Anthony Vasileff

Molecule-level g-C3N4 coordinated transition metals as a new class of electrocatalysts for oxygen electrode reactions

Organometallic complexes with metal-nitrogen/carbon (M-N/C) coordination are the most important alternatives to precious metal catalysts for oxygen reduction and evolution reactions (ORR and OER) in energy conversion devices. Here, we designed and developed a range of molecule-level graphitic carbon nitride (g-C3N4) coordinated transition metals (M-C3N4) as a new generation of M-N/C catalysts for these oxygen electrode reactions. As a proof-of-concept example, we conducted theoretical evaluation and experimental validation on a cobalt-C3N4 catalyst with a desired molecular configuration, which possesses comparable electrocatalytic activity to that of precious metal benchmarks for the ORR and OER in alkaline media. The correlation of experimental and computational results confirms that this high activity originates from the precise M-N2 coordination in the g-C3N4 matrix. Moreover, the reversible ORR/OER activity trend for a wide variety of M-C3N4 complexes has been constructed to provide guidance for the molecular design of this promising class of catalysts.

Anion and Cation Modulation in Metal Compounds for Bifunctional Overall Water Splitting

As substitutes for precious cathodic Pt/C and anodic IrO2 in electrolytic water splitting cells, a bifunctional catalyst electrode (Fe- and O-doped Co2P grown on nickel foam) has been fabricated by manipulating the cations and anions of metal compounds. The modified catalyst electrode exhibits both superior HER and OER performances with high activity, favorable kinetics, and outstanding durability. The overall ability toward water splitting is especially extraordinary, requiring a small overpotential of 333.5 mV to gain a 10 mA cm(-2) current density. A study on the electrocatalytic mechanism reveals that the atomic modulation between cation and anion plays an important role in optimizing the electrocatalytic activity, which greatly expands the active sites in the electrocatalyst. Further, the three-dimensional conductive porous network is highly advantageous for the exposure of active species, the transport of bubble products, and the transfer of electrons and charges, which substantially boosts reaction kinetics and structure stability.

Recent Advances in Atomic Metal Doping of Carbon‐based Nanomaterials for Energy Conversion

Nanostructured metal-contained catalysts are one of the most widely used types of catalysts applied to facilitate some of sluggish electrochemical reactions. However, the high activity of these catalysts cannot be sustained over a variety of pH ranges. In an effort to develop highly active and stable metal-contained catalysts, various approaches have been pursued with an emphasis on metal particle size reduction and doping on carbon-based supports. These techniques enhances the metal-support interactions, originating from the chemical bonding effect between the metal dopants and carbon support and the associated interface, as well as the charge transfer between the atomic metal species and carbon framework. This provides an opportunity to tune the well-defined metal active centers and optimize their activity, selectivity and stability of this type of (electro)catalyst. Herein, recent advances in synthesis strategies, characterization and catalytic performance of single atom metal dopants on carbon-based nanomaterials are highlighted with attempts to understand the electronic structure and spatial arrangement of individual atoms as well as their interaction with the supports. Applications of these new materials in a wide range of potential electrocatalytic processes in renewable energy conversion systems are also discussed with emphasis on future directions in this active field of research.

Rational design of electrocatalysts and photo(electro)catalysts for nitrogen reduction to ammonia (NH3) under ambient conditions

As one of the most important chemicals and carbon-free energy carriers, ammonia (NH3) has a worldwide annual production of ∼150 million tons, and is mainly produced by the traditional high-temperature and high-pressure Haber–Bosch process which consumes massive amounts of energy. Very recently, electrocatalytic and photo(electro)catalytic reduction of N2 to NH3, which can be performed at ambient conditions using renewable energy, have received tremendous attention. The overall performance of these electrocatalytic and photo(electro)catalytic systems is largely dictated by their core components, catalysts. This perspective for the first time highlights the rational design of electrocatalysts and photo(electro)catalysts for N2 reduction to NH3 under ambient conditions. Fundamental theory of catalytic reaction pathways for the N2 reduction reaction and the corresponding material design principles are introduced first. Then, recently developed electrocatalysts and photo(electro)catalysts are summarized, with a special emphasis on the relationship between their physicochemical properties and NH3 production performance. Finally, the opportunities in this emerging research field, in particular, the strategy of combining experimental and theoretical techniques to design efficient and stable catalysts for NH3 production, are outlined.

Size Fractionation of Two-Dimensional Sub-Nanometer Thin Manganese Dioxide Crystals towards Superior Urea Electrocatalytic Conversion.

A universal technique has been proposed to sort two-dimensional (2D) sub-nanometer thin crystals (manganese dioxide MnO2 and molybdenum disulfide MoS2 ) according to their lateral dimensions. This technique is based on tuning the zeta potential of their aqueous dispersions which induces the selective sedimentation of large-sized 2D crystals and leaves the small-sized counterparts in suspension. The electrocatalytic properties of as-obtained 2D ultrathin crystals are strongly dependent on their lateral size. As a proof-of-concept study, the small-sized MnO2 nanocrystals were tested as the electrocatalysts for the urea-oxidation reaction (UOR), which showed outstanding performance in both half reaction and full electrolytic cell. A mechanism study reveals the enhanced performance is associated with the remarkable structural properties of MnO2 including ultrathin (ca. 0.95 nm), laterally small-sized (50-200 nm), and highly exposed active centers.

Emerging Two-Dimensional Nanomaterials for Electrocatalysis

Over the past few decades, the design and development of advanced electrocatalysts for efficient energy conversion technologies have been subjects of extensive study. With the discovery of graphene, two-dimensional (2D) nanomaterials have emerged as some of the most promising candidates for heterogeneous electrocatalysts due to their unique physical, chemical, and electronic properties. Here, we review 2D-nanomaterial-based electrocatalysts for selected electrocatalytic processes. We first discuss the unique advances in 2D electrocatalysts based on different compositions and functions followed by specific design principles. Following this overview, we discuss various 2D electrocatalysts for electrocatalytic processes involved in the water cycle, carbon cycle, and nitrogen cycle from their fundamental conception to their functional application. We place a significant emphasis on different engineering strategies for 2D nanomaterials and the influence these strategies have on intrinsic material performance, such as electronic properties and adsorption energetics. Finally, we feature the opportunities and challenges ahead for 2D nanomaterials as efficient electrocatalysts. By considering theoretical calculations, surface characterization, and electrochemical tests, we describe the fundamental relationships between electronic structure, adsorption energy, and apparent activity for a wide variety of 2D electrocatalysts with the goal of providing a better understanding of these emerging nanomaterials at the atomic level.

The Hydrogen Evolution Reaction in Alkaline Solution: From Theory, Single Crystal Models, to Practical Electrocatalysts

The hydrogen evolution reaction (HER) is a fundamental process in electrocatalysis and plays an important role in energy conversion for the development of hydrogen-based energy sources. However, the considerably slow rate of the HER in alkaline conditions has hindered advances in water splitting techniques for high-purity hydrogen production. Differing from well documented acidic HER, the mechanistic aspects of alkaline HER are yet to be settled. A critical appraisal of alkaline HER electrocatalysis is presented, with a special emphasis on the connection between fundamental surface electrochemistry on single-crystal models and the derived molecular design principle for real-world electrocatalysts. By presenting some typical examples across theoretical calculations, surface characterization, and electrochemical experiments, we try to address some key ongoing debates to deliver a better understanding of alkaline HER at the atomic level.

Three dimensional nitrogen-doped graphene hydrogels with in situ deposited cobalt phosphate nanoclusters for efficient oxygen evolution in a neutral electrolyte

A hybrid electrode of cobalt phosphate (CoPi) on nitrogen doped graphene hydrogels was fabricated by hydrothermal treatment of graphene oxide followed by CoPi electrodeposited in situ, which showed excellent performance toward oxygen reaction in a neutral electrolyte.

Hierarchical 1T-MoS2 nanotubular structures for enhanced supercapacitive performance

Layered transition metal disulfides are currently being widely studied for advanced energy generation and storage applications. Here we report a facile template-assisted solvothermal strategy to obtain a hierarchical nanotubular structure consisting of ultrathin MoS2 nanosheets with a metallic 1T phase. Synchrotron radiation based X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) are used to investigate the structure and electronic properties of the 1T-MoS2, which are largely different from annealed samples. Its hierarchical structure makes the obtained nanotubular 1T-MoS2 an excellent electrode material for supercapacitors, with a high specific capacitance of 328.547 F g−1 at a current density of 1 A g−1 and 243.66 F g−1 at a current density of 15 A g−1. Moreover, the material displays excellent capacitance retention, retaining 98.4% capacity after 5000 cycles at a current density of 3 A g−1. Notably, a high specific capacitance of 250 F g−1 at 1 A g−1 is also achieved in a two-electrode symmetrical cell, suggesting its great potential for new-generation supercapacitors.

NiO as a Bifunctional Promoter for RuO2 toward Superior Overall Water Splitting

Conventional development of nanomaterials for efficient electrocatalysis is largely based on performance-oriented trial-and-error/iterative approaches, while a rational design approach at the atomic/molecular level is yet to be found. Here, inspired by a fundamental understanding of the mechanism for both oxygen and hydrogen evolution half reactions (OER/HER), a unique strategy is presented to engineer RuO2 for superior alkaline water electrolysis through coupling with NiO as an efficient bifunctional promoter. Benefitting from desired potential-induced interfacial synergies, NiO-derived NiOOH improves the oxygen binding energy of RuO2 for enhanced OER, and NiO also promotes water dissociation for enhanced HER on RuO2 -derived Ru. The resulting hybrid material exhibits remarkable bifunctional activities, affording 2.6 times higher OER activity than that of RuO2 and an HER activity comparable to Pt/C. As a result, the simple system requires only 1.5 V to deliver 10 mA cm-2 for overall alkaline water splitting, outperforming the benchmark PtC/NF||IrO2 /NF couple with high mass loading. Comprehensive electrochemical investigation reveals the unique and critical role of NiO on the optimized RuO2 /NiO interface for synergistically enhanced activities, which may be extended to broader (electro)catalytic systems.