Solar-driven multifunctional Au/TiO2@PCM towards bio-glycerol photothermal reforming hydrogen production and thermal storage

Photocatalytic hydrogen production and thermal storage are effective ways to convert solar energy into storable chemical energy and thermal energy, but they only respond to specific spectrum. In order to improve the energy conversion and storage efficiency of solar energy in the solar spectrum, hydrothermal and photo-deposition method were employed to synthesized photothermal catalyst while and Au/TiO₂@PCM composite microcapsules were fabricated by electrostatic adsorption self-assembly methods. Micro-morphologies and structures were detailed characterized by SEM, XRD, UV-Vis, etc. As calculated from the DSC results for effective, enthalpy value, the loading rates of Au/TiO₂ shell for the microcapsule were 12.6% and 15.4% corresponding to rod-shaped and sheet-shaped samples. To test their catalytic performance, the samples were dispersed in the same concentration of glycerol solution, and showed that the light to hydrogen efficiencies were 11.4‰ and 5.0‰ for ATR@PCM and ATF@PCM, respectively with the increasement of 53.8% and 56.1% comparing to their corresponding catalyst nanoparticle suspensions. Photo-thermal conversion efficiencies of ATR@PCM and ATF@PCM were 62.74% and 53.32% after 60 min-irradiations, and they were 48.22% and 25.96% higher than that of Me-PCM. Therefore, it was confirmed that the composite phase change microcapsules prepared in this study have the dual functions of energy storage and photothermal catalysis. Higher solar light to hydrogen energy conversion efficiency may be attained in future study if the stored thermal energy can be successfully employed to activate organic components for helping catalytic hydrogen generation.     

Insights into morphology-dependent Au/TiO2catalyst in glycerol aqueous solutions towards photothermal reforming hydrogen production

Probing the effect of spatial morphology of catalyst on its photothermal catalytic performance is crucial for solar-driven renewable catalytic reforming of hydrogen production. In this study, Au nanoparticles loaded on various morphologies of TiO₂ nanoparticles were synthesized and characterized. The experimental results indicated that decorating TiO₂ with Au nanoparticles could dramatically increase its photocatalytic activities by 20–40 times. The photothermal conversion efficiency of Au/TiO₂ (12.74%–25.54%) was higher than those of TiO₂ due to the introduction of LSPR of Au nanoparticles could effectively improve the utilization of solar spectrum. Titania nanoflower (TNF) nanoparticles with high light absorption capacity, better colloidal dispersion stability, porous properties and narrow band gap represented the highest H₂ productivity (144.13 μmol·g⁻¹·h⁻¹). The coarse surface structure was also conducive to the dispersion of gold particles on the surface of the carrier and the growth rate of Au/TNF hydrogen production (40 times) which was higher than that of other morphology within 2 h. The results of glycerol photothermal hydrogen generation highlighted the effect of temperature on colloidal dispersion stability and hydrogen production capability of nanoparticle suspension. It demonstrated that the photothermal effect aroused a temperature rise that would deteriorate the dispersion stability of the suspension although a local entropy increase in the catalyst nanoparticles might occur. At the same time, the temperature rise caused by the photothermal effect efficiently produces hydrogen in the reaction temperature range. Therefore, an ideal temperature setting for maximal hydrogen generation could be validated and improved the photothermal synergistic impact on biomass-reformed hydrogen generation.     

Efficient photothermal catalytic hydrogen production via plasma-induced photothermal effect of Cu/TiO2 nanoparticles

Developing appropriate photocatalyst with high efficiency is still the basic strategy for practical application of emerging technology. Herein, non-noble metal copper (Cu) nanoparticles were in situ hybrided with TiO₂ by a chemical reduction method. The crystal phase and structure were characterized by XRD, SEM, and TEM measurements. Hydrogen production results showed that Cu nanoparticles significantly improved the photocatalytic hydrogen production rate. The hydrogen production rate was as high as 24160.69 μmol g^?1 h^?1 at 100 °C, which was 36.25 and 8.46 times higher than the hydrogen production rates of pure TiO₂ and 0.13 wt% Cu/TiO₂ at room temperature, respectively. PL spectra, UV–vis spectra, IR images and photoelectrochemical measurements showed that the plasma-induced photothermal effect of Cu/TiO₂ nanoparticles, which raised the temperature of the reaction system and promoted photothermal catalytic performance. Briefly, this work provides a facile fabrication method of noble-metal-free photocatalysts featuring in low-cost and high efficiency. In the future, coupling the photothermal effect of plasmonic Cu to further speed up the kinetics should be another promising research direction for further improving hydrogen production.     

Investigation on the effect of temperature on photothermal glycerol reforming hydrogen production over Ag/TiO2 nanoflake catalyst

Photothermal reforming of biomass-derived hydrocarbons is an efficient approach to generate renewable hydrogen driven by solar. However, the current understanding of the general thermal effect on hydrogen production is limited since the photothermal and thermal radiation from solar is difficult to separate. Herein, an experimental study is carried out by synthesizing a series of photothermal catalysts composed of Ag nanoparticles supported on TiO₂ nanoflake (TNF). The structure of the Ag/TNF was examined by XRD, XPS, and HRTEM, respectively. The local temperature rise of the Ag/TNF was detected during the photothermal reforming reaction of the aqueous bio-glycerol, and its influence on H₂ yield was analyzed. By introducing different weight ratios of Ag nanoparticles on TNF, the equilibrium temperature was obviously increased due to the localized surface plasmon resonance (LSPR) effect and dynamic balance between LSPR and heat dissipation was found. It was observed that increasing the weight ratio of Ag particles could result in an increased temperature and lower hydrogen yields. In fact, such photothermal reforming hydrogen production was a synergistic effect between photogenerated-electrons and phonons. Therefore, precisely regulating the photothermal effect by controlling the metal nanoparticles loading to achieve proper thermal balance and high catalytic activity is one effective countermeasure to enhance hydrogen production.     

Photocatalytic hydrogen production by reforming of methanol using Au/TiO2, Ag/TiO2 and Au-Ag/TiO2 catalysts

Abstract

We have investigated polyvinylalcohol stabilized Au and Ag based nanoparticles supported on titania prepared via sol immobilisation for the anaerobic, ambient temperature reforming of methanol with water for the photocatalytic production of hydrogen. The catalytic activity of the Au/TiO₂ catalysts was strongly affected by the metal loading and calcination temperature. Here, we report the preparation and use of supported Au–Ag nanoparticles, based on either the co-reduction or the consecutive reduction of the two metals. Au–Ag supported catalysts were more active than monometallic Au and Ag catalysts and the preparation methodology had a pronounced effect in terms of catalytic activity of the Au–Ag catalysts. In fact, using a consecutive reduction where Au was firstly reduced followed by reduction of Ag gave materials which exhibited the highest catalytic performance.     

Integrated design of hydrogen production and thermal energy storage functions of Al-Bi-Cu composite powders

In recent years, the hydrolysis of Al-based composite powders to produce hydrogen has become a hot topic in the field of hydrogen energy research. However, the hydrogen generation products of Al-based alloys have not been reasonably utilized. For this purpose, this study proposed a novel research idea to achieve the integrated design of hydrogen production and thermal energy storage functions of Al-based composite powders. Specifically, Al-Bi-Cu composite powders with stable hydrogen production were taken as research objects. The hydrogen was obtained by the reaction of Al-Bi-Cu alloy powders with H₂O for different reaction times, and then the hydrogen generation products were directly sintered at high temperature to obtain Al-Cu alloy based composite phase change thermal energy storage materials. The results indicated that at 50 °C, the hydrogen yield of Al-Bi-Cu alloy powders in 100min, 200min and 400min are 319.9 mL/g, 428.5 mL/g and 665.8 mL/g, respectively. Importantly, the Al-Cu alloy based composite phase change thermal energy storage materials prepared by the hydrogen generation products exhibited an adjustable phase change temperature (577.3 °C ∼ 598.2 °C), high thermal energy storage density (44.1J/g ∼ 153.5J/g), good thermal cycling stability and structural stability.     

Solar-thermal energy conversion and storage of super black carbon reinforced melamine foam aerogel for shape-stable phase change composites

Thermal energy harvesting and storage with phase change materials (PCMs) have attracted extensive exploration in solar-thermal utilization. Solving leakage issue of PCMs and improving the energy absorption, storage and transport are facing great challenges. As a typical aerogel with porous structure and strong light absorption, carbon aerogel (CA) becomes an attractive support material for PCMs. In this work, the carbon aerogels reinforced melamine foam (CA/Foam) were prepared by sol-gel polymerization, freeze drying and carbonization. To further optimize the pore structure and optical properties, CO₂ activation is implemented to obtain the super black reinforced melamine foam, which is named as activated CA/Foam (ACA/Foam). After vacuum adsorption of PW, the prepared paraffin wax/activated carbon aerogel/foam (PW/ACA/Foam) maintains high thermal storage density of 143.4 J/g and shows excellent thermal stability, which can effectively solve the shortcoming of PCMs leakage due to rich pore structure. Encouragingly, the photothermal conversion efficiency of PW/ACA/Foam composite material can reach 92.1% with 5% weight fraction of resorcinol and formaldehyde in the precursor solution. The thermal conductivity of PW/ACA/Foam is 0.71 W/(m·K), 97.2% higher than pure PW, which will be the potential material for composite PCMs applied in solar energy utilization.     

Investigation of hydrogen production potential from different natural water sources in Turkey

Hydrogen production from the electrolysis of water by sea or lake waters used as electrolyte plays a crucial role in providing sustainable hydrogen production. Production of hydrogen from these natural sources is highly utilized from small scale to complex applications due to water resources' inconsumable potential. In this study, the hydrogen production potential of Turkey's different regions such as the Black Sea, Aegean Sea, Marmara Sea, Mediterranean Sea, Lake Van, Ağcaşar Dam, Yeşilırmak, and Kızılırmak rivers are investigated. Solar energy potential values are used as the current sources for simulating their renewable energy hydrogen production values. According to the results, higher hydrogen production rates are obtained from the Marmara and Lake Van regions. It is concluded that the hydrogen production potential is highly dependent on the pH values of the water source and the salinity rate of seawater that is descending from the Mediterranean Sea to the Black Sea region. Besides, solar radiation, sunshine duration, and water temperature are the other essential factors. Moreover, Mediterranean Sea water (Içel-Anamur) has about 23% higher hydrogen production than Lake Van and has the most increased hydrogen production by 80 L m^-2 in May and June.     

The TiO2/Mn0.2Cd0.8S hollow heterojunction with Mn/Cd bimetallic synergy towards photocatalytic hydrogen production enhancement

The TiO₂/Mn_0.2Cd_0.8S hollow heterojunction with Mn/Cd bimetallic synergy is prepared via a continuous chemical-hydrothermal-etching method. There, the TiO₂ shell and Mn_0.2Cd_0.8S nanoparticles were deposited by continuous chemical-hydrothermal method on the surface of SiO₂ template, and subsequently the SiO₂ template was etched via a chemical method. Evaluated by HER, the as-prepared TiO₂/Mn_0.2Cd_0.8S hollow heterojunction exhibits an obvious photocatalytic enhancement to about ~5822.94 μmol/g∙h(~40 folds of TiO₂, ~7 folds of Mn_0.2Cd_0.8S), which can be mainly ascribed to that, the narrow band gap of Mn_0.2Cd_0.8S can increase the visible light energy utilization, the TiO₂/Mn_0.2Cd_0.8S heterojunction and Mn/Cd bimetallic synergy can separate/transfer the photo-generated charge carriers efficiently, and the sufficient specific surface areas and actives from 3D hollow structure can promote the charge carrier diffusing into water quickly for achieving H₂ generation. Additionally, the hollow 3D structure can provide a decent physical-chemical stability to improve the photocatalytic stability.     

氢能制取和储存技术研究发展综述

综述了氢能制取和储存技术研究的最新发展现状。生物质制氢、太阳能热化学循环制氢、太阳能半导体光催化制氢、核能制氢等技术具有资源丰富、使用可再生能源的优点,能克服传统电解水制氢能耗高和矿物原料有限的缺点,成为提高制氢效率、实现规模生产的研究重点。加压压缩储氢技术的研究进展主要体现在改进容器材料和研发吸氯物质方面;液化储氢技术研发重点是降低能耗和成本;金属氢化物储氢技术正努力突破储氢密度低的难题。氢能制取、储存技术正在走向实用阶段,重点技术方向是以水为原料,实现大规模、经济、高效和安全地制氢储氢,推动氢能可持续和洁净的利用,促进能源安全。     

Highly efficient white-LED-light-driven photocatalytic hydrogen production using highly crystalline ZnFe2O4/MoS2 nanocomposites

Designing efficient photocatalytic systems for hydrogen evolution is extremely important from the viewpoint of the energy crisis. Highly crystalline heterostructure catalysts have been established, considering their interface electric field effect and structural features, which can help improve their photocatalytic hydrogen-production activity. In this study, we fabricated a highly crystalline heterojunction consisting of ZnFe₂O₄ nanobricks anchored onto 2D molybdenum disulfide (MoS₂) nanosheets (i.e., ZnFe₂O₄/MoS₂) via a hydrothermal approach. The optimized ZnFe₂O₄/MoS₂ photocatalyst, with a ZnFe₂O₄ content of 7.5 wt%, exhibited a high hydrogen-production rate of 142.1 μmol h⁻¹ g⁻¹, which was 10.3 times greater than that for the pristine ZnFe₂O₄ under identical conditions. The photoelectrochemical results revealed that the ZnFe₂O₄/MoS₂ heterojunction considerably diminished the recombination of electrons and holes and promoted efficient charge transfer. Subsequently, the plausible Z-scheme mechanism for photocatalytic hydrogen production under white-LED light irradiation was discussed. Additionally, the influence of cocatalysts on the photocatalytic hydrogen evolution for the ZnFe₂O₄/MoS₂ heterostructure was investigated. This work has demonstrated a simplified coupling of one-dimensional or zero-dimensional structures with 2D nanosheets for improving the photocatalytic hydrogen production activity as well as confirmed that MoS₂ is a viable substitute for precious metal-free photocatalysis.     

Comparative study of the activity of nickel ferrites for solar hydrogen production by two-step thermochemical cycles

In this work, we compare the activity of unsupported and monoclinic zirconia – supported nickel ferrites, calcined at two different temperatures, for solar hydrogen production by two-step water-splitting thermochemical cycles at low thermal reduction temperature. Commercial nickel ferrite, both as-received and calcined in the laboratory, as well as laboratory made supported NiFe₂O₄, are employed for this purpose. The samples leading to higher hydrogen yields, averaged over three cycles, are those calcined at 700 °C in each group (supported and unsupported) of materials. The comparison of the two groups shows that higher chemical yields are obtained with the supported ferrites due to better utilisation of the active material. Therefore, the highest activity is obtained with ZrO₂-supported NiFe₂O₄ calcined at 700 °C.     

Photoelectrocatalytic hydrogen production of heterogeneous photoelectrodes with different system configurations of CdSe nanoparticles,Au nanocrystals and TiO2 nanotube arrays

The different configurations of CdSe nanoparticles, Au nanocrystals and TiO₂ nanotube arrays play an important role in the photoelectrochemical behavior and photoelectrocatalytic hydrogen production of this heterogeneous photoelectrode system. It is discovered that the photoelectrocatalytic hydrogen production of the TiO₂–CdSe–Au photoelectrode (1.724 mmol g⁻¹ h⁻¹) is about 4 times that of the TiO₂–Au–CdSe photoelectrode (0.430 mmol g⁻¹ h⁻¹) under visible light irradiation. From the comprehensive investigation of their photoelectrochemical behaviors, it is illustrated that the interfacial electrical field has distinct effects on the separation and transportation of photogenerated carriers in these heterostructure photoelectrodes. The directions of the interfacial electrical fields formed at TiO₂–Au and Au–CdSe interfaces are opposite in the TiO₂–Au–CdSe photoelectrode, which hinders the separation of photogenerated electron-hole pairs and subsequent transportation of photogenerated carriers. On the contrary, the directions of the interfacial electrical fields formed at TiO₂–CdSe and CdSe–Au interfaces are identical in the TiO₂–CdSe–Au photoelectrode, which promotes the separation of photogenerated excitons and subsequently enhances their transportation for enlarged photocurrent density. The results of photoelectrocatalytic hydrogen production also confirm our assumption.     

Facile synthesis and electrochemical hydrogen storage of bentonite/TiO2/Au nanocomposite

In this study, the electrochemical hydrogen storage of bentonite composites containing TiO₂ and Au nanoparticles (NPs) has been investigated by cyclic voltammetry (CV) analysis. TiO₂ NPs were first deposited on the bentonite substrate by reflux technique. Au NPs were then prepared by laser ablation in liquid (LAL) method under different laser irradiation times (6, 12, and 18 min), and utilized in the decoration of bentonite/TiO₂ nanocomposite by physical mixing. X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and elemental mapping were carried out in the characterization of the prepared bentonite/TiO₂/Au nanocomposite. The surface and chemical properties of the acquired nanocomposite were analyzed by Brunauer-Emmett-Teller and Fourier transform infrared spectroscopy, respectively. Electrochemical measurement was performed on stainless steel mesh prefabricated electrodes in 1 M KOH electrolyte solution. The B-T/Au nanocomposite prepared under 12 min laser irradiation displayed the highest hydrogen storage capacity (15 Cg^-1).     

Green synthesis of well dispersed TiO2/Pt nanoparticles photocatalysts and enhanced photocatalytic activity towards hydrogen production

Deposition of Pt NPs with preferred dispersion and morphologies on TiO₂ have been the focus of studies in photocatalytic and photoelectrochemical hydrogen production. Green synthesis of TiO₂/Pt NPs nanocomposites with narrow size distribution of Pt NPs still remain a challenge. Herein, we report that sucrose is highly efficient for the preparation of well-dispersed TiO₂/Pt NPs photocatalysts. Moreover, the sucrose could act as an electron donor, showing higher hydrogen production activity under simulated sunlight than pure water. The as-synthesized photocatalysts have been characterized by techniques of transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX), and diffuse reflectance spectroscopy (DRS). Compared with TiO₂/Pt NPs photocatalysts prepared through conventional photodeposition, the photocatalysts as prepared showed higher photocatalytic efficiency. Moreover, the catalyst could be reused easily without apparent degradation of their original photocatalytic activities. This approach presents a promising and low-cost strategy to improve the photocatalytic performance of TiO₂ from biomass.     

Visible light-driven photothermal Au/Ag/TiO2 trihybrid plasmonic nanomaterial for synthetic fuel production

In the present article, a new numerical investigation is conducted to quantify the fluidic flow-photothermal performance of a trihybrid nano-catalyst for biomethane reforming inside a 1 μm micro-reactor on gold-silver nanoparticles coated on titanium oxide (TiO₂). The model generates a two-way coupling between heat, mass, fluid flow and electromagnetic profiles to simulate the plasmonic effect for the plasmonic photocatalyst in a micro-boundary layer adjacent to the catalyst. The effect of light wavelength on operating parameters and system performance was investigated and discussed. This included chemical conversion, the lower heating value of the syngas, mole fractions of species in the gaseous product, and the spatiotemporal velocity profiles. It was found that light absorptance by the nanoparticles is highest when visible light wavelength within 570 nm < λ < 590 nm is used to stimulate the plasmonic nanostructure. Also, the chemical conversion reached 81% at an exposure time of 1 μs of visible light. At λ = 570 nm, the produced syngas had a lower heating value of 311 kJ/mol and syngas quality of 0.16, which is suitable for ethanol production. Also, a maximum temperature elevation of 998 K was achieved which is above the minimum temperature required for reforming methane (823 K). The spatiotemporal velocity and chemical conversion profiles across the micro-reactor showed that at exposure times > 5 μs, both profiles become fully developed resulting in the suppression of chemical conversion.     

CuO@NiO core-shell nanoparticles decorated anatase TiO2 nanospheres for enhanced photocatalytic hydrogen production

Core-shell structured co-catalyst has been created much attention in photocatalytic hydrogen production due to their efficient electron-hole pair separation, suppression of surface back reaction and long term stability. Here, we report the preparation of CuO@NiO hierarchical nanostructures as a co-catalyst deposited on TiO₂ nanospheres for enhanced photocatalytic hydrogen generation. The formation of ultrathin NiO shell over the CuO core was confirmed by TEM analysis. Fabricated core-shell nanostructured CuO@NiO over TiO₂ nanospheres was studied for hydrogen evolution under the direct solar light and it showed a high rate of H₂ production of 26.1 mmol. h⁻¹. g⁻¹_cat. It was scrutinized that the rate of hydrogen production was improved with shell thickness and co-catalyst loading. Systematic investigation on CuO@NiO co-catalyst loading, pH of the medium and glycerol concentration for augmented H₂ production. The recorded rate of hydrogen production is almost six folds greater than that of pristine TiO₂. In the view of largescale synthesis for alternative energy storage applications, the composited photocatalyst was made of by simple mixing method, which could be scaled up without any loss in photocatalytic activity. Further, the stability test of photocatalyst for continuous use found that 82% of initial photocatalytic activity is retained even after three days.     

Facile synthesis of MoS2 QDs/TiO2 nanosheets via a self-assembly strategy for enhanced photocatalytic hydrogen production

The MoS₂ quantum dots (QDs) were interspersed on anatase TiO₂ nanosheets with exposed (001) facets by a facile self-assembly strategy. As expected, the MoS₂ QDs/TiO₂ nanosheets display an excellent photocatalytic performance for hydrogen production, and its hydrogen evolution rate is 139 μmol/h/g. More importantly, the hydrogen evolution rate of MoS₂ QDs/TiO₂ nanosheets is almost 4-fold in comparison to that of nude TiO₂ nanosheets. Based on the detailed characterizations, it can be obtained that the improved photocatalytic activity for hydrogen production can be ascribed to the particular characteristics of MoS₂ QDs, which can intensify the photo-absorption efficiency of TiO₂ nanosheets and enhance the separation and transfer efficiency of photo-excited charge carriers. It is anticipated that this work provides a novel paradigm to fabricate the highly-efficient photocatalysts for hydrogen evolution.     

A review on photoelectrochemical hydrogen production systems: Challenges and future directions

Water photolysis is a fundamental concept in which solar-driven water splitting is utilized to generate renewable hydrogen fuel using semiconductor-based electrochemical systems. The engineering design principles for each system configuration, including single, dual/tandem photoelectrodes, tandem photoelectrochemical-photovoltaic, and multi-junction designs are reviewed. Modeling and numerical simulation of photoelectrochemical processes based on up-to-date multi-scale analysis are presented and discussed. In addition, the achievements made in semiconductor photoelectrode materials and the rational engineering methods needed to improve the solar to hydrogen efficiency are demonstrated. Furthermore, some key accomplishments in different aspects, such as electron-hole recombination, stability, photocorrosion, energy band gap, and photocurrent density are discussed. Moreover, key points on the challenges, opportunities and future directions towards commercialization of viable photoelectrochemical reactors are discussed.