Earth-abundant Transition Metals Research Articles

Interface Decoration Of N-Doped Carbon Nanotube with Fe For Enhancing Oxygen Catalytic Activity

Oxygen electrocatalytic reactions, including oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are extremely important in energy storage and conversion technology. The ORR is happened in cathode electrode in fuel cells or metal air batteries when discharging, the OER is occurred in anode electrode in water splitting or rechargeable metal air batteries when charging. Currently, the high-performance catalyst developed for ORR still relies on platinum (Pt) and its alloys. On the other hand, ruthenium (Ru) oxides were demonstrated to be high performance electrocatalysts for OER. However, their scarcity, limited stability, and aggregation limited the development of electrochemistry energy storage and conversion. Herein, we synthesize a series of transition metal nanoparticles embedded in nitrogen doped carbon nanotubes (M-CNT) and further decorating the interface of N-CNT with Fe element for enhancing oxygen catalytic activities. The results show that the type of transition metal determine the morphologies of N-CNT and the catalytic performance in ORR and OER. After further modification by introducing Fe element, the Fe-CNT based catalyst displays a superior ORR activity, even surpasses that of Pt/C, the Ni-CNT based catalyst with Fe decoration also showes a significant enhancement in OER. This work provides a feasible strategy to develop highly efficient oxygen catalysts with low-cost, earth-abundant transition metal elements via further decoration.

Anchoring Cu1 species over nanodiamond-graphene for semi-hydrogenation of acetylene

The design of cheap, non-toxic, and earth-abundant transition metal catalysts for selective hydrogenation of alkynes remains a challenge in both industry and academia. Here, we report a new atomically dispersed copper (Cu) catalyst supported on a defective nanodiamond-graphene (ND@G), which exhibits excellent catalytic performance for the selective conversion of acetylene to ethylene, i.e., with high conversion (95%), high selectivity (98%), and good stability (for more than 60 h). The unique structural feature of the Cu atoms anchored over graphene through Cu-C bonds ensures the effective activation of acetylene and easy desorption of ethylene, which is the key for the outstanding activity and selectivity of the catalyst.

Molecular spintronics devices exhibiting properties of a solar cell

Almost all the solar cells created so far have been based on electronic charge. This paper reports a photovoltaic effect based on the spin property of electrons. This spin-based photovoltaic effect was observed on magnetic tunnel junction based molecular spintronics devices (MTJMSD). MTJMSDs were produced by covalently bonding organometallic molecular clusters (OMCs) between the top and bottom ferromagnetic electrodes of Co/NiFe/AlOx/NiFe magnetic tunnel junctions along the exposed side edges. The MTJMSD configuration, which showed the photovoltaic effect, also exhibited OMC induced strong antiferromagnetic coupling (Tyagi et al 2015 Nanotechnology 26 305602) and room temperature current suppression (Tyagi et al 2019 Org. Electron. 64 188–194). Our MTJMSD were fabricated below 100 °C temperature and employed earth-abundant transition metals like nickel and iron. This paper shows that the MTJMSD’s photovoltaic effect was susceptible to the magnetic field, temperature, and light intensity. The solar cell efficiency was estimated to be ∼3%. Our MTJMSD approach provides a mass-producible platform for harvesting solar energy and opens a myriad of opportunities to incorporate photogenerated charges for the logic and memory operation in the molecular spintronics devices.

(Invited) Solid Polymer Fuel Cell and Electrolyzer: The Two Sides of Electrochemical Devices in Sustainable Energy Conversion and Storage

The need of sustainable energy sources and converter systems that combine efficiency and reduction of environmental footprint attract increasing interest. This is due to the increasing energy demand over the world (currently of ca. 2 tep per year per inhabitant), which increases the irreversible consumption of the fossil fuels, diseases related to pollutants emissions (NOx, CO) and greenhouse effect (CO2). In this context, fuel cells composed of systems capable of converting directly chemical energy into electrical energy, are receiving special attention mainly due to their ability to generate efficiently electricity and heat. Hydrogen is considered as the ideal energy carrier, which can decrease the carbon footprint. It has an energy density (ca. 33000 Wh kg-1) three times higher than that of gasoline, and during its combustion in a fuel cell, the sole reaction product is water that can be decomposed by electrolysis to obtain again hydrogen and oxygen. Therefore, its utilization in energy conversion (fuel cell) and its production from electrolysis (energy storage) will be addressed during this lecture. Proton exchange membrane fuel cells (PEMFCs) and water electrolyzers (PEMWEs) composed of platinum group metals (PGMs) are now available on the market. But the scarcity of the PGMs requires the development of electrode materials based on earth-abundant transition metals, which is line, for example, with the European roadmap for hydrogen.1 Other molecules such as alcohols and carbohydrates are used as fuels to fabricate autonomous devices that provide low power densities. As an example, the case of glucose is of great interest for cogeneration because the electrochemical process leads to highly functionalized organic molecules into electricity, heat and value-added chemicals. It is furthermore the deliverable form of energy in living organisms and its electrooxidation in physiological media is therefore of upmost importance for numerous medical applications. This lecture will focus on the synthesis of suitable nanomaterials towards each fuel conversion. Various physical characterizations of the prepared materials and their electrochemical analysis permitted to optimize the activity of the electrodes according to their elemental composition and structure. The construction and the electrochemical performances of the direct alcohol fuel cells will be addressed. Complementary analytical techniques were employed to quantify the reaction processes involved in each compartment and to identify the reaction products resulted from the organics combustion. Reference: https://www.fch.europa.eu/sites/default/files/documents/hlg_vision_report_en.pdf Acknowledgements : This work was mainly conducted within the framework of a PhD thesis financially supported by the French National Research Agency (ANR) through ChemBio-Energy, E-air and IMABIC programs. K.B. Kokoh also thanks EDF Company for its financial support.

(Invited) Electronic Structures of Metal Centers in OER Catalyst Models and Electron/Energy Relays in the Excited State Supramolecular Dinuclear Transition Metal Complexes

Electronic Structures of Metal Centers in an OER Catalyst Model. One of the challenges in solar fuels generation is generating multiple redox equivalents for the oxygen evolution reaction (OER) (i.e., 2H2O→O2+4H++4e-) that is a four-electron, four-proton coupled process. Earth-abundant first-row transition metal oxides of cobalt, nickel, and their mixed-metal forms can drive this half-reaction at relatively low overpotentials. In collaboration with Nocera Group, we used a combination of in situ and ex situ X-ray absorption and emission spectroscopies as well as quantum mechanical calculations on OER thin films and their molecular and heterogeneous inorganic analogs. These studies provided insights into the electronic structures of the high-valent states involved in the mechanisms of O-O bond formation and for the high-valent states to drive the bond-forming and bond-breaking steps of OER reactions. Using a Co4O4 cluster as a model for the Co-based OER anode, CoPi, which has a similar topology and can host a stable, but electronically delocalized, mixed-valent Co(IV) state, we employed complementary X-ray spectroscopies, X-ray absorption (XAS) and 1s3p resonant inelastic X-ray scattering (Kβ RIXS), to effectively extract Co(IV) contributions within a spectroscopically active background (Figure 1). Co K- and L-edge X-ray absorption directly probe the 3d-manifold of effectively localized Co(IV), providing a handle on the covalency of the dπ-based redox active molecular orbital (MO) of Co4O4. Kβ RIXS is shown to be highly sensitive to metal cluster oxidation state and oxo-mediated metal-metal coupling in high-valent, delocalized mixed-valent species. We also probed the doubly oxidized Co(III)2(IV)2 state of the Co4O4 cluster, which features a cofacial Co(IV)2 site and is thus a molecular model of the active site in Co-OEC. Electron and Energy Relays in the Excited State Supramolecular Dinuclear Transition Metal Complexes. The rational design of multinuclear transition metal complexes (TMCs) for photochemical catalysis of homogeneous and/or heterogeneous multi-electron reactions (e.g. for producing solar fuels) requires a detailed understanding of the often unique and convoluted excited state charge and energy transfer dynamics in this class of compounds. Using combined optical and X-ray transient spectroscopic measurements, excited state electron electron relays in tetrapyridophenazine-bridged heteroleptic dinuclear Cu(I) bis(phenanthroline) complexes have been investigated as an exemplary system.

Recent Advances in the Design of 3D PGM-Free Molecular Catalysts for ORR

In the past couple of decades great advancements have been made in the development of PGM-free catalysts based on earth-abundant elements, nitrogen, carbon and transition metals (usually Fe or Co), inspired by biological systems such as porphyrins and phthalocyanines.1-6 In order to overcome the poor stability and low catalytic activity of transition-metal complexes, a new class of high temperature-treated (HT-treated) catalysts, composed of the same elements, i.e., a transition metal, carbon and nitrogen, was developed. Although HT-treated PGM-free catalysts exhibit improved activity and stability, their performance remains inferior to PGM catalysts, calling for further improvements to make them a viable alternative to the state-of-the-art materials. In this work, we designed, synthesized and characterized ORR catalysts based on iron, carbon and nitrogen in a well-defined, high surface-area covalent framework (COF) of aerogels. Aerogels are ultralight, porous materials, with ultra-low density and high void volume (> 97%), also known for their unique physicochemical properties such as high porosity, controllable pore size and surface area, low thermal conductivity, just to name a few.7 The variety of precursors used for aerogel synthesis makes them promising candidates for a wide range of applications in catalysts, capacitors, insulators, absorbents, and many more.8-9 In the context of electrocatalysis of fuel cell reactions, carbon-aerogels have been mostly used so far as catalyst supports for PGM and PGM-free catalysts.10-11 In their in form, aerogels can have ultra-high catalytic site density, high surface area, and tunable physical and chemical structures - all very important features for a heterogeneous catalyst. In this talk, we will discuss the synthesis and electrocatalytic properties of an iron-porphyrin aerogel. 5,10,15,20-(tetra-4-aminophenyl)porphyrin (H2TAPP) and Fe(II) were used as the building blocks of the aerogel, which was later heat-treated at 600 °C to enhance electronic conductivity and catalytic activity while preserving its macro-structure. The resulting material has a very high concentration of atomically dispersed catalytic sites (4.01∙1019 sites cm-3), capable of catalyzing the oxygen reduction reaction in alkaline solution (Eonset = 0.93 V vs. RHE, TOF = 0.2 e- site-1 s-1 at 0.8 V vs. RHE). Chen, Z.; Higgins, D.; Yu, A.; Zhang, L.; Zhang, J., A review on non-precious metal electrocatalysts for PEM fuel cells. Energy & Environmental Science 2011, 4 (9), 3167-3192.Zion, N.; Friedman, A.; Levy, N.; Elbaz, L., Bioinspired Electrocatalysis of Oxygen Reduction Reaction in Fuel Cells Using Molecular Catalysts. Advanced Materials 2018, 1800406.Jasinski, R., A new fuel cell cathode catalyst. Nature 1964, 201 (4925), 1212-1213.Levy, N.; Mahammed, A.; Friedman, A.; Gavriel, B.; Gross, Z.; Elbaz, L., Metallocorroles as Non-Precious Metal Electrocatalysts for Highly Efficient Oxygen Reduction in Alkaline Media. ChemCatChem 2016, 8 (17), 2832-2837.Levy, N.; Mahammed, A.; Kosa, M.; Major, D. T.; Gross, Z.; Elbaz, L., Metallocorroles as Nonprecious-Metal Catalysts for Oxygen Reduction. Angew. Chem.-Int. Edit. 2015, 54 (47), 14080-14084.Snitkoff, R. Z.; Levy, N.; Ozery, I.; Ruthstein, S.; Elbaz, L., Imidazole decorated reduced graphene oxide: A biomimetic ligand for selective oxygen reduction electrocatalysis with Metalloporphyrins. Carbon 2019, 143, 223-229.Hrubesh, L. W., Aerogel applications. Journal of Non-Crystalline Solids 1998, 225, 335-342.Mayer, S.; Pekala, R.; Kaschmitter, J., The aerocapacitor: An electrochemical double‐layer energy‐storage device. Journal of the Electrochemical Society 1993, 140 (2), 446-451.Aegerter, M. A.; Leventis, N.; Koebel, M. M., Aerogels handbook. Springer Science & Business Media: 2011.Marie, J.; Berthon-Fabry, S.; Achard, P.; Chatenet, M.; Pradourat, A.; Chainet, E., Highly dispersed platinum on carbon aerogels as supported catalysts for PEM fuel cell-electrodes: comparison of two different synthesis paths. Journal of Non-Crystalline Solids 2004, 350, 88-96.Zhu, C.; Li, H.; Fu, S.; Du, D.; Lin, Y., Highly efficient nonprecious metal catalysts towards oxygen reduction reaction based on three-dimensional porous carbon nanostructures. Chem Soc Rev 2016, 45 (3), 517-531.

Machine-Learning Enabled Search for the Next-Generation Catalyst for Hydrogen Evolution Reaction

As a zero-emission, eco-friendly fuel, hydrogen gas can be generated via electrochemical (EC) water splitting. Achieving high-efficiency water splitting requires the use of a catalyst to minimize the overpotential to drive the hydrogen evolution reaction (HER). Noble metals such as platinum (Pt) can provide an excellent catalytic activity for HER but are too expensive and scarce for broad applications. Therefore, the development of active HER catalysts made from low-cost materials constitutes a crucial challenge in the utilization of hydrogen energy. Earth-abundant transition metal dichalcogenides (TMDs), such as molybdenum disulfide (MoS2), have been discovered recently, which exhibit good activity and stability for electrocatalytic reactions. In order to fully explore the untapped potential of MoS2, the synthesis recipe for MoS2needs to be optimized. Such an optimization process needs scientists to search through a combinatorically large space of experimental parameters, which will be time-consuming and costly if using conventional trial-and-error approaches. In this report, MoS2 HER catalytic activity optimization is performed by examining different combinations of synthesis parameters during the hydrothermal process. To investigate the structure-activity relationship, scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and various electrochemical characterizations have been conducted. A strong correlation between hydrothermal conditions and HER performance matrix has been observed. In order toaccelerate the search for the best synthesis recipe, machine-learning (ML) techniques have been introduced to help identify the optimal parameter combinations for producing MoS2. The hydrothermal parameters with the corresponding onset potentials and Tafel slopes are adopted as prior knowledge and are incorporated into the Bayesian Optimization model. The model will be able to guide the wet chemical synthesis of MoS2and yield the most effective HER catalyst eventually.

Orthorhombic WP co-catalyst coupled with electron transfer bridge UiO-66 for efficient visible-light-driven H2 evolution

The abundant transition metal phosphides co-catalysts on the earth can satisfy the sustainable and clean solar H2 production through photocatalytic water splitting, which is promising to replace the rare precious metals, such as Pt, Au, Pd, Ru and so on. In this paper, we use the temperature-programmed solid phase method to prepare WP nanoparticles. Based on the Density Functional Theory (DFT) calculations, we demonstrate that the WP nanoparticles possess outstanding electrical conductivity and excellent capability to transport electrons. WP nanoparticles are loaded onto the surface of UiO-66 via the ultrasound-assisted impregnation method to induce a highly efficient visible-light photocatalytic H2 production activity of 384 µmol in 5 h, which is 10.67 times than that of pure UiO-66. The catalytic performance is attributed to the excellent metallic conductivity and the favourable Fermi level position of WP nanoparticles. Further studies of PL, TRPL and Mott-Schottky curves, we can not only know that the modification of WP nanoparticles do improve the electron transfer ability, but also that the matched work functions between the EY and UiO-66 provides a feasible thermodynamic path for the transmission of electrons. Our work demonstrates that the earth-abundant transition metal phosphides material have the potential to construct cheaper and high catalytic performance photocatalysts.

Bioinspired Manganese and Iron Complexes for Enantioselective Oxidation Reactions: Ligand Design, Catalytic Activity, and Beyond

The development of efficient methods for the enantioselective oxidation of organic molecules continues to be an important goal in organic synthesis; in particular, the use of earth-abundant metal catalysts and environmentally friendly oxidants in catalytic asymmetric oxidation reactions has attracted significant interest over the last several decades. In nature, metalloenzymes catalyze a wide range of oxidation reactions by activating dioxygen under mild conditions. Inspired by selective and efficient oxidation reactions catalyzed by metalloenzymes, researchers have developed a number of synthetic model compounds that mimic the functionality of metalloenzymes. Among the reported biomimetic model compounds, tetradentate aminopyridine (N4) ligands have emerged as appealing frameworks because of their easy synthesis and facile diversification, and their complexes with metals such as Fe and Mn have proven to be versatile and powerful catalysts for a variety of (enantioselective) oxidation reactions. In this Account, we describe our efforts on the design of chiral N4 ligands and the use of their manganese and iron complexes in asymmetric oxidation reactions with H2O2 as the terminal oxidant, aiming to show general strategies for asymmetric oxidation reactions that can guide the rational design of ligands and relevant metal catalysts. In studies of manganese catalysts, the aryl-substituted (R,R)-mcp [mcp = N,N'-dimethyl-N,N'-bis(pyridine-2-ylmethyl)cyclohexane-1,2-diamine] manganese complexes exhibited high enantioselectivity in the asymmetric epoxidation (AE) of various olefins with H2O2 while requiring stoichiometric acetic acid as an additive for the activation of H2O2. To address this issue, we established bulkier N4 ligands for this catalytic system in which a catalytic amount of sulfuric acid enables the manganese-complex-catalyzed AE with improved stereocontrol and efficiency. In addition, this system was found to be active for the oxidative kinetic resolution of secondary alcohols. Further exploration of the structure-reactivity relationships has shown that aminobenzimidazole N4 ligands derived from l-proline, in which the conventional pyridine donors are replaced by benzimidazoles, act as promising ligands. These novel C1-symmetric manganese catalysts showed dramatically improved activities with unprecedented turnover numbers in the AE reactions. Notably, this class of manganese complexes can catalyze the oxidation of the C-H bonds of spirocyclic hydrocarbons and spiroazacyclic compounds in a highly enantioselective manner, providing ready access to chiral spirocyclic β,β'-diketones and spirocyclic alcohols. Remarkably, iron catalysts with these chiral N4 ligands are effective for AE of olefins, enabling rare examples of highly enantioselective syntheses of epoxides by the iron catalysts. Finally, mechanistic studies provide valuable insights into the roles of the carboxylic acid and sulfuric acid in the catalytic oxidation reactions. Thus, the results described in this Account have demonstrated the importance of tunability and compatibility of the ligands for the development of efficient oxidation catalysts with earth-abundant transition metals and environmentally benign oxidants, and we hope that our study will pave the way for the discovery of efficient oxidation catalysis.

Enantioselective C-H Activation with Earth-Abundant 3d Transition Metals.

Molecular syntheses largely rely on time- and labour-intensive prefunctionalization strategies. In contrast, C-H activation represents an increasingly powerful approach that avoids lengthy syntheses of prefunctionalized substrates, with great potential for drug discovery, the pharmaceutical industry, material sciences, and crop protection, among others. The enantioselective functionalization of omnipresent C-H bonds has emerged as a transformative tool for the step- and atom-economical generation of chiral molecular complexity. However, this rapidly growing research area remains dominated by noble transition metals, prominently featuring toxic palladium, iridium and rhodium catalysts. Indeed, despite significant achievements, the use of inexpensive and sustainable 3d metals in asymmetric C-H activations is still clearly in its infancy. Herein, we discuss the remarkable recent progress in enantioselective transformations via organometallic C-H activation by 3d base metals up to April 2019.

Harnessing Native Iron Ore as an Efficient Electrocatalyst for Overall Water Splitting

AbstractElectrochemical water splitting is a widely accepted approach to generate hydrogen at a scale that is suitable for storing renewable energy. Therefore, the choice of catalyst for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are critical in terms of cost when scaling up this technology. Thus, earth abundant transition metals oxides and sulfides have received significant attention as catalysts for the OER and HER, respectively. However, very few examples of actual Earth abundant materials mined from the Earth's crust have been used as electrocatalysts for these reactions. Here, we demonstrate that a raw iron ore is active for both the HER and OER under alkaline conditions, which is due to the natural abundance of the key elements of iron, nickel, and sulfur. The catalyst is stable for both reactions and can operate at 100 mA cm−2, which is comparable to many chemically synthesised nanomaterials based on these elements. This approach may be attractive for adding value to iron ore while minimising the cost of catalyst production.

Secondary-Sphere Effects in Molecular Electrocatalytic CO2 Reduction.

The generation of fuels and value-added chemicals from carbon dioxide (CO2) using electrocatalysis is a promising approach to the eventual large-scale utilization of intermittent renewable energy sources. To mediate kinetically and thermodynamically challenging transformations of CO2, early reports of molecular catalysts focused primarily on precious metal centers. However, through careful ligand design, earth-abundant first-row transition metals have also demonstrated activity and selectivity for electrocatalytic CO2 reduction. A particularly effective and promising approach for enhancement of reaction rates and efficiencies of molecular electrocatalysts for CO2 reduction is the modulation of the secondary coordination sphere of the active site. In practice, this has been achieved through the mimicry of enzyme structures: incorporating pendent Brønsted acid/base sites, charged residues, sterically hindered environments, and bimetallic active sites have all proved to be valid strategies for iterative optimization. Herein, the development of secondary-sphere strategies to facilitate rapid and selective CO2 reduction is reviewed with an in-depth examination of the classic [Fe(tetraphenylporphyrin)]+, [Ni(cyclam)]2+, Mn(bpy)(CO)3X, and Re(bpy)(CO)3X (X = solvent or halide) systems, including relevant highlights from other recently developed ligand platforms.

Tuning and Mechanistic Insights of Metal Chalcogenide Molecular Catalysts for the Hydrogen-Evolution Reaction

The production of hydrogen through water splitting using earth-abundant metal catalysts is a promising pathway for converting solar energy into chemical fuels. However, existing approaches for fine stoichiometric control, structural and catalytic modification of materials by appropriate choice of earth abundant elements are either limited or challenging. One promising strategy is the design of molybdenum sulfide nanoclusters which mimic the catalytically active sites found in MoS2. These molecules have the unique property of exposing a high degree of active edge sites leading to improved catalytic activity. Here, we explore the implementation of new design principles for the development of efficient molecular HER catalysts. In this work, we prepared [Mo2O2(µ-S)2(S2)2]2– (1) , [Mo2O2(µ-S)2(S2)(S4)]2– (2) and [W2O2(µ-S)2(S2)(S4)]2– (3) by wet-chemical methods and investigated their HER electroactivity. Specifically, we aim to investigate the effects of stoichiometric and structural control resulting from the appropriate choice of the chalcogen elements and their ratio (e.g. O2-/S2 2-, O2-/S2 2-/S4 2-) within the coordination sphere of earth abundant transition metals (e.g. Mo or W). We evaluate the performance of these molecular catalysts for the hydrogen evolution reaction while we propose potential mechanistic pathways in relation to the interaction between catalysts and substrate. The employed design principles offer the opportunity to bridge the gap between molecular and solid-state heterogeneous catalysts when immobilized on a carbon electrode surface. These molecular species represent an exciting class of low-cost earth-abundant materials and display great promise as HER electrocatalysts. Both molybdenum-based catalysts were shown to be exceptionally active towards the HER, with a reported overpotential of just –114 3 mV (at j = 10 mA cm–2) and no catalyst degradation over 1000 cycles. Density functional calculations reveal the effect of the electronic and structural features and confer plausibility to the existence of a unimolecular mechanism in the HER process based on the tested hypotheses. We anticipate these findings to be a starting point for further exploration of molecular catalytic systems. Figure 1

(Invited) Earth-Abundant Transition Metal Single Atom Electrocatalysts for Selective CO2 Reduction in Water

The development of highly selective and earth-abundant electrocatalysts for CO2 reduction is becoming increasingly important for renewable energy applications. The challenge here is the strong competition from water reduction, as well as the low selectivity towards a desired product. In this talk I will introduce the rational tuning of electronic properties of catalytic materials for their significantly improved CO2 reduction performance. By dispersing transition metals into isolated single atoms with electronic structures significantly different from their bulk counterparts, we can dramatically suppress the competing hydrogen evolution and deliver an ultra-high CO2 reduction selectivity of more than 99% under ambient conditions in water.

Hierarchical cobalt phosphide hollow nanoboxes as high performance bifunctional electrocatalysts for overall water splitting

Developing earth-abundant and low-cost transition metal electrocatalysts for overall water splitting is crucial for renewable and sustainable energy technologies. Metal-organic frameworks (MOFs) are one of the most promising precursors for developing efficient and inexpensive catalysts with the large surface area and the abundant porosity. Herein, a new type of hierarchical CoP hollow nanoboxes (CoP NB) is fabricated for overall water splitting. Benefiting from the unique structural features including large specific surface area which can provides numerous active sites, abundant mass diffusion pathways, and the hierarchical and hollow structures, the as-synthesized CoP NB exhibit high activity and superior stability in alkaline media toward hydrogen and oxygen evolution reactions with low overpotentials of 101 mV and 240 mV, respectively, when the current density reaches 10 mA cm−2. Remarkably, when a two-electrode water electrolyzer used CoP NB as both the anode and cathode, a low cell voltage of 1.58 V is sufficiently to afford 10 mA cm−2. Moreover, this electrolyzer can be powered by a single AA battery, making the CoP NB an efficient bifunctional electrocatalyst for overall water splitting. Such good performance is attributed to the high intrinsic activity and superior structural stability. This work offers new prospects for the rational design and synthesis of efficient bifunctional electrocatalysts for application in electrochemical energy devices.

Phosphine-Free Well-Defined Mn(I) Complex-Catalyzed Synthesis of Amine, Imine, and 2,3-Dihydro-1H-perimidine via Hydrogen Autotransfer or Acceptorless Dehydrogenative Coupling of Amine and Alcohol

The application of nontoxic, earth-abundant transition metals in place of costly noble metals is a paramount goal in catalysis and is especially interesting if the air- and moisture-stable ligand s...

Flower-like nickel-cobalt oxide nanomaterials as bi-functional catalyst for electrochemical water splitting

Herein, we demonstrate a highly efficient and stable bi-functional electrode based on flower-like hierarchical nanoporous nickel-cobalt oxide (NP-NiCo2O4) material for electrochemical water splitting reactions. The as-synthesized spinel crystalline nanoporous-NiCo2O4 material enables improved electrocatalytic activity towards both water oxidation and reduction by taking the advantageous of hierarchical nanoporous structure, improved active sites, and electrochemical active surface area, high charge-transfer kinetics and structural durability. The bi-functional NiCo2O4 electrode exhibits augmented current densities and electrode durability with a high mass activity and low overpotential in overall water splitting in alkaline solution, comparable with most of the previously reported Earth-abundant transition metal oxide based catalysts. Based on our discovery in the present investigation we suggest that the flower-like hierarchical nanoporous NiCo2O4 Earth-abundant transition metal oxide electrode would certainly function as a new class of nanomaterials for competent electrochemical bi-functional water splitting catalysts.

Substrate participation ultrafast synthesis of amorphous NiFe nanosheets on iron foam at room temperature toward highly efficient oxygen evolution reaction

Abstract The earth-abundant transition metal based nanomaterials are regarded as state-of-the-art oxygen evolution reaction (OER) electrocatalyst. Recent studies have shown that amorphous materials are more active than their crystalline forms. Herein, we demonstrate a facile and rapid substrate participation method to fabricate amorphous NiFe nanosheets on iron foam (a-NiFe NS/IF) at ambient temperature as a highly efficient electrocatalyst for OER. This method only takes 200 s to fabricate the a-NiFe NS/IF and the electrocatalyst possesses excellent catalytic activities which only needs overpotentials of about 211 and 240 mV to reach 10 and 100 mA cm−2 current densities in 1.0 M KOH.

Mo-doped boron nitride monolayer as a promising single-atom electrocatalyst for CO2 conversion.

The design of new, efficient catalysts for the conversion of CO2 to useful fuels under mild conditions is urgent in order to reduce greenhouse gas emissions and alleviate the energy crisis. In this work, a series of transition metals (TMs), including Sc to Zn, Mo, Ru, Rh, Pd and Ag, supported on a boron nitride (BN) monolayer with boron vacancies, were investigated as electrocatalysts for the CO2 reduction reaction (CRR) using comprehensive density functional theory (DFT) calculations. The results demonstrate that a single-Mo-atom-doped boron nitride (Mo-doped BN) monolayer possesses excellent performance for converting CO2 to CH4 with a relatively low limiting potential of −0.45 V, which is lower than most catalysts for the selective production of CH4 as found in both theoretical and experimental studies. In addition, the formation of OCHO on the Mo-doped BN monolayer in the early hydrogenation steps is found to be spontaneous, which is distinct from the conventional catalysts. Mo, as a non-noble element, presents excellent catalytic performance with coordination to the BN monolayer, and is thus a promising transition metal for catalyzing CRR. This work not only provides insight into the mechanism of CRR on the single-atom catalyst (Mo-doped BN monolayer) at the atomic level, but also offers guidance in the search for appropriate earth-abundant TMs as electrochemical catalysts for the efficient conversion of CO2 to useful fuels under ambient conditions.

Morphology-Controlled Metal Sulfides and Phosphides for Electrochemical Water Splitting.

Because H2 is considered a promising clean energy source, water electrolysis has attracted great interest in related research and technology. Noble-metal-based catalysts are used as electrode materials in water electrolyzers, but their high cost and low abundance have impeded them from being used in practical areas. Recently, metal sulfides and phosphides based on earth-abundant transition metals have emerged as promising candidates for efficient water-splitting catalysts. Most studies have focused on adjusting the composition of the metal sulfides and phosphides to enhance the catalytic performance. However, morphology control of catalysts, including faceted and hollow structures, is much less explored for these systems because of difficulties in the synthesis, which requires a deep understanding of the nanocrystal growth process. Herein, representative synthetic methods for morphology-controlled metal sulfides and phosphides are introduced to provide insights into these methodologies. The electrolytic performance of morphology-controlled metal sulfide- and phosphide-based nanocatalysts with enhanced surface area and intrinsically high catalytic activity is also summarized and the future research directions for this promising catalyst group is discussed.