High-efficiency H2 Production Research Articles

Numerical simulation analysis of biomass gasification and rich-H2 production process in a downdraft gasifier

Biomass gasification technology offers a sustainable solution for managing agricultural waste, mitigating environmental pollution, and enhancing living standards. This work deploys Aspen Plus to simulate a downdraft gasifier with an integrated H2 reforming module. The impact of key factors, including air equivalence ratio (ER), gasification system pressure, water vapor input, gasification agent temperature, and oxygen content, are considered. Specifically, optimal ER initially improved the gasification efficiency, with a peak followed by a decline. Water vapor addition elevated H2 content, while increased gasifying agent temperature and oxygen concentration enhanced efficiency. However, the increased gasification pressure will lead to a decrease in gasification efficiency. Subsequently, the effect of reforming temperature, CaO, and water vapor input in the hydrogen production model was examined. An appropriate excess of water vapor and calcium oxide were crucial for maximizing H2 concentration. As the reforming temperature increased from 200 °C to 600 °C, the H2 concentration showed an initial increase and then stabilizes. However, beyond 600 °C, there was a rapid decline. Under optimal conditions (H2O/C > 1.3, CaO/C > 1.1, temperature 550–600 °C), the product gas generated during gasification and reforming processes achieved a high H2 concentration of 98%–99%. These findings affirmed the substantial potential of biomass gasification in high-efficiency H2 production.

Significantly Enhanced Energy-Saving H2 Production Coupled with Urea Oxidation by Low- and Non-Pt Anchored on NiS-Based Conductive Nanofibers.

Rational designing electrocatalysts is of great significance for realizing high-efficiency H2 production in the water splitting process. Generally, reducing the usage of precious metals and developing low-potential nucleophiles oxidation reaction to replace anodic oxygen evolution reaction (OER) are efficient strategies to promote H2 generation. Here, NiS-coated nickel-carbon nanofibers (NiS@Ni-CNFs) are prepared for low-content Pt deposition (Pt-NiS@Ni-CNFs) to attain the alkaline HER catalyst. Due to the reconfiguration of NiS phase and synergistic effect between Pt and nickel sulfides, the Pt-NiS@Ni-CNFs catalyst shows a high mass activity of 2.74-fold of benchmark Pt/C sample. In addition, the NiS@Ni-CNFs catalyst performs a superior urea oxidation reaction (UOR) activity with the potential of 1.366V versus reversible hydrogen electrode (RHE) at 10mA cm-2 , which demonstrates the great potential in the replacement of OER. Thus, a urea-assisted water splitting electrolyzer of Pt-NiS@Ni-CNFs (cathode)||NiS@Ni-CNFs (anode) is constructed to exhibit small voltages of 1.44 and 1.65V to reach 10 and 100mA cm-2 , which is much lower than its overall water splitting process, and presents a 6.5-fold hydrogen production rate enhancement. This work offers great opportunity to design new catalysts toward urea-assisted water splitting with significantly promoted hydrogen productivity and reduced energy consumption.

Transition metal anchored on red phosphorus to enable efficient photocatalytic H2 generation.

Transition metal (TM) single atom catalysts (SACs) are of great potential for photocatalytic H2 production because of their abundant catalytic active sites and cost-effectiveness. As a promising support material, red phosphorus (RP) based SACs are still rarely investigated. In this work, we have carried out systematic theoretical investigations by anchoring TM atoms (Fe, Co, Ni, Cu) on RP for efficient photocatalytic H2 generation. Our density functional theory (DFT) calculations have revealed that 3d orbitals of TM locate close to the Fermi level to guarantee efficient electron transfer for photocatalytic performances. Compared with pristine RP, the introduction of single atom TM on the surface exhibit narrowed bandgaps, resulting in easier spatial separation for photon-generated charge carriers and an extended photocatalytic absorption window to the NIR range. Meanwhile, the H2O adsorptions are also highly preferred on the TM single atoms with strong electron exchange, which benefits the subsequent water-dissociation process. Due to the optimized electronic structure, the activation energy barrier of water-splitting has been remarkably reduced in RP-based SACs, revealing their promising potential for high-efficiency H2 production. Our comprehensive explorations and screening of novel RP-based SACs will offer a good reference for further designing novel photocatalysts for high-efficiency H2 generation.

Enhanced electrocatalytic activity of POM-derived CoMoS/FCP heterostructures for overall water splitting in alkaline media

For the development of green energy and environmental protection, water splitting is an effective method to achieve high-efficiency H2 production as a clean and pollution-free energy source. However, the kinetics of the reaction are limited as a severe reaction. Thus, it is essential to find an economical and robust bifunctional electrocatalyst to boost the hydrogen evolution reaction (HER) and oxygen evolution reaction reactions (OER). In this work, we designed a bifunctional catalyst, CoMoS/FCP, by using the polyoxometalate (POM) Co2Mo10 as a precursor on carbon paper. The catalyst exhibits excellent performance under alkaline conditions (1 M KOH). The overpotential for the HER at 10 mA·cm−2 is 225 mV, and the overpotential of OER at 20 mA/cm2 is 215 mV. We also prepared an assembled two-electrode electrolyzer in alkaline condition. The electrolyzer has a quite low cell voltage of 1.67 V at a current density of 10 mA·cm−2. Moreover, even after 12 h of durability tests, the current density is only slight diminished. In addition, the electrolyzer operates stably under high current density (100 mA/cm2) at a cell voltage of 1.85 V. This work provides excellent potential for low energy consumption H2 production with the CoMoS/FCP catalyst.

Interface enables faster surface reconstruction in a heterostructured Co–Ni–S electrocatalyst towards efficient urea oxidation

The electrocatalytic urea oxidation reaction (UOR) can be utilized as an alternative anodic reaction for water electrolysis to provide more economic electrons and high-efficiency H2 production.

Solar Photocatalysis

Solar Photocatalysis

A facile one-step strategy to construct 0D/2D SnO2/g-C3N4 heterojunction photocatalyst for high-efficiency hydrogen production performance from water splitting

Fabricating 0D/2D heterojunctions is considered to be an efficient mean to improve the photocatalytic activity of g-C3N4, whereas their applications are usually restricted by complex preparation process. Here, the 0D/2D SnO2/g-C3N4 heterojunction photocatalyst is prepared by a simple one-step polymerization strategy, in which SnO2 nanodots in-situ grow on the surface of g-C3N4 nanosheets. It shows the outstanding photocatalytic H2 production activity relative to g-C3N4 under the visible light, which is due to the formation of 0D/2D heterojunction significantly contributing to the separation of photogenerated charge carriers. In particular, the H2 production rate over the optimal SnO2/g–C3N4–1 sample is 1389.2 μmol h−1 g−1, which is 6.06 times higher than that of g-C3N4 (230.8 μmol h−1 g−1). Meanwhile, the AQE value of H2 production over the SnO2/g–C3N4–1 sample reaches up to a maximum of 4.5% at 420 nm. This work develops a simple approach to design and fabricate g–C3N4–based 0D/2D heterojunctions for the high-efficiency H2 production from water splitting.

Design of AgxAu1−x alloy/ZnIn2S4 system with tunable spectral response and Schottky barrier height for visible-light-driven hydrogen evolution

A 3-dimensional AgxAu1−x alloy/ZnIn2S4 system (AgxAu1−x/ZIS) has been designed and constructed for high-efficiency H2 production ability under visible light. In this system, the AgxAu1−x alloyed nanoparticles (NPs) are deposited on ZIS microsphere self-assembled by ZIS sheets, and have an intimate contact with ZIS. The elaborate construction of AgxAu1−x/ZIS makes it own remarkable advantages in driving and controlling light-related reaction. Firstly, the maximizing of optical adsorption properties can be achieved via coupling of ZIS with plasmonic AgxAu1−x NPs in one system, and the absorption band can be tuned by plasmon hybridization through regulating the proportion of Ag and Au in AgxAu1−x NPs. Secondly, the Schottky barrier height formed at AgxAu1−x NPs and ZIS interface could be adjusted by adapting the Ag-Au metal alloy composition, and the optimal height of Schottky barrier (Ag0.6Au0.4/ZIS) plays a key role in prolonging electron-hole pair lifetimes and making them capable of facilitating chemical reactions. All of these lead to the significant improvement of H2 production ability. The H2 production ability of Ag0.6Au0.4/ZIS is 7.1 times higher than that of ZIS under the same condition after 10 h irradiation. The Apparent quantum yield (AQY) of Ag0.6Au0.4/ZIS is about 8.06%. Based on the results, a mechanism is proposed for Ag0.6Au0.4/ZIS.

Construction of ternary rGO/1D TiO2 nanotubes/3D ZnIn2S4 microsphere heterostructure and mutually-reinforcing synergy for high-efficiency H2 production photoactivity under visible light

Abstract The novel ternary reduced graphene oxide/1D TiO 2 nanotubes/3D ZnIn 2 S 4 microspheres (rGO/TiO 2 /ZIS) heterostructured photocatalyst with high-efficiency H 2 production capacity under visible light illumination is designed and prepared in this work. In rGO/TiO 2 /ZIS system, the 1D TiO 2 nanotubes are tightly inserted in the interspace of flower-like ZnIn 2 S 4 microspheres, which are further covered by rGO, leading to an intimate contact among ZnIn 2 S 4 , TiO 2 and rGO. The exquisite design of rGO/TiO 2 /ZIS makes it possess remarkable superiority in photocatalysis. Firstly, the unique 3D microsphere structure of ZIS increases the surface area and visible light absorption ability caused by their unique hollow structure. More importantly, the matched CB and VB positions between ZIS and TiO 2 contribute to separate photogenerated holes and electrons of ZIS efficiently under visible light; then, the separated electrons on TiO 2 are further transferred to rGO due to the superior-strong electron-attracting ability of rGO. At last, the thoroughly suppressing recombination of photogenerated holes and electrons is achieved by the mutually-reinforcing synergy among ZIS, TiO 2 and rGO, and thus the hydrogen generation capacity of ZIS is significantly enhanced. The H 2 production amount and rate of rGO/TiO 2 /ZIS (2.0 wt% rGO and 50 wt% ZIS) after 10 h are 4623 μmol/g and 462.3 μmol/g/h, respectively, which is 71.1 times of pristine TiO 2 and 1.6 times of ZIS under the same condition. The apparent quantum yield of rGO/TiO 2 /ZIS (2.0 wt% rGO and 50 wt% ZIS) in 10 h is about 0.6888%. This excellent photocatalytic performance is ascribed to the mutually-reinforcing synergy among ZIS, TiO 2 and rGO, which can be confirmed by X-ray photoelectron spectroscopy, photoelectrochemical measurements and photoluminescence spectrum. Based on the photocatalytic and characterization results, the corresponding mechanism is proposed.

Vapour-phase hydrothermal synthesis of Ni2P nanocrystallines on carbon fiber cloth for high-efficiency H2 production and simultaneous urea decomposition

Ni2P nanocrystallines grown on carbon fiber cloth (Ni2P/CFC) was successfully achieved by a facile vapour-phase hydrothermal method. The as-prepared Ni2P/CFC, as an electrocatalyst, exhibited superior electrocatalytic activities toward urea oxidation reaction (UOR) with a potential of 1.42V (vs. RHE) delivering a current density of 10mAcm−2 and hydrogen evolution reaction (HER) with overpotentials of 90 and 155mV at current densities of 10 and 100mAcm−2 in alkaline media. On this basis, a Ni2P/CFC constructed two-electrode system for high-efficiency H2 production and simultaneous urea decomposition was therefore established using commercial urea as reaction source. Besides, such two-electrode system as proof of concept study was also evaluated using human urine as urea source for highly efficient H2 generation with a rate of 0.35μMmin−1 at an applied potential of 1.48V, delivering a current density of 10mAcm−2.

Gas Crossover Mitigation in PEM Water Electrolysis: Hydrogen Cross-over Benchmark Study of 3M's Ir-NSTF Based Electrolysis Catalyst-Coated Membranes

New trends in PEM water electrolysis systems development open up new technology gaps and requirements that have not been discussed before with respect to PEM water electrolysis. For example, hydrogen is considered as one of the best solutions for large-scale energy storage that comes from renewable and intermittent power sources such as wind and solar electricity [1], therefore, new megawatt PEM electrolysers are required. These trends are evident through new large-scale recent installations, especially for Power-to-Gas projects in Europe and plan to treat contaminated water at Fukushima Nuclear Power Plant. Even though PEM electrolysis has in fact been used for quite a few years now without undergoing substantial improvements over those years, however, with the new focus on hydrogen as the energy carrier there is much more interest in low-cost and high-efficiency H2 production. There are two main ways to lower the cost of hydrogen production via PEM water electrolysis: to lower the capital expenses (CAPEX) and/or to lower the operating expenses (OPEX). 3M has recently demonstrated a very effective way to address reducing the high CAPEX by increasing the range of current densities where electrolyzers can operate from a maximum of about state-of-the-art 2.0 A/cm2, to as much as 20 A/cm2 by employing a novel 3M’s proprietary Nano Structured Thin Film (NSTF) catalysts and more conductive 3M PFSA based electrolytes in the electrolyzer MEA [2]. What the cited work does not however addresses is an inherent limitation associated with 3M’s Ir-NSTF based anode catalysts, namely their near complete inertness to HOR. An additional tradeoff between performance and gas-crossover also exists when thinner PEM membranes are used. Resulting high hydrogen cross-over creates a gap in the otherwise complete list of requirements for catalyst coated membrane (CCM) that has to be met to become successfully employed in PEM water electrolyzer [3-4]. This was plainly demonstrated in the early 3M catalyst trials where fuel cell derived Pt alloy based NSTF catalysts were used for water electrolysis. The reported durability of such electrolyzer catalysts was excellent, with performance however leaving room for improvement [5]. The performance aspect of 3M electrolyzer catalysts has since been addressed by switching to electrolyzer specific (and Ir based) catalyst compositions. Such approach has left a utility gap by eliminating hydrogen-crossover mitigating components out of the catalyst. To address this problem alternative means for mitigation strategies have to be devised. In this work we will present some data, such as permeability (gas cross-over) of oxygen and hydrogen as a function of current density and other operational variables, aimed at establishing baselines for un-mitigated hydrogen cross-over of 3M electrolyzer MEAs based on 3M NSTF low-PGM loading catalyst and several types of PerFluoro Sulfonic Acid (PFSA) based PEM membranes, both widely commercially available (such as Nafion™ membranes) and their counterparts made by 3M. Dependence of such unmitigated hydrogen cross-over on applied pressure, pressure differentials, and temperature will be discussed and analyzed with reference to existing models of gas crossover [6-8](. In addition, we will also discuss challenges of in-situ and ex-situ gas –cross over measurements and also intend to present results of our initial attempts to employ alternative (to alloying Ir with Pt) mitigation strategies and gauge their respective effectiveness at various electrolyzer operating conditions and time frames. All proposed X-over mitigation strategies are selected with strong emphasis on compatibility of these candidate solutions with high speed/low cost roll-to-roll manufacturing process that will not be negatively affected by their properties and/or needed modifications. In: D. Bessarabov, H. Wang, H. Li, and N. Zhao (Eds): “PEM Electrolysis for Hydrogen Production: Principles and Applications”, CRC Press., 2015. K. A. Lewinski, S. M. Luopa, “High Power Water Electrolysis as a New Paradigm for Operation of PEM Electrolyzer”, Spring ECS Meeting, Chicago, IL, May 2015. K. A. Lewinski, et al., “NSTF Advances for PEM Electrolysis - the Effect of Alloying on Activity of NSTF Electrolyzer Catalysts and Performance of NSTF Based PEM Electrolyzers”, Fall ECS Meeting, Phoenix, AZ, Oct 2015. K. A. Lewinski, et al., ECS Transactions, 69 (17) , p. 893-917 (2015). M.K. Debe, et al., Journal of The Electrochemical Society, 159 (6), (2012), p. K165-K176. C. Mittelsteadt, M. Umbrell, 207th ECS Meeting, #770 D. Bessarabov, “Gas Permeability of Proton Exchange Membranes”, Chapter 21, in: PEM Fuel Cell Diagnostic Tools , Editor(s): H. Wang, Xiao-Zi Yuan, Hui Li, CRC Press, Pages: 443-473, 2011 M. Schalenbach at al., J. Phys. Chem. C 2015, 119, 25156−25169 Figure 1