Weak Hydrogen Adsorption Research Articles

Nanocrystalline transition metal tetraborides as efficient electrocatalysts for hydrogen evolution reaction at the large current density

While great efforts have been made to improve the electrocatalytic activity of existing materials toward hydrogen evolution reaction (HER), it is also importance for searching new type of nonprecious HER catalysts to realize the practical hydrogen evolution. Herein, we firstly report nanocrystalline transition metal tetraborides (TMB4, TM=W and Mo) as an efficient HER electrocatalyst has been synthesized by a single-step solid-state reaction. The optimized nanocrystalline WB4 exhibits an overpotential as low as 172 mV at 10 mA/cm2 and small Tafel slope of 63 mV/dec in 0.5 M H2SO4. Moreover, the nanocrystalline WB4 outperforms the commercial Pt/C at high current density region, confirming potential applications in industrially electrochemical water splitting. Theoretical study reveals that high intrinsic HER activity of WB4 is originated from its large work function that contributes to the weak hydrogen-adsorption energy. Therefore, this work provides new insights for development of robust nanocrystalline electrocatalysts for efficient HER.

Enhanced acidic hydrogen evolution reaction kinetics via nitrogen-doped iridium nanosheet with optimized hydrogen adsorption energy

The hydrogen evolution reaction (HER) is influenced by the adsorption/desorption of hydrogen intermediates on active sites. Nitrogen doping is a way to alter the electronic structure and boost the activity of metal electrocatalysts although the mechanism remains controversial. Here, nitrogen is incorporated into face-centered cubic iridium nanosheets (N-fcc-Ir-NSs) through the ammonia reduction of metastable two-dimensional pristine trigonal iridium oxide. With a nitrogen content of only 0.8 wt%, N-fcc-Ir-NSs exhibit a low overpotential of 19 mV at −10 mA cmgeo-2 and a Tafel slope of 18.6 mV dec-1 in sulfuric acid. The doped nitrogen reduces hydrogen adsorption energy by modulating the electronic structure of iridium atoms, and the combined effects of iridium sites with strong hydrogen adsorption energy and iridium sites near the nitrogen atoms with weak hydrogen adsorption energy improve the HER activity. Moreover, the presence of nitrogen causes iridium to donate more electrons to hydrogen and promotes hydrogen desorption.

3D Ternary Alloy Artificial Interphase Toward Ultra‐Stable and Dendrite‐Free Aqueous Zinc Batteries

AbstractRechargeable aqueous zinc‐ion batteries (AZIBs) are one of the most promising post‐lithium battery technologies due to their low cost, high safety, and environmental friendliness. However, their practical development is hindered by the issues of Zn metal anodes, including dendrite growth, passivation, hydrogen evolution and other side reactions. Herein, to circumvent these issues, a facile and universal alloy electrodeposition strategy is proposed to construct a 3D structured ternary Zn alloy artificial interphase layer on Zn foil as an anode for high‐performance AZIBs. The density functional theory (DFT) theoretical calculations, in situ optical visualization and spectroscopic results validate that the zincophilic Zn─Sn─Bi@Zn ternary alloy anode with lower migration energy barrier and weak hydrogen adsorption sites can promote the uniform Zn deposition and suppress hydrogen evolution reactions. The Zn─Sn─Bi@Zn//NH4V4O10 full cell demonstrates a high specific capacity 110.4 mAh g−1 even after 10 000 cycles at 5.0 A g−1. Notably, the full cell with a high NH4V4O10 cathode loading mass of ≈20.0 mg cm−2 maintains cyclic stability for 400 cycles. This work proposes an innovative Zn‐based ternary alloy anode methodology as a design strategy for advanced AZIBs and beyond.

Cobalt catalysts for COx-free hydrogen production: Effect of catalyst type on ammonia decomposition in gliding discharge plasma reactor

Hydrogen is considered the cleanest, most environmentally friendly fuel and energy carrier required for the gradual decarbonisation of many industrial sectors. Using ammonia as a Cox-free source of hydrogen is the most reasonable and most applicable method. This paper studies the properties and activity of cobalt catalysts in the ammonia decomposition reaction using a plasma-catalytic system. The effect of catalyst type (supported versus bulk) was evaluated. The catalysts were examined using XRD, STEM-EDX, and sorption techniques (N2 physisorption, TGA-TPR, H2-TPD, CO2-TPD) to reveal the influence of physicochemical properties of these two types of catalysts on the efficiency of NH3 decomposition in the plasma-catalytic process using a gliding discharge plasma. The results disclose that the supported-type catalyst (Ba-Co/CeO2) decomposed NH3 more effectively than the bulk-type catalyst (Co/Ce/Ba). At discharge power of 300 W and flow rate of 180 dm3 h–1 of NH3:N2 mixture (50/50 vol%), the ammonia conversion over the Ba-Co/CeO2 catalyst was 70%, whereas over the Co/Ce/Ba catalyst it was only 21%. The favourable performance of the supported-type catalyst was attributed to a more thermally stable surface area compared with the bulk-type catalyst. Smaller and more stable cobalt nanoparticles (NPs) with numerous weak hydrogen adsorption sites were also seen. Meanwhile, the strong basic sites were generated, improving the electron-donating ability of the surface active sites. High ammonia conversion and relatively low-energy consumption of the plasma-catalytic ammonia decomposition over Ba-Co/CeO2 make it suitable for practical hydrogen production applications, such as fuel cells and hydrogen storage.

Calculation of hydrogen adsorption isotherms and Henry coefficients with mixed CO2 and CH4 gases on hydroxylated quartz surface: Implications to hydrogen geo-storage

Hydrogen is a clean fuel that is becoming increasingly popular in addressing future energy challenges, however, its viable storage requires an understanding of its interaction with underground rock minerals. For this purpose, this study focuses on developing adsorption isotherms and Henry coefficients for hydrogen in hydroxylated quartz surfaces, which are predominant in sandstone and shale rocks. In this study, a molecular-scale hydroxylated quartz structure with a pore space is generated and the Monte Carlo (MC) simulation is utilized to assess the adsorption isotherms and Henry coefficients. Initially, the CO2 adsorption with the hydroxylated quartz is matched with the published data to determine the accuracy of MC simulation and the mineral-fluid interaction. After that, the concentration of H2 within the pore is progressively increased and the competitive adsorption is calculated under various subsurface temperature and pressure conditions. Additionally, CH4 is introduced to understand the competitive adsorption dynamics between H2 and CH4. The findings indicate that increasing pressure results in increasing molecules of hydrogen that monotonically increase H2 adsorption. On the contrary, increasing temperature reduces the affinity of hydrogen with the quartz surface causing a decrease in adsorption capacity and Henry coefficients. Furthermore, a weak single hydrogen adsorption layer is developed at all pressure and temperature conditions, while most of the hydrogen remains as a free gas in the pore. In addition, the hydroxyl group controls most of the adsorption of hydrogen in the hydroxylated quartz. Furthermore, the addition of water film (approximately 1 wt%) reduces the hydrogen adsorption by around 3 %. The H2 adsorption values further experience a notable decrease with the introduction of CO2 and CH4, primarily due to the establishment of a strong adsorption layer caused by the high electrostatic attraction between these gases and the quartz mineral. The study offers crucial microscopic details regarding H2 adsorption alongside CO2 and CH4 gases within hydroxylated quartz pores. These insights support efficient hydrogen geo-storage and larger-scale simulation research.

Hydrogen Spillover Phenomenon at the Interface of Metal-Supported Electrocatalysts for Hydrogen Evolution.

ConspectusHydrogen spillover, as a well-known phenomenon for thermal hydrogenation, generally involves the migration of active hydrogen on the surface of metal-supported catalysts. For thermocatalytic hydrogenation, hydrogen spillover generally takes place from metals with superiority for dissociating hydrogen molecules to supports with strong hydrogen adsorption under a H2 environment with high pressures. The former can bring high hydrogen chemical potential to largely reduce the kinetic barrier of the migration of active hydrogen species from metals to supports. At the same time, the latter can make H* migration thermodynamically spontaneous. For these reasons, hydrogen spillover is a common interfacial phenomenon occurring on metal-supported catalysts during thermocatalysis. Recently, this phenomenon has been observed for the exceptionally enhanced electrocatalytic performance for hydrogen evolution and other electrocatalytic organic synthesis. Different from hydrogen spillover for thermocatalysis under high H2 pressure, hydrogen spillover for electrocatalysis involves the migration of active hydrogen species (H*) from metals with strong hydrogen adsorption to supports with weak hydrogen adsorption, thereby suffering from a thermodynamically unfavorable process accompanied by a high kinetic barrier. Thus, the occurrence of hydrogen spillover at the electrocatalytic interface is not easy, and successful cases are rare. Understanding the underlying nature of hydrogen spillover at the electrocatalytic interface of metal-supported catalysts is critical to the rational design of advanced electrocatalysts.In this Account, we provide in-depth insights into recent advances in hydrogen spillover at the electrocatalytic interface for a significantly enhanced hydrogen evolution performance. Electron accumulation at the metal-support interface induces severe interfacial H* trapping and is recognized as the main factor in the failed hydrogen spillover. Given this, we developed two novel strategies to promote the occurrence of hydrogen spillover at the electrocatalytic interface. These strategies include (i) the introduction of ligand environments to enrich the local hydrogen coverage on metals and lower the barrier for interfacial hydrogen spillover and (ii) the minimization of work function difference between metals and supports (ΔΦ) to relieve electron accumulation and lower the kinetic barrier for hydrogen spillover. Also, we summarize the previously reported strategy of shortening the metal-support interface distance to lower the kinetic barrier for interfacial hydrogen spillover. Afterward, some criteria and methodologies are proposed to identify the hydrogen spillover phenomenon at the electrocatalytic interface. Finally, the remaining challenges and future perspectives are also discussed. Based on this Account, we aim to provide new insights into electrocatalysis, particularly the targeted control of hydrogen spillover at the electrocatalytic interface, and then to offer guidelines for the rational design of advanced electrocatalysts.

Ce3+-Induced metal vacancies engineering of NiSe2 with needle-like structure for alkaline hydrogen evolution

The weak water dissociation ability and hydrogen adsorption of bulk NiSe2 inhibits their HER performance under alkaline conditions. Most work focused on tuning the electron structure and activity of Se sites, the role of Ni atoms in HER process is commonly ignored. In this work, we developed a Ce3+ induced strategy to introduce Ni cationic vacancies (VNi) on NiSe2 and simultaneously regulate its morphology to form hierarchical needle-like structure. The unique nanostructure provides more exposed active sites and facilitates mass and charge transfer. After the introduction of VNi, Ni2+ (t2g6eg2) in NiSe2 can be partially converted to Ni3+ (t2g6eg1) with optimal eg1 electron configuration, which improves the water dissociation barrier and facilitate the fast electron transfer during HER process. The Ni3+ also increases the charge density around the Se atom to improve H adsorption energy on Se sites, thus improving the alkaline HER activity.

Electrochemical partial reduction of Ni(OH)2 to Ni(OH)2/Ni via coupled oxidation of an interfacing NiAl intermetallic compound for robust hydrogen evolution

Ni-based porous electrocatalysts have been widely used in the hydrogen evolution reaction (HER) in alkaline water electrolysis, and the catalysts are produced by selective leaching of Al from Ni-Al alloys. It is well known that chemical leaching of Ni-Al intermetallic compound (IMC) generates a high surface area in Ni(OH)2. However, the Ni(OH)2 produced by leaching the Ni-Al intermetallic compound retards the hydrogen evolution reaction, which is attributed to its weak hydrogen adsorption energy. In this study, we controlled the chemical state of Ni using plasma vapor deposition (PVD) followed by heat treatment, selective Al leaching, and electrochemical reduction. X-ray diffraction (XRD), scanning microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) were used to confirm the phase evolution of the electrocatalysts during fabrication. We reveal that the heat-treated Ni-Al alloy with a thick Ni2Al3 surface layer underwent selective Al leaching and produced biphasic interfaces comprising Ni(OH)2 and NiAl IMCs at the edges of the grains in the outermost surface layer. Coupled oxidation of the interfacing NiAl IMCs facilitated the partial reduction of Ni(OH)2 to Ni(OH)2/Ni in the grains during electrochemical reduction, as confirmed by X-ray photoelectron spectroscopy (XPS). An electrocatalyst containing partially reduced Ni(OH)2/Ni exhibited an overpotential of 54 mV at 10 mA/cm2 in a half-cell measurement, and a cell voltage of 1.675 V at 0.4 A/cm2 for single-cell operation. A combined experimental and theoretical study (density functional theory calculations) revealed that the superior HER activity was attributed to the presence of partially reduced metallic Ni with various defects and residual Al, which facilitated water adsorption, dissociation, and finally hydrogen evolution.

Anisotropic Strain Boosted Hydrogen Evolution Reaction Activity of F-NiCoMo LDH for Overall Water Splitting

Layered double hydroxide (LDH) catalysts provide promising OER activity which can be employed in overall water splitting for hydrogen production. However, their weak surface hydrogen adsorption (Had) and high water dissociation energy can result in the inferior hydrogen evolution reactions (HER) activity. In this paper, a highly efficient HER catalyst of F-doped NiCoMo LDH is successfully designed and synthesized through in situ growing on nickel foam (F-NiCoMo LDH/NF) for overall water splitting. DFT calculations demonstrate that the introduction of Mo and F atoms in NiCo LDH can induce the generation of anisotropic lattice strain, resulting in the generation of high-energy active interface and shifting the d-band centers. Therefore, the adsorption energy of Had is optimized and the water dissociation energy barrier is decreased. As a result, this F-NiCoMo LDH/NF catalyst electrode displays a low overpotential of 107.5 mV at 10 mA cm−2 and a small Tafel slope of 67.2 mV dec−1 for HER. The assembled electrolyzer by employing this catalyst electrode requires only 1.83 V to deliver 300 mA cm−2 and operates stably for 100 h.

Intensifying Hydrogen Spillover for Boosting Electrocatalytic Hydrogen Evolution Reaction.

Hydrogen spillover has attracted increasing interests in the field of electrocatalytic hydrogen evolution reaction (HER) in recent years because of their distinct reaction mechanism and beneficial terms for simultaneously weakening the strong hydrogen adsorption on metal and strengthening the weak hydrogen adsorption on support. By taking advantageous merits of efficient hydrogen transfer, hydrogen spillover-based binary catalysts have been widely investigated, which paves a new way for boosting the development of hydrogen production by water electrolysis. In this paper, we summarize the recent progress of this interesting field by focusing on the advanced strategies for intensifying the hydrogen spillover towards HER. In addition, the challenging issues and some perspective insights in the future development of hydrogen spillover-based electrocatalysts are also systematically discussed.

Hydrogen spillover effect enhanced by carbon quantum dots activated MoS2

The weak hydrogen adsorption and slow catalytic kinetics are unfavorable for MoS2 as a catalyst for hydrogen evolution reaction (HER) in alkaline solution. Herein, carbon quantum dots (CQDs) with high proton adsorption energy were expected to enhance the proton adsorption of MoS2 during the HER process. The CQDs activated MoS2 can establish a suitable hydrogen adsorption gradient due to the surface charge redistribution to promote the hydrogen spillover pathway. After the CQDs were loaded on MoS2, the charge distribution would gradually transfer from the C sites of CQDs to the S sites on MoS2 surface, showing a charge gradient distribution calculated by density functional theory predictions. The adsorbed hydrogen can spill over from hydrogen-enriched CQDs to hydrogen-deficient MoS2 in HER. The process could be monitored by the quasi in-situ electrochemical impedance spectroscopy. The enhanced hydrogen spillover effect by CQDs activated MoS2 can pave the way for the design and preparation of efficient and low-cost catalysts.

Single WTe2 Sheet-Based Electrocatalytic Microdevice for Directly Detecting Enhanced Activity of Doped Electronegative Anions.

The high electrical conductivity of 1T'-WTe2 deserves particular attention and may show a high potential for hydrogen evolution reaction (HER) catalysis. However, the actual activity certainly does not match expectations, and the inferior HER activity is actually still ambiguous at the atomic level. Unraveling the underlying HER behaviors of 1T'-WTe2 will give rise to a new family of HER catalysts. Our structural analysis reveals that the inferior activity could result from insufficient charge density around the Te site and blocked adsorption channel at the W site, which cause too weak hydrogen adsorption. Herein, we fabricated a single WTe2 sheet-based electrocatalytic microdevice for directly extracting enhanced HER activity of doped electronegative F atoms. The overpotential at -10 mA cm-2 reduced to 0.27 V after F doping compared to 0.45 V for the original state. In situ electrochemical measurement and electrical tests on a single sheet indicate that doped F can regulate surface charge and hydrogen adsorption behavior. Furthermore, the theory simulation uncovers that the smaller atomic radius of F contributes to an empty coordination environment; meanwhile, strong electronegativity induces hydrogen adsorption. Thus, the ΔGH* at W sites around the doped F is as low as 0.18 eV. Synergistically modulating the charge properties and opening steric hindrance provides a new pathway to rationally construct electrocatalysts and beyond.

Contributions of oxygen vacancies to the hydrogen evolution catalytic activity of tungsten oxides

The tungsten trioxide attracts less attention due to the low electron transfer kinetics that hinders the interaction of electrons and ions during the hydrogen evolution reaction (HER). But the oxygen vacancy strategy can inspire its electrocatalytic activity for HER because it has a positive effect on improving the charge transfer and compensating for the weak hydrogen adsorption of the tungsten trioxide. By synthesizing a series of substoichiometric tungsten oxides, we reveal the linear relationship between the catalytic activity and the content of oxygen vacancies, which indicates that the oxygen vacancy strategy is an achievable route to enhance the HER for metal oxides.

Electronic modulation of novel W18O49 nanoshuttles for efficient hydrogen evolution reaction

Research on transition metal oxides for hydrogen evolution reaction (HER) is challenging due to their poor electrical conductivity and weak hydrogen adsorption. In this paper, a class of W18O49 nanoshuttles (NSs) with highly bifurcated structure at both ends were synthesized via a hydrothermal method for highly efficient HER. By simply introducing Nb and Pt components, W18O49 can achieve optimal hydrogen adsorption through electronic modulation. The optimized NbPt/W18O49 NSs show an extremely low overpotential of 37 mV to obtain 10 mA cm−2 and an unprecedented small Tafel slope of 23 mV dec−1, superior to commercial Pt/C. The NbPt/W18O49 NSs can endure long-term stability for 18 h with negligible morphology change and performance degradation. Based on the surface valence band spectra of x-ray photoelectron spectroscopy and density functional theory calculations, the improved HER activity is closely related to the optimization of hydrogen binding energy on active sites and activation of inert O sites of W18O49. This study opens a facile avenue of electronic modulation to promote electrocatalytic performance.

Synergistically Coupling Black Phosphorus Quantum Dots with MnO2 Nanosheets for Efficient Electrochemical Nitrogen Reduction Under Ambient Conditions.

The electrochemical nitrogen reduction reaction (NRR) is a promising strategy of nitrogen fixation into ammonia under ambient conditions. However, the development of electrochemical NRR is highly bottlenecked by the expensive noble metal catalysts. As a representative 2D nonmetallic material, black phosphorus (BP) has the valence electron structure similar to nitrogen, which can effectively adsorb the inactive nitrogen molecule and activate its triple bond. In addition, the relatively weak hydrogen adsorption can restrict the competitive and vigorous hydrogen evolution reaction. Herein, ultrafine BP quantum dots (QDs) are prepared via liquid-phase exfoliation and then assembled on catalytically active MnO2 nanosheets through van der Waals interactions. The obtained BP QDs/MnO2 catalyst demonstrates admirable synergetic effects in electrochemical NRR. The monodisperse BP QDs providing major activity manifest excellent ammonia production steadily with high selectivity, which benefits from the robust confinement of the BP QDs on the wrinkled MnO2 nanosheets with decent activity. A high ammonia yield rate of 25.3 µg h-1 mgcat. -1 and faradic efficiency of 6.7% can be achieved at -0.5 V (vs RHE) in 0.1 m Na2 SO4 electrolyte, which are dramatically superior to either component. The isotopic labelling and other control tests further exclude the external contamination possibility and attest the genuine activity.

Hierarchical ultrathin carbon encapsulating transition metal doped MoP electrocatalysts for efficient and pH-universal hydrogen evolution reaction

Molybdenum phosphide (MoP) has been recognized as a promising family of non-noble metal electrocatalysts for hydrogen evolution reaction (HER) by water splitting, but their electrocatalytic HER activities are still far from desirable and the active sites of MoP-based electrocatalysts have rarely been explored. Herein, we demonstrate a novel hybrid nanostructure composed of carbon encapsulating ultra-low Co/Ni-doped MoP nanoparticles, which can be adopted as highly active and stable HER catalysts in pH-universal electrolytes. The optimized carbon-encapsulated MoP nanoparticles with a Ni/Mo molar ratio of 0.02 achieve a low overpotential of 102 mV at 10 mA cm−2 and a small Tafel slope of 58.1 mV dec−1 in 0.5 M H2SO4 solution, outperforming most of previously reported MoP-based electrocatalysts. More importantly, density functional theory based calculations reveal that the △GH* of Ni/Co doped MoP at the Mo site is lower than that at the P site, and the lowest △GH* of the doping form of Ni and Co at Mo site was interstitial and substitutional + interstitial, respectively. Higher catalytic performance is observed on doped Mo-terminated surface especially in the presence of non-stoichiometric Ni and Co defects. The lowest free energy of Ni-doping implies that Ni-doped MoP hybrid nanostructures possess weak hydrogen adsorption energy and excellent HER catalytic activity in a wide pH range. The combined experimental and theoretical study paves the way for the identification of the active sites in MoP-based hybrid electrocatalysts toward high-performance HER.

Integrating Rh Species with NiFe-Layered Double Hydroxide for Overall Water Splitting.

NiFe-layered double hydroxide (LDH) is thought of as a promising bifunctional water-splitting catalyst, owing to its excellent performances for alkaline oxygen evolution reactions (OERs). However, it shows extremely poor activity toward hydrogen evolution reactions (HERs) due to the weak hydrogen adsorption. We demonstrated that the integration of Rh species and NiFe-LDH can dramatically improve its HER kinetics without sacrificing the OER performance. The Rh species were initially integrated into NiFe-LDH as oxidized dopants and metallic clusters (< 1 nm). In 1 M KOH electrolyte, an overpotential of 58 mV is needed to catalyze 10 mA cm-2 HER current density. Furthermore, this catalyst only requires 1.46 V to drive an electrolyzer at 10 mA cm-2. A strong interaction between metallic Rh clusters and NiFe hydroxide during the HER process is revealed. The theoretical calculation shows the Rh ions replace Fe ions as the major active sites that are responsible for OERs.

Hydrogen evolution over N-doped CoS2 nanosheets enhanced by superaerophobicity and electronic modulation

Doping heteroatoms offers an opportunity to tune the electronic structure and promote hydrogen evolution reaction (HER) activity for an electrocatalyst. Herein, N-doped CoS2 nanosheets (N-CoS2 NSs) were deposited on carbon cloth via a hydrothermal and post-sulfuration process. The N-CoS2 NSs intercrossed with each other, exhibiting promising superaerophobicity without any adhesion to underwater bubbles. XPS analyses revealed the presence of electron transfer from Co to N dopant in N-CoS2, further proved by differential charge density and Bader charge analyses of density functional theory calculations. The electron transfer intrinsically altered the electronic structure of N-CoS2 and decreased the Gibbs adsorption energy of hydrogen over Co sites. The metallicity of CoS2 was remained after N doping, ascertaining a fast charge transfer and favorable HER process. The N-CoS2/CC showed an enhanced electrocatalytic HER activity with a Tafel slope of 60.1 mV dec−1 and low overpotential of 112 mV at a current density of 10 mA cm−2. Such promising performance is ascribed to the weak hydrogen adsorption upon N doping as well as the underwater superaerophobicity of N-CoS2/CC electrode. Our work might shed light on designing efficient and inexpensive HER electrocatalysts by tailoring their electronic structure and surface superaerophobicity.

Modulation of Phosphorene for Optimal Hydrogen Evolution Reaction.

Economical and highly effective catalysts are crucial to the electrocatalytic hydrogen evolution reaction (HER), and few-layer black phosphorus (phosphorene) is a promising candidate because of the high carrier mobility, large specific surface area, and tunable physicochemical characteristics. However, the HER activity of phosphorene is limited by the weak hydrogen adsorption ability on the basal plane. In this work, optimal active sites are created to modulate the electronic structure of phosphorene to improve the HER activity and the effectiveness is investigated theoretically by density-functional theory calculation and verified experimentally. The edges and defects affect the electronic density of states, and a linear relationship between the HER activity and lowest unoccupied states (εLUS) is discovered. The medium εLUS value corresponds to the suitable hydrogen adsorption strength. Experiments are designed and performed to verify the prediction, and our results show that a smaller phosphorene moiety with more edges and defects exhibits better HER activity and surface doping with metal adatoms improves the catalytic performance. The results suggest that modified phosphorene has large potential in efficient HER and provides a convenient standard to explore ideal electrocatalysts.

Cobalt catalysts for Fischer–Tropsch synthesis: The effect of support, precipitant and pH value

Abstract In this report, Co-based catalysts supported on ZnO, Al 2 O 3 and ZrO 2 as well as the ZrO 2 derived from different precipitants and different pH values were prepared by co-precipitation method. Their catalytic Fischer–Tropsch synthesis (FTS) performance was investigated in a fixed-bed reactor. The results revealed that Co catalyst supported on ZrO 2 exhibited better FTS catalytic performance than that supported on ZnO or Al 2 O 3 . For the Co/ZrO 2 catalyst, different precipitants showed the following an activity order of NaOH > Na 2 CO 3 > NH 4 OH, and the best pH value is 13. The catalysts were characterized by N 2 adsorption–desorption, XRF, XRD, H 2 -TPR, H 2 -TPD and TEM. It was found that the main factor affecting the CO conversion of the catalyst was the amounts of low-temperature active adsorption sites. Moreover, the selectivity of C 5 + hydrocarbons had a positive relationship with the peak temperature of the weak hydrogen adsorption sites. The higher the peak temperature, the higher the C 5 + selectivity is.