Monolayer Catalysts Research Articles

2D Monolayer Catalysts: Towards Efficient Water Splitting and Green Hydrogen Production.

A viable alternative to non-renewable hydrocarbon fuels is hydrogen gas, created using a safe, environmentally friendly process like water splitting. An important role in water-splitting applications is played by the development of two-dimensional (2D) layered transition metal chalcogenides (TMDCs), transition metal carbides (MXenes), graphene-derived 2D layered nanomaterials, phosphorene, and hexagonal boron nitride. Advanced synthesis methods and characterization instruments enabled an effective application for improved electrocatalytic water splitting and sustainable hydrogen production. Enhancing active sites, modifying the phase and electronic structure, adding conductive elements like transition metals, forming heterostructures, altering the defect state, etc., can improve the catalytic activity of 2D stacked hybrid monolayer nanomaterials. The majority of global research and development is focused on finding safer substitutes for petrochemical fuels, and this review summarizes recent advancements in the field of 2D monolayer nanomaterials in water splitting for industrial-scale green hydrogen production and fuel cell applications.

Synergistic Effects of Dual-Doping with Ni and Ru in Monolayer VS2 Nanosheet: Unleashing Enhanced Performance for Acidic HER through Defects and Strain.

Amidst the escalating quest for clean energy, the hydrogen evolution reaction (HER) in acidic conditions has taken center stage, catalyzing the search for advanced electrocatalysts. The efficacy of these materials is predominantly dictated by the active site density on their surfaces. The propensity is leveraged for monolayer architectures to introduce defects, enhancing surface area, and increasing active sites. Doping enhances defects and fine-tunes catalyst activity. In this vein, defect-enriched monolayer nanosheets doped with nickel and a trace amount of ruthenium in VS2 (SL-Ni-Ru-VS2) are engineered and characterized. Evaluation in 0.5m H2SO4 solution unveils that the catalyst achieves overpotentials as low as 20 and 41mV at current densities of -10 and -100mA cm⁻2. Impressively, the catalyst maintains a mass activity of 13.08 A mg⁻¹Ru, even with minimal Ru incorporation, indicating exceptional catalytic efficiency. This monolayer catalyst sustains its high activity at lower overpotentials, demonstrating its practical applicability. The comprehensive analysis, which combines experimental data and computational simulations, indicates that the co-doping of Ni and Ru enhances the electrocatalytic properties of VS2. This research offers a strategic framework for crafting cutting-edge electrocatalysts specifically designed for enhanced performance in the HER.

Unlocking power of neighboring vacancies in boosting hydrogen evolution reactions on two-dimensional NiPS3 monolayer

This study investigates the effect of defect engineering on the catalytic activity of a NiPS3 monolayer catalyst for the hydrogen evolution reaction (HER). Three different types of vacancies on the basal plane of the monolayer are explored through a multi-step mechanism involving the dissociative adsorption of a water molecule and subsequent electrochemical adsorption of the dissociated proton. Co-formation of vacancies in both Ni and S sites is found to be the most effective in enhancing the catalytic performance of the monolayer. A key resource for the reaction thermodynamics is the S-substitution-like physisorption of a water molecule on a vacant S site, followed by the dissociative occupation of OH and H into vacant sites of S and Ni elements, boosted by the NiS di-vacancy configuration with low activation energy barriers. Investigation reveals the highest contribution of bonding orbitals to the monolayer-H bond makes it the most desirable defect engineering approach for transition metal phosphorus chalcogenides with high HER activities. Overall, this study highlights the significance of controlled defect engineering in augmenting the catalytic performance of NiPS3 monolayer catalysts for HER.

CoO QDs/Bi2MoO6 monolayer: A novel S-scheme heterojunction for highly efficient photocatalytic C2H4 degradation

As a plant hormone, C2H4 causes significant economic losses during the storage and transportation of fruits and vegetables. How to efficiently photocatalytic oxidation of atmospheric C2H4 using sun-light remains a significant challenge at the frontiers of chemistry. Inspired by natural photosynthesis of plant, here, we design a novel S-scheme heterojunction for highly efficient photocatalytic C2H4 degradation. We first conducted density functional theory (DFT) calculations to predict an S-scheme heterojunction can be formed between CoO and Bi2MoO6, and then fabricated a novel CoO Quantum dots (QDs)/Bi2MoO6 monolayer S-scheme heterojunction by using a practical hydrothermal approach to in-situ deposit CoO QDs on a Bi2MoO6 monolayer. Furthermore, the UV–Vis DRS, UPS, in-situ XPS and electron spin resonance (ESR) characterization of DMPO-•O2– signals and DMPO-•OH signals evidence that the transfer pathway of space charge in photocatalytic degradation of ethylene accords with the S-scheme. Moreover, due to the unique structural design, CoO QDs and Bi2MoO6 monolayer form an S-scheme heterojunction, and the intimate contact that enables efficient charge transfer and sufficient redox ability simultaneously, the CoO QDs/Bi2MoO6 monolayer catalyst achieves a remarkable ethylene photocatalytic-degradation rate of 3.27 × 10−2∙min−1, 19.2 times higher than CoO and 22.5 times higher than Bi2MoO6. This work provides novel insights for designing efficient S-scheme photocatalysts for C2H4 degradation.

A DFT study on the copper-single-atom modified 2D electride Ca2N monolayer for ethanol dehydrogenation

Two-dimensional (2D) electrides, with electrons confined in interlayer spaces instead of at atomic proximities, have received considerable attention due to their exotic properties. However, the current exploration of electrides in the field of catalysis urgently needs to be expanded. Here, we report novel thermodynamically stable Cu single-atom-modified 2D electride Ca2N monolayer catalysts for ethanol dehydrogenation using density functional theory calculations. The interaction and synergistic catalytic mechanism of copper single atoms and Ca2N monolayers were thoroughly revealed. The coordination environment of copper greatly affects the reaction sites for ethanol dehydrogenation. Furthermore, it was found that the strong electron transfer ability of Ca2N monolayer promoted the adsorption and activation of ethanol molecules on the catalyst, resulting in a cleavage energy barrier of the O–H bond as low as 0.29 eV on Cu1/Ca2N. Furthermore, turnover frequency (TOF) analysis demonstrates that Cu1/Ca2N exhibits significantly higher activity compared to Ca2N with lower energetic span (δE) of 2.52 eV at 298.15 K for the cycle of ethanol dehydrogenation to acetaldehyde. Our work demonstrates a new avenue to the discovery of 2D electride-based catalysts and provides new insights into the mechanism of ethanol dehydrogenation.

Electrochemical Reduction of CO2 via Single-Atom Catalysts Supported on α-In2Se3.

In this work, the electrochemical CO2 reduction reaction (CO2RR) over transition metal and α-In2Se3 monolayer catalysts was investigated by density functional theory (DFT) and an effective screening medium method-reference interaction site model (ESM-RISM). On the basis of the scaling relationship between the adsorption free energies of intermediates, we constructed the relationships between oxygen-bound intermediates with *O and carbon-bound intermediates with *CHO. The calculation results indicate that *OCHO intermediates are more favorable for the first hydrogenation of CO2 on M@In2Se3 catalysts; thus, the adsorption energy of oxygen-bound species determines the catalytic performance of M@In2Se3. The Co@In2Se3↓-C was predicted to be the most promising catalyst with a low limiting potential of -0.385 V as determined by the computational hydrogen electrode method. Constant potential calculations also demonstrate that the M@In2Se3 catalysts hold great potential for highly efficient CO2RR. This work provides a fundamental understanding for the rational design of ferroelectric single-atom catalysts for the purpose of highly efficient electrocatalytic CO2 reduction.

Molecule Saturation Boosts Acetylene Semihydrogenation Activity and Selectivity on a Core‐Shell Ruthenium@Palladium Catalyst

AbstractIncreasing selectivity without the expense of activity is desired but challenging in heterogeneous catalysis. By revealing the molecule saturation and adsorption sensitivity on overlayer thickness, strain, and coordination of Pd‐based catalysts from first‐principles calculations, we designed a stable Pd monolayer (ML) catalyst on a Ru terrace to boost both activity and selectivity of acetylene semihydrogenation. The least saturated molecule is most sensitive to the change in catalyst electronic and geometric properties. By simultaneously compressing the Pd ML and exposing the high coordination sites, the adsorption of more saturated ethylene is considerably weakened to facilitate the desorption for high selectivity. The even stronger weakening to the least saturated acetylene drives its hydrogenation such that it is more exothermic, thereby boosting the activity. Tailoring the molecule saturation and its sensitivity to structure and composition provides a tool for rational design of efficient catalysts.

Molecule Saturation Boosts Acetylene Semihydrogenation Activity and Selectivity on a Core-Shell Ruthenium@Palladium Catalyst.

Increasing selectivity without the expense of activity is desired but challenging in heterogeneous catalysis. By revealing the molecule saturation and adsorption sensitivity on overlayer thickness, strain, and coordination of Pd-based catalysts from first-principles calculations, we designed a stable Pd monolayer (ML) catalyst on a Ru terrace to boost both activity and selectivity of acetylene semihydrogenation. The least saturated molecule is most sensitive to the change in catalyst electronic and geometric properties. By simultaneously compressing the Pd ML and exposing the high coordination sites, the adsorption of more saturated ethylene is considerably weakened to facilitate the desorption for high selectivity. The even stronger weakening to the least saturated acetylene drives its hydrogenation such that it is more exothermic, thereby boosting the activity. Tailoring the molecule saturation and its sensitivity to structure and composition provides a tool for rational design of efficient catalysts.

Graphdiyne supported single-cluster catalysts catalyzed electrochemical nitrogen reduction reaction: A first-principles investigation

The electrochemical reduction reaction of dinitrogen into ammonia (eNRR) has been considered as one of the most promising candidates to replace the traditional Haber-Bosch process. By using the density functional theory calculations, 20 kinds of atomically dispersed tri-atoms supported on graphdiyne monolayer catalysts MxM′yM″3-x-y/GDY (M, M′, M″ = Cr, Mo, W, Fe) were investigated for the eNRR process. It is found that Cr3/GDY, W3/GDY, and Cr2Mo1/GDY exhibit high stability, selectivity, and activity, with limiting potentials of only −0.36, −0.35, and −0.29 V, respectively. Specifically, by further investigating the most active and exemplar Cr2Mo1/GDY system, in the presence of N2 adsorption on the catalyst, it would promote the desorption of the final product NH3. More importantly, by evaluating the growth energy of the supported atomic metal centers, these catalysts have a very broad theoretical energy window, indicating their possibility of synthesizing. These atomically dispersed metal centers cooperating with the GDY monolayer could promote the multi-step protonation process. Our findings shed light on the rational and precise design of novel catalysts for electrochemical energy conversion and storage.

Humidity tuning CO oxidation on Ti decorated V2CO2 monolayer (MXene) catalyst: A density functional calculation study

Considering the high efficiency and low cost, original single-atom catalyst Ti/V2CO2 is used for CO catalytic oxidation in this work. Besides, density functional theory (DFT) calculations are adopted to explore H2O effects on performance and mechanisms of CO catalytic oxidation. Finally, the single atom of Ti is proven to be evenly distributed on V2CO2 monolayer. Also, it is discovered that CO oxidation cannot occur on Ti/V2CO2 in dry conditions. While, in humid conditions, water molecule is responsible for transferring charge to Ti atom, thus weakening O2 adsorption and causing lower activation energy of 0.71 eV. Rather than directly participating in CO oxidation by generating -OH groups with O2, it prefers to act as a co-catalyst with Ti/V2CO2. Consequently, the energy barrier of rate-limiting step based on Eley-Rideal (ER) mechanism is remarkably reduced from 1.79 to 0.57 eV, due to CO catalytic oxidation with the help of H2O in accelerating the interaction between single O atom and CO molecule. According to our findings, the existence of water can promote Ti/V2CO2 to be an effective single-atom catalyst for catalytic oxidation of CO in a humid environment.

Two-Dimensional (2D) TM-Tetrahydroxyquinone Metal-Organic Framework for Selective CO2 Electrocatalysis: A DFT Investigation.

The resource utilization of CO2 is one of the essential avenues to realize the goal of "double carbon". The metal-organic framework (MOF) has shown promising applications in CO2 catalytic reduction reactions due to its sufficient pore structure, abundant active sites and functionalizability. In this paper, we investigated the electrocatalytic carbon dioxide reduction reactions of single-atom catalysts created by MOF two-dimensional coordination network materials constructed from transition metal-tetrahydroxybenzoquinone using density function theory calculations. The results indicate that for 10 transition metals, TM-THQ single levels ranging from Sc to Zn, the metal atom binding energy to the THQ is large enough to allow the metal atoms to be stably dispersed in the THQ monolayer. The Ni-THQ catalyst does not compete with the HER reaction in an electrocatalytic CO2 reduction. The primary product of reduction for Sc-THQ is HCOOH, but the major product of Co-THQ is HCHO. The main product of Cu-THQ is CO, while the main product of six catalysts, Ti, V, Cr, Mn, Fe, and Zn, is CH4. The limit potential and overpotential of Ti-THQ are the highest, 1.043 V and 1.212 V, respectively. The overpotentials of the other monolayer catalysts ranged from 0.172 to 0.952 V, and they were all relatively low. Therefore, we forecast that the TM-HQ monolayer will show powerful activity in electrocatalytic carbon dioxide reduction, making it a prospective electrocatalyst for carbon dioxide reduction.

Electrochemical Epitaxy: Perspective and Applications

Properties of heteroepitaxial thin films are often dependent on the method and conditions for deposition[1]. In that respect, the electrochemical growth represents energetically different approach as compared to conventional vacuum deposition methods. It offers unique advantages, which can be exploited to get high quality ultra-thin films. The obvious one is that process occurs at an ambient temperature, which allows growth of heteroepitaxial metal overlayers while preserving the integrity of the interface. In recent years, significant progress has been made in controlling the thin film growth modes[2],[3],[4]. Various approaches to manipulate growth kinetics and enhance the evolution of atomically flat epitaxial overlayers were discovered[5],[6],[7]. Some of these findings were successfully implemented in electrochemical epitaxial growth resulting in development of deposition protocols such as Defect Mediated Growth (DMG)[8],[9], Surfactant Mediated Growth (SMG)[10] and growth via Surface Limited Redox Replacement (SLRR)[11],[12] with its sub-derivatives such as SEBALD, ECALD, ECALE, E-less ALD. These methods are used extensively by practitioners in different areas to synthesize monolayer or nanocluster catalysts and ultra-thin films with different compositions and applications.In this talk, we will review current perspective and progress on electrochemical epitaxial growth. Discussion will focus on fundamental and practical details of the relevant phenomena about UPD, SMG, DMG, SLRR and E-less ALD using examples and challenges that are facing researchers in these areas. If time allowed, some out of the box idea will be posted opening podium for discussion.

(Invited) Pd Monolayer Catalyst As Transformative Concept for Electrolytic Hydrogen Isotope Separation

The effect of strain in Pd monolayer catalyst is explored for electrolytic hydrogen isotope separation. Positive/negative strain increases/decreases strength of adsorbed hydrogen bond in overpotential region where recombination of hydrogen atoms is the rate determining step in hydrogen evolution reaction. As a result, the increased/decreased hydrogen isotope separation efficiency of Pd monolayers is expected as compared to bulk Pd. The positive/negative strain rises/lowers diffusion barrier for adsorbed hydrogen atoms. This effect favors/retards recombination of isotopes with smaller mass. As the surface is stretched/compressed, the neighboring adsorption sites separate/approach each other which affects heavier hydrogen isotopes more/less and result in their lower/higher probability for recombination. All these fundamental consideration indicate that Pd monolayers with different level of strain should have much different separation factors than corresponding bulk electrodes. To study described effects, Pd monolayers we synthesized electrochemically on Au(111) and Ru(0001) electrodes each yielding qualitatively different strain levels (Au-positive, Ru-negative). The adsorption strength of hydrogen isotopes is studied by infra-red spectroscopy. These results are input in classical models for isotope separation[1] T calculations. The calculated ratio between the rates of hydrogen and deuterium recombination and separation factors for Pd monolayers and corresponding bulk electrodes are compared to experimentally measured ones. The following discussion focuses on understanding and quantification of strain effects on separation efficiency of Pd monolayers. [1] B. E. Conway, Proceedings of The Royal Society of London, A. Mathematical and Physical Sciences, 247, 400 (1958).

Metal-Confined Synthesis of ZnS2 Monolayer Catalysts for Dinitrogen Electroreduction

Metal-Confined Synthesis of ZnS₂ Monolayer Catalysts for Dinitrogen Electroreduction

SiC Monolayers as Promising Substrates for the Development of Highly Stable Palladium Single Atom Catalysts: A Density Functional Theory Study

Single-atom catalysts have been touted as highly efficient catalysts, but the catalytic single-atom sites are unstable and tend to aggregate into nanoparticles during chemical reactions. In this study, we show that SiC monolayers are promising substrates for the development of highly stable single-atom catalysts (Pd1 /SiC) within the density functional theory. In presence of a Si-vacancy, the diffusion barrier energy of a Pd1 atom embedded in the SiC monolayer is substantially enhanced from 2.3 to 7.8 eV, which is much higher than the reported diffusion barrier energies of graphene, boron nitride and defective MgO of the same catalytic system. Ab initio molecular dynamic calculations at 500 K also confirm the enhanced stability of Pd1 /SiC monolayer (Si-vacancy) such that the Pd1 atom remains embedded in the vacancy. Additionally, the Pd1 /SiC monolayer (Si-vacancy) catalysts show a ∼34 % reduction of activation barrier energy for CO oxidation as compared to pristine catalysts. This work implies that nanostructured SiC materials are promising substrates for the synthesis of highly stable single-atom catalysts.

Ultrafine Co-MoS2 monolayer catalyst derived from oil-soluble single-molecule polyoxometalates for slurry phase hydrocracking

Herein, a novel single-molecule confinement-sulfurization strategy was proposed to construct ultrafine Co-MoS2 monolayer catalysts by using oil-soluble single-molecule polyoxometalates (POMs), (DODA)6Co2Mo10, as precursors. Well-defined Co2Mo10-POM, acting as molecular pre-assembling platform, is introduced for the atomically precise construction of bimetallic sites. Highly efficient conversion of VR under severe condition is realized with (DODA)6Co2Mo10. The origin of prominent catalytic performance can be attributed to the in-situ formation of ultrafine single-layered Mo-based nanosheets with abundant exposed CoMoS active sites. By combining synchrotron radiation-based X-ray absorption spectroscopy and density functional theory calculations, we further discover that there is clearly intimate interaction between Mo and Co atoms and the dissociation of molecular hydrogen at CoMoS phases is energetically preferred, leading to remarkable hydrogenation and coke suppression activity. This work highlights an idea on the rational design and targeted synthesis of ultrafine bimetallic catalysts for slurry phase HCK with dramatically synergistic catalysis.

(Invited) The Exploration of Highly Active Pt and Non-Pt Electrocatalysts for the Oxygen Reduction Reaction in PEMFCs

Due to the high Pt loading applied in cathodes of polymer electrolyte membrane fuel cells (PEMFCs), the fuel cell cost remains very high, which greatly hinders its commercialization in different fields. It is well anticipated the Pt loading level should be reduced from the current 0.4 mg/cm2 to less than 0.1 mg/cm2. On the one hand, high active Pt alloy or monolayer catalysts can be obtained by adjusting compositions and structures. On the other hand, the alternative of non-noble metal catalysts (M-N/C, et al.) is considered as the ultimate solution. However, the local mass transfer of oxygen across the active site surface becomes worse due to significant reductions in their amount or activity, seriously affecting the performance of fuel cells1,2. Herein, a series of ultra-low Pt or M-N/C electrocatalysts with both controlled compositions and structures are synthesized and investigated as the oxygen reduction reaction (ORR) electrocatalyst. Corresponding synthetic mechanisms are comprehensively elucidated by advanced physiochemical characterizations combined with density functional theory (DFT). It is believed that the discussion will provide a solid scientific guideline for the development of highly efficiently electrocatalysts for low-cost PEMFCs. Keywords: highly active, low-Pt, non-Pt, oxygen reduction reaction, proton exchange membrane fuel cells, density functional theory Reference [1] W. Xia, A. Mahmood, Z. Liang, R. Zou, S. Guo, Angewandte Chemie International edtion, 2016, 55, 2650.[2] U. Martinez, S.K Babu, E.F. Holby, P. Zelenay, Current Opinion in Electrochemistry, 2018, 9, 224. Acknowledgements This work was supported in part by National Natural Science Foundation of China (21975157) and the National Key Research and Development Program of China (2016YFB0101201 and 2016YFB0101312).

Bimetallic monolayer catalyst breaks the activity–selectivity trade-off on metal particle size for efficient chemoselective hydrogenations

Bimetallic monolayer catalyst breaks the activity–selectivity trade-off on metal particle size for efficient chemoselective hydrogenations

Catalytic Role of Adsorption of Electrolyte/Molecules as Functional Ligands on Two-Dimensional TM-N4 Monolayer Catalysts for the Electrocatalytic Nitrogen Reduction Reaction.

Two-dimensional single-atom catalysts (2D SACs) have been widely studied on the nitrogen reduction reaction (NRR). The characteristics of 2D catalysts imply that both sides of the monolayer can be catalytic sites and adsorb electrolyte ions or molecules from solutions. Overstrong adsorption of electrolyte ions or molecules on both sides of the catalyst site will poison the catalyst, while the adsorbate on one side of the catalytic site will modify the activity and selectivity of the other side for NRR. Discovering the influence of adsorption of electrolyte ions or molecules as a functional ligand on catalyst performance on the NRR is crucial to improve NRR efficiency. Here, we report this work using the density functional theory (DFT) method to investigate adsorption of electrolyte ions or molecules as a functional ligand. Among all of the studied 18 functional ligands and 3 transition metals (TMs), the results showed that Ru&F, Ru&COOH, and Mo&H2O combinations were screened as electrocatalysis systems with high activity and selectivity. Particularly, the Mo&H2O combination possesses the highest activity with a low ΔGMAX of 0.44 eV through the distal pathway. The superior catalytic performance of the Mo&H2O combination is mainly attributed to the electron donation from the metal d orbital. Furthermore, the functional ligands can occupy the active sites and block the competing vigorous hydrogen evolution reaction. Our findings offer an effective and practical strategy to design the combination of the catalyst and electrolyte to improve electrocatalytic NRR efficiency.

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions

Selective upgrading of biomass-derived benzylic ketones by (formic acid)–Pd/HPC–NH2 system with high efficiency under ambient conditions