Solar Hydrogen Generation Research Articles

Design and Development of Novel Nanostructured Visible-Light Active Photoelectrodes based on TiO2 Nanorods for Solar Hydrogen Generation

Design and Development of Novel Nanostructured Visible-Light Active Photoelectrodes based on TiO2 Nanorods for Solar Hydrogen Generation

Multi-objective optimization configuration of wind-solar coupling hydrogen production system

The existing research on the wind solar coupling hydrogen generation system lacks the evaluation of factors such as the reliability of power supply to the microgrid system. This paper establishes a multi-objective optimization configuration model of wind-solar coupling hydrogen generation system under grid-connected operation mode for hydrogen generation. From the perspective of system economy and stability analysis, the model optimizes the capacity of the wind power unit, photovoltaic unit, energy storage unit, and hydrogen generation unit to improve the economy and reliability of microgrid operation, to minimize load loss rate, system annual cost, renewable energy power generation loss rate, and energy surplus rate.

Bulk Embedding of Ferroelectric Nanodomains in CuBi2O4 Photocathodes Enables Boosted Photoelectrochemical Hydrogen Generation

AbstractIt is widely accepted that metal oxide‐based photoelectrodes (MOPs) hold great promise for future solar hydrogen generation but are facing awkward challenge arising from their low intrinsic carrier mobility. The highly polarized nature of the predominantly ionic metal‐oxygen bond always leads to the formation of small polarons that are responsible for the localized trapping of photo‐generated carriers. Present study explores the reduction of carriers transport barrier via bulk embedding of ferroelectric nanodomains (FNDs) in MOPs that results in a new performance benchmark for the CuBi2O4 photocathode. By embedding laser‐generated sub‐10 nm BaTiO3 nanocrystals in the bulk of CuBi2O4 photocathode, numerous FNDs are created that can lead to two times enhancement of the carrier mobility, which is proposed to originate from the overlaying of the internal electric fields and effective electrons transport channel at the heterointerfaces of BaTiO3/CuBi2O4. Such strategy leads to the CuBi2O4 photocathode with the photocurrent density of up to 3.21 mA cm−2 at 0.6 VRHE, as well as a pronounced absorbed photon‐to‐current efficiency up to 80% at 400 nm. The universal feature of present technology is further verified by laser embedding of SrTiO3 FNDs, providing an effective route for addressing the charge transport limitations in MOPs.

MOF-Derived In2 O3 /CuO p-n Heterojunction Photoanode Incorporating Graphene Nanoribbons for Solar Hydrogen Generation.

Solar-driven photoelectrochemical (PEC) water splitting is a promising approach toward sustainable hydrogen (H2 ) generation. However, the design and synthesis of efficient semiconductor photocatalysts via a facile method remains a significant challenge, especially p-n heterojunctions based on composite metal oxides. Herein, a MOF-on-MOF (metal-organic framework) template is employed as the precursor to synthesize In2 O3 /CuO p-n heterojunction composite. After incorporation of small amounts of graphene nanoribbons (GNRs), the optimized PEC devices exhibited a maximum current density of 1.51mA cm-2 (at 1.6V vs RHE) under one sun illumination (AM 1.5G, 100mW cm-2 ), which is approximately four times higher than that of the reference device based on only In2 O3 photoanodes. The improvement in the performance of these hybrid anodes is attributed to the presence of a p-n heterojunction that enhances the separation efficiency of photogenerated electron-hole pairs and suppresses charge recombination, as well as the presence of GNRs that can increase the conductivity by offering better path for electron transport, thus reducing the charge transfer resistance. The proposed MOF-derived In2 O3 /CuO p-n heterojunction composite is used to demonstrate a high-performance PEC device for hydrogen generation.

Carbon Vacancy-Modified Carbon Nitride Allotropic Composite for Solar Hydrogen Generation Coupled with Selective Oxidation of 5-Hydroxymethylfurfural

Carbon Vacancy-Modified Carbon Nitride Allotropic Composite for Solar Hydrogen Generation Coupled with Selective Oxidation of 5-Hydroxymethylfurfural

Engineering of direct Z-scheme ZnIn2S4/NiWO4 heterojunction with boosted photocatalytic hydrogen production

Exploring efficient and robust photocatalysts for solar hydrogen generation from water reduction is great significant in solving the energy shortage and environment contamination simultaneously. Herein, benefiting from the matchable energy band structures and band bending, the direct Z-scheme ZnIn2S4/NiWO4 heterojunctions were successfully constructed by anchoring p-type NiWO4 nanoparticles onto n-type ZnIn2S4 nanosheets through a facile sonochemical route. By carefully regulating the interfacial structure, the optimized ZnIn2S4/NiWO4 heterostructure without any cocatalyst displays excellent stability and remarkably improved photocatalytic hydrogen evolution activity (16.3 mmol∙g−1∙h−1), more 3.57-folds increment than bare ZnIn2S4 photocatalyst. Mechanistic characterizations demonstrate that the dramatically boosted photocatalytic performance mainly results from the constructed Z-scheme heterostructure and intimately interfacial contact between ZnIn2S4 and NiWO4, which results in the valid interfacial charge transfer channels, powerful redox potential and reduced hydrogen evolution energy barrier, as confirmed by the joint analysis of electron spin resonance (ESR) and photoelectrochemical measurements. More importantly, the photoinduced holes of ZnIn2S4 are rapidly and effectively consumed in the unique Z-scheme charge transfer channels, which greatly favors the suppression of the photocorrosion caused by insufficient hole extraction during the photocatalytic reaction, thereby promoting the overall stability and reusability of the ZnIn2S4/NiWO4 composite photocatalyst. This study paves the way for constructing other Z-scheme nano-heterostructure consisting of p-type and n-type semiconductors with efficient photoactivity and robust stability for energy and environmental applications.

Atomic-Level Regulated 2D ReSe2 : A Universal Platform Boostin Photocatalysis.

Solar hydrogen (H2 ) generation via photocatalytic water splitting is practically promising, environmentally benign, and sustainably carbon neutral. It is important therefore to understand how to controllably engineer photocatalysts at the atomic level. In this work, atomic-level engineering of defected ReSe2 nanosheets (NSs) is reported to significantly boost photocatalytic H2 evolution on various semiconductor photocatalysts including TiO2 , CdS, ZnIn2 S4 , and C3 N4 . Advanced characterizations, such as atomic-resolution aberration-corrected scanning transmission electron microscopy (AC-STEM), synchrotron-based X-ray absorption near edge structure (XANES), in situ X-ray photoelectron spectroscopy (XPS), transient-state surface photovoltage (SPV) spectroscopy, and transient-state photoluminescence (PL) spectroscopy, together with theoretical computations confirm that the strongly coupled ReSe2 /TiO2 interface and substantial atomic-level active sites of defected ReSe2 NSs result in the significantly raised activity of ReSe2 /TiO2 . This work not only for the first time realizes the atomic-level engineering of ReSe2 NSs as a versatile platform to significantly raise the activities on different photocatalysts, but, more importantly, underscores the immense importance of atomic-level synthesis and exploration on 2D materials for energy conversion and storage.

Investigating the Electronic Structure of Prospective Water-Splitting Oxide BaCe0.25Mn0.75O3−δ before and after Thermal Reduction

BaCe$_{0.25}$Mn$_{0.75}$O$_{3-\delta}$ (BCM), a non-stoichiometric oxide closely resembling a perovskite crystal structure, has recently emerged as a prospective contender for application in renewable energy harvesting by solar thermochemical hydrogen generation. Using solar energy, oxygen-vacancies can be created in BCM and the reduced crystal so obtained can, in turn, produce H2 by stripping oxygen from H2O. Therefore, a first step toward understanding the working mechanism and optimizing the performance of BCM, is a thorough and comparative analysis of the electronic structure of the pristine and the reduced material. In this paper, we probe the electronic structure of BCM using the combined effort of first-principles calculations and experimental O K-edge x-ray absorption spectroscopy (XAS). The computed projected density-of-states (PDOS) and orbital-plots are used to propose a simplified model for orbital-mixing between the oxygen and the ligand atoms. With the help of state-of-the-art simulations, we are able to find the origins of the XAS peaks and to categorize them on the basis of contribution from Ce and Mn. For the reduced crystal, the calculations show that, as a consequence of dielectric screening, the change in electron-density resulting from the reduction is strongly localized around the oxygen vacancy. Our experimental studies reveal a marked lowering of the first O K-edge peak in the reduced crystal which is shown to result from a diminished O-2p contribution to the frontier unoccupied orbitals, in accordance with the tight-binding scheme. Our study paves the way for investigation of the working-mechanism of BCM and for computational and experimental efforts aimed at design and discovery of efficient water-splitting oxides.

MoS2 Nanostructures for Solar Hydrogen Generation via Membraneless Electrochemical Water Splitting

Storing and delivering green hydrogen generated by solar energy have the potential to significantly supplement and disburse the share of promising but intermittent renewable energy. In this scenario, robust materials capable of delivering solar-driven electrochemical water splitting for hydrogen generation provide an interesting protocol that is applicable to all sectors of energy. Electrochemical water splitting is the conventional and most prevalent technique for hydrogen generation, which utilizes platinum-based materials for the hydrogen evolution reaction (HER). However, these platinum-based noble metal catalysts possess poor cyclic stability, limiting their commercial application for economical hydrogen generation. Therefore, the development of efficient non-noble metal-based electrocatalysts is urgently needed to produce cost-competitive hydrogen energy. Several kinds of non-noble metal-based heterogeneous electrocatalysts, including carbides, sulfides, selenides, oxides, and phosphides, have been developed and studied. The unique physicochemical properties of carbonaceous materials make them promising candidates to support catalysts. In this paper, molybdenum disulfide (MoS2) nanomaterial catalysts have been synthesized, deposited on carbon fiber (CF)-based materials, and then used for solar hydrogen generation by membraneless electrochemical water splitting. At 430 W/m2 irradiation and 35 °C working temperature, the solar-to-hydrogen conversion efficiency is found to be 2.46%.

TiO2 passivation layers with laser derived p-n heterojunctions enable boosted photoelectrochemical performance of α-Fe2O3 photoanodes

Addressing the carrier loss at the semiconductor-liquid junction of metal oxides is of significance for developing high-performance photoelectrodes for viable solar hydrogen generation, while one of the critical challenges remains in pursuing the top passivation layer with pronounced carrier extraction capability. In the present work, we propose and experimentally verify that artificial engineering of the passivation layer via laser embedding of p-n heterointerfaces leads to significantly improved carrier transfer. By virtue of the advantage of generating nanocrystals in any desired solvents via the technology of laser synthesis and processing of colloids (LSPC), p-type CdTe nanocrystals are successfully embedded in a thin layer of TiO2, which is adopted as an efficient passivation layer to address the excessive surface defects and the slow carrier transfer at α-Fe2O3 photoanodes. The embedded p-n heterointerfaces not only provide an effective built-in electric field that accelerates carrier transport in TiO2 via boosting polaron hopping but also activate hole transfer by shifting up the valence band in TiO2. Such vivid embedding is demonstrated to generate a 12-fold increase for the lifetime of photogenerated electrons, and a 3.9-fold increase for the ηinj at 1.23 VRHE, leading to a 4.4-fold increase in the photocurrent density at 1.23 VRHE. We thus believe the present work provides a universal alternative for regulating the chemical/physical features of semiconductor-liquid junctions at metal oxides.

Stepwise photoassisted decomposition of carbohydrates to H2

Stepwise photoassisted decomposition of carbohydrates to H2

Photocatalytic Overall Water Splitting by SrTiO3: Progress Report and Design Strategies

Overall water splitting (OWS) using particulate photocatalysts is a promising and straightforward route for producing sustainable and clean hydrogen. Strontium titanate (SrTiO3) is a well-documented photocatalyst in both one-step and two-step (Z-scheme) water splitting systems and presents state-of-the-art activities. Nevertheless, SrTiO3 still has inherent restraints, such as structural imperfections and insufficient optical absorption ability. This critical review summarizes the recent progress in photocatalytic overall water splitting using SrTiO3 photocatalyst, primarily focusing on the modification techniques that are being used to alleviate its drawbacks. Concretely, we outline cocatalyst loading, crystal-facet engineering, reduction of bulk defects, heteroatom doping, and constructing Z-Scheme water splitting systems. Following that, recent efforts in developing photocatalyst sheets and panel reactors for large-scale photocatalytic hydrogen generation are discussed. Lastly, current challenges regarding solar hydrogen generation by SrTiO3 photocatalyst are concluded, and future scope is proposed. The knowledge gained here may also be useful for developing other efficient photocatalysts.

Latest avenues on solar light-driven photocatalytic hydrogen generation using surface modified nanomaterials towards sustainable environment and circular bioeconomy

The developing interest in energy has started to work to our advantage in growing clean and electrified energy sources to supplant oil-based commodities.The global use of petroleum derivatives is increasing at an alarming and unsustainable rate, resulting in environmental damage such as releasing toxic contaminants and greenhouse gases. Nanomaterials constantly changing in their configuration may be required to a transition to a green energy-based economy. The photocatalytic water splitting method holds promise for producing hydrogen quickly and effectively. Solar energy can split water to create hydrogen, making it a valuable renewable energy source.Either co-catalysts or dopants have been added to the current photocatalysts for improvement. In this article, novel nanophotocatalysts for rational hydrogen synthesis and modified photocatalysts are discussed. The results can highlight the synthesis of nanostructured materials that demonstrate favorable catalytic properties, which can be achieved as alternative and stable catalysts for efficient hydrogen production withoutmuch environmental adverseimpacts.

Comparative techno-economic analysis of different PV-assisted direct solar hydrogen generation systems

This work provides a robust technoeconomic analysis of a range of direct solar hydrogen generation (DSHG) systems to understand the opportunities and challenges of deploying DSHG to reduce the cost of renewable hydrogen production.

Effect of charge selective contacts on the quasi Fermi level splitting of CuGa3Se5 thin film photocathodes for hydrogen evolution and methylviologen reduction

The defect-copper chalcopyrite CuGa3Se5 is a promising photocathode material for solar hydrogen generation. Here we assess its performance with photoelectrochemical measurements and vibrating Kelvin probe surface photovoltage spectroscopy.

Strategies for reducing the overpotential of one-dimensional Si nanostructured photoelectrodes for solar hydrogen production

Strategies to reduce the overpotential of 1D silicon nanostructured photoelectrodes for solar hydrogen generation: co-catalysts to improve the reaction kinetics, hetero- and homo-junctions to improve carrier collection and enhance photovoltage.

Strain Modulated Electronic and Photocatalytic Properties of MoS2/WS2 Heterostructure: A DFT Study

Solar energy-driven hydrogen generation through the water-splitting (WS) method is an efficient approach to conquer the worldwide energy shortage in the near future and environmental pollution by employing a suitable semiconductor photocatalyst. Herein, structural, electronic, and photocatalytic properties of MoS2/WS2 heterobilayer are thoroughly inspected with biaxial strain for their use in WS applications. Furthermore, among the six considered stacking patterns of the heterostructure (HS), conf-1 has the most stable structure due to its lowermost interlayer binding energy of −18.07 meV/Å2. In addition, MoS2/WS2 HS shows type II band alignments, where MoS2 contributes to the conduction band minima (CBM), and the WS2 monolayer is located at valence band maxima (VBM) positions, respectively, in the HS. Moreover, owing to the smaller effective mass values of the HS than to the constituent monolayers, MoS2/WS2 HS has excellent carrier mobility, which further suggests faster migration of charge carriers and a lower recombination rate during the WS process. An enhanced visible light absorption intensity of 8.3 × 105 cm–1 has been observed for the HS rather than the MoS2 (6.33 × 105 cm–1) and WS2 (7.51 × 105 cm–1) monolayers. The HSs under the biaxial tensile strain of 1% and compressive strain up to 4% are attended suitable CBM and VBM positions with water reduction (WRP) and oxidation potentials (WOP) that are appropriate for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Moreover, under tensile strain, the absorption edges of HS are moderately red-shifted, which makes it as a potential candidate for solar energy harvesting. Our findings open a new research interest in exploring these kinds of 2D vdW HSs experimentally for a WS mechanism, and modulation of their activity can be done by external strain.

Enhanced solar hydrogen generation with the direct coupling of photo and thermal energy – An experimental and mechanism study

The complementary use of solar light and heat to overcome respective drawbacks, such as low solar spectral utilization in photocatalysis and light-to-heat conversion in thermochemistry has been a popular research topic. The photo-thermochemical synergy effect of solar hydrogen production with methanol steam reforming reactions using Cu/ZnO/Al2O3 catalyst is experimentally investigated in this study. Solar energy directly shines onto the surface of the catalyst, causing the synergistic effect of light and heat. Experimental results show that the photo-thermochemical reaction can reduce the reaction temperature by more than 10 °C at 188 °C compared with the thermochemical reaction, while increasing hydrogen production by 32.9%. Further mechanism studies show that hot electrons excited by the irradiation of sunlight on Cu and ZnO promote the production of the key intermediates (hydroxyl groups) in the process of the thermochemical methanol steam reforming, which can explain the increase in hydrogen yield under photo-thermochemical conditions. These findings are different from thermochemical reactions, and provide a new route for mid-and-low temperature hydrogen production.

Highly efficient sputtered Ni-doped Cu2O photoelectrodes for solar hydrogen generation from water-splitting

Hydrogen gas can be converted to electricity through fuel cells and is considered as a friendly energy source. Herein, pure Cu2O and Ni-doped Cu2O thin films were deposited on glass substrates using the RF/DC-sputtering technique for hydrogen production via the photoelectrochemical (PEC) water-splitting process. The preferred orientation for pure and Ni-doped Cu2O films was (111) crystallographic plane. The average nanograins size was decreased from 32.17 nm for pure to 10.40 nm through the doping process with Ni content. Field-emission scanning electron microscopy (FE-SEM) and ImageJ analysis showed that the pure Cu2O and Ni-doped Cu2O were composed of normal distribution of nanograins in a regular form. The optical bandgap of the Cu2O film was decreased from 2.35 eV to 1.9 eV after doping with 2.6 wt% of Ni-dopants. The photoluminescence (PL) spectra for all the sputtered films were recorded at room temperature to examine the effect of Ni-dopants in the Cu2O lattice. Pure and Ni-doped Cu2O films were applied for PEC water splitting for hydrogen (H2) production under white light and monochromatic illumination. The PEC studies displayed that increasing the Ni content up to 2.6 wt% in the pure Cu2O films led to an increase in the photocurrent density to reach −5.72 mA/cm2. The optimum photoelectrode was studied for reproducibility, stability, and electrochemical impedance. The incident photon to current conversion efficiency (IPCE%) was 16.35% at 490 nm, and the applied bias photon to current conversion efficiency (ABPE%) was 0.90% at 0.65 V. Consequently, Ni-doped Cu2O photoelectrodes are efficient and low-cost for practical and industrial solar H2 production.

Photocatalytic Water Splitting: How Far Away Are We from Being Able to Industrially Produce Solar Hydrogen?

Solar water splitting (SWS) has been researched for about five decades, but despite successes there has not been a big breakthrough advancement. While the three fundamental steps, light absorption, charge carrier separation and diffusion, and charge utilization at redox sites are given a great deal of attention either separately or simultaneously, practical considerations that can help to increase efficiency are rarely discussed or put into practice. Nevertheless, it is possible to increase the generation of solar hydrogen by making a few little but important adjustments. In this review, we talk about various methods for photocatalytic water splitting that have been documented in the literature and importance of the thin film approach to move closer to the large-scale photocatalytic hydrogen production. For instance, when comparing the film form of the identical catalyst to the particulate form, it was found that the solar hydrogen production increased by up to two orders of magnitude. The major topic of this review with thin-film forms is, discussion on several methods of increased hydrogen generation under direct solar and one-sun circumstances. The advantages and disadvantages of thin film and particle technologies are extensively discussed. In the current assessment, potential approaches and scalable success factors are also covered. As demonstrated by a film-based approach, the local charge utilization at a zero applied potential is an appealing characteristic for SWS. Furthermore, we compare the PEC-WS and SWS for solar hydrogen generation and discuss how far we are from producing solar hydrogen on an industrial scale. We believe that the currently employed variety of attempts may be condensed to fewer strategies such as film-based evaluation, which will create a path to address the SWS issue and achieve sustainable solar hydrogen generation.