High-temperature treatment to engineer the single-atom Pt coordination environment towards highly efficient hydrogen evolution

Development of high-performance and cost-effective catalysts for electrocatalytic hydrogen evolution reaction(HER)play crucial role in the growing hydrogen economy.Recently,the atomically dispersed metal catalysts have attracted increasing attention due to their ultimate atom utilization and great potential for highly cost-effective and high-efficiency HER electrocatalyst.Herein,we propose a hightemperature treatment strategy to furtherly improve the HER performance of atomically dispersed Ptbased catalyst.Interestingly,after appropriate high-temperature treatment on the atomically dispersed Pt0.8@CN,the Pt species on the designed N-doped porous carbon substrate with rich defect sites can be re-dispersed to single atom state with new coordination environment.The obtained Pt0.8@CN-1000 shows superior HER performance with overpotential of 13 m V at 10 m A cm^(-2)and mass activity of 11,284 m A/mgPtat-0.1 V,much higher than that of the pristine Pt0.8@CN and commercial Pt/C catalyst.The experimental and theoretical investigations indicate that the high-temperature treatment induces the restructuring of coordination environment and then the optimized Pt electronic state leads to the enhanced HER performances.This work affords new strategy and insights to develop the atomically dispersed high-efficiency catalysts.

Dependence of Atomic-Scale Si(110) Surface Roughness on Hydrogen Introduction Temperature after High-Temperature Ar Annealing

The atomic-scale surface roughness of Si(110) reconstructed via high-temperature Ar annealing is immediately increased by non uniform accidental oxidation during the unloading process (called reflow oxidation) during high-temperature Ar annealing. In particular, for a reconstructed Si(110) surface, characteristic line-shaped oxidation occurs at preferential oxidation sites appearing in pentagonal pairs in the directions of Si[-112] and/or [-11-2]. We previously reported that the roughness increase of reconstructed Si(110) due to reflow oxidation can be restrained by replacing Ar gas with H2 gas at 1000&#176C during the cooling to 100&#176C after high-temperature Ar annealing. It was speculated that preferential oxidation sites on reconstructed Si(110) were eliminated by H2 gas etching and hydrogen termination of dangling bonds. Thus, it is necessary to investigate the effect of H2 gas etching and hydrogen termination behavior on the reconstructed Si(110) surface structure. In this study, we evaluated in detail the relationship between the temperature at which the H2 gas replaces the Ar in high-temperature Ar annealing and the reconstructed Si(110) surface structure. The maximum height of the roughness on the reconstructed surface was the same as if Ar gas was used when the H2 gas introduction temperature was 200&#176C, although the amount of reflow oxidation was decreased to 70% by hydrogen termination. Furthermore, line-shaped oxidation still occurs when H2 gas replaces Ar at this low temperature. Therefore, we conclude that oxidation is caused by slight Si etching at low temperatures, and thus the preferential oxidation sites on the reconstructed structure must be eliminated by hydrogen etching in order to form an atomically smooth Si(110) surface.

HEALING OF HYDROGEN ATTACK CRACK IN AUSTENITE STAINLESS STEEL UNDER HEAT TREATMENT

The specimens of 304 austenite stainless steel with the hydrogen attackbubbles or cracks were heat treated at 600 deg C for 6h. The SEM and TEM observations on thespecimens before and after the heat treatment showed that the bubbles or cracks could be healedcompletely by heat treatment. The healing of hydrogen attack bubbles or cracks is closely related toheat diffusion of Fe and C atoms in austenite. The driving force of crack healing results from theplastic deforming energy E_s induced by the growth of hydrogen attack bubbles or cracks. Thecritical condition of healing of bubbles or cracks is E_s >= 2 gamma/r (where gamma is the surfacetension, r is the radius of bubbles or half length of crack). During healing of the hydrogen attackbubbles or cracks, the recovery, polygonization and recrystallization of the sub-grain also occured.

Effect of hydrogen attack on acoustic emission behavior of low carbon steel

In order to investigate the effect of hydrogen attack degree on acoustic emission(AE) behavior of low carbon steel during tensiling, specimens made of Low carbon steel was exposed to hydrogen gas of 18 MPa at 450 and 500℃ for 240, 480 and 720 h respectively. Experimental results show that with increase of the hydrogen attack degree, the totally AE activity decreases during tensiling. In addition, the count of AE signals with high amplitude for the specimens with hydrogen attack keeps a constant which is less than that without hydrogen attack. It is concluded that AE signals originate in the specimens with hydrogen attack from intergranular fracture induced by methane blisterings or/and microcracks on grain boundaries.

THE EFFECT OF BORON TREATMENT ON THE HYDROGEN ATTACK BEHAVIOR 0F 1.25Cr-0.5Mo STEELS

1.25Cr-0.5Mo steels with different Ti-B or Al-B treatment were exposed in 18 MPa hydrogen atmosphere at 480℃ fo f 100, 500 and 1000 h respectively. Tensile and bend properties of steels before and after hydrogen changing were tested. The results show that the different mechanical properties of the steels with different B content have different responses to high temperature high pressure hydrogen charging processes.After hydrogen changing, more loss of ductility can be found in the steel not treated with B than those in the steels treated with B. Metallographic analyses indicated that decarburization occurred in all the steels. Furthermore, many methane bubbles were found by SEM analysis in the surface decarburization layer in the steel without B,while only a few bubbles, the number and size of which decreased with increasing B content, were found in steels with B treatment. In addition, hydrogen determination results manifested that after being exposed in hydrogen atmosphere the steel containing no B had higher hydrogen content than that of steels containing B. All this suggests that B treatment improved the HA resistance of 1.25Cgr-0.5Mo steel, and the more B the steel contained the more perceptible the effect.

HYDROGEN ATTACK ON AUSTENITIC STEEL 304 UNDER HIGH TEMPERATURE AND HIGH PRESSURE

The hydrogen attack of austenitic stainless steel 304 exposed to hydrogen under the pressure of 5 MPa at 733 K for 2×10~4 h in service was detected.The microstructure has been studied by SEM and TEM.Hydrogen was determined with molten samples which had tempered at.573,673,773,873,and 973 K for 6 h.The results showed that hydrogen attack in this steel was due to methane bubbles which resulted in occuring of Cr_(23)C_6.Thermodynamic analysis of hydrogen attack for stainless steel 304 was discussed.

INVESTIGATION OF INFLUENCE OF HYDROGEN ATTACK ONFATIGUE PROPERTIES OF PRESSURE VESSEL STEELS

Influence of hydrogen attack on mechanical and fatigue properties of 1020, 15CrMo and 2.25Cr-1Mo steels has been studied, which were exposed to gaseous hydrogen at pressure of 18MPa and 300-480℃ for up to 480h. The results of fatigue test showed that hydrogen attack (HA) resulted in an obvious change in fatigue properties of 1020 and 15CrMo steels, however, 2.25Cr-1Mo steel showed a lower susceptibility to hydrogen attack due to the addition of Cr and Mo. Fatigue crack behaviour for 1020 steel is attributed to hydrogen attack damage and the crack closure induced by the rough cracking surface, which lead to a valley on △Kth～HA% plot. The change in the fatigue behaviour of 15CrMo steel is possibly caused by severe surface decarburization.

On the intergranular fracture behavior of high-temperature plastic deformation of 1420 Al-Li alloy

The tensile deformation hot simulation test of as-cast 1420 Al-Li alloy was performed on Gleeble-1500 Thermal Simulator in the deformation temperature range from 350 to 450 ℃ and the strain rate range from 0.01 to l0.0s-1.The tensile fracture behavior of the 1420 Al-Li alloy at high temperature was studied experimently. The results show that the tensile fracture mode of the 1420 Al-Li alloy at high temperature is changed from typical transgranular ductile fracture to intergranular brittle fracture with the increase of the deformation temperature and the strain rate. It is made out that the precipitation of LiH is the fundamental reason for the intergranular brittle fracture of the 1420 Al-Li alloy at high temperature. The mechanism of hydrogen embrittlement of the 1420 Al-Li alloy at high temperature was discussed, and it was proposed that the hydrogen embrittlement at high temperature is an integrated function of the dynamic and the static force, which enrichs the theories of hydrogen embrittlemen t.

MAGNETIC ACOUSTIC EMISSION CHARACTERISTICS OF HYDROGEN ATTACKED LOW CARBON STEEL

Hydrogen attack occurred in low carbon steel and steel 25CrMo which had been exposed in hydrogen under 18MPa at 450 and 500℃ for 240,480 and 720 h.The methane bubbles and microcracks grow along grain boundaries.The degree of hydrogen attack increases with increasing exposure time and temperature.Magnetic acoustic emission(MAE) was used to detect the degree of hydrogen attack.The results show that the characteristics of MAE for samples of low carbon steel and steel 15CrMo with hydrogen attack have changed obviously comparing to the samples without hydrogen attack,and the MAE signals was sensitive to the degree of hydrogen attack at the last stage of hydrogen attack.The magnetic detection way,as a new method of nonrestrictive testing of hydrogen attack,can be used to detect the hydrogen attack in practice.

Macroscopic Structural Analysis on a 10 kW Class Lab-Scale Process Heat Exchanger Prototype under a High-Temperature Gas Loop Condition

A PHE (Process Heat Exchanger) is a key component in transferring high-temperature heat generated from a VHTR (Very High Temperature Reactor) to a chemical reaction for the massive production of hydrogen. Last year, a 10 kW class lab-scale PHE prototype made of Hastelloy-X was manufactured at the Korea Atomic Energy Research Institute (KAERI), and a performance test of the PHE prototype is currently underway in a small-scale nitrogen gas loop at KAERI. The PHE prototype is composed of two kinds of flow plates: grooves 1.0 mm in diameter machined into the flow plate for the primary coolant, and waved channels bent into the flow plate for the secondary coolant. Inside the 10 kW class lab-scale PHE prototype, twenty flow plates for the primary and secondary coolants are stacked in turn. In this study, to understand the macroscopic structural behavior of the PHE prototype under the steady-state operating condition of the gas loop, high-temperature structural analyses on the 10 kW class lab-scale PHE prototype were performed for two extreme cases: in the event of contacting the flow plates together, and when not contacting them. The analysis results for the extreme cases were also compared.

Healing of hydrogen-attacked cracks in split specimens with recovering heat treatment in vacuum

The healing mechanism of hydrogen-attacked cracks in low carbon steel andCr-Mo steel and its influencing factors during the healing process were studied by recovering heattreatment of split specimens in vacuum. The result showed that crack pacing turns much smaller underthe condition of pure heating, especially for crack tips. The healing effect is well related to thelength of cracks with the shorter in priority. By the primary mechanism of thermal diffusion, ironand carbon atoms must diffuse at the high speed in steel to realize that plasticity deformationenergy exceeds and overcomes surface tensile force energy. In addition, phase transformation andstress-stain relationship also have positive effects on the process.

Molecule aging induced by electron attacking

Here we propose a new concept of"molecule aging":with some special treatment,a molecule could be"aged"by losing some unknown tiny particles or pieces from atoms in the molecule,Such"aging"or loss of unknown tiny particles does not change apparently its molecular structure or chemical composition,but some physicochemical properties could be changed irreversibly.We further confirm such"molecule aging"via a long-term electron attacking to age water(H_(2)O)molecules.The IR spectra show no structural difference between the fresh water and the aged one,while the NMR spectra show that the electron attacking can decrease the size of water clusters.Such facts indicate that the electron attacking indeed can"affect"the structure of water molecule slightly but without damaging to its basic molecule frame.Further exploration reveals that the hydrogen evolution reaction(HER)activity of the aged water molecule is lower than the fresh water on the same Pt/C electrocatalyst.The density functional theory calculations indicate that the shortened O-H bond in H_(2)O indeed can present lower HER activity,so the observed size decrease of water clusters from NMR probably could be attributed to the shortening of O-H bond in water molecules.Such results indicate significantly that the molecule aging can produce materials with new functions for new possible applications.

INTRODUCTION OF NEW ANTICORROSIVE DESIGN FOR REACTORS EXPOSED TO HIGH TEMPERATURE AND HIGH PRESSURE HYDROGEN

This paper integrates the characteristic of structure design and manufacture and maintenance for Chinese flat steel band wound pressure vessel(UCWPV) with the problems existing in current in service high temperature and pressure vessel exposed to hydrogen. In view of economy and safety it is suggested that it be practicable for UCWPV to act as reactors for platreating, hydrogenating, and catforming. UCWPV has not only potential advantages, but also removes shortages present in in-service reactors for hydrogen.

ADISCUSSION ON THE PROBLEMS PRESENT IN IN SERVICE HYDROGENATION REACTORS

Thispaperintroduces materialandstructureofthe hydrogenation reactors, and analysesthe problems presentin use of hydrogenation reactors. Main factors which can lead to stoppingworkof reactors, are hydrogen attack, hydrogen embrittlement, temper embrittlement andstripsof overlap weldinglayer,andsomeproposalsare putforward forsafeoperation ofre actors. Finallyitissuggested thatitbe notenough only by advancing the reactor material,and adoptingthe new design and structureof reactorisimperative.

高温氢损伤失效行为与控制措施研究进展

石化设备的腐蚀问题一直困扰着石油化工企业,对企业安全生产和装置长周期运行产生不良影响。随着石油炼制、合成氨及甲醇等工业的发展,生产装置不断出现高温氢损伤问题,需要采取合理措施降低高温临氢设备和管道的损伤风险。归纳分析了高温临氢环境下碳钢和低合金钢的高温氢损伤腐蚀机理、影响因素、检测方法及其适用性;此外,介绍了高温氢损伤敏感性评价方法及量化等级,并从合理选材、衬里防护和运行操作等方面提出了腐蚀控制措施,为高温临氢环境设备和管道的安全运行提供经验借鉴与技术支撑。

Structure and high-temperature electrochemical properties of La_(0.60)Nd_(0.15)Mg_(0.25)Ni_(3.3)Si_(0.10) hydrogen storage alloys

The structure and high-temperature electrochemical properties of the as-cast and annealed （940 °C, 8 h） La0.60Nd0.15Mg0.25Ni3.3Si0.10 hydrogen storage alloys were investigated. The X-ray diffraction revealed that the multiphase structure of the as-cast alloy with LaNi5 phase as the main phase was converted into a double-phase structure with La2Ni7 phase as the main phase after annealing. The surface morphology studied by scanning electronic microscope （SEM） showed that the annealed alloy had a much higher anti-corrosion ability than the as-cast alloy. Both alloys presented excellent activation characteristics at all test temperatures. The maximum discharge capacity of the as-cast alloy decreased when the test temperature increased, while the temperature almost had no effect on the annealed alloy. As the test temperature increased, the cyclic stability and charge retention of both alloys decreased, and these properties were improved significantly by annealing.

热处理愈合不锈钢氢蚀裂纹实验研究

对含氢腐蚀甲烷气泡和裂纹的３０４不锈钢进行了６００℃ ，６ｈ的再热处理. ＳＥＭ观察表明，氢蚀气泡和裂纹发生了完全愈合．氢蚀气泡和裂纹的愈合机制是热扩散，Ｆｅ和 Ｃ在奥氏体中的快速扩散是 ３０４不锈钢中氢蚀裂纹的自愈合的必要条件．发生氢蚀裂纹愈合的动力是氢蚀气泡长大导致的塑性变形能Ｅｓ，在Ｆｅ，Ｃ和Ｈ原子扩散都足够快的情况下，氢蚀气泡和裂纹的愈合条件是 Ｅｓ≥ ２γ／ｒ（γ为界面表面张力，ｒ为气泡半径或裂纹半长）．氢蚀气泡或裂纹的愈合过程伴随亚晶长大、多边形化的高温回复过程甚至再结晶.

一种新型高温测氢传感器探头的研究

利用 Ｙｂ３＋掺杂的ＳｒＣｅＯ３在高温时的Ｈ＋导电特性制作了 ＳｒＣｅ０．９５Ｙｂ０．０５Ｏ３－α高 温测氢探头，并在高温条件下利用该探头对氢在４５＃钢中的扩散行为进行了研究 和分析。所得结果与理论模型计算的结果一致。

稠油热采蒸汽输送管的氢蚀爆裂及其预防

对某油田稠油热采蒸汽输送管爆裂事故进行了分析．发现爆裂部位有局部腐蚀，腐蚀部位的基体中有脱碳及沿晶裂纹，且该处基体中有很高的氢含量．

热处理作用下碳钢氢腐蚀裂纹愈合规律

对含氢腐蚀裂纹的碳钢进行再热处理后，ＳＥＭ观察表明，氢蚀裂纹发生了不同程度 的愈合．实验结果表明：长度约为１０μｍ的碳钢氢蚀裂纹完全愈合的热处理条件是从室温到 １０００℃热循环 ５次，共 １０ｈ．氢蚀裂纹的愈合机制是热扩散，发生氢蚀裂纹愈合的动力是氢蚀 气泡或裂纹长大导致的塑性变形能Ｅｓ．在铁、碳和氢原子扩散都足够快的情况下，氢蚀裂纹愈 合的条件是Ｅｓ大于裂纹愈合所必须克服的表面张力能．