Three-dimensional hierarchical Co(OH)F nanosheet arrays decorated by single-atom Ru for boosting oxygen evolution reaction

Electronic coupling with the support plays a crucial role in boosting the intrinsic catalytic activity of a single-atom catalyst. Herein, the three-dimensional (3D) hierarchical Co(OH)F nanosheet arrays modified by singleatom Ru (SA-Ru/Co(OH)F) are prepared by a facile one-step hydrothermal method under mild conditions, which exhibit excellent activity with an overpotential of 200 and 326 mV at 10 and 500 mA cm(-2), respectively, as well as robust stability for oxygen evolution reaction (OER) in 1.0 mol L-1 KOH electrolyte. The study of electronic structures and surface chemical states before and after OER testing reveals that the strong electronic coupling between single-atom Ru and Co(OH)F induces the charge redistribution in SA-Ru/Co(OH)F and suppresses the excessive oxidation of Ru into higher valence state (more than +4) under high OER potential. This work provides a strategy to stabilize single-atom Ru by Co(OH)F that can enhance the activity and durability for OER under large current densities

Oxygen-deficient SnO2 nanoparticles with ultrathin carbon shell for efficient electrocatalytic N2 reduction

For high-efficiency NH3 synthesis via ambient-condition electrohydrogenation of inert N2, it is pivotal to ingeniously design an active electrocatalyst with multiple features of abundant surfacial deficiency, good conductivity and large surface area. Here, oxygen-deficient SnO2 nanoparticles encapsulated by ultrathin carbon layer (d-SnO2@C) are developed by hydrothermal deposition coupled with annealing process, as promising catalysts for ambient electrocatalytic N2 reduction. d-SnO2@C exhibits high activity and excellent selectivity for electrocatalytic conversion of N2 to NH3 in acidic electrolytes, with Faradic efficiency as high as 12.7% at ???0.15 V versus the reversible hydrogen electrode (RHE) and large NH3 yield rate of 16.68 ??g h???1 mgcat???1 at ???0.25 V vs. RHE in 0.1 mol L???1 HCl. Benefiting from the structural superiority of enhanced charge transfer efficiency and optimized surface states, d-SnO2@C also achieves excellent long-term stability

Exploring the Dominant Role of Atomic- and Nano-Ruthenium as Active Sites for Hydrogen Evolution Reaction in Both Acidic and Alkaline Media

Ru nanoparticles (NPs) and single atoms (SAs)-based materials have been investigated as alternative electrocatalysts to Pt/C for hydrogen evolution reaction (HER). Exploring the dominant role of atomic- and nano-ruthenium as active sites in acidic and alkaline media is very necessary for optimizing the performance. Herein, an electrocatalyst containing both Ru SAs and NPs anchored on defective carbon (RuSA+NP/DC) has been synthesized via a Ru-alginate metal-organic supramolecules conversion method. RuSA+NP/DC exhibits low overpotentials of 16.6 and 18.8 mV at 10 mA cm(-2) in acidic and alkaline electrolytes, respectively. Notably, its mass activities are dramatically improved, which are about 1.1 and 2.4 times those of Pt/C at an overpotential of 50 mV in acidic and alkaline media, respectively. Theoretical calculations reveal that Ru SAs own the most appropriate H* adsorption strength and thus, plays a dominant role for HER in acid electrolyte, while Ru NPs facilitate the dissociation of H2O that is the rate-determining step in alkaline electrolyte, leading to a remarkable HER activity

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School of Energy and Chemical Engineering (Battery Science and Technology)clos

Data-driven Nonlinear Parametric Model Order Reduction Framework using Deep Hierarchical Variational Autoencoder

A data-driven parametric model order reduction (MOR) method using a deep artificial neural network is proposed. The present network, which is the least-squares hierarchical variational autoencoder (LSH-VAE), is capable of performing nonlinear MOR for the parametric interpolation of a nonlinear dynamic system with a significant number of degrees of freedom. LSH-VAE exploits two major changes to the existing networks: a hierarchical deep structure and a hybrid weighted, probabilistic loss function. The enhancements result in a significantly improved accuracy and stability compared against the conventional nonlinear MOR methods, autoencoder, and variational autoencoder. Upon LSH-VAE, a parametric MOR framework is presented based on the spherically linear interpolation of the latent manifold. The present framework is validated and evaluated on three nonlinear and multiphysics dynamic systems. First, the present framework is evaluated on the fluid-structure interaction benchmark problem to assess its efficiency and accuracy. Then, a highly nonlinear aeroelastic phenomenon, limit cycle oscillation, is analyzed. Finally, the present framework is applied to a three-dimensional fluid flow to demonstrate its capability of efficiently analyzing a significantly large number of degrees of freedom. The performance of LSH-VAE is emphasized by comparing its results against that of the widely used nonlinear MOR methods, convolutional autoencoder, and $\beta$-VAE. The present framework exhibits a significantly enhanced accuracy to the conventional methods while still exhibiting a large speed-up factor

Building High-Rate Nickel-Rich Cathodes by Self-Organization of Structurally Stable Macrovoid

Nickel-rich materials, as a front-running cathode for lithium-ion batteries suffer from inherent degradation issues such as inter/intragranular cracks and phase transition under the high-current density condition. Although vigorous efforts have mitigated these current issues, the practical applications are not successfully achieved due to the material instability and complex synthesis process. Herein, a structurally stable, macrovoid-containing, nickel-rich material is developed using an affordable, scalable, and one-pot coprecipitation method without using surfactants/etching agents/complex-ion forming agents. The strategically developed macrovoid-induced cathode via a self-organization process exhibits excellent full-cell rate capability, cycle life at discharge rate of 5 C, and structural stability even at the industrial electrode conditions, owing to the fast Li-ion diffusion, the internal macrovoid acting as "buffer zones" for stress relief, and highly stable nanostructure around the void during cycling. This strategy for nickel-rich cathodes can be viable for industries in the preparation of high-performance lithium-ion cells

Fe, Al-co-doped NiSe(2)nanoparticles on reduced graphene oxide as an efficient bifunctional electrocatalyst for overall water splitting

Developing low-cost and highly efficient electrocatalysts for overall water splitting is of far-reaching significance for new energy conversion. Herein, dual-cation Fe, Al-co-doped NiSe(2)nanoparticles on reduced graphene oxide (Fe, Al-NiSe2/rGO) were prepared as a bifunctional electrocatalyst for overall water splitting. The dual-cation doping can induce a stronger electronic interaction between the foreign atoms and host catalyst, for optimizing the adsorption energy of reaction intermediates. Meanwhile, the leaching out of Al from the crystal structure of the target product during the alkaline wash creates more defects and increases the active site exposure. As a result, the Fe, Al-NiSe2/rGO catalyst exhibits excellent catalytic activities for both the OER and HER with an overpotential of 272 mV @eta(10)for the OER in 1.0 M KOH and 197 mV @eta(10)for the HER in 0.5 M H2SO4, respectively. A two-electrode electrolyzer using Fe, Al-NiSe2/rGO as the anode and cathode shows a low voltage of 1.70 V at the current density of 10 mA cm(-2). This study emphasizes the synergistic contribution of the dual-cation co-doping effect and more defects created by Al leaching to boost the performance of water splitting

Ru-incorporated oxygen-vacancy-enriched MoO2 electrocatalysts for hydrogen evolution reaction

Designing highly efficient Pt-free electrocatalysts with low overpotential for the alkaline hydrogen evolution reaction (HER) remains a significant challenge. In this paper, we successfully construct Ru-incorporated oxygen-vacancy-enriched MoO2 nanosheets (Ru/MoO2_x) for the HER through a "one stone two birds " strategy. This strategy can solve two urgent problems simultaneously, the intrinsic electrochemical activity of original MoO(2 )is far from satisfactory and the H2O adsorption/dissociation abilities of Ru are weak. Specifically, the oxygen-vacancy-enriched MoO3 serves as an excellent platform for anchoring and trapping Ru ions. In-depth analyses indicate that the incorporation of Ru nanoclusters induces transition from MoO3 to MoO2, generates oxygen vacancies, and creates Ru-O-Mo sites. The synergistic effect of Ru nanoclusters, Ru-O-Mo sites and oxygen-vacancy-enriched MoO2 will endow the obtained catalyst excellent electrocatalytic activity. In particular, the optimal Ru/MoO2_x electrocatalyst delivered a low overpotential of 29 mV at 10 mA cm(_2) in a basic electrolyte

FexNiy/CeO2 loaded on N-doped nanocarbon as an advanced bifunctional electrocatalyst for the overall water splitting

Developing a highly efficient and cost-effective electrocatalyst for catalyzing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is fundamentally important for the practical application of the overall water splitting technique. Herein, a bifunctional electrocatalyst constituted by FexNiy and CeO2 nanoparticles supported on the N-doped nanocarbon (NC) is fabricated by a simple one-pot pyrolysis of the homogeneous mixture of Fe, Ni, Ce nitrates and melamine. The synergistic effect of each component in the FexNiy/CeO2/NC gives rise to outstanding electrocatalytic activities and stability toward the HER and OER. For hydrogen evolution, the FexNiy/CeO2/NC shows a smaller overpotential of 260 mV to achieve a current density of 50 mA cm(-2) in a 1 M KOH electrolyte. More significantly, a small overpotential of 240 mV for FexNiy/CeO2/NC affords an oxygen evolution current density of 10 mA cm(-2), far lower than that of the benchmark IrO2. The practicability and electrocatalytic activity of the prepared FexNiy/CeO2/NC under practical operation conditions are also investigated. In particular, the FexNiy/CeO2/NC-based overall water splitting cell only needs a cell voltage of 1.70 V to output 10 mA cm(-2) in alkaline electrolytes, comparable to that of the IrO2 parallel to Pt/C cell. The present study may pioneer a new avenue for developing novel bifunctional electrocatalysts with high-performance and low cost for water splitting

Coupling a Low Loading of IrP 2 , PtP 2 , or Pd 3 P with Heteroatom-Doped Nanocarbon for Overall Water-Splitting Cells and Zinc-Air Batteries

Noble metal-based catalysts are currently the most advanced electrocatalysts for many applications, such as for energy conversion and for chemical industry. Because of the high cost and scarcity of noble metals, reducing the usage is a practical way to achieve scalable applications. Herein, for the first time, three novel electrocatalysts composed of noble metal phosphide (IrP 2 , Pd 3 P, or PtP 2 ) nanoparticles with N,P-codoped nanocarbon were synthesized by the pyrolysis of mixtures of IrCl 4 , PdCl 2 , or PtCl 4 with phytic acid under an ammonia atmosphere. With an ultralow loading of Pd (1.5 ??g), Pt (1.4 ??g), or Ir (1.6 ??g) on the electrode, the Pd 3 P/NPC, PtP 2 /NPC, and IrP 2 /NPC catalysts, respectively, exhibited excellent trifunctional catalytic activities for the oxygen reduction reaction, hydrogen evolution reaction, and oxygen evolution reaction. Notably, the IrP 2 /NPC-, Pd 3 P/NPC-, and PtP 2 /NPC-based water-splitting cells required only 1.62, 1.65, and 1.68 V, respectively, to deliver the current density of 10 mA cm -2 . Furthermore, the IrP 2 /NPC-, Pd 3 P/NPC-, and PtP 2 /NPC-based zinc-air batteries exhibited higher specific capacities than that of Pt/C. IrP 2 /NPC exhibited a comparable performance to that of Pt/C-IrO 2 for use in rechargeable zinc-air batteries