Ni N4 Research Articles

Single nickel atoms anchored on porous N-doped nanocarbon with dual reaction sites for highly-efficient transfer hydrogenation of furfural to furfuryl alcohol

The non-precious metal single-atom catalysts (SACs) supported on carbon materials for the catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes (UAL) still suffer from the problems of harsh reaction conditions and low activity. In this work, nickel SACs anchored on porous N-doped nanocarbon (Ni1/NC900) with dual reaction sites were synthesized using the high internal-phase emulsion (HIPE) template method combined with impregnation. The Ni1/NC900 catalyst exhibited remarkable catalytic activity for the CTH of furfural (FF) to furfuryl alcohol (FFA), achieving > 99.0 % conversion and selectivity at 100 °C for 60 min, with a turnover frequency (TOF) of 2908.1 h−1, surpassing other reported nickel-based catalysts by 1–3 orders of magnitude. The excellent catalytic performance of Ni1/NC900 was attributed to the high mass transfer efficiency (HMTE) of the support and the dual reaction sites of Ni–N4 and pyridinic N, where Ni–N4 as Lewis acidic site for adsorption of FF and isopropanol (i-PrOH), while the adjacent pyridinic N as Lewis basic site for the deprotonation of i-PrOH. The isotope labeling experiments revealed that the hydrogenation of FF was accomplished by proton transfer with i-PrOH, in agreement with the intermolecular hydride transfer mechanism. Furthermore, Ni1/NC900 demonstrated excellent stability and well general applicability, demonstrating its potential for industrial applications. This work provides a reference for the application of carbon-based non-precious metal SACs in the CTH reaction of UAL.

Customizing pyridinic nitrogen coordination in Ni–N–C for electrocatalytic CO2 reduction towards CO

Nickel anchored N-doped carbon electrocatalysts (Ni–N–C) are rapidly developed for the electrochemical reduction reaction of carbon dioxide (CO2RR). However, the high-performanced Ni–N–C analogues design for CO2RR remains bewilderment, for the reason lacking of definite guidance for its structure-activity relationship. Herein, the correlation between the proportion of nitrogen species derived from various nitrogen sources and the CO2RR activity of Ni–N–C is investigated. The x-ray photoelectron spectroscopy (XPS) spectrum combined with the CO2RR performance results show that pyridinic-N content has a positive correlation with CO2RR activity. Moreover, density functional theory (DFT) demonstrates that pyridinic-N coordinated Ni–N4 sites offers optimized free energy and favorable selectivity towards CO2RR compared with pyrrolic-N. Accordingly, Ni–Na–C with highest pyridinic-N content (ammonia as nitrogen source) performs superior CO2RR activity, with the maximum carbon monoxide faradaic efficiency (FECO) of 99.8% at −0.88 V vs. RHE and the FECO surpassing 95% within potential ranging of −0.88 to −1.38 V vs. RHE. The building of this parameter for CO2RR activity of Ni–N–C give instructive forecast for low-cost and highly active CO2RR electrocatalysts.

Synergistic electronic structure modulation in single-atomic Ni sites dispersed on Ni nanoparticles encapsulated in N-rich carbon nanotubes synthesized at low temperature for efficient CO2 electrolysis

Ni, N-doped carbon materials (Ni–N–C) are prosperous candidates for the electrochemical CO2 reduction reaction (CO2RR) due to their outstanding activity and selectivity. However, the role of the coexisting uncoordinated N-doped sites and Ni nanoparticles (Ni-NPs) in overall CO2RR has been overlooked in prior studies. To address this gap, a low temperature synthesis method developed for Ni-NP-encapsulated Ni–N–C nanotube (Ni-NCNT) catalysts with atomically dispersed Ni–N4 and abundant uncoordinated N-doped sites, where Ni-NPs increase the electron density on Ni–N–C nanotube through carbon network and synergistically enhances the CO2RR activity. The systematic analysis reveals the cooperative role of Ni-NPs and uncoordinated N-doped sites in altering the electronic structure of Ni–N4 sites. The results of control experimental studies confirm the synergistic interaction of uncoordinated N-doped sites boost the CO2RR activity of Ni–N4 sites. Additionally, density functional theory calculations show that the strong interaction between the Ni-NPs and Ni–N–C did not affect the electronic structures of the Ni–N4 centers, but rather alter the electronic structure of uncoordinated pyridinic-N sites. This variation led to decreased the energy barriers of rate-limiting steps of COOH* formation on Ni–N4 and N-doped sites, resulting in excellent CO2RR performance.

High-density single-atomic Ni–N4 sites for efficient Fenton-like reactions

A cascade anchoring strategy was developed to construct Ni–NC single atom catalysts with high-density Ni–N4 sites, enabling an excellent Fenton-like catalytic performance.

Preparation and application of carbon nanotubes loaded atomic-level Ni–N4 catalyst for lithium-sulfur battery

Lithium-sulfur batteries (LSBs) are promising candidates as next-generation secondary batteries due to their advantages with respect to cost and energy density. However, their practical application is hindered by their slow kinetics and the shuttle behavior of soluble polysulfide ions. Herein, we successfully prepared a three-dimensional porous conductive catalyst material with an atomic-level Ni–N4 structure. The results showed that a strong adsorption of lithium polysulfides (LiPSs) by the Ni–N4 catalytic active sites and a strong catalytic effect on the conversion of LiPSs in the sulfur reduction reaction (SRR) as well as the lithium sulfide oxidation reaction (SOR) were achieved, effectively inhibiting the shuttle effect of polysulfide ions and promoting the sulfur cathode kinetics process. Thus, the LSBs exhibited an excellent performance with a specific capacity of 829.8 mAh g–1 and an average coulombic efficiency of 98.8 % after 420 cycles at a high rate of 1 C. Our work provides new insights and novel efforts to solve the shuttle effect in LSBs.

Atomically Dispersed Fe–N4 and Ni–N4 Independent Sites Enable Bidirectional Sulfur Redox Electrocatalysis

Single-atom catalysts (SACs) with high atom utilization and outstanding catalytic selectivity are useful for improving battery performance. Herein, atomically dispersed Ni-N4 and Fe-N4 dual sites coanchored on porous hollow carbon nanocages (Ni-Fe-NC) are fabricated and deployed as the sulfur host for Li-S battery. The hollow and conductive carbon matrix promotes electron transfer and also accommodates volume fluctuation during cycling. Notably, the high d band center of Fe in Fe-N4 site demonstrates strong polysulfide affinity, leading to an accelerated sulfur reduction reaction. Meanwhile, Li2S on the Ni-N4 site delivers a metallic property with high S 2p electron density of states around the Femi energy level, enabling a low sulfur evolution reaction barrier. The dual catalytic effect on Ni-Fe-NC endows sulfur cathode high energy density, prolonged lifespan, and low polarization.

Inter-Metal Interaction with a Threshold Effect in NiCu Dual-Atom Catalysts for CO2 Electroreduction.

Dual-atom catalysts (DACs) have become an emerging platform to provide more flexible active sites for electrocatalytic reactions with multi-electron/proton transfer, such as the CO2 reduction reaction (CRR). However, the introduction of asymmetric dual-atom sites causes complexity in structure, leaving an incomprehensive understanding of the inter-metal interaction and catalytic mechanism. Taking NiCu DACs as an example, herein, a more rational structural model is proposed, and the distance-dependent inter-metal interaction is investigated by combining theoretical simulations and experiments, including density functional theory computation, aberration-corrected transmission electron microscopy, synchrotron-based X-ray absorption fine structure, and Monte Carlo experiments. A distance threshold around 5.3Å between adjacent NiN4 and CuN4 moieties is revealed to trigger effective electronic regulation and boost CRR performance on both selectivity and activity. A universal macro-descriptor rigorously correlating the inter-metal distance and intrinsic material features (e.g., metal loading and thickness) is established to guide the rational design and synthesis of advanced DACs. This study highlights the significance of identifying the inter-metal interaction in DACs, and helps bridge the gap between theoretical study and experimental synthesis of atomically dispersed catalysts with highly correlated active sites.

Boosting aqueous non-flow zinc–bromine batteries with a two-dimensional metal–organic framework host: an adsorption-catalysis approach

We develop a high-performance aqueous non-flow zinc–bromine battery with nickel polyphthalocyanine as a cathode host, where the atomically dispersed Ni–N4 sites enable strong bromine adsorption and efficient bromine redox reactions.

Single Nickel Atom Catalysts Enable Fast Polysulfide Redox for Safe and Long‐Cycle Lithium–Sulfur Batteries (Small 51/2022)

Lithium-Sulfur Batteries In article number 2205470, Wei Chen, Ming Huang, Fei Li, and co-workers find that Ni single-atom catalysts (SACs) with Ni–N4 catalytic sites can promote the interfacial conversion redox of lithium polysulfides (LiPS) by accelerating the transformation kinetic and suppress the undesirable shuttle effect by immobilizing LiPS. This work opens up a new avenue for developing single-atom catalysts to accelerate the kinetic conversion of LiPS for highly stable Li–S batteries.

Constructing single‐atom Ni on N‐doped carbon via chelation‐anchored strategy for the hydrogenolysis of lignin

AbstractThe efficient utilization of lignin remains a great challenge due to its complex nonrepetitive structure and the lack of efficient catalyst. Herein, a single‐atom catalyst Ni@N‐C was designed via a facile chelation‐anchored strategy. Ni atoms were immobilized on the N‐doped carbon carrier by a two‐stage pyrolysis of a mixture of d‐glucosamine hydrochloride, nickel acetate, and melamine. d‐glucosamine hydrochloride as a chelating agent prevented the aggregation of Ni2+, and melamine provided enough N to anchor Ni by forming Ni–N4 structure. Ni@N‐C gave a 31.2% yield of aromatic compounds from lignin hydrogenolysis, which was twice higher than that achieved by Ni cluster catalyst. Based on the experimental and density functional theory (DFT) calculation results, the higher activity of Ni@N‐C was attributed to its lower H2 dissociation energy and the reduced energy barriers of the transition states. The strategy described opens an efficient green avenue for preparing single‐atom catalyst that possesses outstanding activity in lignin depolymerization.

Pyrrolic N‐Stabilized Monovalent Ni Single‐Atom Electrocatalyst for Efficient CO2 Reduction: Identifying the Role of Pyrrolic–N and Synergistic Electrocatalysis

AbstractEngineering the electronic structure of metal, N‐doped carbon catalysts is a potential strategy for increasing the activity and selectivity of CO2 electroreduction reaction (CO2RR). However, establishing a definitive link between structure and performance is extremely difficult due to constrained synthesis approaches that lack the ability to precisely control the specific local environment of MNC catalysts. Herein, a soft‐template aided technique is developed for the first time to synthesize pyrrolic N4Ni sites coupled with varying N‐type defects to synergistically enhance the CO2RR performance. The optimal catalyst helps attain a CO Faradaic efficiency of 94% at a low potential of −0.6 V and CO partial current density of 59.6 mA cm−2 at −1 V. Results of controlled experimental investigations indicate that the synergy between NiN4 and metal free defect sites can effectively promote the CO2RR activity. Theoretical calculations revealed that the pyrrolic N coordinated NiN4 sites and C atoms next to pyrrolic N (pyrrolic NC) have a lower energy barrier for the formation of COOH* intermediate and optimum CO* binding energy. The pyrrolic N regulate the electronic structure of the catalyst, resulting in lower CO2 adsorption energy and higher intrinsic catalytic activity.

Nickel polyphthalocyanine with electronic localization at the nickel site for enhanced CO2 reduction reaction

Nickel phthalocyanine (NiPc) can be at first glance a compelling catalyst for CO2 reduction reaction (CO2RR) because of its Ni–N4 site. Unfortunately, the pristine NiPc possesses a low catalytic activity resulting from the poor CO2 adsorption and activation capabilities of the electron-deficiency Ni site. Herein, we develop nickel polyphthalocyanine (NiPPc) with extended conjugation to tailor the electronic density at the Ni active site. The enlarged π conjugation of NiPPc evokes the d-electrons localization, increasing the electronic density at the Ni site, which enhances its CO2 adsorption and activation. Consequently, NiPPc supported on carbon nanotubes (NiPPc/CNT) in a flow cell delivers an excellent activity of −300 mA cm−2 for CO2RR with the CO selectivity of 99.8%, which is much higher than that of NiPc dispersed on carbon nanotubes. NiPPc/CNT exhibits an outstanding stability for CO2RR of more than 30 h at a current density of −100 mA cm−2 with an ultrahigh selectivity for CO, exceeding 99.7%. This work showcases a new way of tuning the electronic density of catalytic sites.

Rational design of M-N4-Gr/V2C heterostructures as highly active ORR catalysts: a density functional theory study.

Inspired by the composites of N-doped graphene and transition metal-based materials as well as MXene-based materials, heterostructures (M–N4–Gr/V2C) of eight different transition metals (M = Ti, Cr, Mn, Fe, Co, Ni, Cu, and Zn) doped with nitrogen-coordinated graphene and V2C as potential catalysts for the oxygen reduction reaction (ORR) using density functional theory (DFT) were designed and are described herein. The calculations showed that the heterostructure catalysts (except for Zn–N4–Gr/V2C) were thermodynamically stable. Ni–N4–Gr/V2C and Co–N4–Gr/V2C showed higher activities towards the ORR, with overpotentials as low as 0.32 and 0.45 V, respectively. Excellent catalytic performance results were observed from the change in electronic structure caused by the strong interaction between V2C and the graphene layers as well as the synergistic effect between the MN4 groups and the graphene layers. This study further provides insights into the practical application of ORR catalysts for MXene systems through the modulation of the electronic structure of two-dimensional materials.

Atomically-dispersed NiN4–Cl active sites with axial Ni–Cl coordination for accelerating electrocatalytic hydrogen evolution

The NiN4–Cl SAs/N–C electrocatalyst consisting of NiN4–Cl active sites with axial Ni–Cl coordination was synthesized. The axial Cl-coordination modulates the electronic configuration of Ni–N4 sites and enhances the interaction of Ni–H efficiently.

Metal–organic framework with atomically dispersed Ni–N4 sites for greatly-raised visible-light photocatalytic H2 production

The depletion of traditional fossil fuels and related environmental issues have increased the demand for clean and sustainable energy resources to achieve carbon neutrality. Active, robust and cheap photocatalysts are required for large-scale photocatalytic H2 evolution reaction (p-HER), which transforms solar energy into chemical energy. Here we report the decoration of Ni-imidazole framework (NiIm) with CdS nanorods for p–HER. The p–HER rate of CdS/NiIm hybrid sharply increased by about 14.23 times to 21,712 µmol h−1 g–1 when compared with that of CdS alone. Physicochemical characterizations and theoretical calculations reveal strong interactions at the CdS/NiIm interface and the presence of numerous Ni–N4 active sites on NiIm leading to the significant performance enhancement. This work demonstrates that NiIm acts as an affordable and abundant co-catalyst that remarkably enhances the p–HER, and enlightens the further development in the design and preparation of metal−organic framework-based materials for various applications in photocatalysis and related subjects.

Enhancement of Mass Transfer for Facilitating Industrial‐Level CO2 Electroreduction on Atomic NiN4 Sites

AbstractHerein, an active catalyst A‐Ni@CMK is developed with the atomically dispersed NiN4 moieties on the mesoporous carbon for the electrocatalytic CO2 reduction reaction (CO2RR) through a step‐by‐step pore‐filling synthetic strategy. Concretely, the as‐synthesized catalyst A‐Ni@CMK exhibits outstanding catalytic performance for CO2RR in the H‐cell with a Faradaic efficiency of CO (FECO) > 80% in a wide electrochemical potential window (−0.5 to −0.9 V vs RHE) and a large CO partial current density (jCO) of 24 and 51 mA cm−2 at −0.6 and −0.8 V versus RHE, respectively. Notably, jCO for A‐Ni@CMK can further reach the industrial‐level values of 366 mA cm−2 at −0.8 V versus RHE, respectively, with the FECO > 95% in the flow cell, surpassing those for all the thus far reported NiNC catalysts and representing one of the best values for the catalysts for CO2RR. Moreover, comparative experimental studies in combination with density functional theory calculations demonstrate that the intrinsic high activity of the atomic NiN4 sites towards CO2RR results in high selectivity. Nevertheless, the mesoporous channels favor the mass transmission for both reactant CO2 and gas‐product CO, which in turn enhances the reaction kinetics, leading to the improved overall performance of the as‐prepared A‐Ni@CMK catalyst for CO2‐to‐CO conversion.

Atomically dispersed Ni–N4 species and Ni nanoparticles constructing N-doped porous carbon fibers for accelerating hydrogen evolution

Single-atom catalysis has aroused enormous attention due to the highly exposed active sites and nearly 100% atomic utilization. However, the relatively low metal atoms loading limits their catalytic activities. Herein, we report N-doped carbon fibers supported Ni single atoms and nanoparticles hybrid (Ni SA/NP-NCF-800) by the combined strategies comprising electrospinning, pyrolysis, and etching. The in-situ formed SiO2 and Ni particles serve as the hard templates to create highly porous architecture throughout the entire fibers, enabling the Ni species to efficiently anchor on carbon matrix to generate a high single atoms loading of 1.83 wt%, as well as provide accessible channels for mass transport and electrolyte diffusion. The unique configuration endows the hybrid with outstanding hydrogen evolution performance along with the low overpotential and robust long-term durability in 1 M KOH. The synchrotron radiation analysis and density functional theory calculations experimentally and theoretically reveal the isolated Ni was coordinated with neighboring four N atoms, which could lead to the re-arranged electron structure of Ni nanoparticles. The synergistic effect of atomically dispersed Ni and nanoparticles leads to the significantly enhanced water adsorption/dissociation abilities and optimized H adsorption free energy in alkaline media, thus paving a new avenue to design single atoms based electrocatalysts.

A New Strategy for Accelerating Dynamic Proton Transfer of Electrochemical CO2 Reduction at High Current Densities

AbstractDeveloping single‐atom electrocatalysts with high activity and superior selectivity at a wide potential window for CO2 reduction reaction (CO2RR) still remains a great challenge. Herein, a porous NiNC catalyst containing atomically dispersed NiN4 sites and nanostructured zirconium oxide (ZrO2@Ni‐NC) synthesized via a post‐synthetic coordination coupling carbonization strategy is reported. The as‐prepared ZrO2@Ni‐NC exhibits an initial potential of −0.3 V, maximum CO Faradaic efficiency (F.E.) of 98.6% ± 1.3, and a low Tafel slope of 71.7 mV dec−1 in electrochemical CO2RR. In particular, a wide potential window from −0.7 to −1.4 V with CO F.E. of above 90% on ZrO2@Ni‐NC far exceeds those of recently developed state‐of‐the‐art CO2RR electrocatalysts based on NiN moieties anchored carbon. In a flow cell, ZrO2@Ni‐NC delivers a current density of 200 mA cm−2 with a superior CO selectivity of 96.8% at −1.58 V in a practical scale. A series of designed experiments and structural analyses identify that the isolated NiN4 species act as real active sites to drive the CO2RR reaction and that the nanostructured ZrO2 largely accelerates the protonation process of *CO2− to *COOH intermediate, thus significantly reducing the energy barrier of this rate‐determining step and boosting whole catalytic performance.

Fe-Ni Alloy Nanoclusters Anchored on Carbon Aerogels as High-Efficiency Oxygen Electrocatalysts in Rechargeable Zn-Air Batteries.

In this work, Fe-Ni alloy nanoclusters (Fe-Ni ANCs) anchored on N, S co-doped carbon aerogel (Fe-Ni ANC@NSCA catalysts) are successfully prepared by the optimal pyrolysis of polyaniline (PANI) aerogels derived from the freeze-drying of PANI hydrogel obtained by the polymerization of aniline monomers in the co-presence of tannic acid (TA), Fe3+ , and Ni2+ ions. In addition, the optimal molar ratio of the TA, Fe3+ , and Ni2+ ions for synthesis of Fe-Ni ANC@NSCA catalysts are 1:2:5, which can guarantee the formation of carbon aerogel composed of quasi-2D porous carbon sheets and the formation of high-density Fe-Ni ANCs with an ultrasmall size between 2 to 2.8nm. These Fe-Ni ANCs consisting of N4 -Fe-O-Ni-N4 moiety are proposed as a new type of active species for the first time, to the best of the authors' knowledge. Thanks to their unique features, the Fe-Ni ANC@NSCA catalysts show excellent performance in oxygen reduction reaction with a half-wave potential (E1/2 ) of 0.891 V and oxygen evolution reaction (260mV @ 10mA cm-2 ) in alkaline media as bifunctional catalysts, which are better than the state-of-the-art commercial Pt/C catalysts and RuO2 catalysts. Moreover, Zn-air battery assembled with the Fe-Ni ANC@NSCA catalysts also shows a remarkable performance and exceptionally high stability over 500 h at 5mA cm-2 .

Constructing Precise Coordination of Nickel Active Sites on Hierarchical Porous Carbon Framework for Superior Oxygen Reduction.

Single-atom catalysts (SACs) with specific coordination environment are expected to be efficient electrocatalysts for oxygen reduction reaction (ORR). Herein, NiN4 C10 coordination site is constructed through encapsulating Ni2+ into the cavity of ZIF-8 as a self-sacrificing precursor and anchoring it on 3D N-doped carbon frameworks. The NiN4 C10 catalyst shows excellent ORR activity and stability, with a high half-wave potential (0.938V vs RHE), which is currently the best performances in Ni-based SACs. The remarkable performance with high ORR activity in alkaline solution is attributed to the single-atom nickel active sites with faster electron transport and suitable electronic structure. Moreover, the power density of zinc-air battery assembled by NiN4 C10 as cathode is 47.1% higher than that of the commercial Pt/C. This work not only provides a facile method to prepare extremely active Ni-based SACs, but also studies the intrinsic mechanism toward the oxygen reduction reaction under alkaline condition.