Enhanced Hydrogen Generation Research Articles

Modified CeO2 as active support for iron oxides to enhance chemical looping hydrogen generation performance

Chemical looping hydrogen generation (CLG) is a promising pathway that can offer both the high purity hydrogen as well as the efficient CO2 capture capability. However, this process was significantly hindered by the lack of active oxygen carriers at relatively low temperatures. Mixed ionic-electronic (MIEC) supported iron oxides exhibit desirable redox performance for the improved oxygen-ion conductivity. In this work, we prepared several AxCe1-xO2-δ (A = Gd, La; x = 0, 0.1, 0.3) supported Fe2O3 for hydrogen production at 750 °C. It was shown that Fe2O3/Gd0.3Ce0.7O2-δ shows the highest hydrogen generation performance and stability over 50 redox cycles. The reactivity follows the sequence of: Fe2O3/Gd0.3Ce0.7O2-δ > Fe2O3/La0.1Ce0.9O2-δ > Fe2O3/Gd0.1Ce0.9O2-δ > Fe2O3/La0.3Ce0.7O2-δ. The fundamental investigation shows that the doping of rare earth (Gd, La) into CeO2 contributes to the formation of oxygen vacancies, thus improving the lattice oxygen diffusion. The enhanced hydrogen generation performance attributes to the high lattice oxygen diffusion to improve the reactivity and inhibiting outward diffusion of Fe. The roughly linear relation between the oxygen vacancy concentration and chemical looping performance can be extended to predict the performance of oxygen carriers for other chemical looping applications, methane reforming, combustion, and ethane dehydrogenation, etc.

Hydrogen production enhancement using hot gas cleaning system combined with prepared Ni-based catalyst in biomass gasification

This paper investigates the hot gas temperature effect on enhancing hydrogen generation and minimizing tar yield using zeolite and prepared Ni-based catalysts in rice straw gasification. Results obtained from this work have shown that increasing hot gas temperature and applying catalysts can enhance energy yield efficiency. When zeolite catalyst and hot gas temperature were adjusted from 250 °C to 400 °C, H2 and CO increased slightly from 7.31% to 14.57%–8.03% and 17.34%, respectively. The tar removal efficiency varies in the 70%–90% range. When the zeolite was replaced with prepared Ni-based catalysts and hot gas cleaning (HGC) operated at 250 °C, H2 contents were significantly increased from 6.63% to 12.24% resulting in decreasing the hydrocarbon (tar), and methane content. This implied that NiO could promote the water-gas shift reaction and CH4 reforming reaction. Under other conditions in which the hot gas temperature was 400 °C, deactivated effects on prepared Ni-based catalyst were observed for inhibiting syngas and tar reduction in the HGC system. The prepared Ni-based catalyst worked at 250 °C demonstrate higher stability, catalyst activity, and less coke decomposition in dry reforming. In summary, the optimum catalytic performance in syngas production and tar elimination was achieved when the catalytic temperature was 250 °C in the presence of prepared Ni-based catalysts, producing 5.92 MJ/kg of lower heating value (LHV) and 73.9% tar removal efficiency.

Porous Ni-Mo bimetallic hybrid electrocatalyst by intermolecular forces in precursors for enhanced hydrogen generation

Hydrogen generated by water splitting devices is a promising way to solve energy issues, which is limited by Pt-based precious catalysts. Developing efficient Pt-free electrocatalyst for hydrogen evolution reaction (HER) is highly essential for the practical applications. Herein, we report a soft-template method to fabricate an efficient porous bimetallic hybrid material, dubbed Ni/Mo6Ni6C@C. Benefiting from the bimetallic feature and porous structure, Ni/Mo6Ni6C@C exhibits low overpotentials of 101 and 122 mV at 10 mA cm−2 with robust stability in alkaline and acidic media, respectively. Theoretical calculations demonstrate that the C sites of the Mo6Ni6C possess the most excellent electrocatalytic activity due to its Gibbs free energy of hydrogen adsorption closer to 0 eV. Moreover, the superior stability, metallic character and mechanical property are characterized by first-principles calculations, which are advantageous for the Mo6Ni6C to be the HER catalyst. This study supplies a concise strategy to prepare the highly efficient bimetallic electrocatalyst for HER.

Exploring the alternative MnO-Na2CO3 thermochemical cycle for water splitting

Abstract Thermochemical cycles for H2O and CO2 splitting using CeO2 have demonstrated high efficiency (> 5%) and fast kinetics. Alternative multistage cycles based on stoichiometric oxides, such as Mn-Na, can potentially provide much larger efficiencies under less stringent operation conditions. However, these cycles consist of three stages operating at very different temperatures (from 50 °C to 1500 °C) and, accordingly, the overall energy yield of the cycle critically depends on efficient heat recovery. Despite of this, recently the Mn3O4–Na2CO3 cycle has shown a remarkable H2 production and high stability. To further enhance hydrogen generation rate, in this work we explore the feasibility of the novel cycle based on MnO, which can potentially increase the yield per cycle. Several samples of MnO with different physicochemical characteristics were investigated to establish the influence on the oxide physicochemical properties on hydrogen generation. A maximum conversion of 47 %, with a productivity of 20.1 μmol H2 min−1 g−1 were obtained using the MnO sample with relatively large surface area. As expected, this productivity is notably better than that obtained with Mn3O4 under identical conditions. Furthermore, the results obtained here reveals that low temperature hydrolysis under CO2 atmosphere can improve the Na extraction by more than 10 %. This enhances the cyclability of the process and it may allow coupling hydrogen production with CO2 capture. Furthermore, the thermal reduction of the solid product recovered after the carbonation stage yields nearly pure MnO, confirming experimental the feasibility of completing this alternative cycle.

In situ tuning of band gap of Sn doped composite for sustained photocatalytic hydrogen generation under visible light irradiation

The significance of Sn dopant on the photocatalytic performance of Iron/Titanium nanocomposite towards photocatalytic hydrogen generation by water splitting reaction is investigated. Iron/Titanium nanocomposite modified by Sn4+ dopant acts as a suitable photocatalyst for induced visible light absorption facilitating pronounced charge separation efficiency. Various characterization techniques reveal the heterojunction formation of hematite Fe2O3 with anatase - rutile mixed phase of TiO2 employing Sn doping, where Sn4+ dopant accomplishes the phase transformation of anatase to rutile, entering into the TiO2 lattice. This extended the lifetime of photogenerated charge carriers and enhanced the quantum efficiency of the photocatalyst. The band gap of the nanocomposite is tuned to ~2.4 eV, favoring visible light absorption. A hydrogen generation activity of 1102.8 μmol, approximately five times higher than the lone system (216.5 μmol) is achieved for the 5% Sn doped system for an average of 5 h. Heterojunctions of hematite with anatase-rutile mixed phase, generated as a consequence of tin doping facilitated the enhanced hydrogen generation activity of photocatalyst.

Enhanced hydrogen generation efficiency of methanol using dielectric barrier discharge plasma methodology and conducting sea water as an electrode

In this work, methanol decomposition method has been discussed for the production of hydrogen gas with the application of plasma. A simple dielectric barrier discharge (DBD) plasma reactor was designed for this purpose with two types of electrode. The DBD plasma reactor was experimented by substituting one of the metal electrodes with feebly conducting sea water which yielded better efficiency in producing hydrogen gas. Experimental parameters such as; discharge voltage and time were varied by maintaining a discharge gap of 1.5 mm and the plasma discharge characteristics were studied. Filamentary type micro-discharges were found to be formed which was observed as numerous streamer clusters in the current waveform. Gas chromatographic study confirmed the production of hydrogen gas with residence time around 3.6 min. Although, the concentration (%) of H2 was high (98.1 %) and consistent with copper electrode assembly, the rate of formation and concentration was found to be the highest (98.7 %) for water electrode for specific discharge voltage. The energy efficiency was found to be 0.5 mol H2/kWh and 1.2 mol H2/kWh for metal (Cu) and water electrodes respectively. The electrode material significantly affects the plasma condition and hence the rate of hydrogen production. Compositional analysis of the water used as electrode showed a minimal change in the composition even after the completion of the experiment as compared to the untreated water. Methanol degradation study shows the presence of untreated methanol in the residue of the plasma reactor which has been confirmed from the absorption spectra.

CoAl LDH@Ni-MOF-74 S-Scheme Heterojunction for Efficient Hydrogen Evolution

Metal–organic frameworks (MOFs) and layered double hydroxides (LDHs) have been considered to be one of the most promising and worthy hot spot materials to develop advanced catalysts for efficient hydrogen evolution due to their prominent characteristics, including unique structures, environmentally friendly nature, high redox activities, and homogeneously effective utilization of transition metal atoms. In this work, the delicate S-scheme heterojunction photocatalyst, CoAl LDH@Ni-MOF-74, was rationally designed and successfully constructed by coupling Ni-MOF-74 with CoAl LDH based on their peculiar structure, excellent electronic properties, and opposite surface potential for enhancing hydrogen generation activity under visible light irradiation. The CoAl LDH nanolayers evenly and dispersedly load on the surface of Ni-MOF-74. The CoAl LDH@Ni-MOF-74 exhibited higher photocatalytic hydrogen evolution activity compared with Ni-MOF-74 and CoAl LDH alone, mainly because the formation of the CoAl LDH@Ni-MOF-74 S-scheme heterojunction accelerated the recombination of several electrons (from conduction band (CB) of Ni-MOF-74) and holes (from valence band (VB) of CoAl LDH) and prevented the recombination of other electrons (from CB of CoAl LDH) and holes (from VB of Ni-MOF-74).

Inter-embedded Au-Cu2O heterostructure for the enhanced hydrogen production from water splitting under the visible light

Constructing the heterostructure with noble metals on semiconductors is recognized as a prospective approach to enhance hydrogen generation. In this study, Au-Cu2O heterostructure particles (HPs) with unique inter-embedded heterostructures were controllably fabricated by a universal reaction between Cu particles and HAuCl4 solution. Besides, the boosted catalytic performance from the plasmon effects, Au-Cu2O inter-embedded heterostructure exhibits additional structural advantages to promote the photocatalytic property of hydrogen generation overall water splitting. Under the visible light, the H2 evolution rate of the Au-Cu2O HPs is 152 and 22 times higher than that of pure Cu2O and traditional Cu2O@Au HPs with Au anchored on the surface of Cu2O, respectively. On one hand, inter-embedded heterostructure brings more contact areas as the active sites to carry out the direct electron transfer and electromagnetic transfer for the reduction. On the other hand, the finite difference time domain (FDTD) simulations indicate that enhanced electromagnetic fields of Au-Cu2O HPs form a netlike structure to maximumly accelerate the transfer of hot electrons and separate the electron–hole pairs. Under the joint action of the two, the inter-embed heterostructure exhibits superior photocatalytic property, demonstrating that this study could instruct the design of other metal–semiconductor photocatalysts.

Enhanced hydrogen generation via hydrolysis of Mg–Mg2NiH4 system

Producing hydrogen via hydrolysis of light weighted metal-based materials is a promising technology for exploiting portable hydrogen–air fuel cells. Various additives have been designed to catalyze the hydrolysis behavior of Mg-based materials. In most cases, however, the kinetic promotion is in the expense of the systematic hydrogen generation yield. In this work, Mg–Mg2NiH4 system with extraordinary hydrolysis property is explored for hydrogen generation in 3.5% NaCl aqueous solution for the first time. The Mg-10 wt% Mg2NiH4 composite releases 845.1 mL g−1 (yield of 94.7%) hydrogen in just 20 s, with a maximum hydrogen generation rate (mHGR) of 6391 mL g−1 min−1. Our results have experimentally shown the synergistic effect between Mg and Mg2NiH4 on hydrolysis reaction. The in-situ ultrafine Ni particles derived from the rapid hydrolysis of Mg2NiH4 form a large amount of micro-galvanic cells with Mg, accelerating the electrochemical corrosion of Mg efficiently. In turn, the hydrolysis reaction of Mg2NiH4 can be dramatically driven by the local solution heat due to the violent exothermic reaction of Mg. The cooperative effect provides fresh strategy designing high-property hydrolysis materials with no substantial loss of the hydrogen supply capacity.

On the nature of Pt-carbon interactions for enhanced hydrogen generation

Understanding the metal-support interactions in heterogeneous catalysis is critical yet complicated to tailor-design the catalysts with desirable properties. Exemplified with Pt-catalyzed ammonia borane (AB) hydrolysis, a dramatic increase of 20 folds in the catalytic activity is achieved by engineering the Pt-carbon interactions via adopting four different carbon materials (AC, CNT, f-CNF and p-CNF) as the catalyst supports. Multiple characterization techniques reveal that the Pt-carbon electronic interactions, including electron transfer and interfacial bonding, are deemed to be mainly responsible for the remarkable enhancement in the hydrogen generation rate. The molar ratio of electron-withdrawing group to electron-donating group (nEWG/nEDG) is further identified as a descriptor of catalyst in terms of Pt binding energy, which exhibits an almost linear relationship with the catalytic activity. Moreover, a comparison of Pt catalyst pre-treatments, i.e., H2 and AB reduction as well as Ar calcination, suggests that the Pt-O-C linkages within the Pt-carbon interactions are highly stable yet inferior to this reaction. As a result, combining the merits of the highest Pt binding energy as well as the minimum Pt-O-C linkages, the Pt/p-CNF delivers the highest catalytic activity. The insights presented here could shed new lights on the nature of Pt-carbon interactions, which could be extended to the design and manipulation of other metal-carbon catalysts.

Boosting the on-demand hydrogen generation from aqueous ammonia borane by the visible-light-driven synergistic electron effect in antenna-reactor-type catalysts with plasmonic copper spheres and noble-metal-free nanoparticles

To tailor the electronic behavior of catalytically active species in heterogeneous catalysts is beneficial for regulating their catalytic performance in various reaction including hydrogen generation. Herein, we rationally synthesize a series of antenna-reactor-type catalysts with the combination of plasmonic Cu spheres (55, 130, 190, 270 and 440 nm) with catalytically active Co or Ni nanoparticles (NPs), which are used for hydrogen generation from aqueous ammonia borane (NH3BH3) at 298 K. All the catalysts show the higher activities under visible light irradiation than in the dark and the optimal Co-based catalyst has the highest room-temperature photocatalytic activity with the total turnover frequency (TOF) value of 164.8 min−1, which outperforms the values of all the reported non-noble metal catalysts. The capture of photogenerated electrons, the monochromatic light-dependent activity and hydrogen generation of different catalysts verify that there exists the visible-light-driven synergistic electron effect bewteen plasmonic Cu spheres with energetic electrons and Co NPs with excited electrons generated by interband transitions. This leads to the electron density enrichment of Co NPs and the resultantly enhanced hydrogen generation activity under visible light irradiation.

Decoration of Graphene Quantum Dots on TiO2 Nanostructures: Photosensitizer and Cocatalyst Role for Enhanced Hydrogen Generation

Production of H2 fuel from photocatalytic splitting of water is one of the most demanding researches in terms of sustainable development in energy sector. In our quest to find an effective photocat...

Effects of different Al2O3 support on HDPE gasification for enhanced hydrogen generation using Ni-based catalysts

This study examined the effects of Ni loading on different types of alumina (γ-Al2O3, mesoporous Al2O3, 13 nm-sized Al2O3, and <50 nm-sized Al2O3) for high-density polyethylene gasification for enhanced hydrogen generation. The catalytic activity of Ni loaded alumina was observed in the order of 13 nm-sized Al2O3> mesoporous Al2O3> (<50 nm-sized Al2O3) > γ-Al2O3 for the gas yield and γ-Al2O3> (<50 nm Al2O3) > mesoporous Al2O3 > 13 nm Al2O3 for the oil yield, respectively. In addition, the production of hydrogen from Ni loaded alumina showed an increasing trend in the order of (<50 nm-sized Al2O3) > γ-Al2O3> 13 nm-sized Al2O3.> mesoporous Al2O3. In contrast, CO showed the trend as Ni/mesoporous Al2O3> Ni/13 nm-sized Al2O3> Ni/γ-Al2O3> (Ni/<50 nm Al2O3). The highest level of hydrogen production from the Ni/<50 nm-sized Al2O3 catalyst might be because of its highest Ni dispersion and surface area. The use of Ni-loaded nm-sized alumina could be an excellent method for increased hydrogen production compared to other types of alumina available.

Polymer decoration of carbon support to boost Pt-catalyzed hydrogen generation activity and durability

Decorating the catalyst support with organic moieties to integrate multiple functionalities into metal particles offers a unique platform to promote the catalytic performance. Here, we report a mechanism-driven strategy to functionalize CNT with dual polymers, endowing the supported Pt catalyst with simultaneously enhanced hydrogen generation activity and durability. Kinetics analysis, multiple characterization and DFT calculations reveal that the PDDA acts as electron-acceptor to capture electrons from the Pt particles toward strengthened adsorption of reactants, while the PVP acts as structure-directing agent to induce the catalyst morphology evolution with a preferential exposure of Pt(1 1 1) active sites. Such electronic and geometric synergy by co-functionalizing PDDA and PVP gives rise to a 3-fold increase in the hydrogen generation activity, together with remarkably improved catalytic durability due to the suppressed adsorption of B(OH)4− over the Pt(1 1 1). The strategy reported here might shed new lights on establishing the functionalization protocols to design carbon supported metal catalysts with the targeted properties.

Effects of Surface Terminations of 2D Bi2WO6 on Photocatalytic Hydrogen Evolution from Water Splitting.

Two-dimensional (2D)-structured photocatalysts with atomically thin layers not only have the potential to enhance hydrogen generation efficiency but also allow more direct investigations of the effects of surface terminations on photocatalytic activity. Taking 2D Bi2WO6 as a model, we found that the configuration of bilayer Bi2O2 sandwiched by alternating WO4 layers enabled the thermodynamic driving potential for photocatalytic hydrogen evolution. Without Pt deposition, the H2 generation efficiency can reach to 56.9 μmol/g/h by 2D Bi2WO6 as compared with no activity of Bi2WO6 nanocrystals under simulated solar light. This configuration is easily functionalized by adsorption of Cl-/Br- to form Bi-Cl/Bi-Br bonds, which leads to the decrease of recombination in photogenerated charge carriers and narrower band gaps. This work highlights an effective way to design photocatalysts with efficient hydrogen evolution by tuning the surface terminations.

Samarium (III)-doped ZnO/graphitic−C3N4 composites for enhanced hydrogen generation from water under visible light photocatalysis

Abstract Samarium (Sm+3) was doped with ZnO via a facile wet chemical route for visible−light assisted production of hydrogen. Furthermore, Sm−doped ZnO coupled with g−C3N4 (SAZOC) composite was generated by one step solid–state transformation method, which was then characterized by different techniques to evaluate their structural, morphological and optical properties. X-ray photoelectron spectra of the composites confirmed successful doping of Sm+3 into ZnO and transmission electron microscopy demonstrated a clear heterojunction between g−C3N4 and Sm−doped ZnO nanoparticles. The composites showed excellent H2 production ability; the optimal H2 generation rate (10.25 mmol g−1 h−1) was achieved by incorporating 10% Sm−doped ZnO. The composites were stable for about 10 h without losing photo−activity. The enhanced photo−activity was due to synergistic effects of ZnO and g−C3N4, and Sm+3 that acted as a co-catalyst in the reaction, allowing high electron−hole separation in the heterojunction and making it promising for hydrogen generation via water splitting.

Enhanced Hydrogen Generation from Empty Fruit Bunches by Charcoal Addition into a Downdraft Gasifier

AbstractHydrogen production by co‐gasification of empty fruit bunches of palm oil could be enhanced by adding charcoal. Physiochemical characterization of raw feedstocks was performed to determine their exergy potentiality. The raw feedstocks, gasified charcoal, and the end product of produced gas were analyzed by different techniques. Gasification experiments were performed using a pilot‐scale downdraft gasifier. The heating value, composition of product gas, yield of hydrogen, and exergy efficiency were used to verify the improvement of hydrogen production during the co‐gasification process. Charcoal with empty fruit bunches of palm oil leads to a much higher yield of hydrogen than lower charcoal ratios or solely empty fruit bunches. This enhanced hydrogen fuel can contribute to future energy demand.

Energy level tuning of CdSe colloidal quantum dots in ternary 0D-2D-2D CdSe QD/B-rGO/O-gC3N4 as photocatalysts for enhanced hydrogen generation

Colloidal quantum dots (QD) electronic properties are tailorable via modifications of its quantum confinement environment. Herein, surface-chemistry-mediated approach through the application of unique surface thiol ligands (thioglycolic acid, glutathione, 3-mercaptopropioninc acid and N-Acetylcysteine) exhibited energy level and gap shifts in aqueous CdSe QDs. Trends in the photocatalytic performance employing ligand-specific CdSe QDs are consistent with their respective measured energy and gap level. Results underscore that a still underutilized mean of surface-chemistry-mediated modification of colloidal CdSe QDs can be employed as a versatile parameter in the performance optimizations of QD photocatalysts for photocatalytic hydrogen (H2) reactions. This optimized CdSe QD is further utilized as sensitizers to bolster and facilitate effective charge transfer across the ternary, multi-level heterointerfaces of 0D-2D-2D CdSe QD/B-rGO/O-gC3N4. Upon loading, the ternary composite achieved a maximum H2 evolution of 1435 μmol h−1 g−1 even without the help of precious metal co-catalyst which is otherwise required when used as individual unit. This augmented photoactivity is attributed to the synergetic effect of CdSe sensitization and p-n junction administered by the p-type B-rGO and n-type O-gC3N4.

Enhanced hydrogen generation performance of CaMg2-based materials by ball milling

The hydrolysis properties of CaMg2-based materials can be enhanced via tailoring the milling durations or/and doping with the Ni element.

Quasi-hydrophilic black silicon photocathodes with inverted pyramid arrays for enhanced hydrogen generation

Micro-/nanostructured silicon (Si) photoelectrodes are promising for efficient solar-driven water splitting. In this work, an elaborate study on textured Si photocathodes is reported. Compared to conventional textured Si photocathodes, the well-designed Si photocathode with randomly-distributed inverted pyramid arrays (SiIPs) generates a larger photovoltage of 440 mV for its higher effective minority carrier density, and produces a higher photocurrent density at a high reverse bias voltage due to its quasi-hydrophilicity. With the help of cobalt disulfide (CoS2) nanocrystals, sluggish charge kinetics of SiIP photocathodes can be further improved. The optimal SiIP/CoS2 photocathode yields an onset potential of 0.22 V vs. reversible hydrogen electrode (RHE) and a saturated photocurrent density of 10.4 mA cm-2 at -0.45 V (vs. RHE). Besides, this cathode produces a stable photocurrent density of ∼6.60 mA cm-2 at 0 V (vs. RHE) for 12 000 s in acidic media. Notably, our work presents a facile and inexpensive method to fabricate efficient Si photoelectrodes, which may promote the evolution of textured Si-based electrodes for potential photoelectrochemical and photocatalytic applications.