Local Coordination Environment Research Articles

Fine-tuned local coordination environment of Pt-N in nanocarbons for efficient propane dehydrogenation.

Based on the disturbance of electronic density, nitrogen-doped nanocarbons show promising properties to anchor metal clusters. However, precisely regulating the coordination mode between N species and the active site remains challenging. Herein, we rationally designed three N types (graphitic N, pyridinic N and pyrrolic N) in nanocarbons to anchor Pt clusters for the benchmark propane dehydrogenation. The specific activity of the pyridinic-N-doped catalyst was 147.54 molC3H6 molPt-1 h-1 at 550 °C, which was 1.3 times higher than those of graphitic- and pyrrolic-N-doped catalysts. Unlike the regular tetrahedron Pt cluster in the graphitic-N catalyst or the distorted three-layered Pt cluster in the pyrrolic-N catalyst, the Pt cluster in the pyridinic-N catalyst was an inverted tetrahedron, which increased the contact degree without geometric repulsion towards C-H bond scission. The geometric parameters of detached H and C atoms in the methylene group for the pyridinic N catalyst was decreased to strengthen the C-H bond scission. After CH3CHCH3* adsorption, the Bader charge of the Pt active site also became highly positive, which tailored the d-band center closer to the Fermi level and provided more vacant orbitals for C-H bond breakage. Therefore, pyridinic N in nanocarbons is promising to anchor small-sized Pt for alkane dehydrogenation in terms of geometric and electronic effects.

Uleashing efficient and CO-resilient alkaline hydrogen oxidation of Pd3P through phosphorus vacancy defect engineering

A high-performance and highly CO-resilient hydrogen oxidation reaction (HOR) electrocatalyst is heralded as core material to solve the commercial deployment of hydrogen fuel cells. Phosphorus vacancies, as a type of delicate point defect, could effectively and flexibly modulate the catalytic performance. Therefore, based on the vacancy design philosophy of “less is more”, we synthesize a phosphorus-vacancy-rich Pd3P@C (Vp-Pd3P@C) catalyst with bowl-like hemisphere structure for alkaline HOR, for the first time. The Vp-Pd3P@C catalyst exhibits remarkable mass activity and exchange current density of 1.66 mA μgPd–1 and 3.2 mA cm<font style=’color:red’>–2, respectively, surpassing those of Pd3P@C (0.45 mA μgPd–1, 1.78 mA cm<font style=’color:red’>–2) and commercial Pt/C (0.3 mA μgPt–1, 2.29 mA cm<font style=’color:red’>–2). Intriguingly, the catalyst can tolerate 1000 ppm CO that Pt/C catalyst lacks. Density functional theory calculations uncover that the optimal local coordination environment and favorable electronic structure that rooted from phosphorus vacancy enable optimum adsorption kinetics of hydrogen and hydroxyl while concomitantly suppressing Pd 4d → CO 2π* back donation, contributing to the remarkable HOR reactivity and CO tolerance.

Tuning catalytic performance of platinum single atoms by choosing the shape of cerium dioxide supports.

The local coordination environment of single atom catalysts (SACs) often determines their catalytic performance. To understand these metal-support interactions, we prepared Pt SACs on cerium dioxide (CeO2) cubes, octahedra and rods, with well-structured exposed crystal facets. The CeO2 crystals were characterized by SEM, TEM, pXRD, and N2 sorption, confirming the shape-selective synthesis, identical bulk structure, and variations in specific surface area, respectively. EPR, XPS, TEM and XANES measurements showed differences in the oxygen vacancy density following the trend rods > octahedra > cubes. AC-HAADF-STEM, XPS and CO-DRIFTS measurements confirmed the presence of only single Pt2+ sites, with different surface platinum surface concentrations. We then compared the performance of the three catalysts in ammonia borane hydrolysis. Precise monitoring of reaction kinetics between 30-80 °C gave Arrhenius plots with hundreds of data points. All plots showed a clear inflection point, the temperature of which (rods > octahedra > cubes) correlates to the energy barrier of ammonia borane diffusion to the Pt sites. These activity differences reflect variations in the - facet dependent - degree of stabilization of intermediates by surface oxygen lone pairs and surface-metal binding strength. Our results show how choosing the right macroscopic support shape can give control over single atom catalysed reactions on the microscopic scale.

Design of a Single-Atom In-N3-S site to Modulate Exciton Behavior in Carbon Nitride for Enhanced Photocatalytic Performance.

Rational tailoring of the local coordination environment of single atoms has demonstrated a significant impact on the electronic state and catalytic performance, but the development of catalysts beyond noble/transition metals is profoundly significant and highly desired. Herein, the main-group metal indium (In) single atom is immobilized on sulfur-doped porous carbon nitride nanosheets (In@CNS) in the form of three nitrogen atoms coordinated with one sulfur atom (In-N3-S). Both theoretical calculations and advanced characterization investigations clearly elucidated that the single-atomic In-N3-S structures on In@CNS are powerful in promoting the dissociation of excitons into more free carriers as well as the charge separation, synergistically elevating electron concentration by 2.19 times with respect to pristine CNS. Meanwhile, the loading of In single atoms on CNS is responsible for altering electronic structure and lowering the Gibbs free energy for hydrogen adsorption. Consequently, the optimized In@CNS-5.0 exhibited remarkable photocatalytic performance, remarkable water-splitting and tetracycline hydrochloride degradation. The H2 production achieved to 10.11mmolh-1g-1 with a notable apparent quantum yield of 19.70% at 400nm and remained at 10.40% at 420nm. These findings open a new perspective for in-depth comprehending the effect of the main-group metal single-atom coordination environment on promoting photocatalytic performance.

The influence of crystal chemistry on lithium isotopic fractionation in pegmatite minerals

The understanding of lithium (Li) isotopic fractionation controlled by mineral species, especially those containing trace or minor amounts of Li (e.g., a few to tens of ppm), is hindered by lack of knowledge about the crystal chemistry of Li-bearing minerals. In this study, we performed solid-state Nuclear Magnetic Resonance (NMR) experiments, employing the Li7 Magic Angle Spinning (MAS) to investigate the local coordination environments of Li in minerals and their impact on Li isotopic fractionation. Our investigation focused on four coexisting minerals sourced from the Koktokay No. 3 pegmatite dike in the Xinjiang, China, namely quartz, K-feldspar, muscovite, and tourmaline, which has Li content and δLi7 value of 14.6 ppm and 3.90‰, 19.3 ppm and 7.09‰, 430 ppm and − 14.2‰, and 108 ppm and 13.42‰, respectively. Muscovite displayed the lowest δLi7 value, whereas tourmaline exhibited the highest value, and a considerable variation of 27.62‰ in δLi7 value was observed between muscovite and tourmaline. The analysis of Li7 MAS-NMR spectra further revealed distinct Li coordination environments among these minerals. A notable counterintuitive negative correlation exists between the δLi7 value and the chemical shift for the four Li-bearing minerals. This negative correlation contrasts to the expected Li isotopic fractionation under equilibrium conditions, in which enrichment of heavy Li isotopes is accompanied with large chemical shifts in Li-bearing minerals. This unexpected observation can be potentially attributed to nonequilibrium conditions of crystallization of the investigated minerals, coupled with fast diffusion of Li6 in minerals, boasting abnormally high coordination numbers due to weak LiO chemical bonds. Essentially, our study suggests that Li isotopic fractionation among Li-bearing minerals in pegmatite can be significant and is intricately influenced by both crystal chemistry and chemical diffusion.

(Digital Presentation) In-Situ Spectroelectrochemistry to Unveil the Mechanism of Green Ammonia Production on the Ti2n Nitride Mxene

Electrochemical nitrogen reduction reaction (NRR) is used to convert nitrogen (N2) to ammonia (NH3) at ambient temperature and pressure. In general, acidic electrolytes are used to provide protons (H+) for the reduction process. However, this leads to a low NH3 selectivity because of H2 by-product formation via the hydrogen evolution reaction (HER). Recently, we showed that a Ti2N MXene is active and selective for NRR, and provided preliminary evidence that this catalyst works through a Mars-van Krevelen (MvK) mechanism rather than conventional associative/dissociative mechanisms. To improve the selectivity of the NRR process, the electrolyte was shifted from acidic to neutral pH values. From this, it was seen that NRR in 0.1M Na2SO4 was able to achieve a selectivity significantly greater than that of 0.1M HCl. We also observed that at more cathodic potentials, the material begins to irreversibly decompose into TiO2 as evidenced by cyclic voltammetry analysis before and after chronoamperometry experiments. To further understand the performance of this material, we use in-situ/operando techniques, including X-ray absorption spectroscopy (XAS) and Fourier-transform infrared (FTIR) spectroscopy, to deconvolute the mechanism of NH3 production. We use XAS to track the Ti oxidation state shift and degree of shift as a function of reaction time and applied potential. We also use XAS to track the change in the atomic bond lengths at the local coordination environment of the Ti atoms throughout time and voltage. Furthermore, we use FTIR to elucidate in real-time the adsorption of NRR reactive species and intermediates on the MXene surface. All findings are further corroborated with density functional theory (DFT) calculations to track the reaction energy pathway over each intermediate. We plan to expand these findings to other materials and systems, and use the knowledge obtained from these studies to design optimal electrolytic conditions to produce NH3 through NRR.

Construction of local coordination environment of iron sites over g-C3N4/PCN-222(Fe) composite with high CO2 photoreduction performance

Photocatalytic conversion of CO2 to usable fuels provides a new strategy for solving energy problems and the greenhouse effect. Porphyrin-based metal-organic frameworks (MOFs) are promising in photocatalysis due to their remarkable light harvesting ability, and the metal active site and its coordination environment can be further adjusted to achieve the high activity. In this work, g-C3N4/PCN-222 composites with different porphyrin metal centers were fabricated and the g-C3N4/PCN-222(FeIII) catalyst showed the highest photocatalytic CO2 reduction performance than that of g-C3N4/PCN-222(FeII) and other g-C3N4/PCN-222(M, M = Co, Ni, Cu, Zn) composites. Experimental studies and theoretical calculations showed that the axial coordination in g-C3N4/PCN-222(FeIII) distorts the square planar field (Fe-N4) to quasi-octahedral coordination, which led to the moderate adsorption ability of CO2 reduction intermediate (*CO), resulting in the high photocatalytic activity.

Modulation of Phase Transition in Cobalt Selenide with Simultaneous Construction of Heterojunctions for Highly-Efficient Oxygen Electrocatalysis in Zinc-Air Battery.

Phase transformation of cobalt selenide (CoSe2 ) can effectively modulate its intrinsic electrocatalytic activity. However, enhancing electroconductivity and catalytic activity/stability of CoSe2 still remains challenging. Heterostructure engineering may be feasible to optimize interfacial properties to promote the kinetics of oxygen electrocatalysis on a CoSe2 -based catalyst. Herein, a heterostructure consisting of CoSe2 and cobalt nitride (CoN) embedded in a hollow carbon cage is designed via a simultaneous phase/interface engineering strategy. Notably, the phase transition of orthorhombic-CoSe2 to cubic-CoSe2 (c-CoSe2 ) accompanied by in situ CoN formation is realized to build the c-CoSe2 /CoN heterointerface, which exhibits excellent/highly stable activities for oxygen reduction/evolution reactions (ORR/OER). Notably, heterostructure can modulate the local coordination environment and increase Co-Se/N bond lengths. Theoretical calculations show that Co-site (c-CoSe2 ) with an electronic state near Fermi energy level is the main active site for ORR/OER.Energetical tailoring of the d-orbital electronic structure of the Co atom of c-CoSe2 in heterostructure by in situ CoN incorporation lowers thermodynamic barriers for ORR/OER. Attractively, a zinc-air battery with a c-CoSe2 -CoN cathode displays excellent cycling stability (250h) and charge/discharge voltage loss (0.953/0.96V). It highlights that heterointerface engineering provides an option for modulating the bifunctional activity of metal selenides with controlled phase transformation.

Theoretical and experimental investigation of the coordination effect on photocatalytic CO2 reduction efficiency of cobalt single atom catalyst

Visible-light-driven carbon dioxide (CO2) reduction, which converts CO2 into value-added fuels, is an intriguing strategy to simultaneously mitigate the energy crisis and achieve a carbon–neutral economy. Single-atom catalysts (SACs) with homogeneously dispersed definite active sites and adjustable coordination environments show great potential in catalyzing photocatalytic CO2 reduction reaction (CO2RR). According to previously reported studies, the catalytic performance of SACs applied in various fields has a great relationship with their local coordination environment of metal centers. However, in-depth investigation of the coordination effect, which has been widely explored to regulate the electronic structure of SACs, on the activity, selectivity, and stability of CO2 photoreduction has never been reported. Herein, a series of Co single atom photocatalysts with diverse N coordination number (CoSA-Nx/C, x = 2, 3, and 4) were synthesized and their photocatalytic CO2RR performance was examined. Theoretical and experimental investigation demonstrated that the photocatalytic CO2RR activity of Co SACs can be effectively adjusted by fine-regulating the N coordination. The optimal CoSA-N2/C photocatalyst with two-coordinate N atoms with increased unoccupied Co 3d electronic orbitals possesses enhanced CO2 adsorption and activation as well as reduced energy barrier for *COOH intermediate generation, thus showing superior photoconversion of CO2-to-CO performance with 10110 μmol g−1h−1 CO evolution yield, 82.6 % CO selectivity, and long-term stability. This work promotes the future rationally design and synthesis of photocatalysts applied in targeted reactions at atomic scale.

Giant enhancement of photoluminescence in Mn4+-activated Ba2CaWO6 phosphors via heterovalent doping with rare-earth ions

Currently, Mn4+-activated phosphors have attracted extensive attention for their versatile applications in general lighting, display and plant cultivation. Owing to 3d3 electronic configuration of Mn4+ ion, modifying its local coordination environment emerges as a potent method to tailor its luminescence behavior. Herein, a heterovalent substitution strategy is reported to greatly enhance the photoluminescence (PL) of Ba2CaWO6:Mn4+. The effects of the substitution of rare-earth ions (Ln3+ = Lu3+, Y3+, Gd3+, La3+) for Ca2+ ions on the PL properties of the phosphor are studied in detail. The PL spectral change of Mn4+ induced by Ln3+ substitution is clarified in terms of the local structure of [WO6] octahedron and the valence state of Mn. By selection of Ln3+ ions and optimization of Ln3+ doping concentration, the emission intensity of Ba2Ca0.85Gd0.15WO6:0.25Mn4+ phosphor reaches up to 46.3 times as that of Ba2CaWO6:0.25Mn4+. Besides, the Ba2Ca0.85Gd0.15WO6:0.25Mn4+ phosphor exhibits an internal quantum yield of 56.9 % and a thermal stability of 72.6 %@423 K. Finally, Ba2Ca0.85Ln0.15WO6:Mn4+ based phosphor conversion LED devices are demonstrated, which can be potentially employed for indoor plant lighting.

Anionic Regulation and Heteroatom Doping of Ni‐Based Electrocatalysts to Boost Biomass Valorization Coupled with Hydrogen Production

AbstractElectrocatalytic biomass valorization coupled with hydrogen production provides an efficient and economical way to achieve a zero‐carbon economy. Ni‐based electrocatalysts are promising candidates due to their intrinsic redox capabilities, but the rational design of active Ni site coordination is still a huge challenge. Herein, the combined strategies of surface reconstruction and heteroatom doping are adopted to modify Ni3S2 pre‐catalysts and the obtained bimetallic catalyst exhibits superior electrocatalytic performance toward 5‐hydroxymethylfurfural (HMF) oxidation to 2,5‐furanedicarboxylic acid (FDCA). Specifically, the oxysulfide‐coordinated amorphous NiOOH (NiOOH‐SOx) active phase is in situ constructed following the anionic regulation mechanism, which endows numerous defects and unsaturated sites for anodic HMF oxidation. Cu heteroatom doping further modulates the electronic structure of active sites with abundant Lewis acidic sites, offering advanced capability for HMF adsorption. Several operando characterization techniques (in situ Raman, infrared, and electrochemical impedance spectroscopies) are performed to disclose the reaction pathway and structure‐activity‐potential relationship. Theoretical results further demonstrate that Cu doping and oxyanionic regulation effectively modulate the local coordination environment of Ni sites and correspondingly tailor the intermediate adsorption behavior and then promote the reaction kinetics. Moreover, a two‐electrode system is assembled to pair HMF oxidation with cathode hydrogen production, demonstrating better energy conversion efficiency.

Activation of peroxymonopulfate by graphene-supported single-atom FeN5 with an ultra-low dose at low temperature: Nonradical mechanism and antibacterial activity

The catalytic activity of single-atom catalysts (SACs) is closely related to the coordination environment of metal center. Here, a new peroxymonosulfate (PMS) activation strategy based on graphitic carbon nitride-supported Fe SACs (FeCN) containing a five-coordinated structure (FeN5) exhibited remarkable catalytic performance towards doxorubicin hydrochloride (DOX) with an ultra-low-dose catalyst (10 mg·L−1) at a low temperature (4 °C). Singlet oxygen (1O2) and high-valent iron-oxo species (HV-Fe)-dominated nonradical processes are responsible for the degradation and rapid inactivation of Escherichia coli (E. coil) and S. aureus. Density functional theory (DFT) calculations demonstrated that the terminal O of PMS adsorbed onto Fe-N5 sites facilitated the subsequent homolysis of the OO bond to genarate 1O2 and HV-Fe. This work not only develops an efficient catalyst by fine-tuning the local coordination environment but also provides an insight into the mechanism of the nonradical-species-mediated PMS process as well as potential application at the device level.

The 5d-5p-3d orbital hybridization induced by light incorporation of Cu into surface-uneven Pt3Sn intermetallic nanocubes customizes dual-intermediates adsorptions for CO-resilient methanol oxidation

Catalysts with excellent performances for methanol oxidation reaction (MOR) are supposed to equip with a weaker *CO adsorption but a stronger *OH adsorption. Herein, light incorporation of Cu is implemented into surface-uneven Pt3Sn intermetallic nanocubes to manipulate crucial CO*/OH* intermediates adsorptions for boosting MOR electrocatalysis. The generated ternary Cu0.2Pt3Sn/CNTs intermetallic preserves the uneven cubic shape of non-doped Pt3Sn/CNTs, providing a defect-rich surface structure for affording abundant available active sites. More importantly, the incorporated Cu induces a strong Pt 5d-Sn 5p-Cu 3d orbital hybridization, which upgrades the electron density of Pt but reversely downgrades that of Sn. Such delicately tailored local coordination environments of Pt and Sn result in an intrinsically attenuated CO* adsorption on Pt sites but a promoted OH* adsorption on Sn sites, remarkably diminishing the energy barrier of CO* oxidation. The elaborately customized dual-intermediates adsorptions combined with the defect-rich cubic architecture superiorities consequently contribute to highly elevated MOR performance.

Orbital Coupling of PbO7 Node in Single-Crystal Metal-Organic Framework Enhances Li-O2 Battery Electrocatalysis.

Optimizing the local coordination environment of metal centers in metal-organic frameworks (MOFs) is crucial yet challenging for regulating the overpotential of lithium-oxygen (Li-O2) batteries. Herein, we report the synthesis of a class of PbO7 nodes in a single crystal MOF (naphthalene-lead-MOF, known as Na-Pb-MOF) to significantly enhance the kinetics of both discharge and charge processes. Compared to the PbO6 node in the single-crystal tetramethoxy-lead-MOF (4OMe-Pb-MOF), the bond length between Pb and O in the PbO7 node of Na-Pb-MOF increases, resulting in weaker Pb 5d-O 2p orbital coupling, which optimizes the adsorption interaction toward intermediates, and thereby promotes the rate-determining steps of both the reduction of LiO2 to Li2O2 and the oxidation of LiO2 to O2 for reducing the activation energy of the overall reaction. Consequently, Li-O2 batteries based on Na-Pb-MOF electrocatalysts exhibit a low total charge-discharge overpotential of 0.52 V and an excellent cycle life of 140 cycles.

Improving Ruddlesden-Popper electrocatalysts through interstitial fluorination-driven rearrangements of local coordination environment

Anion-doping is an attractive strategy to regulate the local coordination environment of oxygen electrodes in solid oxide fuel cells (SOFCs), which is generally regarded as a substitution for O-sites. In this work, the interstitial fluorine anion-doping in Sr3Fe2O7-δ, a Ruddlesden-Popper oxide with a two-layered structure, has been observed for the first time. The X-ray absorption fine structure analysis and Rietveld refined X-ray diffraction results demonstrate that the fluorine anion dopants occupy the rock-salt layer forming the stronger metal-fluorine bonds to activate oxygen ions. Density functional theory calculations further verify fluorine anions' ability to insert into tetrahedral intervals consisting of four Sr2+ in the rock-salt layer. The elevated proportion of O22−/O− and Fe4+ are obtained, which are commonly deemed in favor of oxygen reduction reaction. The fluorine anion-doped oxygen electrode exhibits more than a 20% drop in area specific resistance measured from 600 to 750 °C. In addition, the symmetric cell with Sr3Fe2O7-δF0.1 single-phase cathode shows excellent durability within a 1000 h thermal cycling and long-term tests in air atmosphere. A high peak power density of 888 mWcm−2 is achieved at 700 °C, showing a 35% improvement.

Spatial Structure Engineering of Interactive Single Platinum Sites toward Enhanced Electrocatalytic Hydrogen Evolution

AbstractRegulating site‐to‐site interactions between active sites can effectively tailor the electrocatalytic behavior of single‐atom catalysts (SACs). The conventional SACs suffer from low density of single atoms and lack of site‐to‐site interactions between them. Herein, a series of interactive Pt SACs with controllable Pt–Pt spatial correlation degree and local coordination environment is developed by integrating densely populated Pt single atoms in the sub‐lattice of a Co3O4 matrix. The obtained interactive Pt‐Co3O4 catalysts demonstrate remarkable electrocatalytic performance toward hydrogen production, outperforming those of isolated single atom‐ and nanoparticle‐based catalysts. The intrinsic catalytic activity of interactive Pt‐Co3O4 catalysts is closely dependent on the spatial structure of Pt sites with the adjusted d‐band center by regulating contents and atomic configuration of Pt sites. This work provides fundamental insights for the structure‐property relationship on interactive single active sites, which is expected to direct the rational design of highly efficient SACs.

Regulating Oxygen Redox Chemistry through the Synergistic Effect of Transition-Metal Vacancy and Substitution Element for Layered Oxide Cathodes.

Reversible oxygen redox (OR) is considered as a paradigmatic avenue to boost the energy densities of layered oxide cathodes. However, its activation is largely coupled with the local coordination environment around oxygen, which is usually accompanied with irreversible oxygen release and unfavorable structure distortion. Herein, it is revealed that the synergistic effect of transition-metal (TM) vacancy and substitution element for modulating the OR activity and reversibility of layered Na0.67 MnO2 through multimodal operando synchrotron characterizations and electrochemical investigations. It is disclosed that TM vacancy can not only suppress the complicated phase transition but also stimulate the OR activity by creating nonbonding O 2p states via the Na─O─vacancy configurations. Notably, the substitution element plays a decisive role for regulating the reversibility of vacancy-boosted OR activity: the presence of strong Al─O bonds stabilizes the Mn-O motifs by sharing O with Al in the rigid Mn─O─Al frameworks, which mitigates TM migration and oxygen release induced by TM vacancy, leading to enhanced OR reversibility; while the introduction of weak Zn─O bonds exacerbates TM migration and irreversible oxygen release. This work clarifies the critical role of both TM vacancy and substitution element for regulating the OR chemistry, providing an effective avenue for designing high-performance cathodes employing anionic redox.

Nitrogen Plasma Activates CoMn-Layered Double Hydroxides for Superior Electrochemical Oxygen Evolution.

Bimetallic layered double hydroxide is considered an ideal electrocatalytic material. However, due to the poor electrical conductivity of the bimetallic layered structure, obtaining highly active and stable catalysts through facile regulation strategies remains a great challenge. Herein, we use a simple corrosion strategy and nitrogen plasma technology to convert cobalt-based metal-organic frameworks into nitrogen-doped CoMn bimetallic layered double hydroxides (CoMn-LDH). Under the condition of regulating the local coordination environment of the catalytic active site and the presence of rich oxygen vacancy defects, N@CoMn-LDH/CC generates a low overpotential of 219 mV at 10 mA cm-2, which exceeds that of the commercial RuO2 catalyst. Density functional theory calculation shows that nitrogen doping improves the adsorption energy of the Mn site for oxygen evolution intermediates and reduces the reaction energy barrier of the Co site. Meanwhile, experiments and theoretical calculations verify that the mechanism of nitrogen doping regulating the oxygen evolution reaction (OER) follows the lattice oxygen oxidation mechanism, avoiding the collapse of the structure caused by catalyst reconstruction, thus improving the stability of oxygen evolution. This work provides a new simple strategy for the preparation of catalysts for a superior electrocatalytic oxygen evolution reaction.

DFT study of N-modified graphene-loaded monometallic cobalt for acetylene hydrochlorination reaction

The density functional theory (DFT) was used to systematically investigate the effects of non-precious metal catalysts doped with different numbers of N atoms, graphene-CoNx (x = 1,2,3,4), on reaction mechanism of acetylene hydrochlorination reaction. It was found that three graphene-CoNx (x = 1,2,3) catalysts can activate C2H2 and HCl and absorb them on their surface. The electron transfer between the metal atom and the N and C atoms attached to it can be used as a descriptor of catalytic properties. Moreover, the catalytic activity of graphene-CoNx (x = 1,2,3) decreased with the decrease in the number of N atoms. One of the graphene-CoN3 catalysts has the lowest reaction energy barrier of 0.77 eV free energy. This work reveals the local coordination environment of N-doped graphene-loaded single-atom Co-catalyzed acetylene plus hydrogen chloride, which provides a theoretical basis for the design of efficient green catalysts.

Highly Effective Electrochemical Water Splitting with Enhanced Electron Transfer between Ni2Co Layered Double Hydroxide Nanosheets Dispersed on Carbon Substrate

A reasonable design of nickel-based catalysts is key to efficient and sustainable energy conversion. For electrocatalytic materials in alkaline electrolytes, however, atomic-level control of the active sites is essential. Moreover, the well-defined surface structure contributes to a deeper understanding of the catalytic mechanism. Here, we report the loading of defective nickel–cobalt layered double hydroxide nanosheets (Ni2Co-LDH@C) after carbonization of silk. Under the precise regulation of the local coordination environment of the catalytic active site and the presence of defects, Ni2Co-LDH@C can provide an ultra-low overpotential of 164.8 mV for hydrogen evolution reactions (HERs) at 10 mA cm−2, exceeding that of commercial Pt/C catalysts. Density functional theory calculations show that Ni2Co-LDH@C optimizes the adsorption energy of the intermediate and promotes the O-O coupling of the active site in the oxygen evolution reaction. When using Ni2Co-LDH@Cs as cathodes and anodes to achieve overall water splitting, a low voltage of 1.63 V is required to achieve a current density of 10 mA cm−2. As an ideal model, Ni2Co-LDH@C has excellent water splitting properties and has the potential to develop water–alkali electrocatalysts.