Transition Metal Single-atom Catalysts Research Articles

Metal-organic framework derived single-atom catalysts for electrochemical CO2 reduction.

With maximum atomic utilization, transition metal single atom catalysts (SACs) show great potential in electrochemical reduction of CO2 to CO. Herein, by a facile pyrolysis of zeolitic imidazolate frameworks (ZIFs) assembled with tiny amounts of metal ions, a series of metal-nitrogen-carbon (M-N-C) based SACs (M = Fe, Ni, Mn, Co and Cu), with metal single atoms decorated on a nitrogen-doped carbon support, have been precisely constructed. X-ray photoelectron spectroscopy (XPS) for M-N-C showed that the N 1s spectrum was deconvoluted into five peaks for pyridinic (∼398.3 eV), M-N coordination (∼399.6 eV), pyrrolic (∼400.4 eV), quaternary (∼401.2 eV) and oxidized (∼402.9 eV) N species, demonstrating the existence of M-N bonding. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) indicates homogeneous distribution of metal species throughout the N-doped carbon matrix. Among the catalysts examined, the Fe-N-C catalyst exhibits the best catalytic performance in electrocatalytic CO2 reduction reaction (CO2RR) with nearly 100% faradaic efficiency for CO (FECO) at -0.9 V vs. the reversible hydrogen electrode (RHE). Ni-N-C is the second most active catalyst towards CO2RR performance, then followed by Mn-N-C, Co-N-C and Cu-N-C. Considering the optimum activity of Fe-N-C catalyst for the CO2RR, we then further investigate the effect of pyrolysis temperature on CO2RR of the Fe-N-C catalyst. We find the Fe-N-C catalyst pyrolyzed at 1000 °C exhibits the best catalytic activity in CO2RR with excellent CO selectivity.

Single Ni active sites with a nitrogen and phosphorus dual coordination for an efficient CO2 reduction.

Transition metal single-atom catalysts (SACs) have emerged as a research hotspot in CO2RRs. However, tuning the electronic configuration of a metal single-atom by employing new heteroatoms still remains a challenge. Herein, a carbon matrix loaded with a N and P co-coordinated Ni single-atom (denoted as Ni-NPC) was prepared for an efficient CO2RR. XANES and EXAFS were conducted to explore the coordination environment and charge distribution of the Ni-NPC catalyst. DFT calculations indicated that the Ni atom gained electrons from the P atom, and the Ni-NPC sample had a decreased energy barrier of +0.97 eV after doping with P atoms, which was favorable to overcome the limiting-step bottleneck for promoting CO2RR. Due to the rich Ni atomic active sites and superior P-doping effect, Ni-NPC exhibited a maximum FECO of 92% with a high current density of 22.6 mA cm-2 at -0.8V vs. RHE, which was far superior to those of NC, NPC and Ni-NC catalysts. Moreover, both the FECO and current density of the Ni-NPC catalyst remained stable for more than 16 h at -0.8 V vs. RHE, indicating a high stability for long-term CO2RR experiments.

Understanding trends in the mercury oxidation activity of single-atom catalysts

Transition metal single-atom catalysts with nitrogen-doped carbon substrates were designed and analyzed as the catalysts to oxidize Hg0 with O2, using density functional theory calculations, scaling relation analysis, and microkinetic modeling.

Screening of transition metal single-atom catalysts supported by a WS2 monolayer for electrocatalytic nitrogen reduction reaction: insights from activity trend and descriptor.

The electrocatalytic nitrogen reduction reaction (NRR), as an alternative green technology to the Haber-Bosch process, can efficiently synthesize ammonia under ambient conditions and has a reduced carbon footprint. Here we systematically investigate the NRR activity and selectivity of transition metal (TM) single-atom catalyst (SAC) anchored WS2 monolayers (TM@WS2) by means of first-principles calculations and microkinetic modeling. The construction of the reaction activity trend and the identification of an activity descriptor, namely *N2H adsorption energy, facilitate the efficient screening and rational design of SACs with high activity. Manipulating the adsorption strength of the pivotal *N2H intermediate is a potential strategy for enhancing NRR activity. Utilizing the limiting potential difference of NRR and the hydrogen evolution reaction (HER) as a selectivity descriptor, we screen three SACs with excellent activity and selectivity toward NRR, i.e., Re@WS2, Os@WS2 and Ir@WS2 with favorable limiting potentials of -0.44 V, -0.38 V and -0.69 V. By using the explicit H9O4+ model, the kinetic barriers of the rate-determining steps (0.47 eV-1.15 eV) of the solvated proton transfer on the screened SACs are found to be moderate, indicative of a kinetically feasible process. Microkinetic modeling shows that the turnover frequencies of N2 reduction to NH3 on Re@WS2, Os@WS2 and Ir@WS2 are 1.52 × 105, 8.21 × 102 and 4.17 × 10-4 per s per site at 400 K, achieving fast reaction rates. The coexistence of empty and occupied 5d orbitals of candidate SACs is beneficial for σ donation and π* backdonation, endowing them with extraordinary N2 adsorption and activation. Moreover, the screened SACs possess good dispersity and thermodynamic stability. Our work provides a promising solution for the efficient screening and rational design of high-performance electrocatalysts toward the NRR.

First Principles Screening of Transition Metal Single-Atom Catalysts for Nitrogen Reduction Reaction

First Principles Screening of Transition Metal Single-Atom Catalysts for Nitrogen Reduction Reaction

Non-precious transition metal single-atom catalysts for the oxygen reduction reaction: progress and prospects.

The massive exploitation and use of fossil resources have created many negative issues, such as energy shortage and environmental pollution. It prompts us to turn our attention to the development of new energy technologies. This review summarizes the recent research progress of non-precious transition metal single-atom catalysts (NPT-SACs) for the oxygen reduction reaction (ORR) in Zn-air batteries and fuel cells. Some commonly used preparation methods and their advantages/disadvantages have been summarized. The factors affecting the ORR performances of NPT-SACs have been focused upon, such as the substrate type, coordination environment and nanocluster effects. The loading mass of a metal atom has a direct effect on the ORR performances. Some general strategies for stabilizing metal atoms are included. This review points out some existing challenges of NPT-SACs, and also provides ideas for designing and synthesizing NPT-SACs with excellent ORR performances. The large-scale preparation and commercialization of NPT-SACs with excellent ORR properties are prospected.

Screening of transition metal single atom catalysts supported on B36 cluster for nitrogen fixation

Developing efficient catalysis for dinitrogen (N2) fixation is a very important and challenging issue in chemistry. A large number of recent studies have shown that boron containing materials have good catalytic activity for nitrogen reduction reaction (NRR). Meanwhile, many theoretical and experimental studies also focus on the pure boron cluster system. The small size and extremely lack of electrons of the pure boron cluster system make its catalytic performance after being anchored with transition metals (TM) become very promising. Herein, we reported that the potential of a series of TM atoms (including Sc–Zn, Nb, Mo, Ru, Rh, Pd, Ta, W, Re, Os, Ir, Pt) anchored on B36 cluster for NRR. It is found that the Re-anchored B36 is the most promising candidate with a limiting potential of −0.48 V via distal mechanism, and it also has good stability, catalytic activity and selectivity for NRR. It is worth noting that there are relatively rare researches on Re-based catalysts for N2 fixation, our findings suggest that the Re-doped materials should receive attention for NRR.

Low-cost single-atom transition metals on two-dimensional SnO nanosheets for efficient hydrogen evolution catalysis in all pH-range

The exploration of electrocatalysts with high performance of hydrogen evolution reaction (HER) in all media is essential for developing clean energies. Single-atom catalysts (SACs) have attracted wide attentions owing to their maximum atom utilization and excellent catalytic activity. In this work, the HER activities of transition metal (TM) (TM = Fe, Co, Ni and Cu) SACs on two-dimensional SnO monolayer are studied using density functional theory. We found that the low-cost TM SACs can exhibit high HER activity in wide pH-range. Especially, Co SACs show promising catalytic activity with the Gibbs free energy of hydrogen adsorption (ΔGH∗) as low as ∼ 0.015 eV, which are also high active in either acidic or alkaline environments. With the experimentally inevitable oxygen vacancies in SnO, the ΔGH∗ of Co, Ni and Cu SACs are almost zero, which are competitive with the precious catalyst Pt(111) (-0.09 eV). The exceptional HER activity is correlated to the enhanced electron states close to the Fermi level as well as the d-band center positions of the TM. Our work opens new avenues for engineering low-cost TM SACs with pH-universal HER performance, which is of great importance in practical applications.

Zeolite-encapsulated single-atom catalysts for efficient CO2 conversion

Zeolite-supported single-atom catalysts (SACs) have emerged as a novel class of cheap and tuneable catalysts that can exhibit high activity, selectivity and stability. In this work, we conduct an extensive screening by means of density functional theory calculations to determine the usefulness of 3d, 4d and 5d transition metal (TM) SACs-supported in MFI-type Silicalite-1 zeolite for CO2 conversion. Two reaction mechanisms are considered, namely the redox - direct CO2 dissociation - and associative - hydrogen-assisted CO2 dissociation - mechanisms. Early TM SACs exhibit the lowest energy barriers, which follow the redox mechanism. These energy barriers raise when going right in the periodic table up to group 10, where they become prohibitive and the associative mechanism should dominate. By also considering their resistance to aggregation, we support the use of Sc, Y, La, Ru, Rh, Ni, Pd and Pt as potentially active and stable catalysts for CO2 conversion, given their low energy barriers and strong interaction with the zeolite framework.

High performance SACs for HER process using late first-row transition metals anchored on graphyne support: A DFT insight

For ever-growing demand of clean and renewable energy resources, finding a low-cost, earth abundant, and an efficient electrocatalyst to replace platinum-based catalysts for hydrogen evolution reaction (HER) has drawn the interest of scientific community. In present work, first-row transition metal single atom catalysts supported on graphyne surface have been designed and investigated using density functional theory approach. The results indicate that among all considered systems, the highest thermodynamic stability and best HER catalytic performance is computed for Ni single atom catalyst (SAC) anchored on graphyne support with low ΔGH∗ value of 0.08 eV. We have calculated density of states, energies of HOMO, LUMO and HOMO-LUMO gap for our designed single atom catalysts as well as hydrogen adsorption. Our results indicate that Ni anchored on graphyne support can be a promising candidate for noble metal free, earth abundant, and low cost electrocatalyst to efficiently catalyze hydrogen evolution reaction process.

Central metal and ligand effects on oxygen electrocatalysis over 3d transition metal single-atom catalysts: A theoretical investigation

Metal single-atom catalysts (SACs) have recently emerged as promising alternatives to precious metal-based electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) under alkaline conditions. Currently, the role of the metal centre and local coordination environment on the ORR/OER activity of metal SACs remains unclear. Herein, we employed density functional theory (DFT) calculations to systematically study oxygen electrocatalysis on 60 different 3d transition metal SACs (scandium to zinc, supported on heteroatom-doped graphene supports), encompassing three symmetric nitrogen coordination configurations (i.e., M−Nn−C, n = 4, 3, 2) and three asymmetric coordination configurations (i.e., M−N3X−C, X = P, S, B). The calculations reveal the central metal and the coordinating atoms strongly influence oxygen electrocatalysis over 3d transition metal SACs, predominantly by tuning the adsorption free energy of adsorbed hydroxyl (ΔG*OH, a key descriptor of both ORR and OER activity). Dual limiting potential volcano curves were constructed for ORR and OER, with Ni-N2-C identified as the optimal synthetic target for bifunctional ORR/OER electrocatalysis, closely followed by Fe-N4-C, Co-N4-C, Co-N2-C, and Ni-N3P-C.

Decarboxylation-Induced Defects in MOF-Derived Single Cobalt Atom@Carbon Electrocatalysts for Efficient Oxygen Reduction.

Developing transition metal single-atom catalysts (SACs) for oxygen reduction reaction (ORR) is of great importance. Zeolitic imidazolate frameworks (ZIFs) as a subgroup of metal-organic frameworks (MOFs) are distinguished as SAC precursors, due to their large porosity and N content. However, the activity of the formed metal sites is limited. Herein, we report a decarboxylation-induced defects strategy to improve their intrinsic activity via increasing the defect density. Carboxylate/amide mixed-linker MOF (DMOF) was chosen to produce defective Co SACs (Co@DMOF) by gas-transport of Co species to DMOF upon heating. Comparing with ZIF-8 derived SAC (Co@ZIF-8-900), Co@DMOF-900 with more defects yet one fifth Co content and similar specific double-layer capacitance show better ORR activity and eight times higher turnover frequency (2.015 e s-1 site-1 ). Quantum calculation confirms the defects can weaken the adsorption free energy of OOH on Co sites and further boost the ORR process.

Atomically dispersed low-cost transition metals catalyze efficient hydrogen evolution on two-dimensional SnO nanosheets

Two-dimensional (2D) electrocatalyst plays an important role in hydrogen production via water splitting. In this work, the first-principles calculation was used to investigate the hydrogen evolution reaction (HER) performance of transition metal (TM) single atom catalysts (SACs) on 2D SnO nanosheets. Among the TM considered (TM = V, Cr, Mn, Fe, Co, Ni, Cu and Pt), V, Fe, Co, Ni, Cu and Pt can effectively improve the catalytic activity of SnO. More importantly, the low-cost Co can exhibit promising HER performance with the Gibbs free energy as low as ~0.015 eV, which is competitive with the precious catalyst Pt. The theoretical exchange current densities of Co SACs can reach ~10−16 A/site. The exciting HER activity is mainly facilitated through the d-d hybridization between the TM and Sn atoms on the SnO surface, which introduces new electron states near the Fermi level. Our work highlights the complexity and diversity of the effect of TM SACs on SnO nanosheets and implies their potential applications as efficient HER electrocatalysts.

Electrocatalytic Nitrogen Reduction by Transition Metal Single-Atom Catalysts on Polymeric Carbon Nitride

Electrocatalytic Nitrogen Reduction by Transition Metal Single-Atom Catalysts on Polymeric Carbon Nitride

Typical transition metal single-atom catalysts with a metal-pyridine N structure for efficient CO2 electroreduction

It is of great importance to establish a definite relationship between structure and catalytic properties for developing highly efficient single-atom catalysts (SACs); however, this remains a challenge. Herein, three single atoms anchored on a nitrogen-doped carbon matrix (M-N-C, M = Fe, Co, Ni) with a metal-pyridine N structure were prepared and investigated as catalysts for electrochemical CO2 reduction. M-N-C exhibit promising capability for CO2-to-CO conversion with the selectivity order of Ni > Co > Fe and the activity order of Co > Ni > Fe, in contrast to the previously reported performance order of Ni > Fe > Co. Among M-N-C catalysts, Ni-N-C shows superior selectivity (approximately 100% CO Faradaic efficiency from −0.66 V to −0.96 V), whereas Co-N-C exhibits high activity (CO current density = −24.24 mA cm−2 and CO turnover frequency = 7182 h−1 at −0.86 V) and capability of yielding syngas (CO/H2 = 0.5∼2.11). Density functional theory calculations support the experimental selectivity and activity orders. This study presents a new possibility for improving the catalytic performance of SACs by investigating the coordinated environments of metal atoms.

Electrochemical Energy Storage: Harnessing the Extracellular Electron Transfer Capability of Geobacter sulfurreducens for Ambient Synthesis of Stable Bifunctional Single‐Atom Electrocatalyst for Water Splitting (Adv. Funct. Mater. 22/2021)

In article number 2010916, Srikanth Pedireddy, Pascal E. Saikaly, and co-workers report a facile synthesis strategy of single-atom catalysts (SACs) at room temperature by harnessing the extracellular electron transfer capability of Geobacter sulfurreducens. This strategy can be successfully extended for the synthesis of various transition metal SACs by merely altering the metal precursors. Without further heat treatment, the dried catalysts exhibit excellent electrocatalytic activity for oxygen and hydrogen evolution reactions.

Carbon and Oxygen Coordinating Atoms Adjust Transition Metal Single-Atom Catalysts Based On Boron Nitride Monolayers for Highly Efficient CO2 Electroreduction.

Although single-atom catalysts (SACs) with transition metal-nitrogen complexes have been studied widely, investigations that use light-element atoms to adjust the coordination environment of the central metal atoms in metal-nitrogen complexes are still rare but show enormous potential for various electrocatalytic reactions. Herein, we design novel SACs based on monolayer BN adjusted by B, C, or O coordinating atoms as catalysts for the CO2 reduction reaction (CRR). These SACs are denoted as M@BN_D (BN = monolayer boron nitride; D = B, C, or O atom; M = Co, Cr, Fe, Mn, Mo, Pd, Pt, Ru, V, W, Ni, Zn, Zr, Ag, Au, Cu, or Ti atom) and are investigated as CRR catalysts using density functional theory calculations. Among these structures, we identified some promising candidate catalysts for CRR with impressive low limiting potential (UL): Pt@BN_C with a UL of -0.18 for the product CH4 and Co@BN_C and Au@BN_O with UL of -0.41 and -0.37 V, respectively, for the product CH3OH. In particular, Pt@BN_C shows a remarkable reduction in UL for the product CH4 compared to any existing catalysts, synthesized or predicted. In addition, the ultralow UL for CRR on Pt@BN_C was derived from the unique bonding feature between the single metal atom and adsorbates and the modulation of ionic interactions induced by the coordination effect of the C atom.

Elucidating the electro-catalytic oxidation of hydrazine over carbon nanotube-based transition metal single atom catalysts

Elucidating the reaction mechanism of hydrazine oxidation reaction (HzOR) over carbon-based catalysts is highly propitious for the rational design of novel electrocatalysts for HzOR. In present work, isolated first-row transition metal atoms have been coordinated with N atoms on the graphite layers of carbon nanotubes via a M-N4-C configuration (MSA/CNT, M=Fe, Co and Ni). The HzOR over the three single atom catalysts follows a predominant 4-electron reaction pathway to emit N2 and a negligible 1-electron pathway to emit trace of NH3, while their electrocatalytic activity for HzOR is dominated by the absorption energy of N2H4 on them. Furthermore, FeSA/CNT reverses the passivation effect on Fe/C and shows superior performance than CoSA/CNT and NiSA/CNT with a recorded high mass activity for HzOR due to the higher electronic charge of Fe over Co and Ni in the M-N4-C configuration and the lowest absorption energy of N2H4 on FeSA/CNT among the three MSA/CNT catalysts.

Electronic Spin Moment As a Catalytic Descriptor for Fe Single-Atom Catalysts Supported on C2N.

The electrocatalytic activity of transition-metal-based compounds is strongly related to the spin states. However, the underlying relationship connecting spin to catalytic activity remains unclear. Herein, we carried out density functional theory calculations on oxygen reduction reaction (ORR) catalyzed by Fe single-atom supported on C2N (C2N-Fe) to shed light on this relationship. It is found that the change of electronic spin moments of Fe and O2 due to molecular-catalyst adsorption scales with the amount of electron transfer from Fe to O2, which promotes the catalytic activity of C2N-Fe for driving ORR. The nearly linear relationship between the catalytic activity and spin moment variation suggests electronic spin moment as a promising catalytic descriptor for Fe single-atom based catalysts. Following the revealed relationship, the ORR barrier on C2N-Fe was tuned to be as low as 0.10 eV through judicious manipulation of spin states. These findings thus provide important insights into the relationship between catalytic activity and spin, leading to new strategies for designing transition metal single-atom catalysts.

Single atom catalysts supported on N-doped graphene toward fast kinetics in Li–S batteries: a theoretical study

We built a novel strategy to systematically screen 3d to 5d transition metal single atom catalysts supported on N-doped defective graphene, M@N3/G and M@N4/G, toward fast kinetics in Li−S batteries. Cr@N4/G and Mn@N4/G are preferentially recommended.