Hydrogen Energy Applications Research Articles

Design and modulation principles of molybdenum carbide-based materials for green hydrogen evolution

The green production of hydrogen from electrocatalytic water splitting is an important base and promising direction for the future of the large-scale application of hydrogen energy. The key of green hydrogen evolution depends on the development of low-cost and highly active electrocatalysts. Molybdenum carbides (MoxC), as a typical of earth-abundant transition-metal material, have accumulated great attention due to their low cost, earth abundance, electrical conductivity, similar d-band state to Pt, and regulated morphology/electronic structures. In this paper, recent researches focusing on MoxC for efficient HER in a wide pH range are summarized from respects of modulation of unique morphology, electronic structure, and electrode interface step by step. Briefly, modulation of morphology influence the apparent activity of catalyst, modulation of electronic structure of active sites by heteroatom doping and designing heterointerface boost intrinsic HER kinetics, and modulation of electrode interface via hybridization of MoxC structures with carbon materials can ensure the fast electron transfer and boost the activity. Besides the above methods discussed, perspective and challenges of designing MoxC as the substitute of Pt-based electrocatalyst for practical hydrogen generation in a wide pH range are pointed out.

Surface-Modified Titanium Dioxide Nanofibers with Gold Nanoparticles for Enhanced Photoelectrochemical Water Splitting

High-stability, high-efficiency, and low-cost solar photoelectrochemical (PEC) water splitting has great potential for hydrogen-energy applications. Here, we report on gold/titanium dioxide (Au/TiO2) nanofiber structures grown directly on a conductive indium tin oxide substrate, and used as photoelectrodes in PEC cells for hydrogen generation. The titanium dioxide nanofibers (TiO2 NFs) are synthesized using electrospinning, and are surface-modified by the deposition of gold nanoparticles (Au NPs) using a simple photoreduction method. The structure and morphology of the materials were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The surface plasmon resonance (SPR) of the Au NPs was investigated by ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy. The PEC properties of the as-prepared photoelectrodes were measured. The obtained photoconversion efficiency of 0.52% under simulated-sunlight illumination by a 150 W xenon lamp of the Au/TiO2 NFs structure with 15 min UV irradiation for Au NP deposition was the highest value from comparable structures. Working photoelectrode stability was tested, and the mechanism of the enhanced PEC performance is discussed.

Oxygen vacancy excites Co3O4 nanocrystals embedded into carbon nitride for accelerated hydrogen generation

Highly active and robust non-noble metal catalysts are the key to large-scale application of hydrogen energy. In this article, abundant oxygen vacancies are injected into Co3O4 nanocrystals by controlling oxidation. These Co3O4 nanocrystals with oxygen vacancies are embedded into carbon nitride sheets. In the hydrolysis of ammonia borane, oxygen vacancies boost Co3O4 nanocrystalline catalyst to exhibit an outstanding catalytic activity. The hydrogen generation rate reaches up to 11,410 mL min−1 gCo−1 (313 K) owing to the presence of oxygen vacancies in Co3O4. In the stability tests, Co-CN-O-100 still maintains excellent catalytic activity with a specific rate of 9070 mL min−1 gCo−1 (80 %) after five cycles. The carbon nitride retards the growth of Co3O4 NCs and prevents active components from leaching. An oxygen vacancy-relating catalytic mechanism is proposed for the acceleration of rate-determining step of hydrolysis of ammonia borane according to a density functional theory simulation. This work makes a demonstration for the potential of oxygen vacancies in the development of energy catalysis.

Low-temperature hydrogen release through LiAlH4 and NH4F react in Et2O

The application of hydrogen energy urgently requires a high-capacity hydrogen storage technology that can release hydrogen at low temperature. The composite of LiAlH4 and NH4F has a hydrogen storage capacity of up to 8.06 wt%, but the release of hydrogen requires a reaction temperature of about 170 °C, and the reaction is difficult to control. In this work, the reaction between LiAlH4 and NH4F is proposed to be carried out in diethyl ether to improve its hydrogen release performance. It exhibits good hydrogen release performance over a wide temperature range of −40–25 °C, and the hydrogen release capacity at −40 °C, −20 °C, 0 °C and 25 °C can reach 4.41 wt%, 6.79 wt%, 6.85 wt% and 7.78 wt%, respectively. The activation energy of the reaction is 38.41 kJ mol−1, which is much lower than many previously reported catalytic hydrolysis systems that can release hydrogen at room temperature. Our study demonstrates a high-performance hydrogen storage system with very low operating temperature, which may lay the foundation for the development of practical mobile/portable hydrogen source in the north and the Arctic.

Facile synthesis and characterization of nano-Pd loaded NiCo microfibers as stable catalysts for hydrogen generation from sodium borohydride

Development of low-cost and high-efficiency catalysts for hydrogen generation represents the significant challenge for realizing hydrogen economy. NiCo and nano-Pd loaded NiCo microfibers with high surface area has been successfully developed by electrospinning and following vacuum thermal treatment. Towards hydrogen generation, the catalyst exhibits efficient TOF as high as 350 and 680 mL min−1 gcat−1 for NiCo and nano-Pd loaded NiCo microfibers, providing superior performance compared with the most promising reported catalysts. The excellent catalytic activity remain above 90% confirming the remarkable durability. The insights uncovered here inspire and guide the rational design of advanced catalysts for the rapidly developing hydrogen energy applications.

Increasing operational flexibility of integrated energy systems by introducing power to hydrogen

Owing to the limited operating regions of combined heat and power (CHP) units, the operation of integrated energy systems suffers from low flexibility, low-cost efficiency, renewable curtailment etc. Meanwhile, as the capacity of renewable energies keeps growing and integrating into power systems, various methods, such as installing electric boilers to enable electricity-heat conversion, have been developed to absorb excessive renewables and increase system operation flexibility. To further increase the system operation flexibility, this study explores the possibilities of utilising electrolysers and hydrogen storage tanks to enable electricity-hydrogen-heat conversion. To better visualise the enhanced flexibility, this study presents extra flexibilities from electric boilers, electrolysers and hydrogen tanks as the equivalent operating region expansion for CHP units. In this study, the system is modelled as a mixed-integer optimisation problem which balances the electricity, heat and hydrogen demands in a 24-hour period. A 6-bus test system is used in the case studies to illustrate the effectiveness of implementing electrolysers and hydrogen storage tanks. The optimisation results show the application of hydrogen energy improves the system operation flexibility, reduces wind curtailment, thereby decreasing fuel consumption and carbon emission.

A Survey of Hydrogen Energy and I-Energy Applications: Household Intelligent Electrical Power Systems

I-energy and its applications used in the smart grid are chosen as attractive research issues due to their widespread applications in the smart home. In this vein, the optimization of energy demand in smart home appliances, in a smart grid, is considered the main challenge faced by power companies during peak periods regarding its considerable effect on the global power system stabilities. Therefore, this paper aims to show explicitly the performance of smart grid on electricity and hydrogen applications with reused communication methods. To facilitate the understanding of the communication-reused methods in the smart grid, several components are identified and presented in terms of improvements, benefits and lack of features. In the smart grid, most innovation communications are being used as wireline and wireless bundle, where the main features are aggregated. Indeed, reducing consumers’ electricity bills in smart home electrical systems relies on increasing the relationship between the highest energy demand and annual energy use. The most appropriate research has been reviewed on optimization approaches discussing the smart home electric system. The examined methods are categorized into trustworthy and metaheuristic algorithms.

LaFeO3 synthesised by solid-state method for enhanced sorption properties of MgH2

Environment pollution becomes more serious in recent years. Thus, hydrogen energy has been considered as a suitable energy carrier due to its renewability, clean and environmentally friendly. In the application of hydrogen energy, there are problems in the storage which need to be solved. Therefore, the aim of this research is to enhance the hydrogen storage performance of MgH2 by the addition of LaFeO3 as a catalyst through ball milling technique. The result showed that the LaFeO3-doped MgH2 appeared to have a better performance on the sorption properties compared to the MgH2 samples. For the onset desorption temperature, the temperature was reduced from 420 °C (as received MgH2) to 300 °C (LaFeO3-doped MgH2). In addition, the LaFeO3-doped MgH2 sample was able to desorb about 3.7 wt% of H2 within 15 min at 320 °C, while the undoped sample just released 1.4 wt% of H2 under the same condition. For the absorption kinetics, the LaFeO3-doped MgH2 and milled MgH2 sample had absorbed about 6.1 wt% and 4.1 wt% of H2 within 30 min, respectively. The activation energy of the doped sample showed a reduction to 107 kJ/mol, which revealed an improvement in kinetics. The existence of in situ MgO, La2O3 and Fe strongly affected the hydrogenation performance of MgH2 that led to the enhancement of the hydrogen storage properties of MgH2.

Nanoscale zinc oxide based heterojunctions as visible light active photocatalysts for hydrogen energy and environmental remediation

ABSTRACT In the recent years, zinc oxide has emerged as one of the promising alternate materials to titania for photocatalytic applications due to its several advantages properties. This review recapitulates the ongoing advancement in the field of ZnO-based heterojunctions as visible light responsive photocatalysts for energy conversion (hydrogen evolution) and environmental remediation (pollutants degradation) applications. After a short introduction about zinc oxide materials, the various approaches utilized in the design and development of efficient ZnO-based nanoheterostructures has been discussed in detail. Specifically, strategies such as coupling ZnO with other semiconductors, supporting on carbonaceous materials, decorating with noble metal nanoparticles, doping with heteroatoms and engineering defects in the semiconductor material have been elaborated with a particular emphasis on hydrogen energy and organic pollutants removal. Finally, the future perspective of this material has been highlighted. This comprehensive review not only summarizes the recent literature in this topic, but also provides a detailed insight on the scope of this material for hydrogen energy and environmental remediation applications.

Fabrication of CdS@1T-MoS2 core-shell nanostructure for enhanced visible-light-driven photocatalytic H2 evolution from water splitting

Abstract CdS@1T-MoS2 composites with core-shell structure were synthesized through a hydrothermal treatment followed by a solvothermal treatment. Nanosized CdS particles were coated by a thin 1T-MoS2 shell to form efficient heterojunction, as demonstrated by transmission electron microscopy images and X-ray photoelectron spectroscopy. Under visible-light irradiation, CdS@1T-MoS2 composites with the MoS2/CdS weight ratio of 0.5 exhibit the highest photocatalytic performance and the H2 evolution rate reached 2.67 mmol h−1 g−1, which is 50 times that of single 1T-MoS2 and 10 times that of single CdS. 1T-MoS2, as a cocatalyst, donates the composites fast charge transfer ability and the high H2 evolution activity, while the intimate heterojunction between CdS core and 1T-MoS2 shell greatly increase the separation efficiency of photo-induced electron-hole pairs, as demonstrated by the electrochemical and PL results, resulting in the remarkable photocatalytic performance of the composites. This study supplies a facile and efficient strategy to develop the photocatalysts with boosted performance for hydrogen energy application.

1T/2H MoSe2-on-MXene heterostructure as bifunctional electrocatalyst for efficient overall water splitting

Designing inexpensive yet active bifunctional electrocatalysts to directly split water is extremely desirable for the ever-broader applications of hydrogen energy. Herein, we present a cost-efficient multiphasic 1T/2H MoSe2-on-MXene nanosheets heterostructure (denote as 1T/2H MoSe2/MXene) as electrocatalyst for efficient overall water splitting. On one hand, the 1T/2H MoSe2 possesses abundant active sites providing relatively high electrocatalytic activity. On the other hand, the MXene nanosheets serve as high-conductive 2D substrates capable of promoting charge transfer ability and preventing 1T/2H MoSe2 from aggregation. Consequently, the 1T/2H MoSe2/MXene catalyst in alkaline media exhibits remarkable synergy in both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity having advantage over pure 1T/2H MoSe2, MXene and 2H MoSe2/MXene counterparts. To be specific, for HER performance, the 1T/2H MoSe2/MXene reveals an overpotential (95 mV) and Tafel slope (91 mV dec−1); for OER performance, the 1T/2H MoSe2/MXene shows an overpotential (340 mV) and Tafel slope (90 mV dec−1). Particularly, when 1T/2H MoSe2/MXene serving as bifunctional electrocatalyst for overall water splitting, only 1.64 V is requested to attain a current density of 10 mA cm−2. The 1T/2H MoSe2/MXene heterostructure also exhibits good durability in overall water splitting system.

Anion doped bimetallic selenide as efficient electrocatalysts for oxygen evolution reaction

The development of highly efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) is of great importance in advancing the practical applications of green and sustainable hydrogen energy. Doping with either cations or non-metallic anions is a typical strategy used to improve the electrocatalytic activity for OER catalysts. In this study, an anion doped bimetallic selenide Co0.75Fe0.25(S0.2Se0.8)2 solid solution is prepared via the simultaneous sulfuration and selenylation of a scalably produced CoFe-layered double hydroxide (CoFe-LDH) precursor, using commercially available sulfur and selenium powders as S and Se sources, respectively. Electrocatalytic test shows that the anion doped bimetallic selenide Co0.75Fe0.25(S0.2Se0.8)2 electrode requires an overpotential of 293 mV and a low Tafel slope of 77 mV dec−1 at a current density of 10 mA cm−2 in an alkaline media, and it exhibits the significantly enhanced electrocatalytic performance for the OER compared with its counterparts of Co0.75Fe0.25S2 and Co0.75Fe0.25Se2. The enhanced electrocatalytic performance is supported experimentally by the results of charge-transfer resistance and electrochemically active surface area. Our LDH precursor-based protocol can provide a strategy to prepare non-metallic anion doped bimetallic selenides as efficient electrocatalysts for water splitting.

Hydrogen sensors based on Pt-decorated SnO2 nanorods with fast and sensitive room-temperature sensing performance

Hydrogen energy has been regarded as one of the most promising green and renewable energy in future society. The development and application of fast and cost-effective hydrogen sensors are of great significant for the safe application of hydrogen energy. In this work, high-performance semiconductor hydrogen sensors with fast room-temperature (RT) hydrogen response were fabricated by using Pt-decorated SnO2 nanorods. The SnO2 nanorods with tetragonal phase were synthesized through a hydrothermal method, and then decorated by Pt nanoparticles by a photochemical reduction method under UV irradiation. The hydrogen sensing performance of the SnO2 nanorods at RT were greatly enhanced after the Pt-decoration. The sensor response was gradually increased from 27.10% to 87.35% with Pt/Sn mol ratio increasing from 0 to 3.63%. Meanwhile, the response and recovery process were also accelerated with increasing Pt loading amount. The room-temperature response and recovery time of the sensor with Pt/Sn ratio of 3.63% was down to 0.33 and 29.60 s, respectively. The sensor also exhibited outstanding repeatability and selectivity against CO and CH4. Moreover, the impact of humidity on the sensor performance were also investigated. The sensor response was decreased with increasing environmental humidity, which could be partially recovered after the humidity was decreased. The remarkably accelerated sensor performance could be attributed to the catalytic property of Pt nanoparticles with spillover effect and the contribution of Pt-induced metal-semiconductor contact effect to the hydrogen response of the sensors.

The multiple selections of fostering applications of hydrogen energy by integrating economic and industrial evaluation of different regions

There are three major applications (portable, stationary, transportation) of hydrogen energy (HE), and each application play a unique and important role in the sustainable development of energy system. In different regions within a country, different applications of HE are preferred. This paper therefore explores the process to decide the optimal region to develop each of the three subtypes of HE applications. To this end, the Analytical Hierarchy Process (AHP) and a fuzzy Technique the Order of Preference by Similarity to Ideal Solution (TOPSIS) method are used in the present study. Based on a literature review and in-depth interviews with officers, experts, the managers of HE-related enterprises, and consumers, the present study comes up with two selection criteria, namely, the acceptance on the applications of hydrogen energy (i.e., market entry barriers and customer's acceptance), and the integrity of hydrogen energy industrial chain on three applications (i.e., production stage, distribution stage, and marketing stage). This paper uses a case study to explore the functioning of three applications of hydrogen energy in the industrial, cultural and restricted residence regions. Four main findings emerges from this study: (1) the market structure of the portable, stationary and transportation application of HE should be pure competitive, oligopolistic, and monopolistic competition respectively; (2) the customer's acceptance for different applications is different, due to different neighborhood concerns about the quality of life; (3) the cost and benefit of different applications depend on different factors, including government policy, technological improvements and social preferences; (4) in order to promote all HE applications, the process to decide the optimal region to develop a specific HE application depends on the comparative advantages of the application.

Recent progresses in H2-PEMFC at DICP

Abstracts Proton exchange membrane fuel cell (PEMFC) as a power supply device has attracted wide attention in China and abroad for its advantages of high energy density, energy conversion efficiency and zero pollution. With the vigorous support of China's national policy, research institutes and enterprises have carried out extensive and pragmatic work on the basic materials, key components, stacks, auxiliary systems of PEMFCs, as well as the hydrogen station construction in order to realize the wide application of hydrogen energy. PEMFC System and Engineering Research Center of DICP is one of the earliest players in the H2-PEMFCs field. Advances have been achieved in the fields of low-platinum contained catalysts, PEMs, high-efficiency MEAs, low-cost metal bipolar plates, low-temperature and impurity air environment adaptability, stacks and systems. This paper introduces recent progresses of H2-PEMFCs at DICP in key materials, components, stacks, systems and the applications. The engineering status of proton exchange membrane water electrolysis (PEMWE) and the alkaline anion exchange membrane fuel cells (AEMFCs) are also summarized.

WXy /g-C3 N4 (WXy =W2 C, WS2 , or W2 N) Composites for Highly Efficient Photocatalytic Water Splitting.

The development of earth-abundant, economical, and efficient photocatalysts to boost water splitting is a key challenge for the practical large-scale application of hydrogen energy. In this study, g-C3 N4 loaded with different tungsten compounds (W2 C, WS2 , and W2 N) is found to exhibit enhanced photocatalytic activities. W2 C/g-C3 N4 displays the highest activity for the photocatalytic reaction with a H2 evolution rate of up to 98 μmol h-1 , as well as remarkable recycling stability. The excellent photocatalytic activity of W2 C/g-C4 N3 is attributed to the suitable band alignment in W2 C/g-C4 N3 and high HER activity of the W2 C cocatalyst, which promotes the separation and transfer of carriers and hydrogen evolution at the surface. These findings demonstrate that the tungsten carbide cocatalyst is more active for the photocatalytic reaction than the sulfide or nitride, paving a way for the design of novel and efficient carbides as cocatalysts for photocatalysis.

Tailoring the Porosity in Iron Phosphosulfide Nanosheets to Improve the Performance of Photocatalytic Hydrogen Evolution.

Metal sulfide photocatalysts are typically required during water splitting to produce hydrogen. However, the rapid recombination of photogenerated electron-hole pairs in these highly unstable photocatalysts has restricted hydrogen production to small-scale batch reactions. In this work, porous transition-metal thiophosphites were used to enable continuous long-term hydrogen production through photocatalysis. A wide bandgap (2.04 eV) was essential for generating hydrogen at a rate of 305.6 μmol h-1 g-1 , 180 % faster than nonporous FePS3 nanosheets. More importantly, the high in-plane stiffness of these approximately 7 nm thick porous FePS3 nanosheets ensured structural stability during 56 h of continuous photocatalysis reactions. The reaction results with D2 O instead of H2 O indicated that hydrogen mainly came from H2 O. Furthermore, a sacrificial reagent (triethylamine) was photodegraded into diethylamine and acetaldehyde through a monoelectronic oxidation process, as indicated by HPLC and LC-MS. This synthesis strategy reported for FePS3 porous nanosheets paves a new pathway for designing other dianion-based inorganic nanocrystals for hydrogen energy applications.

Numerical analysis of the effects of particle radius and porosity on hydrogen absorption performances in metal hydride tank

Slow hydrogen absorption rate and low capacity of a metal hydride tank are the main bottlenecks restricting the practical applications of hydrogen energy. It is crucial to avoid of reducing system gravimetric/volumetric capacity by the additional components for enhancing the hydrogen absorption rate. In this work, we present a new method to increase the hydrogen absorption rate on the basis of the influence of particle radius and porosity to the performance of a LaNi5 tank. A model considering the effects of volume expansion on mass, heat transfer and kinetics is proposed and solved by the finite element method, which constructs the relationship of the hydrogen absorption rate of a metal hydride tank with particle radius and porosity. The results indicate that larger particle radius and higher porosity is of benefit to the hydrogen absorption reaction. Compared with the model without volume expansion, a slightly slower hydrogen absorption rate is given by the model with volume expansion, which is attributed to the decreased thermal diffusivity. The simulation results obtained by the model with volume expansion agree well with the experimental data. The LaNi5 tank is further optimized based on the model with volume expansion, from which the hydrogen absorption time at 90% of maximum hydrogen capacity can be reduced from 1394.12 to 474.83 s when the particle radius is 100 μm and porosity is 0.63.

Mg@C60 nano-lamellae and its 12.50 wt% hydrogen storage capacity

The design and synthesis of new hydrogen storage materials with high capacity are the prerequisite for extensive hydrogen energy application which can be achieved by multi-site hydrogen storage. Herein, a Mg@C60 nano-lamellae structure with multiple hydrogen storage sites has been prepared through a simple ball-milling process in which Mg nanoparticles (∼5 nm) are homogeneously dispersed on C60 nano-lamellae. The as-obtained C60/Mg nano-lamellae displays an excess hydrogen uptake of 12.50 wt% at 45 bar, which is far higher than the theoretical value (7.60 wt%) of metal Mg and the US Department of Energy (DOE) target (5.50 wt%, 2020 year), also the experimental values reported by now. The enhanced hydrogen storage mainly comes from several storage sites: MgH2, Hx–C60 (CH chemical bonding), H2@C60 (the endohedral H2 in C60). Interestingly, the hybridization of Mg and C60 not only facilitate the dissociation of H2 molecules to form CH bonding with C60, but also promote the deformation of C60 and access H2 molecules into the cavity of C60. This work provides new insight into the underlying chemistry behind the high hydrogen storage capacities of a new class of hydrogen storage materials, fullerene/alkaline-earth metals nanocomposites.

Coating the porous Al2O3 substrate with a natural mineral of Nontronite-15A for fabrication of hydrogen-permeable palladium membranes

Substrate surface modification is a key pretreatment during fabrication of composite palladium membranes for hydrogen purification in hydrogen energy applications. The suspension of a natural porous material, Nontronite-15A mineral, without any organic additives was employed in dip-coating of the porous Al2O3 substrate. The Nontronite-15A mineral was characterized by SEM, XRD, TG−DSC and granulometry analysis. The surface and cross-section of the coated porous Al2O3 tubes were observed by SEM, and their pore size distribution and nitrogen flux were also measured. Palladium membranes were fabricated over the coated Al2O3 tubes by a suction-assisted electroless plating. The optimal loading amount of the Nontronite-15A mineral is just to fill in and level up the surface cavities of the Al2O3 substrate rather than to form an extra continuous layer. A thin and selective palladium membrane was successfully obtained, and its permeation performances were tested. The kinetic analyses on the hydrogen flux indicate that the hydrogen permeation behavior exhibits typical characteristics for most of the palladium membranes. During the stability test at 450 °C for 192 h, no membrane damage was detected, and the hydrogen flux increased slightly.