Enhanced Catalytic Hydrogen Evolution Reaction in Phosphorene Nanosheet via Cobalt Intercalation

Searching alternatives to Pt-based catalyst for producing hydrogen via water splitting has gathered enormous attention to develop renewable energy. Phosphorene has been investigated widely for its large surface area, low cost, and high carrier mobility, however, the poor activity in hydrogen evolution reaction (HER) and low conductivity limit its practical application. Herein, on the basis of first-principles calculations, we demonstrate that the catalytic HER in phosphorene can be enhanced significantly with cobalt intercalations. The Co-intercalated phosphorene is metallic with charge transfer from Co atoms to phosphorene, which could enhance the catalytic activity of phosphorene. In addition, the calculated Gibbs free energy of hydrogen adsorption on Co-intercalated phosphorene bilayer is comparable to that on Pt(111) surface, independent of the degree of hydrogen coverage. Our study implies that the Co intercalation provides an effective approach to enhance the catalytic HER inphosphorene.     

石墨烯基催化剂的设计合成与电催化应用

为了解决能源匮乏和环境污染的问题,研究人员正致力于寻找清洁可持续的新能源。 其中,氧气还原、氧气析出、析氢反应等是紧密联系新型清洁能源获取和存贮的重要电化学反应。 为了提高其能量转化效率,电催化剂(如碳载铂Pt/C)被广泛地用于降低其反应活化能、提高能量转化效率。 近年来,石墨烯作为一种具有高比表面积和优异导电性的二维碳材料受到了广泛关注。 通过表面杂原子掺杂、缺陷调控和引入催化活性组分等方式,获得了催化性能与贵金属催化剂相媲美,且低价格和高稳定性的非贵金属石墨烯基催化材料。 针对氧气还原、氧气析出和析氢反应在燃料电池、金属-空气电池和电催化水分解中的应用,本文概括综述了通过表/界面结构性质调控提高石墨烯电催化性能和稳定性,获得具有双功能或复合催化性能的石墨烯基催化剂的最新研究进展。 最后总结和展望了亟待解决的问题及未来的发展趋势。     

Pnictogen (As,Sb, Bi) Nanosheets for Electrochemical Applications Are Produced by Shear Exfoliation Using Kitchen Blenders

Layered materials are of high importance because of their anisotropy and as a source of 2D materials. Whilst there is a plethora of multi‐elemental 2D materials, the number mono‐elemental 2D materials is rather limited. Herein, we demonstrate that aqueous shear exfoliation can be used to obtain As, Sb, and Bi exfoliated nanosheets. Morphological and chemical characterization of the exfoliated materials shows a decrease in thickness, sheet‐to‐nanosheet scale, and partial oxidation owing to a higher surface area. The electrochemical performance is tested in terms of inherent electrochemistry, electron transfer, and sensing applications as demonstrated with ascorbic acid. Potential energy‐related applications are evaluated in the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR), with shear‐exfoliated Sb having the best electrochemical performance overall. These findings will have a profound impact on the preparation and application of 2D mono‐elemental materials.     

Theoretical Investigation on the Hydrogen Evolution,Oxygen Evolution,and Oxygen Reduction Reactions Performances of Two-Dimensional Metal-Organic Frameworks Fe3(C2X)12 (X = NH,O, S)

Two-dimensional metal-organic frameworks (2D MOFs) inherently consisting of metal entities and ligands are promising single-atom catalysts (SACs) for electrocatalytic chemical reactions. Three 2D Fe-MOFs with NH, O, and S ligands were designed using density functional theory calculations, and their feasibility as SACs for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) was investigated. The NH, O, and S ligands can be used to control electronic structures and catalysis performance in 2D Fe-MOF monolayers by tuning charge redistribution. The results confirm the Sabatier principle, which states that an ideal catalyst should provide reasonable adsorption energies for all reaction species. The 2D Fe-MOF nanomaterials may render highly-efficient HER, OER, and ORR by tuning the ligands. Therefore, we believe that this study will serve as a guide for developing of 2D MOF-based SACs for water splitting, fuel cells, and metal-air batteries.     

Strategies for Improving the Catalytic Performance of 2D Covalent Organic Frameworks for Hydrogen Evolution and Oxygen Evolution Reactions

Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been deemed as clean and sustainable strategies to solve the energy crisis and environmental problems. Various catalysts have been developed to promote the process of HER and OER. Among them, two-dimensional covalent organic frameworks (2D COFs) have received great attention due to their diverse and designable structure. In this minireview, we mainly summarize the diverse linkages of 2D COFs and strategies for enhancing the catalytic performance of 2D COFs for HER and OER, such as introducing active building blocks, metal ions and tailored linkages. Furthermore, a brief outlook for the development directions of COFs in the field of HER and OER is provided, expecting to stimulate new opportunities in future research.     

Recent Advances of Single-atom Catalysts for Electro-catalysis

Single-atom catalysis is the “hot spot” in the field of catalysis due to the special geometries, electronic states, and their unique catalytic performance. Single-atom catalysts(SACs), isolated metal atoms dispersed on the support, show the highest atom efficiency, cutting down the potential cost in the industrial process. Consequently, this “homo-hetero” catalyst could be a promising candidate for the next-generation catalysts. The applications for the SACs are widely reported, like gas-solid reactions, organic reactions, and electro-catalysis. In this mini- review, we will focus on the recent work of SACs on electro-catalysis, including hydrogen evolution reaction(HER), oxygen reduction reaction(ORR), oxygen evolution reaction(OER), CO₂ reduction reaction(CO₂ RR), and nitrogen reduction reaction(NRR).     

Phosphorene Supported Single-Atom Catalysts for CO Oxidation: A Computational Study

Single-atom catalysts (SACs) have attracted extensive attention owing to their high catalytic activity. The development of efficient SACs is crucial for applications in heterogeneous catalysis. In this article, the geometric configuration, electronic structure, stabilitiy and catalytic performance of phosphorene (Pn) supported single metal atoms (M=Ru, Rh, Pd, Ir, Pt, and Au) have been systematically investigated using density functional theory calculations and ab initio molecular dynamics simulations. The single atoms are found to occupy the hollow site of phosphorene. Among the catalysts studied, Ru-decorated phosphorene is determined to be a potential catalyst by evaluating adsorption energies of gaseous molecules. Various mechanisms including the Eley-Rideal (ER), Langmuir-Hinshelwood (LH) and trimolecular Eley-Rideal (TER) mechanisms are considered to validate the most favourable reaction pathway. Our results reveal that Ru−Pn exhibits outstanding catalytic activity toward CO oxidation reaction via TER mechanism with the corresponding rate-determining energy barrier of 0.44 eV, making it a very promising SAC for CO oxidation under mild conditions. Overall, this work may provide a new avenue for the design and fabrication of two-dimensional materials supported SACs for low-temperature CO oxidation.     

Current progress of molybdenum carbide-based materials for electrocatalysis: potential electrocatalysts with diverse applications

Electrocatalysts are the cores of many electrochemical reactions including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), nitrogen reduction reaction (NRR), and CO₂ reduction reaction (CO₂RR). Recent advances in research have demonstrated the potentials of molybdenum carbide-based catalysts for these reactions arising out of their unique electronic structure and physicochemical properties. In this review, we systematically summarize the recent advances of molybdenum carbide-based catalysts in these electrochemical processes. The corresponding synthesis strategies, structure and electrocatalytic performance of the catalysts are discussed and the relationships of the process-structure-property are highlighted. In addition, the catalytic mechanisms are analyzed based on the structure characterization and theoretical calculations results. Finally, the existing challenges and future perspectives are put forward for further development of molybdenum carbide-based catalysts.     

Bifunctional Electrocatalyst with 0D/2D Heterostructure for Highly Efficient Hydrogen and Oxygen Generation

A novel MoS₂ quantum dots/CoSe₂ nanosheet (MoS₂ QDs/CoSe₂) hybrid with 0D/2D heterostructure has been developed. The CoSe₂ nanosheets (NSs) enable an excellent oxygen evolution reaction (OER) activity with increasing vacancy configuration on one hand, while the MoS₂ QDs serve as an eminent hydrogen evolution reaction (HER) catalyst on the other. By integrating MoS₂ QDs and CoSe₂ NSs, the hybrid exhibits excellent electrocatalytic performances in HER and OER. The unique 0D/2D hetero‐interface increases the exposed active sites and facilitates electron transfer, thereby boosting the electrocatalytic activity. Relatively low overpotentials of 82 mV and 280 mV are required to drive the current density of 10 mA/cm² for HER and OER, with corresponding Tafel slopes of 69 and 75 mV/dec, respectively. As such, this work provides an efficient yet simple approach to construct bifunctional electrocatalysts with enhanced activity and stability.     

二维金属有机框架纳米片的合成及在超电容和电催化领域的应用

二维金属有机框架(2D MOF)纳米片具有丰富且易暴露的表面活性位点、 高度有序的孔结构以及多样且可调的化学成分, 在电化学能量存储与转化中有利于降低反应电位, 提高扩散速率和反应速率. 关于2D MOF应用于电化学存储与转化的研究已有大量报道. 本文综合评述了近几年2D MOF的合成进展及其在超电容(SC)、 析氧反应(OER)、 析氢反应(HER)、 氧还原反应(ORR)和二氧化碳还原反应(CRR)的应用, 并对2D MOF作为电催化材料的研究现状和发展前景进行了总结与展望.     

Enhancing Hydrogen Evolution Activity of Au(111) in Alkaline Media through Molecular Engineering of a 2D Polymer

The electrochemical splitting of water holds promise for the storage of energy produced intermittently by renewable energy sources. The evolution of hydrogen currently relies on the use of platinum as a catalyst—which is scarce and expensive—and ongoing research is focused towards finding cheaper alternatives. In this context, 2D polymers grown as single layers on surfaces have emerged as porous materials with tunable chemical and electronic structures that can be used for improving the catalytic activity of metal surfaces. Here, we use designed organic molecules to fabricate covalent 2D architectures by an Ullmann‐type coupling reaction on Au(111). The polymer‐patterned gold electrode exhibits a hydrogen evolution reaction activity up to three times higher than that of bare gold. Through rational design of the polymer on the molecular level we engineered hydrogen evolution activity by an approach that can be easily extended to other electrocatalytic reactions.     

Earth-Abundant Transition-Metal-Based Bifunctional Electrocatalysts for Overall Water Splitting in Alkaline Media

The depletion of fossil fuels has accelerated the search for clean, sustainable, scalable, and environmentally friendly alternative energy sources. Hydrogen is a potential energy carrier because of its advantageous properties, and the electrolysis of water is considered as an efficient method for its industrial production. However, the high-energy conversion efficiency of electrochemical water splitting requires cost-effective and highly active electrocatalysts. Therefore, researchers have aimed to develop high-performance electrode materials based on non-precious and abundant transition metals for conversion devices. Moreover, to further reduce the cost and complexity in real-world applications, bifunctional catalysts that can be simultaneously active on both the anodic (i.e., oxygen evolution reaction, OER) and cathodic (i.e., hydrogen evolution reaction, HER) sides are economically and technically desirable. This Minireview focuses on the recent progress in transition-metal-based materials as bifunctional electrocatalysts, including several promising strategies to promote electrocatalytic activities for overall water splitting in alkaline media, such as chemical doping, defect (vacancy) engineering, phase engineering, facet engineering, and structure engineering. Finally, the potential for further developments in rational electrode materials design is also discussed.     

First-Principles Study of Ultrathin Molybdenum Sul des Nanowires: Electronic and Catalytic Hydrogen Evolution Properties

Molybdenum sulfides nanomaterials, such as one-dimensional (1D) nanotubes, nanoribbons, and two-dimensional (2D) nanosheets, have attracted intensive research interests for their novel electronic, optical, and catalytic properties. On the basis of first-principles calculation, here, we report a new series of 1D ultrathin molybdenum sulfides nanowires, including Mo₂S₆、Mo₃S₆ and Mo₆S₁₀ nanowires. Our results demonstrate that these ultrathin nanowires are both thermal and lattices dynamically stable, confirmed with the calculated phonon spectrum and Born-Oppenheimer molecular dynamic simulation at the temperature up to 600 K. The calculated elastic constant is 21.33, 103.22, and 163.00 eV/? for Mo₂S₆, Mo₃S₆, and Mo₆S₁₀ nanowires, respectively. Mo₂S₆ and Mo₃S₆ nanowires are semiconductors with band gap of 1.55 and 0.46 eV, while Mo₆S₁₀ nanowires is metal, implying their potential applications in electronics and optoelectronics. In particular, ultrathin molybdenum sulfides nanowires can be used as catalysts for hydrogen evolution reaction. The calculated Gibbs free energy change for hydrogen evolution is about -0.05 eV for Mo₂S₆ nanowire, comparable with those of Pt and H-MoS₂. The prediction of these 1D molybdenum sulfides nanowires may enrich the 1D family molybdenum sulfides and make a supplement to understand the high performance of hydrogen evolution reaction in transition-metal dichalcogenides.     

Electrocatalytic Behavior of an Amide Functionalized Mn(II) Coordination Polymer on ORR,OER and HER

The new 3D coordination polymer (CP) [Mn(L)(HCOO)]_n (Mn-CP) [L = 4-(pyridin-4-ylcarbamoyl)benzoate] was synthesised via a hydrothermal reaction using the pyridyl amide functionalized benzoic acid HL. It was characterized by elemental, FT-IR spectroscopy, single-crystal and powder X-ray diffraction (PXRD) analyses. Its structural features were disclosed by single-crystal X-ray diffraction analysis, which revealed a 3D structure with the monoclinic space group P21/c. Its performance as an electrocatalyst for oxygen reduction (ORR), oxygen evolution (OER), and hydrogen evolution (HER) reactions was tested in both acidic (0.5 M H₂SO₄) and alkaline (0.1 M KOH) media. A distinct reduction peak was observed at 0.53 V vs. RHE in 0.1 M KOH, which corresponds to the oxygen reduction, thus clearly demonstrating the material’s activity for the ORR. Tafel analysis revealed a Tafel slope of 101 mV dec⁻¹ with mixed kinetics of 2e⁻ and 4e⁻ pathways indicated by the Koutecky–Levich analysis. Conversely, the ORR peak was not present in 0.5 M H₂SO₄ indicating no activity of Mn-CP for this reaction in acidic media. In addition, Mn-CP demonstrated a noteworthy activity toward OER and HER in acidic media, in contrast to what was observed in 0.1 M KOH.     

Platinum Group Metal–free Catalysts for Hydrogen Evolution Reaction in Microbial Electrolysis Cells

Hydrogen gas is a green energy carrier with great environmental benefits. Microbial electrolysis cells (MECs) can convert low‐grade organic matter to hydrogen gas with low energy consumption and have gained a growing interest in the past decade. Cathode catalysts for the hydrogen evolution reaction (HER) present a major challenge for the development and future applications of MECs. An ideal cathode catalyst should be catalytically active, simple to synthesize, durable in a complex environment, and cost‐effective. A variety of noble‐metal free catalysts have been developed and investigated for HER in MECs, including Nickel and its alloys, MoS₂, carbon‐based catalysts and biocatalysts. MECs in turn can serve as a research platform to study the durability of the HER catalysts. This personal account has reviewed, analyzed, and discussed those catalysts with an emphasis on synthesis and modification, system performance and potential for practical applications. It is expected to provide insights into the development of HER catalysts towards MEC applications.     

Controlled Synthesis of 3D Flower‐like Ni2P Composed of Mesoporous Nanoplates for Overall Water Splitting

Developing efficient non‐noble metal and earth‐abundant electrocatalysts with tunable microstructures for overall water splitting is critical to promote clean energy technologies for a hydrogen economy. Herein, novel three‐dimensional (3D) flower‐like Ni₂P composed of mesoporous nanoplates with controllable morphology and high surface area was prepared by a hydrothermal method and low‐temperature phosphidation as efficient electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Compared with the urchin‐like Ni_x P_y , the 3D flower‐like Ni₂P with a diameter of 5 μm presented an efficient and stable catalytic performance in 0.5 m H₂SO₄, with a small Tafel slope of 79 mV dec⁻¹ and an overpotential of about 240 mV at a current density of 10 mA cm⁻² with a mass loading density of 0.283 mg cm⁻². In addition, the catalyst also exhibited a remarkable performance for the OER in 1.0 m KOH electrolyte, with an overpotential of 320 mV to reach a current density of 10 mA cm⁻² and a small Tafel slope of 72 mV dec⁻¹. The excellent catalytic performance of the as‐prepared Ni₂P may be ascribed to its novel 3D morphology with unique mesoporous structure.     

Facile Synthesis of Black Phosphorus: an Efficient Electrocatalyst for the Oxygen Evolving Reaction

Black phosphorus (BP) as a new 2D material has attracted extensive attention because of its unique electronic, optical, and structural properties. However, the difficulties associated with BP synthesis severely hinder the further development of BP for any potential applications. On the other hand, searching for other potential applications of BP is also a big challenge. A facile strategy was developed for preparation of BP supported on Ti foil (BP‐Ti) in a thin‐film form. Surprisingly, the as‐prepared BP shows advanced electrocatalytic activity for the oxygen evolution reaction (OER). To improve the OER activity of the electrocatalyst, BP was grown on a carbon nanotube network (BP‐CNT), showing even better activity. The results demonstrate that BP can be prepared by a facile method and may be applied as an electrocatalyst.     

Phosphorene: a Potential 2D Material for Highly Efficient Polysulfide Trapping and Conversion

Effectively trapping lithium polysulfide species and accelerating the reaction conversion kinetics are the main strategies to improve the performance of lithium-sulfur(Li-S) batteries. Since the researchers found in 2014 that two-dimensional(2D) phosphorene nanosheets could be exfoliated from the bulk black phosphorus, numerous researches have been devoted to exploring the phosphorene with unique properties for the application in Li-S batteries. In this review, we summarize the recent theoretical and experimental progress of phosphorene for Li-S batteries. Besides, we also introduce the relationship between the interfacial interaction on phosphorene and the performance enhancement of Li-S batteries. Furthermore, future challenges and remaining opportunities for phosphorene in Li-S batteries are finally discussed.     

光催化制氢研究进展

The photocatalytic hydrogen evolution reaction (PHER) has gained much attention as a promising strategy for the generation of clean energy. As opposed to conventional hydrogen evolution strategies (steam methane reforming, electrocatalytic hydrogen evolution, etc.), the PHER is an environmentally friendly and sustainable method for converting solar energy into H₂ energy. However, the PHER remains unsuitable for industrial applications because of efficiency losses in three critical steps: light absorption, carrier separation, and surface reaction. In the past four decades, the processes responsible for these efficiency losses have been extensively studied. First, light absorption is the principal factor deciding the performance of most photocatalysts, and it is closely related to band-gap structure of photocatalysts. However, most of the existing photocatalysts have a wide bandgap, indicating a narrow light absorption range, which restricts the photocatalytic efficiency. Therefore, searching for novel semiconductors with a narrow bandgap and broadening the light absorption range of known photocatalysts is an important research direction. Second, only the photogenerated electrons and holes that migrate to the photocatalyst surface can participate in the reaction with H₂O, whereas most of the photogenerated electrons and holes readily recombine with one another in the bulk phase of the photocatalysts. Hence, tremendous effort has been undertaken to shorten the charge transfer distance and enhance the electric conductivity of photocatalysts for improving the separation and transfer efficiency of photogenerated carriers. Third, the surface redox reaction is also an important process. Because water oxidation is a four-electron process, sluggish O₂ evolution is the bottleneck in photocatalytic water splitting. The unreacted holes can easily recombine with electrons. Sacrificial agents are widely used in most catalytic systems to suppress charge carrier recombination by scavenging the photogenerated holes. Moreover, the low H₂ evolution efficiency of most photocatalysts has encouraged researchers to introduce highly active sites on the photocatalyst surface. Based on the abovementioned three steps, multifarious strategies have been applied to modulate the physicochemical properties of semiconductor photocatalysts with the aim of improving the light absorption efficiency, suppressing carrier recombination, and accelerating the kinetics of surface reactions. The strategies include defect generation, localized surface plasmon resonance (LSPR), element doping, heterojunction fabrication, and cocatalyst loading. An in-depth study of these strategies provides guidance for the design of efficient photocatalysts. In this review, we focus on the mechanism and application of these strategies for optimizing light absorption, carrier separation and transport, and surface reactions. Furthermore, we provide a critical view on the promising trends toward the construction of advanced catalysts for H₂ evolution.     

Self-supporting Atmosphere-Assisted Synthesis of 1D Mo2C-based Catalyst for Efficient Hydrogen Evolution

One-dimensional materials exhibit fascinating properties in electrocatalytic applications but their fabrication faces the challenge of tedious and complicated operations. We have developed a bottom-up strategy to construct a 1D metal carbide catalyst (Mo₂C@NC) consisting of ultrafine Mo₂C nanoparticles embedded within nitrogen-doped carbon layers by simply calcining a mixture of ammonium molybdate, urea and melamine. Experimental results and thermodynamic calculations demonstrate that the retainable pyrolysis-generated self-supporting atmosphere plays a crucial role in the crystalline phase and morphology of materials. When functioned as an electrocatalyst for the hydrogen evolution reaction (HER), the achieved Mo₂C@NC presents an excellent catalytic activity as well as outstanding stability. This work could shed fresh light onto the facile synthesis of effective HER catalysts with 1D nanostructure.