Graphene Support Research Articles

Unveiling Inequality of Atoms in Ultrasmall Pt Clusters: Oxygen Adsorption Limited to the Uppermost Atomic Layer

The concept of preferential atomic and molecular adsorption site is of primary relevance in heterogeneous catalysis. In the case of ultrasmall size‐selected clusters, distinguishing the role played by each atom in a reaction is extremely challenging due to their reduced size and peculiar structures. Herein, it is revealed how the inequivalent atoms composing graphene‐supported Pt12 and Pt13 clusters behave differently in the photoinduced dissociation of O2, with only those in the uppermost layer of the clusters being involved in the reaction. In this process, the epitaxial graphene support plays a fundamental active role: its corrugation and pinning induced by the presence of the clusters are crucial for defining the preferential adsorption site on the Pt atomic agglomerates, facilitating the lateral diffusion of physisorbed oxygen at a distance that induces its selective adsorption in the topmost layer of the clusters, and inducing an inhomogeneous charge distribution within the clusters which directly affects the O2 adsorption. The inhomogeneous oxidation of the clusters is resolved by means of synchrotron‐based X‐ray photoelectron spectroscopy and supported by ab initio density functional theory calculations. The possibility to identify the active sites on Pt clusters induced by cluster–support interactions has the potential to enhance the experimentally supported design of nanocatalysts.

Pt Nanoparticles Electrochemically Deposited onto Heteroatom-Doped Graphene Supports as Electrocatalysts for ORR in Acid Media

Platinum nanoparticles (PtNPs) are attached to different single heteroatom-doped (N, S, P, and B) and dual heteroatom-doped (N, B and N, P) graphene nanosheets via electrochemical deposition using the chronoamperometric method, which allowed for strong attachment of the PtNPs onto the support surface. The effect of the support material on the electrocatalytic activity of the PtNPs on the oxygen reduction reaction (ORR) in acidic media is examined. The PtNPs supported on boron-doped graphene exhibit the highest specific activity (1.26 mA cm−2), and the PtNPs supported on nitrogen and boron dual heteroatom-doped graphene exhibit the highest mass activity (0.70 A mg−1) at 0.9 V vs reversible hydrogen electrode. The kinetics of the ORR vary significantly depending on the dopants, thus concluding that the heteroatom doping of the graphene support material affects the electrocatalytic activity of PtNPs toward the ORR.

The Impact of Carbon Corrosion Towards Oxygen Reduction Reaction Activity on Atomically Dispersed M-N-C Catalysts

Atomically dispersed Pt group metal free (PGM free) M-N-C catalysts offer a promising pathway towards a clean energy future.1 This class of materials has proven to be a viable substitute for commercial Pt/C to catalyze oxygen reduction reaction (ORR) with similar activity at only a fraction of the raw material cost.2 To gain a wider market adoption, however, M-N-C catalysts need to significantly improve its durability compared to Pt and its alloys in a real-world operating condition. Towards this end, substantial efforts have focused on making more durable M-N-C catalysts while simultaneously maintaining and improving its ORR activity.3,4 As part of the effort to understand the fundamental aspects that control M-N-C catalysts’ durability during ORR condition, we employ a combined approach using first principles density functional theory (DFT) and density functional tight binding theory (DFTB) to identify the impact of carbon corrosion occurring on M-N-C catalyst towards ORR activity. Our starting atomic representation of the ORR active site is the “C10” type local structure composed of FeN4C10 local defect5 embedded in a monolayer graphene support of varying cell size. As carbon corrosion occurs and consequently creating local carbon vacancies surrounding the active site, we then obtain a family of FeN4C11 and FeN4C12 type of local structures. Our DFT calculations of OH binding energy on these corrosion derived structures suggest that the presence of C vacancies and the subsequent H passivation on dangling C introduces elastic structural deformation to various degree that decreases the theoretical ORR limiting potential. This decrease in DFT calculated ORR limiting potential across a family of FeN4C10, FeN4C11, and FeN4C12 local structures can be attributed to a mechanical energy arising from the surface reconstructions. Reference D. A. Cullen et al., Nat Energy, 6, 462–474 (2021).G. Wu, K. L. More, C. M. Johnston, and P. Zelenay, Science, 332, 443–447 (2011).E. F. Holby, G. Wang, and P. Zelenay, ACS Catal., 10, 14527–14539 (2020).T. Patniboon and H. A. Hansen, ACS Catal., 11, 13102–13118 (2021).H. T. Chung et al., Science, 357, 479–484 (2017).

CO2 electroreduction on single atom catalysts: Role of the local coordination

Single Atom Catalysts (SACs) are a new frontier in catalysis, merging the positive aspects of both homogeneous and heterogenous catalysts. CO2 electrochemical reduction is a key reaction for the energy transition. In this work, we investigate the role of the local coordination on the activation of CO2 on SACs, by means of density functional theory (DFT) calculations. We scrutinize 20 transitional metal atoms embedded in a graphene support. The results indicate that the local coordination has a critical role both to the binding energy of the metal to the support and the activation of CO2. The role of the environment around the active site is as important as the nature of the metal atom. At the same time, the stability of reaction intermediates strongly depends on the local coordination. In some cases, the relative stability of the intermediates changes as function of the environment, affecting the selectivity of the reaction. This study provides evidence of the importance of the local coordination in single-atom catalysis, a crucial aspect if one is interested in providing a rationale to the reactivity, or in predicting novel catalysts.

Hydrogenated graphene support for accelerating alkaline hydrogen evolution reaction

Up to now, Platinum is still wildly regarded as the state-the-art catalyst toward hydrogen evolution reaction (HER) in acid, however alkaline HER is limited by its poor activity for water dissociation. In this regard, hydrogenated graphene (HG) was emerged as a functional support to boost alkaline HER for Pt catalysts. As a result, the optimized Pt/HG (4.15 % wt Pt) showed a wonderful activity in terms of an overpotential of 54 mV at 10 mA cm−2 as well as a Tafel slope of 30.28 mV dec−1, superior to the counterparts and even 20 wt% commercial Pt/C. Such a high activity was attributed to the fact HG can optimize electronic state and exposed facet of Pt to accelerate alkaline HER. In addition, density function theory (DFT) calculation revealed the energy barrier for H transfer from HG to Pt only required 0.02 eV, in line with experimental analysis. This work provides a promising strategy to design advanced catalysts toward alkaline HER and beyond.

Nitrogen reduction reaction enhanced by single-atom transition metal catalysts on functionalized graphene: A first-principles study

Ammonia production seeks alternatives to the conventional Haber-Bosch process, with nitrogen reduction reaction (NRR) emerging promising. Addressing the challenge of efficient catalysts, the functionalized graphene-based single atom catalysts (SACs) stand out. While prior studies have favored heteroatom-doped catalysts, the coordination of metal centers with nitrogen atoms remains underexplored. This work investigates transition metal (TM) SACs on nitrogen-doped graphene (N3G) using density functional theory (DFT) for electro-catalytic NRR. Results highlight the stability of V@N3G, Mo@N3G, W@N3G, with binding energies of −7.77, −5.43, and −3.89 eV, respectively. Insights into work function, d-band center, N–N bond, and IR stretching's role in N2 activation are gained through this study. Bader charge analysis reveals electron redistribution between the support and adsorbed N2. Employing Computational Hydrogen Electrode (CHE) method, comparative free energy diagrams for TM@N3G (V, Mo, W) via., enzymatic, consecutive, alternating, and distal pathways outline potential rate determining step (PDS) with and without the Implicit solvation method. Remarkably, W@N3G catalyst exhibits the lowest PDS in the presence of solvation energy, surpassing other catalysts. The multi-adsorption of N2 on W@N3G enhances NRR process, stabilizing intermediates for efficient ammonia production. This computational study sheds light on metal center SACs on functionalized graphene support as a potential electro-catalyst for efficient and stable NRR.

Ir noble metal atoms/clusters on graphene support: Insights from aberration corrected-STEM and density functional theory

The interactions of Iridium (Ir) noble metal atoms/clusters (Ir NMAs/NMCs) with graphene are investigated due to their remarkable catalytic performance, resulting from the use of 100 % metal atoms compared to nanoparticle counterparts. Using scanning transmission electron microscopy (STEM), various forms of Ir dispersed on graphene were observed, including single atoms, dimers, and trimers clusters. The STEM data further revealed inter-atomic distances of 2.83 Å and 2.96 Å for dimers and trimers which were 20 % and 17 % larger than the numbers found through density functional theory (DFT) calculations. The DFT calculations further showed that the Dirac-cone of graphene at Ir NMAs/NMCs locations changes to metallic form due to the emergence of energy states at the Fermi level. This effect results in non-zero effective masses of charge carriers but enhances their density of states (DOS) by 2-fold which is believed to increase the energy absorption efficiency of graphene in the infra-red range of radiation.

Carbon Corrosion Induced by Surface Defects Accelerates Degradation of Platinum/Graphene Catalysts in Oxygen Reduction Reaction.

Graphene supported electrocatalysts have demonstrated remarkable catalytic performance for oxygen reduction reaction (ORR). However, their durability and cycling performance are greatly limited by Oswald ripening of platinum (Pt) and graphene support corrosion. Moreover, comprehensive studies on the mechanisms of catalysts degradation under 0.6-1.6V versus RHE (Reversible Hydrogen Electrode) is still lacking. Herein, degradation mechanisms triggered by different defects on graphene supports are investigated by two cycling protocols. In the start-up/shutdown cycling (1.0-1.6V vs.RHE), carbon oxidation reaction (COR) leads to shedding or swarm-like aggregation of Pt nanoparticles (NPs). Theoretical simulation results show that the expansion of vacancy defects promotes reaction kinetics of the decisive step in COR, reducing its reaction overpotential. While under the load cycling (0.6-1.0V vs.RHE), oxygen containing defects lead to an elevated content of Pt in its oxidation state which intensifies Oswald ripening of Pt. The presence of vacancy defects can enhance the transfer of electrons from graphene to the Pt surface, reducing the d-band center of Pt and making it more difficult for the oxidation state of platinum to form in the cycling. This work will provide comprehensive understanding on Pt/Graphene catalysts degradation mechanisms.

Oxygen Electroreduction Reaction on Iron, Nitrogen-doped Nanocarbons: Structure – Reactivity Relationship

Theoretical calculations at the revPBE0-D3(PCM)/def2-TZVP level were performed to investigate the mechanism of the oxygen reduction reaction (ORR) on the FeN4-doped NCMs (graphene, single-walled (6,6)-armchair and (12,0)-zigzag carbon nanotubes) as catalysts. The effect of the support and relative orientation of FeN4 fragment in the catalyst structure on the ORR activity and stability of the differently adsorbed successive intermediates (O2*, HO2*, O*, HO*, H2O2*, H2O*) is discussed. Special attention is given to the possible poisoning effect of CO. The relative catalytic activity of the metal center and the adjacent C2 site of the carbon support are analyzed depending on the structure of the support. The metal catalytic center on the armchair nanotube and graphene supports is prone to deactivation by poisoning with CO, whereas in the zigzag nanotube supported catalyst the metal center is tolerant to CO. The four-electron mechanism of ORR is shown to be preferable over the two-electron mechanism in both acidic and alkaline media, both on the metal and C2 centers.

Insights into neodymium interaction with carboxylate-graphene-like support in presence of nitrate: A comparative DFT investigation

Recently, we demonstrated that carboxylate mesoporous carbon improved the adsorption of rare earth elements as neodymium (Nd). Here, calculations based on Density Functional Theory were carried out to give insight on binding of the Nd with carboxylates. Different phenyl carboxylate-Nd complexes were first identified, considering nitrate and water molecules as ligands, in order to obtain reliable carboxylate-graphene models. The optimized structures are used to compute the binding and complexation energies then the competition for metal between carboxylate group and solvent was analysed. The results, in agreement with the experimental evidence, indicated that the Nd favors the anchored carboxylate groups compared to the bulk water. Findings showed that, the graphene support did not significantly alter the carboxylate-Nd binding energies. The partial charges revealed the coupling electron-withdrawing effect of the nitrate and water oxygens. The binding and complexation energies provided here can be regarded as references for designing of REE chelating sorbents.

Tuning the electrocatalytic activity of MoS2 nanosheets via the in situ hybridization with ruthenium and graphene network

The quest for highly efficient, stable, and non-precious electrocatalysts as alternatives to Pt in the hydrogen evolution reaction (HER) at ambient temperature is paramount. Two-dimensional (2D) layered transition metal dichalcogenides (TMDs), notably MoS2, have emerged as promising noble-metal-free candidates. However, MoS2′s limited active edge sites and sluggish electron transfer kinetics present challenges in achieving efficient HER activity under both acidic and basic conditions. In this study, we introduce a composite catalyst composed of 2D MoS2 nanosheets enveloped by graphene networks, with uniform dispersion of ruthenium (Ru) nanoparticles within the extended 2D structure. This ternary hybrid catalyst exhibits excellent catalytic activity, with a low onset overpotential of 60 mV at 10 mA cm−2, a small Tafel slope of 38 mV dec-1, and remarkable durability during continuous 10-hour operation at 100 mV potential in 1.0 M KOH, without substantial activity loss. The conductive graphene support effectively prevents the restacking of exfoliated MoS2 nanosheets, enhancing mass transport and charge transfer kinetics. Ru incorporation induces the partial phase transformation of MoS2 from its trigonal (2H) to octahedral (1 T) phase, concurrently generating sulfur vacancies. The induced phase transformation not only activates the inert basal planes of MoS2 but also reduces the energy barrier for the adsorption/desorption of H* intermediates. Beyond the structural advantages, the intrinsic synergistic effects, primarily related to electronic structure modulation and defect engineering, contribute significantly to the enhanced electrochemical HER performance. In summary, this study not only introduces an efficient, cost-effective alternative to Pt-based electrocatalysts but also lays the foundation for designing other TMD-based hybrid catalysts, characterized by abundant exposed active sites and reduced barriers for hydrogen binding energy, thereby advancing electrochemical hydrogen production.

Screening of transition metal dual-atom catalysts for hydrogen evolution reaction based on high-throughput calculation and searching surrogate prediction model using simple features

Dual-atom catalysts for hydrogen evolution reaction have received widespread attention, but precise screening and prediction of high-performance catalysts through simple methods remains a challenge. In this study, we perform high-throughput density functional theory (DFT) calculation and machine learning (ML) to screen and predict the transition metal dual-atom catalysts with N-doped graphene support (TMDACs) for acidic hydrogen evolution reaction (HER). The Fe_Zn and V_Fe DACs were proposed to be the most promising candidates for Pt-based catalyst toward acidic HER from 406 TMDACs, based on the characteristics of HER activity, formation, thermodynamic stability, abundance, environmental friendliness. The Fe_Zn and V_Fe DACs with excellent HER performance is due to the synergistic effect deriving from the interaction between H and dual metal atoms in TMDACs. By determining 6 different ML models with four kind of input features, we find the artificial neural networks (ANN) model can predict the HER performance of TMDACs most accurately only using simple input features, including one-hot-encoding of atomic number and Gibbs free energies of transition metal single-atom catalysts. This work not only proposed the potential TMDACs with high HER performance, but also verified that the ANN model can accurately predict the HER activity of diatomic catalysts with simple input features.

Film Thickness Effect in Restructuring NiO into LiNiO2 Anode for Highly Stable Lithium-Ion Batteries

The long-term stability of energy-storage devices for green energy has received significant attention. Lithium-ion batteries (LIBs) based on materials such as metal oxides, Si, Sb, and Sn have shown superior energy density and stability owing to their intrinsic properties and the support of conductive carbon, graphene, or graphene oxides. Abnormal capacities have been recorded for some transition metal oxides, such as NiO, Fe2O3, and MnO/Mn3O4. Recently, the restructuring of NiO into LiNiO2 anode materials has yielded an ultrastable anode for LIBs. Herein, the effect of the thin film thickness on the restructuring of the NiO anode was investigated. Different electrode thicknesses required different numbers of cycles for restructuring, resulting in significant changes in the reconstituted cells. NiO thicknesses greater than 39 μm reduced the capacity to 570 mAh g−1. The results revealed the limitation of the layered thickness owing to the low diffusion efficiency of Li ions in the thick layers, resulting in non-uniformity of the restructured LiNiO2. The NiO anode with a thickness of approximately 20 μm required only 220 cycles to be restructured at 0.5 A g−1, while maintaining a high-rate performance for over 500 cycles at 1.0 A g−1, and a high capacity of 1000 mAh g−1.

One‐Step Synthesis of Copper Single‐Atom Nanozymes for Electrochemical Sensing Applications

Single‐atom nanozymes (SANs) combine the natural enzymatic properties of nanomaterials with the atomic distribution of metallic sites over a suitable support. Unfortunately, their synthesis is complicated by some key factors, like poor metallic loading, aggregation, time consumption, and low yield. Herein, copper SANs, with a surface metal loading (1.47% ± 0.16%) are synthesized, through a green, facile, minimal solution processing, single‐step procedure, using a CO2 laser to promote the anchoring of the metallic precursor while simultaneously generating the laser‐scribed graphene (LSG) support out of a polyimide sheet. The presence of the atomic Cu on the LSG surface is verified using high‐angle‐annular dark‐field–scanning transmission electron microscopy and X‐ray photoelectron spectroscopy. To explore the advantages incurred by the incorporation of Cu SANs on LSG, the material is used as a working electrode on an electrochemical sensor for the amperometric detection of H2O2, achieving a detection limit of 2.40 μM. The findings suggest that CuSANs can confer enhanced sensitivity to H2O2, which is essential for oxidative stress assessment, reaching values up to 130.0 μA mM−1 cm−2.

Unveiling the Morphology of Carbon-Supported Ru Nanoparticles by Multiscale Modeling.

Simulating the behavior of metal nanoparticles on supports is crucial for boosting their catalytic performance and various nanotechnology applications; however, such simulations are limited by the conflicts between accuracy and efficiency. Herein, we introduce a multiscale modeling strategy to unveil the morphology of Ru supported on pristine and N-doped graphene. Our multiscale modeling started with the electronic structures of a supported Ru single atom, revealing the strong metal-support interaction around pyridinic nitrogen sites. To determine the stable configurations of Ru2-13 clusters on three different graphene supports, global energy minimum searches were performed. The sintering of the global minimum Ru13 clusters on supports was further simulated by ab initio molecular dynamics (AIMD). The AIMD data set was then collected for deep potential molecular dynamics to study the melting of Ru nanoparticles. This study presents comprehensive descriptions of carbon-supported Ru and develops modeling approaches that bridge different scales and can be applied to various supported nanoparticle systems.

Biomimetic nucleotide-graphene hybrids for electrocatalytic oxygen conversion: Quantifying biomolecule mass loading

Metal-free electrocatalysts for the electrochemical conversion of gases constitute an important asset for a sustainable energy transition. Nucleotides act as redox mediators in the electron transport chain to reduce oxygen in cellular respiration. The biomimicry of such an efficient natural mechanism could be utilized to address the challenges associated with electrochemical gas conversion technologies, such as sluggish kinetics and high overpotentials. Multiple descriptors are generally reported to benchmark the activity of electrocatalysts where the turnover frequency (TOF) is claimed to be the most accurate criterion. Here, a library of graphene nanosheets-nucleotide hybrid materials was prepared, and the electrocatalytic performance towards ORR/OER reactions of a graphene-flavin mononucleotide hybrid was evaluated by rotating disc electrode experiments and TOF estimation. The determination of catalyst loading and dispersion is especially relevant when assessing the intrinsic activity of a catalyst and, therefore, the amount of nucleotide electrocatalyst loaded into the graphene support was thoroughly quantified by a combination of characterization techniques. Density functional theory calculations supported the observed experimental trends, both on the adsorption rate of a given nucleotide on graphene and the catalytic activity of a specific hybrid material. This work constitutes an avenue to predict nature-mimicking electrocatalysts for efficient energy storage.

Graphene sandwich–based biological specimen preparation for cryo-EM analysis

High-quality specimen preparation plays a crucial role in cryo-electron microscopy (cryo-EM) structural analysis. In this study, we have developed a reliable and convenient technique called the graphene sandwich method for preparing cryo-EM specimens. This method involves using two layers of graphene films that enclose macromolecules on both sides, allowing for an appropriate ice thickness for cryo-EM analysis. The graphene sandwich helps to mitigate beam-induced charging effect and reduce particle motion compared to specimens prepared using the traditional method with graphene support on only one side, therefore improving the cryo-EM data quality. These advancements may open new opportunities to expand the use of graphene in the field of biological electron microscopy.

Catalytic effects of graphene structures on Pt/graphene catalysts.

Pt/C catalysts have been considered the ideal cathodic catalyst for proton exchange membrane fuel cells (PEMFCs) due to their superior oxygen reduction reaction (ORR) catalytic activity at low temperatures. However, oxidation and corrosion of the carbon black support at the cathode result in the agglomeration of Pt particles, which reduces the active sites in the Pt/C catalyst. Graphene supports have shown great promise to address this issue, and therefore, finding out the main structural features of the graphene support is of great significance for guiding the rational construction of graphene-based Pt (Pt/graphene) catalysts for optimized ORR catalysts. In order to systematically study the influence of the structural features of the graphene support on the electro-catalytic properties of Pt/graphene catalysts, we prepared porous nitrogen-doped reduced graphene oxide (P-NRGO), nitrogen-doped reduced graphene oxide (NRGO), treated P-NRGO (TP-NRGO) and reduced graphene oxide (RGO) with different nitrogen species contents (7.76, 7.54, 3.24, and 0.14 at%), oxygen species contents (18.68, 18.12, 6.34 and 21.12 at%), specific surface areas (370.4, 70.6, 347.7 and 276.2 m2 g-1) and pore volumes (1.366, 0.1424, 1.3299 and 1.0414 cm3 g-1). The ORR activity of the four Pt/graphene catalysts when listed in the order of their half-wave potentials (E 1/2) and peak power densities was found to be as Pt/P-NRGO > Pt/NRGO > Pt/TP-NRGO > Pt/RGO. The long-term durability of Pt/P-NRGO for the operation of H2-air PEMFCs is better than that of commercial Pt/C catalysts. The excellent ORR catalytic performance of Pt/P-NRGO compared to that of the other three Pt/graphene catalysts is ascribed to the high nitrogen species content of P-NRGO that can facilitate the uniform dispersion of Pt particles and provide accessible active sites for ORR. The results indicate that the specific surface area (SSA) and heteroatom dopants have strong influence on the Pt particle size, and that the nitrogen species of graphene supports play a more important role than the oxygen species, specific surface area and pore volume for the Pt/graphene catalysts in providing accessible active sites.

Synergistic interaction between NiPt nanoparticles and phosphorus-doped graphene support boosts hydrogen generation from hydrazine borane

The Ni0.6Pt0.4/P-rGO catalyst exhibits excellent catalytic activity and recycling stability for hydrazine borane dehydrogenation at 323 K.

Cryo-electron microscopy at the Faculty of Biology of Lomonosov Moscow State University

This paper demonstrates an example of a successful upgrade of a JEOL JEM-2100 analytical transmission electron microscope to a low-resolution cryo-electron microscope designed for routine tasks of sample preparation and quality evaluation. As a result of the upgrade, the instrument allows the subnanometer resolution of protein molecule reconstructions (within 8 Å). The influence of graphene and amorphous carbon support films to prevent the effect of preferred orientation of protein particles in the frozen sample is discussed.