Active Sites For Hydrogen Adsorption Research Articles

In Situ Growth of Interfacially Nanoengineered 2D-2D WS2/Ti3C2Tx MXene for the Enhanced Performance of Hydrogen Evolution Reactions.

In line with current research goals involving water splitting for hydrogen production, this work aims to develop a noble-metal-free electrocatalyst for a superior hydrogen evolution reaction (HER). A single-step interfacial activation of Ti3C2Tx MXene layers was employed by uniformly growing embedded WS2 two-dimensional (2D) nanopetal-like sheets through a facile solvothermal method. We exploited the interactions between WS2 nanopetals and Ti3C2Tx nanolayers to enhance HER performance. A much safer method was adopted to synthesize the base material, Ti3C2Tx MXene, by etching its MAX phase through mild in situ HF formation. Consequently, WS2 nanopetals were grown between the MXene layers and on edges in a one-step solvothermal method, resulting in a 2D-2D nanocomposite with enhanced interactions between WS2 and Ti3C2Tx MXene. The resulting 2D-2D nanocomposite was thoroughly characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) analyses before being utilized as working electrodes for HER application. Among various loadings of WS2 into MXene, the 5% WS2-Ti3C2Tx MXene sample exhibited the best activity toward HER, with a low overpotential value of 66.0 mV at a current density of -10 mA cm-2 in a 1 M KOH electrolyte and a remarkable Tafel slope of 46.7 mV·dec-1. The intercalation of 2D WS2 nanopetals enhances active sites for hydrogen adsorption, promotes charge transfer, and helps attain an electrochemical stability of 50 h, boosting HER reduction potential. Furthermore, theoretical calculations confirmed that 2D-2D interactions between 1T/2H-WS2 and Ti3C2Tx MXene realign the active centers for HER, thereby reducing the overpotential barrier.

First-principles study on a Li-decorated two-dimensional g-C6N6 monolayer: A promising ambient temperature reversible H2 storage material

Designing novel materials that exhibit superior reversibility and function under ambient conditions can facilitate the development of hydrogen energy applications. Two-dimensional (2D) g-C6N6 monolayers show great potential for use in hydrogen storage owing to their nanoporous structure, ultralight mass, and flexible electronic structure. However, the hydrogen storage potential of these materials is limited by the naturally weak interaction between 2D materials and hydrogen molecules caused by van de Waals forces. To address this issue, we studied the hydrogen storage performance of the complex by decorating active Li ions on a 2D g-C6N6 substrate through first-principles calculations. Our results showed that modifying the Li ions did not cause the original planar structure to deform but rather induced more active sites for hydrogen adsorption by establishing an electrostatic field between the Li ions and the g-C6N6 monolayer. Through this modification, reversible hydrogen storage was achieved under ambient conditions with an average adsorption energy of −0.197 eV/H2 and a high gravimetric capacity of 5.88 wt%. The electronic properties of the material were systematically investigated, and the results suggested that the enhanced capacity of the Li@ g-C6N6 system to store hydrogen resulted from the formation of a polarization field and the induced electrostatic effect. Our research offers a new possibility for achieving reversible hydrogen energy storage at room temperature.

In-situ transformation into MoP/MoS2 heterogeneous structure with rich S-vacancy enhanced hydrogen evolution reaction

The surface modification strategy has broken through the restriction of hydrogen evolution activity caused by low conductivity inert surfaces of MoS2 during hydrogen evolution reaction. In this work, a new strategy for regulating the interface structure between MoS2 and MoP using sulfur vacancy is proposed, which is derived from the synthesis of molybdenum disulfide nanotubes with rich S-vacancy (Sv-MoS2) by reduction. Subsequently, Sv-MoS2 was phosphated by introducing a P source, and the obtained (MoP/Sv-MoS2-8) composite. The introduction of P atoms provides more active sites for hydrogen adsorption and desorption by replacing S atoms to form (Mo-P) covalent bonds, further increase the number of S vacancies to activate the inert interface. The synthesized MoP/Sv-MoS2-8 has excellent catalytic activity and good cyclic stability, showing a lower Tafel slope of 60 mV·dec−1 at a current density of 10 mA·cm−2, and no potential attenuation after the cyclic stability test for 24 h. The excellent HER performance is mainly due to the synergistic effect of P atom doping and S vacancy, which greatly reduces the energy barrier of the Volmer step and the adsorption/desorption of the H* intermediate step.

Asymmetric orbital hybridization in Zn-doped antiperovskite Cu1−xZnxNMn3 enables highly efficient electrocatalytic hydrogen production

Rational design of efficient and robust earth-abundant alkaline hydrogen evolution reaction (HER) catalysts is a key factor for developing energy conversion technologies. Currently, antiperovskite nitride CuNMn3 has garnered significant interest due to its remarkable properties such as negative/zero thermal expansion and magnetocaloric effects. However, when utilized as hydrogen evolution catalysts, it encounters large challenge resulting from excessively strong/weak interactions with adsorbed H on Mn/Cu active sites, which leads to low HER activity. In this study, we introduce an asymmetric orbital hybridization strategy in Zn-doped Cu1−xZnxNMn3 by leveraging the localization of Zn electronic states to reconfigure the electronic structures of Cu and Mn, thereby reducing the energy barrier for water dissociation and optimizing Cu and Mn active sites for hydrogen adsorption and H2 production. Electrochemical evaluations reveal that Cu0.85Zn0.15NMn3 with x = 0.15 demonstrates exceptional electrocatalytic activity in alkaline electrolytes. A low overpotential of 52 mV at 10 mA cm−2 and outstanding stability over a 150-h test period are achieved, surpassing commercial Pt/C. This research offers a novel strategy for enhancing HER performance by modulating asymmetric hybridization of electron orbitals between multiple metal atoms within a material structure.

Ni(OH)2 Derived from NiS2 Induced by Reflux Playing Three Roles for Hydrogen/Oxygen Evolution Reaction

Developing efficient and promising non-noble catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is vital but still a huge challenge for the clean energy system. Herein, we have integrated the active components for OER (Ni(OH)2) and HER (NiS2 and Ni(OH)2) into Ni(OH)2@NiS2 heterostructures by a facile reflux method. The in-situ formed Ni(OH)2 thin layer is coated on the surface of hollow NiS2 nanosphere. The uniform Ni(OH)2@NiS2 hollow sphere processes enlarge the electrochemically active specific surface area and enhance the intrinsic activity compared to NiS2 precursor, which affords a current density of 10 mA cm−2 at the overpotential of 309 mV and 100 mA cm−2 at 359 mV for OER. Meanwhile, Ni(OH)2@NiS2 can reach 10 mA cm−2 at 233 mV for HER, superior to pure NiS2. The enhanced performance can be attributed to the synergy between Ni(OH)2 and NiS2. Specifically, Ni(OH)2 has three functions for water splitting: providing active sites for hydrogen adsorption and hydroxyl group desorption and working as real OER active sites. Moreover, Ni(OH)2@NiS2 displays great stability for OER (50 h) and HER (30 h).

Metal-rich heterostructure of Ag-doped FeS/Fe2P for robust hydrogen evolution

The transition metal phosphides (TMPs) with highly active and low-cost are imperative electrocatalysts for hydrogen evolution reaction (HER). In particular, metal-rich interface engineering of iron phosphide could effectively modify the active sites for HER and accelerate the charge transfer, thus achieving the promoted efficiency. Herein, we report metal-rich heterostructure of Ag-doped Fe2P shell attached to FeS core on Fe foams (FeS/Fe2P–Ag@IF) for HER, which are synthesized by a simple hydrothermal method with subsequent low-temperature phosphorization. Notably, the phosphorization process simultaneously achieves the partial conversion of FeS to Fe2P, and complete reduction of Ag2S to Ag. Furthermore, the metal-rich structure of Fe2P increases the active sites for hydrogen adsorption, which consequently contributes to hydrogen evolution. Simultaneously, the successful doping of metallic Ag enhanced the electroconductivity and the stability of the electrocatalyst. Benefiting from the ternary synergistic effect at FeS/Fe2P–Ag@IF and metallic Ag doping, the optimal Ag-doped FeS/Fe2P electrocatalyst exhibits a low overpotential of 214.9 mV at 100 mA cm−2, even surviving at this large current density with long-term stability. This promising strategy involving metallic Ag doping may be a suitable option for the development of iron-based metal-rich phosphides heterostructured for HER.

Two-Dimensional High-Entropy Metal Phosphorus Trichalcogenides for Enhanced Hydrogen Evolution Reaction.

Developing earth-abundant and highly effective electrocatalysts for hydrogen evolution reaction (HER) is a prerequisite for the upcoming hydrogen energy society. Two-dimensional (2D) high-entropy metal phosphorus trichalcogenides (MPCh3) have the advantages of both near-continuous adsorption energies of high-entropy alloys (HEAs) and large specific surface area of 2D materials, which are excellent catalytic platforms. As a typical 2D high-entropy catalyst, Co0.6(VMnNiZn)0.4PS3 nanosheets with high-concentration active sites are successfully demonstrated to show enhanced HER performance: an overpotential of 65.9 mV at a current density of 10 mA cm-2 and a Tafel slope of 65.5 mV dec-1. Decent spectroscopy characterizations are combined with density function theory analyses to show the scenario for the enhancement mechanism by a high-entropy strategy. The optimized S sites on the edge and P sites on the basal plane provide more active sites for hydrogen adsorption, and the introduced Mn sites boost water dissociation during the Volmer step. Two-dimensional high-entropy MPCh3 provides an avenue for the combination of HEAs and 2D materials to enhance the HER performance, which also provides an alternative materials platform to explore and design superior catalysts for various electrochemical systems.

Effect of flower-like Ni/C nanocrystal on electrochemical hydrogen storage properties of Co–P alloy

The flower-like Ni/C nanocrystal were synthesized by solvo-thermal method, and Co–P alloy was prepared by mechanical alloying method. Finally, different proportions of Ni/C nanocrystal and Co–P alloy were mixed by ball milling method to form the Co–P + Ni/C composites. Compared with the pristine alloy, the Co–P + Ni/C composite electrode shows better discharge capacity and cyclic stability. When the weight ratio of Ni/C nanocrystal reached 5%, the maximum discharge capacity of the Co–P + Ni/C composite electrode reached 635.8 mAh/g at a discharge current density of 30 mA/g, and its capacity retention rate reached 66.3% after 50 cycles. Linear polarization, electrochemical impedance spectroscopy and potentiometric polarization tests of the Co–P + Ni/C composites and Co–P alloy were caried out. The nickel particles in the flower-like Ni/C nanocrystal showed excellent electrocatalysis, and the special lamellar structure of Ni/C nanocrystal could increase the specific surface area of the alloy and provide more active sites for hydrogen adsorption, thus improving the discharge capacity of the electrode. The flower-like Ni/C nanocrystal coated on the surface separates the electrolyte from the alloy and improved the corrosion resistance of the alloy. In addition, the special lamellar structure and excellent electrical conductivity of Ni/C nanocrystal enhanced the exchange current density of the composite electrode and reduced the charge transfer resistance. Therefore, the unique structure and electrocatalysis of flower-like Ni/C nanocrystal can effectively improve the electrochemical properties of Co–P alloy. This work presents a simple and feasible method to improve the electrochemical hydrogen storage performance of Co–P alloy by adding Ni/C nanocrystal to the alloy by mechanical alloying.

Efficient Hydrogen Evolution on Nanoscale Graphdiyne.

Self-active metal-free graphdiyne (GDY) is used, which has a precise chemical structure, as a model carbon-based metal-free electrocatalyst to assess its activity in the hydrogen evolution reaction (HER) and to understand the origin of electrocatalytic performance at the atomic level. The studies reveal that the unusual electrocatalytic properties of GDY originate from its unique nanostructure, which can simultaneously provide highly active sites for hydrogen adsorption and facilitate the electron-transfer process for proton reduction. Accordingly, GDY can act as a metal-free efficient HER electrocatalyst with Pt-like HER activity, but with long-term durability superior to that of Pt/C under the wide pH range (from acidic to basic). To the best of knowledge, such HER performance is better than that of other reported metal-free electrocatalysts and most transition-metal electrocatalysts-even Pt-based ones.

In-situ grown nickel-cobalt bimetallic nanowire arrays for efficient hydrogen evolution reaction

Nickel-based nanowire arrays with different cobalt content were prepared via a modified template-assisted electrodeposition method for hydrogen evolution reaction. The experimental results proved that, compared with samples of other ratios, the nanowire arrays with a nickel-cobalt atomic ratio of 32:1 exhibited better hydrogen evolution performance, and an overpotential of 103 mV was required to obtain a current density of 10mAcm−2, while the nanowire arrays with a ratio of nickel-cobalt of 3:1 required an overpotential of 171 mV to achieve the same current density. The density functional theory (DFT) calculations performed were consistent with the experimental results that Ni-based materials doped with 1Co had better electrocatalytic activity than those doped with 2Co. The excellent hydrogen evolution performance of catalyst was attributed to the synergy between nickel and cobalt atoms and the nanowire structure increased the specific surface area exposing more active sites for hydrogen adsorption and adsorption.

Ru doping in Ni(OH)2 to accelerate water reduction kinetics for efficient hydrogen evolution reaction

Water dissociation reaction (Volmer step) is the main restrictive factor that gives rise to the sluggish reaction kinetics for hydrogen evolution reaction (HER) in alkaline solution. In this paper, Ru doped Ni(OH)2 deposited on Ti mesh (abbreviated as TM) was synthesized by one-pot hydrothermal method. SEM, TEM, XRD, Raman, and XPS analysis indicated that both surface morphology and electronic structure had an apparent change, but phase structure maintained unchanged after Ru doping. HER activities of Ru doped Ni(OH)2/TM samples in 1.0 M KOH were investigated in detail. Ru doped Ni(OH)2/TM prepared with 0.2 mM RuCl3 precursor (denoted as Ru doped Ni(OH)2/TM-0.2) presented excellent HER performance with an overpotential of 135 mV at −10 mA/cm2 and the lowest Tafel slope of 63.7 mV/dec. This electrocatalyst also maintained long-term stability even operating for 15 h. Experimental results demonstrated that Ru doping into Ni(OH)2 could enhance charge transfer rate, increase electrocatalytically active surface area (ECSA) and, most importantly, accelerate Volmer step and also provide appropriate Ru active sites for hydrogen adsorption, which endowed Ru doped Ni(OH)2/TM-0.2 with superior HER activity and durability.

Transition metal-metal oxide hybrids as versatile materials for hydrogen storage

Metal atom located on metal oxide (MMO) is a promising material with various applications such as hydrogen storage. As one of the metal oxides, niobium oxide (NbO) presents fascinating properties that make it a possibly applicable in MMOs. Here, we investigated the feasibility of transition metal-NbO hybrids as MMO materials for application in the hydrogen storage technology. In this respect, the hydrogen adsorption of transition metals (Fe, Ni, Cu, Pd, Ag, and Pt) decorated on the NbO nanocluster has been explored using density functional theory calculations. We found that the adsorption energy of the H2 molecule on the NbO adsorbent is remarkably increased by locating the transition metals on the NbO metal oxide. Our results reveal that the transition metals decorated on the NbO nanocluster can act as active sites for hydrogen adsorption. Among the studied transition metals, Pt shows the highest hydrogen capacity up to 6.52 wt%.

Effects of microstructure and phase composition on the electrochemical activation properties of Ti1.8(VFe)CrNi0.2 + xwt.%LaNi5(x=0, 2.5, 4, 5, 6, 10, 20) metal hydride alloys

Ti-V-based alloys possess the tremendous hydrogen storage capacity, but low electrochemical activity. In order to improve the electrochemical properties of this kind of alloys, a commercial hydrogen storage alloy, LaNi5, with higher electrochemical activity were introduced and re-melted with Ti1.8(VFe)CrNi0.2 as master alloy. The new metal hydride composite alloys, Ti1.8(VFe)CrNi0.2 + x wt.% LaNi5 (x = 0, 2.5, 4, 5, 6, 10, 20), were prepared and their solidification microstructure and electrochemical characteristics were investigated in this work. It was found that the structural features of the composite alloys varied regularly with increase of amount of LaNi5. Meanwhile, the microstrain and dislocation, respectively, formed in the major phase and minor phase of the composites. The changes of structural features, especially, the microstrain and dislocation, provided more active sites for hydrogen adsorption, and the symbiosis relation between the phases from the master and the new phases from LaNi5 brought about more crystal interfaces as diffusion path for hydrogen atoms. As a result, hydrogen atoms can be diffused easily from the major phase to minor phase. The results indicated that the composite Ti1.8(VFe)CrNi0.2 + 5 wt% LaNi5 exhibits the best maximum discharge capacity of 360 mAh/g after 9 cycles. It is found that there are parallel zone axes and similar Kikuchi poles in major phases, and TiNi minor phase of the composite with 5 wt%LaNi5. It is evident that there exists a symbiosis relation between the major phases and TiNi minor phase.

Efficient and stable electrocatalyst for hydrogen evolution reaction prepared by hybrid technique in surface engineering: Electrochemical and magnetron sputtering methods

Developing low-cost, stable, and robust electrocatalysts is significant for high effective hydrogen evolution reaction (HER). In this work, a coating system with Cu2O/NiMoCu on stainless steel (SS) is employed as a highly active and stable catalyst for HER in acidic solutions. Electrochemical measurements for as-designed system on SS show a low onset overpotential, small Tafel slope of ∼32 mV/decade and long-term durability over 7 days of HER operation. To further inspections of electrocatalytic behavior of as-prepared system in HER, the EIS measurements are performed at several overpotentials and temperatures. It is found that high hydrogen evolution activity and stability of Cu2O/NiMoCu hybrid is likely due to special morphology of Cu2O which result in large number of active sites for hydrogen adsorption, and a synergetic effect giving electronic structure suitable for the HER.

Hydrogenated MoS2 QD-TiO2 heterojunction mediated efficient solar hydrogen production.

Herein, we report the development of a hydrogenated MoS2 QD-TiO2 (HMT) heterojunction as an efficient photocatalytic system via a one-pot hydrothermal reaction followed by hydrogenation. This synthetic strategy facilitates the formation of MoS2 QDs with an enhanced band gap and a proper heterojunction between them and TiO2, which accelerates charge transfer process. Hydrogenation leads to oxygen vacancies in TiO2, enhancing the visible light absorption capacity through narrowing its band gap, and sulfur vacancies in MoS2, which enhance the active sites for hydrogen adsorption. Due to the band gap reduction of hydrogenated TiO2 and the band gap enhancement of the MoS2 QDs, the energy states are rearranged to create a reverse movement of electrons and holes facilitated the charge transfer process which enhance life-time of photo-generated charges. The photocatalyst showed stable, efficient and exceptionally high noble metal free sunlight-induced hydrogen production with a maximum rate of 3.1 mmol g-1 h-1. The developed synthetic strategy also provides flexibility towards the shape of the MoS2, e.g. QDs/single or few layers, on TiO2 and offers the opportunity to design novel visible light active photocatalysts for different applications.

Kinetics of hydrogen evolution reaction in alkaline electrolysis on a Ni cathode in the presence of Ni–Co–Mo based ionic activators

This paper presents investigations on the influence of in-situ ionic activation using combination of three d-metals: Ni, Co and Mo on the hydrogen evolution reaction (HER) mechanism and kinetics. Polarization measurements were performed to obtain kinetic parameters for the HER and the results are presented to show Tafel slopes, exchange current densities and apparent energy of activation. The values of the kinetic parameters confirm the existence of two Tafel slopes, in the case of NiCoMo based ionic activators (i.a.) in the investigated temperature range, with very high values of the exchange current density. Electrochemical impedance spectroscopy measurements were employed to further investigate the origin of the obtained electrocatalytic effect on the HER. The measurements were performed at several overpotentials and temperatures. It was found that co-deposition of Ni, Co and Mo species on the Ni cathode results in a large number of active sites for hydrogen adsorption, and a synergetic effect giving electronic structure suitable for the HER, are the main factors contributing to the enhanced HER kinetics. It was shown that EIS measurements had a crucial role in determining the HER mechanism, especially with the complex in-situ activation of the alkaline electrolysis.

Room Temperature Hydrogen Physisorption on Exposed Metals in A Highly Cross‐Linked Organo‐Iron Complex

Room Temperature Hydrogen Physisorption on Exposed Metals in A Highly Cross‐Linked Organo‐Iron Complex

Acid-Resistant Catalysis without Use of Noble Metals: Carbon Nitride with Underlying Nickel

A nanocomposite able to function as a hydrogenation catalyst under strongly acidic conditions without the presence of noble metals is synthesized and thoroughly studied. This specially designed catalyst possesses a unique structure composed of carbon nitride (CN) with underlying nickel, in which the nickel endows the CN with new active sites for hydrogen adsorption and activation while it itself is physically isolated from the reactive environment and protected from poisoning or loss. The CN is inert for hydrogenation without the help of nickel. The catalyst shows good performance for hydrogenation of nitro compounds under strong acidic conditions, including the one-step hydrogenation of nitrobenzene in 1.5 M H2SO4 to produce p-amoniophenol, for which the acid in the reaction system has restricted the catalyst only to noble metals in previous studies. Further characterization has demonstrated that the nickel in the catalyst is in an electron-deficient state because some of its electron has been donated to...

Sulfur Poisoning and Regeneration of Ni-Based Anodes in Solid Oxide Fuel Cells

The effect of hydrogen sulfide on the performance of nickel/yttria-stabilized zirconia (YSZ) cermet anode for solid oxide fuel cells has been studied under various operating conditions. In all cases, a small amount of (ppm level) causes a sharp drop in cell performance within the first few minutes of exposure, followed by a gradual but persistent deterioration in performance for several days. The extent of anode degradation caused by sulfur poisoning increases with increasing concentration, increasing cell voltage (i.e., closer to open-circuit voltage or decreasing cell current density), or decreasing cell operating temperature. The initial sharp degradation in performance is attributed to rapid adsorption of sulfur onto the Ni surface, which blocks the active sites for hydrogen adsorption and oxidation. However, the mechanism for the subsequent slow degradation is still not clear. Upon removal of from the fuel stream, the anode performance can be recovered fully or partially, depending on operating conditions and duration of exposure. The rate of the recovery process increases with operating temperature and cell current density.

Electrodeposition of zinc from high acid zinc chloride solutions

Electrowinning of zinc from zinc chloride solutions, acidified by HCl, was conducted in a cation exchange membrane cell. The current efficiency was correlated with the deposit morphology. The deposits having lesser surface defects, which act as active sites for hydrogen adsorption, exhibited higher current efficiency. The (1 1 0) preferred texture was observed on the deposits grown in high acid solution containing gelatin. High temperature (40 oC) and high current density decreased the current efficiency and the preferred texture.