Hydrogen Oxidation Research Articles

Unraveling Stoichiometry Effect in Nickel‐Tungsten Alloys for Efficient Hydrogen Oxidation Catalysis in Alkaline Electrolytes

AbstractAnion‐exchange membrane fuel cells provide the possibility to use platinum group metal‐free catalysts, but the anodic hydrogen oxidation reaction (HOR) suffers from sluggish kinetics and its source is still debated. Here, over nickel‐tungsten (Ni−W) alloy catalysts, we show that the Ni : W ratio greatly governs the HOR performance in alkaline electrolyte. Experimental and theoretical studies unravel that alloying with W can tune the unpaired electrons in Ni, tailoring the potential of zero charge and the catalytic surface to favor hydroxyl adsorption (OHad). The OHad species coordinately interact with potassium (K+) ions, which break the K+ solvation sheath to leave free water molecules, yielding an improved connectivity of hydrogen‐bond networks. Consequently, the optimal Ni17W3 alloy exhibits alkaline HOR activity superior to the state‐of‐the‐art platinum on carbon (Pt/C) catalyst and operates steadily with negligible decay after 10,000 cycles. Our findings offer new understandings of alloyed HOR catalysts and will guide rational design of next‐generation catalysts for fuel cells.

Unraveling Stoichiometry Effect in Nickel-Tungsten Alloys for Efficient Hydrogen Oxidation Catalysis in Alkaline Electrolytes.

Anion-exchange membrane fuel cells provide the possibility to use platinum group metal-free catalysts, but the anodic hydrogen oxidation reaction (HOR) suffers from sluggish kinetics and its source is still debated. Here, over nickel-tungsten (Ni-W) alloy catalysts, we show that the Ni : W ratio greatly governs the HOR performance in alkaline electrolyte. Experimental and theoretical studies unravel that alloying with W can tune the unpaired electrons in Ni, tailoring the potential of zero charge and the catalytic surface to favor hydroxyl adsorption (OHad). The OHad species coordinately interact with potassium (K+) ions, which break the K+ solvation sheath to leave free water molecules, yielding an improved connectivity of hydrogen-bond networks. Consequently, the optimal Ni17W3 alloy exhibits alkaline HOR activity superior to the state-of-the-art platinum on carbon (Pt/C) catalyst and operates steadily with negligible decay after 10,000 cycles. Our findings offer new understandings of alloyed HOR catalysts and will guide rational design of next-generation catalysts for fuel cells.

Phase manipulating toward Ni catalysts via lattice nitrogen endows high energy density hydrogen gas battery

Metastable structures commonly generate unique catalytic effects. However, it is challenging to prepare due to thermodynamic limitations. Here, we first propose a nitrogen insertion strategy for Ni phase manipulating in alkaline hydrogen oxidation reaction (HOR). With the incremental lattice nitrogen, face centered cubic (fcc), bi-mixed fcc and N-induced an unconventional hexagonal close packed (N-u-hcp), tri-mixed fcc-Ni/N-u-hcp-Ni/Ni3N and Ni3N phase evolves successively, with corresponding volcanic HOR activities. Specifically, the biphasic fcc-Ni/N-u-hcp-Ni shows highest activity of 67 A g−1. Theoretical calculations show that lattice nitrogen reduce the formation energy of biphasic Ni, and this biphasic structure could provide electron rich interface to optimize the adsorption of H* and OH*. As a proof-of-concept for Ni-H2 battery, the gas diffusion electrode prepared with this biphasic Ni catalyst achieves an 8 Ah Ni-H2 battery with 163 Wh kg−1. This study provides an inspiration for the controllable synthesis of metastable nano-catalysts and demonstrates the efficient catalysis in practical hydrogen energy applications.

Iridium-Based Alkaline Hydrogen Oxidation Reaction Electrocatalysts.

The hydroxide exchange membrane fuel cells (HEMFCs) are promising but lack of high-performance anode hydrogen oxidation reaction (HOR) electrocatalysts. The platinum group metals (PGMs) have the HOR activity in alkaline medium two to three orders of magnitude lower than those in acid, leading to the high required PGMs amount on anode to achieve high HEMFC performance. The mechanism study demonstrates the hydrogen binding energy of the catalyst determines the alkaline HOR kinetics, and the adsorbed OH and water on the catalyst surface promotes HOR. Iridium (Ir) has a unique advantage for alkaline HOR due to its similar hydrogen binding energy to Pt and enhanced adsorption of OH. However, the HOR activity of Ir/C is still unsatisfied in practical HEMFC applications. Further fine tuning the adsorption of the intermediate on Ir-based catalysts is of great significance to improve their alkaline HOR activity, which can be reasonably realized by structure design and composition regulation. In this concept, we address the current understanding about the alkaline HOR mechanism and summarize recent advances of Ir-based electrocatalysts with enhanced alkaline HOR activity. We also discuss the perspectives and challenges on Ir-based electrocatalysts in the future.

Durability and kinetic effects of CO2-rich oxidizing streams on LSCF-based solid oxide fuel cells

In the SOS–CO2 cycle, a novel hybrid cycle for blue power production, the solid oxide fuel cell's (SOFC) cathode is supplied with a CO2-rich oxidizing stream (e.g., 21 % O2 79 % CO2 vol.). The durability of state-of-the-art anode-supported SOFCs (25 cm2, SolydEra) with LSCF-GDC/LSC (La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.1Ce0.9O3+δ/La0.6Sr0.4CoO3+δ) cathodes was tested at atmospheric pressure for 1090 h with 7 % humidified H2 and reformate, at 700 °C and 0.85 V. The SOFC performance was investigated with periodic I/V curves and electrochemical impedance spectroscopy (EIS) measurements. The results highlighted a 24 % power density loss when air was replaced with the O2/CO2 mixture (672 mW/cm2 in air vs. 508 mW/cm2 in O2/CO2 with humidified H2). A stable power output was observed, and complete reversibility was found when the air supply was restored. A distribution of relaxation times (DRT) analysis of the EIS spectra allowed to extract an anodic rate equation for the hydrogen oxidation reaction (HOR) and evaluate the frequency region affected by cathodic CO2. The kinetic effect of CO2 was also studied via EIS on symmetric button cells at varying O2 and CO2 amounts, and a power-law rate equation was derived. The results verify the feasibility of the SOS–CO2 cycle feed conditions at 700 °C and atmospheric pressure.

Phosphorus-Modified Palladium and Tungsten Carbide/Mesoporous Carbon Composite for Hydrogen Oxidation Reaction of Proton Exchange Membrane Fuel Cells.

A composite material of tungsten carbide and mesoporous carbon was synthesized by the sol-gel polycondensation of resorcinol and formaldehyde, using cetyltrimethylammonium bromide as a surfactant and Ludox HS-40 as a porogen, and served as a support for Pd-based electrodes. Phosphorus-modified Pd particles were deposited onto the support using an NH3-mediated polyol reduction method facilitated by sodium hypophosphite. Remarkably small Pd nanoparticles with a diameter of ca. 4 nm were formed by the phosphorus modification. Owing to the high dispersion of Pd and its strong interaction with tungsten carbide, the Pd nanoparticles embedded in the tungsten carbide/mesoporous carbon composite exhibited a hydrogen oxidation activity approximately twice as high as that of the commercial Pt/C catalyst under the anode reaction conditions of proton exchange membrane fuel cells.

Synergistic Modulation of Multiple Sites Boosts Anti‐Poisoning Hydrogen Electrooxidation Reaction with Ultrasmall (Pt0.9Rh0.1)3V Ternary Intermetallic Nanoparticles

Promoting the hydrogen oxidation reaction (HOR) activity and poisoning tolerance of electrocatalysts is crucial for the large‐scale application of hydrogen‐oxygen fuel cell. However, it is severely hindered by the scaling relations among different intermediates. Herein, lattice‐contracted Pt‐Rh in ultrasmall ternary L12‐(Pt0.9Rh0.1)3V intermetallic nanoparticles (~2.2 nm) were fabricated to promote the HOR performances through an oxides self‐confined growth strategy. The prepared (Pt0.9Rh0.1)3V displayed 5.5/3.7 times promotion in HOR mass/specific activity than Pt/C in pure H2 and dramatically limited activity attenuation in 1000 ppm CO/H2 mixture. In‐situ Raman spectra tracked the superior anti‐CO* capability as a result of compressive strained Pt, and the adsorption of oxygen‐containing species was promoted due to the dual‐functional effect. Further assisted by density functional theory calculations, both the adsorption of H* and CO* on (Pt0.9Rh0.1)3V were reduced compared with that of Pt due to lattice contraction, while the adsorption of OH* was enhanced by introducing oxyphilic Rh sites. This work provides an effective tactic to stimulate the electrocatalytic performances by optimizing the adsorption of different intermediates severally.

Synergistic Modulation of Multiple Sites Boosts Anti-Poisoning Hydrogen Electrooxidation Reaction with Ultrasmall (Pt0.9Rh0.1)3V Ternary Intermetallic Nanoparticles.

Promoting the hydrogen oxidation reaction (HOR) activity and poisoning tolerance of electrocatalysts is crucial for the large-scale application of hydrogen-oxygen fuel cell. However, it is severely hindered by the scaling relations among different intermediates. Herein, lattice-contracted Pt-Rh in ultrasmall ternary L12-(Pt0.9Rh0.1)3V intermetallic nanoparticles (~2.2 nm) were fabricated to promote the HOR performances through an oxides self-confined growth strategy. The prepared (Pt0.9Rh0.1)3V displayed 5.5/3.7 times promotion in HOR mass/specific activity than Pt/C in pure H2 and dramatically limited activity attenuation in 1000 ppm CO/H2 mixture. In situ Raman spectra tracked the superior anti-CO* capability as a result of compressive strained Pt, and the adsorption of oxygen-containing species was promoted due to the dual-functional effect. Further assisted by density functional theory calculations, both the adsorption of H* and CO* on (Pt0.9Rh0.1)3V were reduced compared with that of Pt due to lattice contraction, while the adsorption of OH* was enhanced by introducing oxyphilic Rh sites. This work provides an effective tactic to stimulate the electrocatalytic performances by optimizing the adsorption of different intermediates severally.

Local Charge Transfer Unveils Antideactivation of Ru at High Potentials for the Alkaline Hydrogen Oxidation Reaction.

The activity of Ru-based alkaline hydrogen oxidation reaction (HOR) electrocatalysts usually decreases rapidly at potentials higher than 0.1 V (vs a reversible hydrogen electrode (RHE)), which significantly limits the lifetime of fuel cells. It is found that this phenomenon is caused by the overadsorption of the O species due to the overcharging of Ru nanoparticles at high potentials. Here, Mn1Ox(OH)y clusters-modified Ru nanoparticles (Mn1Ox(OH)y@Ru/C) were prepared to promote charge transfer from overcharged Ru nanoparticles to Mn1Ox(OH)y clusters. Mn1Ox(OH)y@Ru/C exhibits high HOR activity and stability over a wide potential range of 0-1.0 V. Moreover, a hydroxide exchange membrane fuel cell with a Mn1Ox(OH)y@Ru/C anode delivers a high peak power density of 1.731 W cm-2, much superior to that of a Pt/C anode. In situ X-ray absorption fine structure (XAFS) analysis and density functional theory (DFT) calculations reveal that Mn in Mn1Ox(OH)y clusters could receive more electrons from overcharged Ru at higher potentials and significantly decrease the overadsorption of the O species on Ru, thus permitting the HOR on Ru to proceed at high potentials. This study provides guidance for the design of alkaline HOR catalysts without activity decay at high potentials.

Sub-2 nm Microstrained High-Entropy-Alloy Nanoparticles Boost Hydrogen Electrocatalysis.

High-entropy alloys (HEAs) confine multifarious elements into the same lattice, leading to intense lattice distortion effect. The lattice distortion tends to induce local microstrain at atomic level and thus affect surface adsorptions toward different adsorbates in various electrocatalytic reactions, yet remains unexplored. Herein, this work reports a class of sub-2nm IrRuRhMoW HEA nanoparticles (NPs) with distinct local microstrain induced by lattice distortion for boosting alkaline hydrogen oxidation (HOR) and evolution reactions (HER). This work demonstrates that the distortion-rich HEA catalysts with optimized electronic structure can downshift the d-band center and generate uncoordinated oxygen sites to enhance the surface oxophilicity. As a result, the IrRuRhMoW HEA NPs show a remarkable HOR kinetic current density of 8.09mA µg-1 PGM at 50mV versus RHE, 8.89, 22.47 times higher than those of IrRuRh NPs without internal strain and commercial Pt/C, respectively, which is the best value among all the reported non-Pt based catalysts. IrRuRhMoW HEA NPs also display great HER performances with a turnover frequency (TOF) value of 5.93 H2 s-1 at 70mV versus RHE, 4.6-fold higher than that of Pt/C catalyst, exceeding most noble metal-based catalysts. Experimental characterizations and theoretical studies collectively confirm that weakened hydrogen (Had) and enhanced hydroxyl (OHad) adsorption are achieved by simultaneously modulating the hydrogen adsorption binding energy and surface oxophilicity originated from intensified ligand effect and microstrain effect over IrRuRhMoW HEA NPs, which guarantees the remarkable performances toward HOR/HER.

Protective layers of zirconium alloys used for claddings to improve the corrosion resistance

Abstract Zirconium alloys are used as a cladding material for fuel elements in nuclear reactors. In the case of severe accident conditions, the possible rapid oxidation of zirconium in steam or/and air may result in intense hydrogen generation and hydrogen–oxide mixture explosion. Advanced technologies for increasing the corrosion resistance of claddings are being investigated in two directions: (a) protective coatings on Zr alloys and (b) the use of new materials for claddings. Coatings with silicon may provide a more protective barrier than the ZrO2 films formed on an alloy cladding during nuclear plant operations. These coatings may also serve as a protective barrier during high-temperature accidents. The current work aimed at developing protective coatings with silicon on zirconium alloys. Multielemental Zr–Si–Cr coatings were formed on Zry-2 alloy using the physical vapor deposition (PVD) method. Long-term oxidation tests were carried out under the following conditions: 360°C/195 bar/63 days/water-simulating PWR water. Obtained results show the protective character of formed layers. The material in the form of silicon carbide grains covered with yttrium–aluminum garnet (SiC + YAG) was prepared using the sol–gel method. The formed powder is the main component for coating formation on Zr–1Nb alloy using the method of suspension plasma spraying (SPS).

Tailoring OH* adsorption strength on Ni/NbOx for boosting alkaline hydrogen oxidation reaction via oxygen vacancy

Tailoring OH* adsorption strength on Ni/NbOx for boosting alkaline hydrogen oxidation reaction via oxygen vacancy

Advances in CO-tolerant anode catalysts for proton exchange membrane fuel cells

Pt-based catalysts are often used in a proton exchange membrane fuel cell due to their high activities to oxygen reduction and hydrogen oxidation reaction. However, these catalysts are easily poisoned by CO, resulting in a significant reduction of fuel cell performance. The use of CO-tolerant catalysts can effectively solve this problem. The CO poisoning mechanism and anti-poisoning strategies were briefly discussed in this article. It mainly focused on the research progress on CO-tolerant catalysts in three aspects: Pt alloy catalysts, metal oxide composite catalysts, and blocking layer covered catalysts. The advantages and limitations of various catalysts in recent years were also discussed. Creating a porous blocking layer covered on the surface of the catalyst can effectively enhance the CO-tolerance of the catalysts which could be a promising approach for developing anti-poison catalysts other than CO-tolerance. Finally, the prospects for future development of CO-tolerant fuel cell catalysts were described.

Boosting borohydride oxidation kinetics by manipulating hydrogen evolution and oxidation through octahedral Pt–Ni/C for high-performance direct borohydride fuel cells

Direct borohydride fuel cells (DBFCs) outperform the other direct liquid fuel cells by a higher open circuit voltage and energy density. However, their benign performance and efficiency are highly dependent on high-performance anode catalysts. This study delves into the enhancement of borohydride oxidation reaction (BOR) kinetics through an octahedral Pt–Ni/C catalyst. The Pt(111) facets of the catalyst exhibit a combination of abundant active sites exposed for BOR and the inherent ability to suppress hydrolysis reaction. Furthermore, the synergistic incorporation of Ni modifies the electronic structure of Pt, resulting in enhanced OH− adsorption and hydrogen oxidation reaction (HOR) activity. This multifaceted approach not only mitigates hydrogen accumulation but also boosts the overall BOR efficiency. The elaborate electrochemical measurements along with comprehensive characterizations elucidate the superior catalytic activity and stability of Pt–Ni/C over commercial Pt/C catalysts. Specifically, DBFCs employing the Pt–Ni/C catalyst manifest considerably higher open circuit voltage (1.05 V), peak power density (1.82 W cm−2) and fuel efficiency (63.96 %) than those of DBFCs employing Pt/C catalyst. Through these efforts, we provide significant insight into the design of high-performance anode catalyst for DBFCs.

Particle swarm optimization for a hybrid freight train powered by hydrogen or ammonia solid oxide fuel cells

All diesel-only trains in the UK will be phased out by 2040. Hydrogen and ammonia emerge as alternative zero-carbon fuel for greener railway. Solid Oxide Fuel Cells (SOFCs) provide an alternative prime mover option, which efficiently convert zero-carbon fuels into electricity without emitting nitrogen oxides (NOx), unlike traditional engines. Superior to Proton Exchange Membrane Fuel Cells (PEMFCs) in efficiency, SOFCs fulfil MW-scale power needs and can use ammonia directly. This study investigates innovative strategies for integrating SOFCs into hybrid rail powertrains using hydrogen or ammonia. Utilizing an optimization framework incorporating Particle Swarm Optimization (PSO), the study aims to minimize operational costs while considering capital and replacement expenditures, powertrain performance, and component sizing. The findings suggest that hybrid powertrains based on ammonia-fueled SOFCs may potentially reduce costs by 30% compared to their hydrogen counterparts, albeit requiring additional space for engine compartments. Ammonia-fueled SOFCs trains also exhibit a 5% higher efficiency at End-of-Life (EoL), showing less performance degradation than those powered by hydrogen. The State of Charge (SoC) of the batteries in range of 30–70% for both cases is identified as most cost-effective.

Design of Multifunctional Electrocatalysts for ORR/OER/HER/HOR: Janus Makes Difference.

Multifunctional electrocatalysts for hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) have broad application prospects; However, realization of such kinds of materials remain difficulties because it requires the materials to have not only unique electronic properties, but multiple active centers to deal with different reactions. Here, employing density functional theory (DFT) computations, it is demonstrated that by decorating the Janus-type 2D transition metal dichalcogenide (TMD) of TaSSe with the single atoms, the materials can achieve multifunctionality to catalyze the ORR/OER/HER/HOR. Out of sixteen catalytic systems, Pt-VS (i.e., Pt atom embedded in the sulfur vacancy), Pd-VSe, and Pt-VSe@TaSSe are promising multifunctional catalysts with superior stability. Among them, the Pt-VS@TaSSe catalyst exhibits the highest activity with theoretical overpotentials ηORR = 0.40V, ηOER = 0.39V, and ηHER/HOR = 0.07V, respectively, better than the traditional Pt (111), IrO2 (110). The interplays between the catalyst and the reaction intermediate over the course of the reaction are then systematically investigated. Generally, this study presents a viable approach for the design and development of advanced multifunctional electrocatalysts. It enriches the application of Janus, a new 2D material, in electrochemical energy storage and conversion technology.

Genomic and phenotypic characterization of 26 novel marine bacterial strains with relevant biogeochemical roles and widespread presence across the global ocean.

Prokaryotes dominate global oceans and shape biogeochemical cycles, yet most taxa remain uncultured and uncharacterized as of today. Here we present the characterization of 26 novel marine bacterial strains from a large isolate collection obtained from Blanes Bay (NW Mediterranean) microcosm experiments made in the four seasons. Morphological, cultural, biochemical, physiological, nutritional, genomic, and phylogenomic analyses were used to characterize and phylogenetically place the novel isolates. The strains represent 23 novel bacterial species and six novel genera: three novel species pertaining to class Alphaproteobacteria (families Rhodobacteraceae and Sphingomonadaceae), six novel species and three new genera from class Gammaproteobacteria (families Algiphilaceae, Salinispheraceae, and Alteromonadaceae), 13 novel species and three novel genera from class Bacteroidia (family Flavobacteriaceae), and one new species from class Rhodothermia (family Rubricoccaceae). The bacteria described here have potentially relevant roles in the cycles of carbon (e.g., carbon fixation or energy production via proteorhodopsin), nitrogen (e.g., denitrification or use of urea), sulfur (oxidation of sulfur compounds), phosphorus (acquisition and use of different forms of phosphorus and remodeling of membrane phospholipids), and hydrogen (oxidation of hydrogen to obtain energy). We mapped the genomes of the presented strains to the Tara Oceans metagenomes to reveal that these strains were globally distributed, with those of the family Flavobacteriaceae being the most widespread and abundant, while Rhodothermia being the rarest and most localized. While molecular-only approaches are also important, our study stresses the importance of culturing as a powerful tool to further understand the functioning of marine bacterial communities.

Surface oxygen defect engineering to enhance La0.5Sr0.5Fe0.9Mo0.1O3-δ electrochemical performance for reversible symmetric solid oxide cells

Perovskite oxide-based materials are promising electrode materials for reversible symmetric solid oxide cells (RSSOCs) as they exhibit good catalytic activity and stability in oxidizing and reducing atmospheres. In this study, A-site deficient (La0.5Sr0.5)0.95Fe0.9Mo0.1O3-δ (95LSFMo) is synthesized as an electrode material for RSSOCs. The A-site defect in La0.5Sr0.5Fe0.9Mo0.1O3-δ increases the surface oxygen vacancy concentration, promoting the transport of oxygen ions and enhancing the catalytic activities of oxygen reduction (ORR) and hydrogen oxidization reaction (HOR). 95LSFMo|LSGM|95LSFMo symmetric cell achieves a maximum power density (MPD) of 1.14 W cm−2 at 850 °C. Furthermore, the adsorption and reduction of H2O is also improved. In 50 %H2O-H2, 95LSFMo cell shows a current density of −1.71 A cm−2 at 850 °C and 1.3 V in electrolysis mode and a peak power density of 0.82 W cm−2 in fuel cell mode. The corresponding hydrogen production rate reaches 714.78 ml cm-2h−1. Moreover, the 95LSFMo cell exhibits good reversibility as well as SOEC stability.

Atomically dispersed Iridium on Mo2C as an efficient and stable alkaline hydrogen oxidation reaction catalyst

Hydroxide exchange membrane fuel cells (HEMFCs) have the advantages of using cost-effective materials, but hindered by the sluggish anodic hydrogen oxidation reaction (HOR) kinetics. Here, we report an atomically dispersed Ir on Mo2C nanoparticles supported on carbon (IrSA-Mo2C/C) as highly active and stable HOR catalysts. The specific exchange current density of IrSA-Mo2C/C is 4.1 mA cm−2ECSA, which is 10 times that of Ir/C. Negligible decay is observed after 30,000-cycle accelerated stability test. Theoretical calculations suggest the high HOR activity is attributed to the unique Mo2C substrate, which makes the Ir sites with optimized H binding and also provides enhanced OH binding sites. By using a low loading (0.05 mgIr cm−2) of IrSA-Mo2C/C as anode, the fabricated HEMFC can deliver a high peak power density of 1.64 W cm−2. This work illustrates that atomically dispersed precious metal on carbides may be a promising strategy for high performance HEMFCs.

Mechanisms of formation and shape control of pentagonal Pd-nanostars and their unique properties in electrocatalytic methanol oxidation and membrane separation of high-purity hydrogen

Membranes on palladium alloy basis with surface modified by nanoparticles with high catalytic activity are useful in deep hydrogen purification and single-stage process of high-purity hydrogen production. This paper reports the development and improvement of methods for synthesis of Pd-based pentatwinned nanoparticles of strictly specified morphology with certain shapes, facets and composition. The competing effect of surfactants and optimization of the halide ions ratio in solution make it possible to direct a particle growth towards formation of pentatwinned Pd-nanostars. Pd–23%Ag coatings synthesized on the surface showed uniquely high peak current density of up to 238 mA cm−2 in alkaline methanol oxidation reaction. This is due to both increased surface area and greater catalytic activity of nanostars’ facets. A record increase in hydrogen permeability of up to 12.5 mmol s−1 m−2 at 100 °C has been achieved for palladium-silver membranes with modified surface. This indicates an acceleration of sorption/desorption stages. The developed method for controlling morphology of nanoscale coatings opens the way to the production of membrane hydrogen filters, which operate at room temperature.