a novel light-weight solid-state hydrogen storage system for various applications. With an impressive theoretical gravimetric hydrogen capacity of 5.2 wt.-%, PVN stands out for its attractiveness as a hydrogen carrier. The material possesses advantageous characteristics, including moldability, low toxicity, and ease of storage, making it a promising candidate for both stationary and mobile hydrogen storage applications. Experimental findings demonstrate that PVN can be hydrogenated by up to 76 % utilizing an Ru/Al2O3 catalyst at 250 °C for 24 h. Confirmation of the hydrogenation reaction, which results in poly(2-vinyldecalin), was achieved through characterization techniques such as FTIR, 1H NMR, and spectroscopic ellipsometry. The study of the effects of hydrogen pressure and reaction time identified moderate conditions as favorable, though a further exploration of different catalysts is suggested for optimal conversion. A palladium-based catalyst was employed to release hydrogen from the hydrogenated polymer, demonstrating almost complete reversibility of the hydrogenation of poly(2-vinylnaphthalene) with a dehydrogenation yield of 90 %.

Data-driven models for the prediction of H2 generation through chemical reaction and performance evaluation of on-board hydrogen fuelled sintering tube furnace

Hydrogen is emerging as a sustainable fuel for the future. In this present work, data-driven modelling tools viz. Radial Basis Function Neural Network (RBFNN) and Least Square Fit (LSF) method, are employed to determine the rate of production of H2 gas by the chemical reaction between aluminium and water in the presence of aq. NaOH. Reactions are carried out at NaOH concentrations of 1M–5M, water temperatures 303K–333K. Hydrogen gas obtained at 333K/4M is found to have a yield of ⁓88 % of the theoretical yield. The activation energy of the reaction is found to be 57.62 kJ mol−1. The fitted models are validated with experimental results for two unknown conditions. The correlation coefficient obtained for the RBFNN model is 0.999, which indicates the high reliability of the model. On-board production of H2 gas by the chemical reaction was used for heating a sintering tube furnace. The hot products of the combustion of hydrogen and air at various fuel-air ratios were used to heat the sintering tube furnace. The maximum thermal efficiency obtained for the furnace is 76.22 % at a fuel-air ratio of 1:60 corresponds to a fuel-air equivalent ratio (λ) of 0.57.

Enhancing the performance of spinel La-doped CoFe2O4 oxygen carriers for chemical looping hydrogen generation

Chemical-looping hydrogen generation (CLHG) is a clean and efficient method for sustainable hydrogen production. The industrial advancement of the CLHG technology hinges on the development of highly active and selective oxygen carriers (OCs). In this study, the performances of three spinel OCs (ZnFe2O4, CoFe2O4, and NiFe2O4) were investigated in a fixed-bed reactor. CoFe2O4 demonstrated the best reactivity and highest hydrogen yield. In addition, doping CoFe2O4 with varying amounts of La further improved its performance. The highest hydrogen yield (393mL/g) was observed for CoFe2O4 doped with 10 % by mass of La. The characterization results indicated that La not only facilitated the formation of oxygen vacancies but also accelerated lattice oxygen transfer. Furthermore, an optimized La doping level was found to boost the crystallinity of the oxygen carrier, leading to improved cycling performance. The insights gained from probing the performance of La-doped CoFe2O4 OCs are expected to contribute to the development of novel OCs for scaled-up CLHG technology.

DFT modeling of reaction of H2 with O2 pre-adsorbed on In2O3(011) surface

The DFT approach is used for the first time to model the reaction of hydrogen with oxygen molecule adsorbed on the defective surface of In2O3(011). This reaction is crucial for hydrogen detection by In2O3 sensor. The activation energies are calculated using two mechanisms involving the formation of both an adsorbed water molecule and hydroxyl groups on the In2O3(011) surface. One hydroxyl group is formed due to the bonding of OH with the surface metal atom, and the other due to the bonding of hydrogen with oxygen of the lattice. Both reactions are characterized by the presence of a potential barrier and are exothermic. The activation energies of the two reactions are calculated by the climbing-image nudged elastic band method to be 0.99 eV and 0.98 eV. The results of the calculations are compared with available experimental data. It is also shown that the presence of a surface neutral oxygen vacancy leads to the formation of a vacancy state below the Fermi level, and the electron density is concentrated on the fourfold coordinated indium atom.

Construction of CdS nanosphere with rare earth metal modification over acid theory with boosted photocatalytic hydrogen reaction

Absorption of light, surface reaction and carriers transfer are three main aspects that affect the whole photocatalytic process and activity. Surface modification strategy is widely adopted to promote the light response while still presented poor carriers transfer. Therefore, rare earth metal was introduced to regulate the surface property of the photocatalyst, which shows enhanced photocatalytic performance of 4567.0 μmol h−1 g−1 under optimal rare earth doping compare to 1553.3 μmol h−1 g−1 of pure CdS. The addition of Gd could expose more reactive centers and reduce the recombination of photo-generated carriers. Meanwhile, the doping of Gd could extend the light absorption and accelerate the hydrogen production kinetics.

Electrocatalysis of hydrogen and oxygen electrode reactions in alkaline media by Rh-modified polycrystalline Ni electrode

Developing novel electrocatalysts for energy conversion applications is of utmost importance for reaching the energy security of modern society. Here we present a comprehensive investigation of rhodium-modified polycrystalline nickel as an electrocatalyst for hydrogen and oxygen electrode reactions in alkaline media. The surface modification of nickel electrodes was achieved by facile galvanic displacement (up to 30 s) from a highly concentrated acidic Rh3+ solution. The results demonstrate a significant enhancement in the electrocatalytic activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on the Rh-modified Ni electrodes, positioning galvanic displacement as a viable approach to engineering advanced electrocatalysts for clean energy applications. On the other hand, the hydrogen oxidation (HOR) and oxygen reduction reaction (ORR) activities of the Rh-modified electrodes are lower compared to polycrystalline platinum. It is suggested that semiconducting Rh2O3 has a detrimental role on the HOR and ORR performance, while the activities of HER and OER, dominantly taking place on metallic Rh and conductive RhO2, are very high. This research sheds light on the mechanisms underlying the enhanced electrode kinetics on Rh-modified Ni electrodes and provides insights into the development of efficient and cost-effective electrocatalysts for renewable energy technologies.