Reaction Of Hydrogen Research Articles

High-safety lithium metal pouch cells for extreme abuse conditions by implementing flame-retardant perfluorinated gel polymer electrolytes

Lithium metal anodes coupled with nickel-rich cathodes promise high-energy-density batteries. Nonetheless, the overall safety of lithium metal batteries is compromised by the use of conventional thermally unstable and flammable carbonate-based electrolytes, which hinders their practical applications, especially under abuse conditions. Herein, a flame-retardant perfluorinated gel polymer electrolyte (PFGPE) is developed by in situ copolymerization of perfluorobutyl acrylate (PFBA) monomer with pentaerythritol tetraacrylate (PETEA) crosslinker. PFBA decomposes at high temperatures to generate fluorine radicals that eliminate hydrogen and hydroxyl radical chain combustion reactions in the gas phase, reducing the combustion risk of electrolytes. Additionally, the co-pyrolysis of the carbonate-based electrolytes and the copolymerization matrix produces a P- and F- containing char layer in the condensed phase, blocking the heat and oxygen required for combustion. A large-format PFGPE modified Li metal pouch cell (4.4 Ah, 381 Wh kg−1) achieves 120 cycles with 83.4% of capacity retention under a lean electrolyte of 3 g Ah−1 and a negative/positive capacity ratio of 1.82. Moreover, the modified pouch cell exhibits enhanced thermal safety characteristics and passes international standard tests (GB/T 31485–2015) for mechanical nail penetration and thermal abuse. This innovative approach represents a significant milestone towards the advancement of high-safety Li metal batteries.

NEW STEREOSELECTIVE CATALYSTS FOR THE HYDROGENATION OF SUNFLOWER OIL

The work is devoted to the creation of new stereoselective catalysts for the hydrogenation of sunflower oil, which can significantly reduce the trans-isomers of fatty acids. Thus, on nickel catalysts used in industry, the content of trans-isomers of fatty acids reaches up to 30%. Platinum deposited on diatomite (processed natural clay) 0.2 to 1% is offered as a catalyst. Methodology. The hydrogenation was carried out in an autoclave, excluding external diffusion inhibition, at hydrogen pressures ranging from 0.25 to 1.0 MPa and temperatures ranging from 90 to 110°C. Results and discussion. Chromatographic analysis was used in all cases to determine the isomeric composition of fatty acids, making it possible for the first time to change hydrogen pressure and reaction temperature without changing the isomeric composition. This allows the study of how stereoisomeric composition changes during the hydrogenation of fatty acids. Various physical methods are used to verify catalysts: TPD, BET, and TEM, etc., which can determine catalyst particle size, hydrogen adsorption forms, and specific surfaces. Conclusion. These characteristics were correlated with the activity and stereoselectivity of the studied catalysts. Trans-fatty acids are found to be two to three times lower on platinum catalysts than on nickel catalysts.

Surface reconstruction of RuO2/Co3O4 amorphous-crystalline heterointerface for efficient overall water splitting

The rational construction of amorphous-crystalline heterointerface can effectively improve the activity and stability of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, RuO2/Co3O4 (RCO) amorphous-crystalline heterointerface is prepared via oxidation method. The optimal RCO-10 exhibits low overpotentials of 57 and 231 mV for HER and OER at 10 mA cm−2, respectively. Experimental characterization and density functional theory (DFT) results show that the optimized electronic structure and surface reconstruction endow RCO-10 with excellent catalytic activity. DFT results show that electrons transfer from RuO2 to Co3O4 through the amorphous-crystalline heterointerface, achieving electron redistribution and moving the d-band center upward, which optimizes the adsorption free energy of the hydrogen reaction intermediate. Moreover, the reconstructed Ru/Co(OH)2 during the HER process has low hydrogen adsorption free energy to enhance HER activity. The reconstructed RuO2/CoOOH during the OER process has a low energy barrier for the elementary reaction (O*→*OOH) to enhance OER activity. Furthermore, RCO-10 requires only 1.50 V to drive 10 mA cm−2 and maintains stability over 200 h for overall water splitting. Meanwhile, RCO-10 displays stability for 48 h in alkaline solutions containing 0.5 M NaCl. The amorphous-crystalline heterointerface may bring new breakthroughs in the design of efficient and stable catalysts.

The Effect of Ignition Procedure on Flashback of Hydrogen-Enriched Flames

Abstract The impact of different ignition sequences on the ignition dynamics of CH4-H2 flames in a bluff body burner is investigated at atmospheric conditions. Experiments are performed over a wide range of operating conditions covering pure methane injection (PH0) to pure hydrogen injection (PH100). A perforated plate of total porosity σ=0.17 is positioned at the outlet of the combustion chamber to increase the chamber back pressure and trigger transient flashback during ignition. Time-series of pressure, OH* chemiluminescence and OH-PLIF images of the propagating flame branch are recorded simultaneously to characterize the ignition process. Two ignition procedures are investigated. For ignition procedure A, designated as an early ignition procedure, the spark is initiated before fuel injection. For ignition procedure B, designated as a late ignition, the spark is only activated after the fuel injection. The impact of the fuel air mixing on the final stabilization state is investigated by changing the fuel delivery time (dt) before the initial spark. Three different time delays are considered dt = 1, 3, and 5 s. The final state of the flame is found to be highly sensitive to the selected ignition procedure and increasing dt favors the occurrence of flashback. At constant power, the magnitude of the pressure peak is driven by a competition between the fuel mass flowrate at the moment of ignition and the high reactivity of hydrogen, which shifts the flammability limit toward lower equivalence ratios, hence generating a lower reaction rate. For procedure A, the peak of the chamber over pressure shows a nonmonotonic growth for increasing levels of H2 in the fuel blend, while it linearly increases for procedure B. Experiments are then conducted at a fixed injection flow velocity Ub = 5 m s–1 and fixed laminar burning velocity Sl0=0.25 m s–1 by varying the level of hydrogen enrichment. For procedure A, the over pressure amplitude decreases with increasing the hydrogen enrichment leading to a soft ignition for all CH4-H2 blends. Under ignition procedure B, the amplitude of the over pressure reached during ignition is found to be relatively unaffected by the hydrogen concentration, but the flame stabilization mode shows a strong dependence to both the level of H2-enrichment and fuel delivery time dt. OH* as well as OH-PLIF images reveal that the trajectory of the flame leading point changes as dt increases. The different dynamics of the flame leading points is likely to be the cause the different types of stabilization modes observed.

Hydrogen Reactions with Dopants and Impurities in Solar Silicon from First Principles

A theoretical account of some of the most likely hydrogen‐related reactions with impurities in n‐ and p‐type solar‐grade silicon is presented. These include reactions with dopants and carbon, which are relevant in the context of lifetime degradation of silicon solar cells, most notably of light‐ and elevated temperature‐induced degradation of the cells. Among the problems addressed, a comparative study of acceptor‐enhanced dissociation of hydrogen molecules in B‐ and Ga‐doped material, their subsequent reaction steps toward formation of acceptor–hydrogen pairs, the proposal of mechanisms which explain the observed kinetics of photo‐/carrier‐induced dissociation of PH and CH pairs in n‐type Si, analysis of reactions involving direct interactions between molecules with P and C, and the assignment of several electron and hole traps with detailed atomistic‐ and wavefunction‐resolved models is highlighted.

A heterostructure of interlayer-expanded 1T phase MoS2 and spherical MoO2 for efficient and stable hydrogen evolution

The inferior hydrogen evolution reaction (HER) catalytic performance of MoS2 can be attributed to its small edge ratio, large inert substrate surface, and poor electrical conductivity, while the multiple strategies are expected to be employed simultaneously to modulate the electronic structure of MoS2 and yield catalysts with superior HER catalytic performance. Here, we report a MoS2 containing a 1 T phase with expanded layer spacing and construct it as a heterostructured material with MoO2 (MoO2 @E-MoS2). Specifically, the presence of the 1 T phase and expanded layer structure of MoS2 can enhance electrode conductivity, increase active site exposure, promote H2O adsorption, and optimize the Gibbs-free energy of hydrogen. The constructed heterostructure can modulate the electronic structure of the catalyst, enhance electron transfer at the interface, elevate water adsorption energy, and reduce the hydrogen reaction energy barrier. Moreover, density functional theory calculations indicate that the S site of MoS2 in this catalyst exhibits a higher affinity for H2O adsorption, while the Mo site demonstrates a greater capacity for H* adsorption/desorption. Ultimately, MoO2 @E-MoS2 shows low overpotentials of 93 and 99 mV at a current density of 10 mA cm−2, as well as exceptional long-term stabilities exceeding 70 and 130 h at current densities ranging from 10 to 30 mA cm−2 in acidic and alkaline media, respectively.

Proton Relay for the Rate Enhancement of Electrochemical Hydrogen Reactions at Heterogeneous Interfaces.

Proton transfer is critically important to many electrocatalytic reactions, and directed proton delivery could open new avenues for the design of electrocatalysts. However, although this approach has been successful in molecular electrocatalysis, proton transfer has not received the same attention in heterogeneous electrocatalyst design. Here, we report that a metal oxide proton relay can be built within heterogeneous electrocatalyst architectures and improves the kinetics of electrochemical hydrogen evolution and oxidation reactions. The volcano-type relationship between activity enhancement and pKa of amine additives confirms this improvement; we observe maximum rate enhancement when the pKa of a proton relay matches the pH of the electrolyte solution. Density-functional-theory-based reactivity studies reveal a decreased proton transfer energy barrier with a metal oxide proton relay. These findings demonstrate the possibility of controlling the proton delivery and enhancing the reaction kinetics by tuning the chemical properties and structures at heterogeneous interfaces.

Transition-metal sulfides with excellent hydrogen and oxygen reactions: A mini-review

In order to create sustainable, environmentally friendly energy systems, the Hydrogen Evolution Reaction and Oxygen Evolution Reaction must be prioritized. Transition metal sulfides (TMSs) have been studied extensively as catalysts for both HER and OER because of their high activity, cheap cost, and availability. However, its low stability and conductivity limit its usefulness. Recent research efforts have focused on developing TMS-based nanocomposites, which combine the advantageous properties of TMSs with those of other materials, in order to overcome these concerns. The latest advances in TMS-based nanocomposites for oxygen reduction reaction and hydrogen reduction reaction are outlined in this article. We begin by discussing the broad concepts of HER and OER and the problems of TMSs in these reactions. We have comprehensively addressed the role of Sulfur atoms in electrocatalytic water splitting. We also emphasize the need to improve the contact between TMSs and other materials to enable effective charge transfer. Lastly, we evaluate the performance of TMS-based nanocomposites in HER and OER and compare their activity to that of other cutting-edge catalysts. We also examine the remaining research problems and potential in this subject. TMS-based nanocomposites show significant potential for practical applications of HER and OER in renewable energy systems.

Effect of hydrogen on nickel oxide reduction on the surface of nozzle blade of a gas turbine unit

Currently, there is a growing interest in the use of hydrogen in the composition of fuel mixtures for turbojet engines and gas turbine units (GTU). The effect of hydrogen on heat-resistant nickel alloys of gas turbine blades has been little studied. In this regard, this work is devoted to studying the effect of hydrogen on nickel oxide reduction on the surface of the nozzle blade of a gas turbine engine. Hydrogen is a good reducing agent. Therefore, this article discusses the effects of hydrogen under various conditions with metal oxides, and methods of metal oxides reduction on the surface of the blades of a gas turbine engine. The thermodynamics of the interaction of aluminum, titanium, nickel and tungsten oxides with hydrogen fluoride and reactions of fluoride with hydrogen was investigated in the temperature range 273 – 1373 K. It was established that the interaction of aluminum oxide with hydrogen fluoride occurs in the temperature range from 273 to 1073 K, titanium oxide with hydrogen fluoride – from 273 to 373 K, nickel oxide with hydrogen fluoride – from 273 to 873 K. In this case, of the resulting fluorides, only nickel fluoride interacts with hydrogen at temperatures above 673 K. Hydrogen interacts with nickel oxide throughout the entire temperature range, and with tungsten oxide at temperatures above 1173 K. We studied the effect of hydrogen on heat-resistant nickel alloys of gas turbine blades subjected to preliminary fluorination and not treated with fluorine compounds. Nickel oxide reduction with hydrogen proceeds better after the preliminary fluorination process. In this case, particles 2 – 5 μm in size containing 90.16 % Ni are formed on the surface of the blade sample. Without fluorination, this process at 1223 K and duration of 1 h does not occur.

New synthetic method for ring-fused quinazoline by palladium-catalyzed oxidative cyclization of 2-aminobenzyl alcohol: Chiral separation and structural analysis

We demonstrate the borrowing hydrogen reaction of readily available 2-aminobenzyl alcohol 1, which is a new synthetic strategy for the construction of ring-fused quinazoline systems. The cascade reaction involves the dehydrogenative oxidation of alcohol 1 to the corresponding aldehyde 3 followed by self-condensation and reduction utilizing the benzyl Pd(II) system. The racemate 2 was successfully separated by chiral HPLC, affording a pair of enantiomers with high purity (>99 % ee) in a 1:1 ratio. The absolute configuration of one enantiomer was established via X-ray crystallography of its heavy atom analog. The structures of the racemate 2 and the pure enantiomer 2a were characterized by single-crystal X-ray analysis.

Turbulent Flame Speed and Flame Characteristics of Lean Premixed H2-CH4 Flames at Moderate Pressure Levels

Abstract Carbon dioxide emissions in gas turbine power generation can be reduced by adding an increasing amount of hydrogen to the existing natural gas-fueled combustion systems. To enable safe operation, more insight on how H2 addition affects turbulent flame speed and other important flame characteristics is needed. In this work, the investigation of hydrogen addition effects on certain flame properties has been carried out in a high-pressure axial-dump combustor at gas turbine relevant conditions. OH planar laser induced fluorescence (PLIF) was applied to retrieve flame front contours and turbulent flame speed. The results show that as the concentration of hydrogen in the fuel mixture increases, turbulent flame speed and flame characteristics change drastically. Two main regimes can be identified: From 0 to 50% vol. Hydrogen, the turbulent flame speed increases weakly in an almost linear fashion, while from 50% vol. to 100% vol. the trend sharply changes and the higher reactivity of hydrogen, combined with a lower Lewis number, cause thermal-diffusive instability and preferential diffusion effects to become increasingly strong, leading to very high burning rates. The presented results help to understand and to define the relevant modifications that are necessary to successfully operate gas turbine combustor systems with high H2 content fuels.

Two-dimensional Ga2XY monolayer containing vacancies for highly efficient electrocatalytic hydrogen reaction: based on first-principles calculations

Hydrogen energy as an excellent substitute for traditional fossil fuels, has received widespread attention. There is an urgent need to find an efficient and environmentally friendly electrocatalyst to increase hydrogen production. In this study, the Ga2XY (X, Y=O, S, Se, Te, X≠Y) system of group III-VI compounds was constructed, and the HER catalytic properties of its vacancy structure were investigated based on first principles. The research results show that all the structures are stable, and the introduction of O vacancy and Ga vacancy can significantly improve the structure’s Gibbs free energy (ΔGH). When the H atom is adsorbed on the bottom Ga atom, the HER with Ga2OSe structure containing outer Ga vacancy is very excellent, and its ΔGH can reach 0.07 eV, which is significantly superior to the currently recognized best HER catalyst Pt. Our research provides a new strategy for the design of HER electrocatalysts and a new method for the regulation of Ga2XY monolayers.

Exploring hydrogen storage potential in depleted Western Australian hydrocarbon reservoirs: A petrophysical and petrographic analysis

Hydrogen, recognised as a clean and sustainable energy carrier with excellent transportation fuel properties, drives numerous countries towards a hydrogen-based economy due to its high utilisation efficiency and minimal environmental impact. However, the gaseous nature of hydrogen necessitates larger storage surface areas. Underground Hydrogen Storage (UHS) has emerged as a promising and efficient method to overcome this challenge. Currently, only a handful of UHS locations exist globally due to the novelty of this field. With its abundant depleted hydrocarbon reservoirs boasting significant storage capacity, Western Australia presents a suitable region for hydrogen storage.This paper comprehensively analyses petrophysical and petrographic characteristics, employing XRD, MIP, and Micro-CT techniques on sandstone and claystone samples obtained from several fields in Western Australia. The suitability of these samples for hydrogen storage is evaluated based on mineral composition and porosity. The analysis reveals that more than 96% of Quartz is present in the sandstone samples. The claystone samples exhibit a mineral composition comprising Quartz, Calcite, K-feldspar, Kaolinite, Pyrite, Albite, and Muscovite. The study suggests that hydrogen storage in formation rock is favourable due to the low reactivity of hydrogen with silicate minerals, but interactions with cap rock minerals should be considered.Micro-CT results indicate the connected porosity in the 17.23–4.67% range. Pore distribution in sandstones ranges from nanometers to millimetres, with a substantial proportion of connected pores in the intermediate range, which is conducive to hydrogen storage. This is particularly advantageous as the hydrogen-water system is highly water-wet, with hydrogen primarily occupying medium and larger pores, minimising hydrogen trapping. In claystone, most pores were below 3 nm, but instrumental constraints limited their quantification. In conclusion, the petrophysical and petrographic analysis underscores the potential of Western Australian depleted hydrocarbon reservoirs for hydrogen storage. Understanding the mineralogical reactions with cap rock minerals is crucial, while the favourable pore distribution in sandstones further supports the viability of hydrogen storage.

Recent Progress, Challenges, and Future Prospects in Solar H2 Evolution via Pure/Sea Water Splitting Using Nanocomposites as Photocatalysts under Solar Light

AbstractPhotocatalytic pure/sea water splitting driven by solar light, emerges as the most promising strategy to address both the global energy crisis and environmental degradation. Research efforts have mainly resulted in the development of artificial photocatalytic solar hydrogen generation systems applicable to both freshwater and sea water. During long‐term testing, sea water demonstrated enhanced stability compared to pure water, offering experimental advantages in designing novel techniques aimed at reducing hydrogen generation costs, alleviating freshwater scarcity, and optimizing the utilization of natural water resources. Moreover, sea water splitting proves to be more effective in producing solar hydrogen due to the potential sacrificial action of salt ions, which promote hydrogen evolution within the photocatalytic system. This review comprehensively outlines the fundamental principles of photocatalytic H2 production, examines the efficiencies and recent progress in hydrogen generation, explores the challenges faced, and envisions the future prospects of enhancing hydrogen production efficiency and reactivity through photocatalytic pure/sea water splitting.

Substituent Effects and Mechanistic Insights on the Catalytic Activities of (Tetraarylcyclopentadienone)iron Carbonyl Compounds in Transfer Hydrogenations and Dehydrogenations.

(Cyclopentadienone)iron carbonyl compounds are catalytically active in carbonyl/imine reductions, alcohol oxidations, and borrowing hydrogen reactions, but the effect of cyclopentadienone electronics on their activity is not well established. A series of (tetraarylcyclopentadienone)iron tricarbonyl compounds with varied electron densities on the cyclopentadienone were prepared, and their activities in transfer hydrogenations and dehydrogenations were explored. Additionally, mechanistic studies, including kinetic isotope effect experiments and modifications to substrate electronics, were undertaken to gain insights into catalyst resting states and turnover-limiting steps of these reactions. As the cyclopentadienone electron density increased, both the transfer hydrogenation and dehydrogenation rates increased. A catalytically relevant, trimethylamine-ligated iron compound was isolated and characterized and was observed in solution under both transfer hydrogenation and dehydrogenation conditions. Importantly, it was catalytically active in both reactions. Kinetic isotope effect data and initial rates in transfer hydrogenation reactions with 4'-substituted acetophenones provided evidence that hydrogen transfer from the catalyst to the carbonyl substrate occurred during the turnover-limiting step, and NMR spectroscopy supports the trimethylamine adduct as an off-cycle resting state and the (hydroxycyclopentadienyl)iron hydride as an on-cycle resting state. In transfer dehydrogenations of alcohols, the use of electronically modified benzylic alcohols provided evidence that the turnover-limiting step involves the transfer of hydrogen from the alcohol substrate to the catalyst. The trimethylamine-ligated compound was proposed as the primary catalyst resting state in dehydrogenations.

Competing Excited-State Hydrogen and Proton-Transfer Processes in 6-Azaindole-S3,4 and 2,6-Diazaindole-S3,4 Clusters (S=H2 O, NH3 ).

Excited state hydrogen (ESHT) and proton (ESPT) transfer reaction pathways in the three and four solvent clusters of 6-azaindole (6AI-S3,4 ) and 2,6-diazaindole (26DAI-S3,4 )(S=H2 O, NH3 ) were computationally investigated to understand the fate of photo-excited biomolecules. The ESHT energy barriers in (H2 O)3 complexes (39.6-41.3 kJmol-1 ) were decreased in (H2 O)4 complexes (23.1-20.2 kJmol-1 ). Lengthening the solvent chain lowered the barrier because of the relaxed transition states geometries with reduced angular strains. Replacing the water molecule with ammonia drastically decreased the energy barriers to 21.4-21.3 kJmol-1 in (NH3 )3 complexes and 8.1-9.5 kJ mol-1 in (NH3 )4 complexes. The transition states were identified as Ha atom attached to the first solvent molecule. The formation of stronger hydrogen bonds in (NH3 )3,4 complexes resulted in facile ESHT reaction than that in the (H2 O)3,4 complexes. The ESPT energy barriers in 6AI-S3,4 and 26DAI-S3,4 were found to range between 40-73 kJmol-1 . The above values were significantly higher than that of the ESHT processes and hence are considered as a minor channel in the process. The effect of N(2) insertion was explored for the very first time in the isolated solvent clusters using local vibrational mode analysis. In DAI-S4 , the higher Ka (Ha ⋯Sa ) values depicted the increased photoacidity of the N(1)-Ha group which may facilitate the hydrogen transfer reaction. However, the increased N(6)⋯Hb bond length elevated the reaction barriers. Therefore, in the ESHT reaction channel, the co-existence of two competing factors led to a marginal/no change in the overall energy barriers due to the N(2) insertion. In the ESPT reaction pathway, the energy barriers showed notable increase upon N(2) insertion because of the increased N(6)⋯Hb bond length.

Pt/C‐catalyzed Selective Hydrogenation of Nitroarenes to N‐arylhydroxylamines under Mild Conditions

AbstractThe synthesis of N‐arylhydroxylamines through the in‐situ hydrogenation of nitroarenes over commercial Pt/C catalyst was investigated. The effects of various reaction conditions including hydrogen donor, solvent, catalyst dosage, temperature and reaction time on the selective hydrogenation of nitrobenzene (NB) to N‐phenylhydroxylamine (PHA) were systematically investigated. The results showed that the yield of N‐phenylhydroxylamine reached 87.2 % using hydrazine hydrate as hydrogen donor in N,N‐dimethylformamide solvent at 30 °C for 60 min. And the catalyst showed no obvious activity loss after a 6‐times recycle. Meanwhile, the developed methodology can also transform a range of nitroarenes to the corresponding N‐arylhydroxylamines in excellent yields (74–99 %).

Bifunctional Electrode Design Targeting Co‐Enhanced Kinetics and Mass Transport for Hydrogen and Water Oxidation Reactions (Adv. Funct. Mater. 40/2023)

Bifunctional Electrode Design Targeting Co‐Enhanced Kinetics and Mass Transport for Hydrogen and Water Oxidation Reactions (Adv. Funct. Mater. 40/2023)

Variable metal valence states with band-edge shift over in-situ annealed CuTi-LDH nanosheets for efficient hydrogen and oxygen reduction reactions

Variable metal valence states with band-edge shift over in-situ annealed CuTi-LDH nanosheets for efficient hydrogen and oxygen reduction reactions

Near-Atomic-Scale Superfine Alloy Clusters for Ultrastable Acidic Hydrogen Electrocatalysis.

As a commercial electrode material for proton-exchange membrane water electrolyzers and fuel cells, Pt-based catalysts still face thorny issues, such as insufficient mass activity, stability, and CO tolerance. Here, we construct a bifunctional catalyst consisting of Pt-Er alloy clusters and atomically dispersed Pt and Er single atoms, which exhibits excellent activity, durability, and CO tolerance of acidic hydrogen evolution and oxidation reactions (HER and HOR). The catalyst possesses a remarkably high mass activity and TOF for HER at 63.9 times and 7.2 times more than that of Pt/C, respectively. More impressively, it can operate stably in the acidic electrolyte at 1000 mA cm-2 for more than 1200 h, thereby confirming its potential for practical applications at the industrial current density. In addition, the catalyst also demonstrates a distinguished HOR performance and outstanding CO tolerance. The synergistic effects of active sites give the catalyst exceptional activity for the hydrogen reaction, while the introduction of Er atoms greatly enhances its stability and CO tolerance. This work provides a promising idea for designing low-Pt-loading acidic HER electrocatalysts that are durable at ampere-level current densities and for constructing HOR catalysts with high CO tolerance.