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Journal ArticleDOI

Atomic-Step Enriched Ruthenium–Iridium Nanocrystals Anchored Homogeneously on MOF-Derived Support for Efficient and Stable Oxygen Evolution in Acidic and Neutral Media

TL;DR: In this article, an efficient and stable oxygen evolution reaction (OER) in an acidic or neutral medium is of paramount importance for hydrogen production via proton exchange membrane water electrolysis (PEWEM).
Abstract: Achieving an efficient and stable oxygen evolution reaction (OER) in an acidic or neutral medium is of paramount importance for hydrogen production via proton exchange membrane water electrolysis (...
Citations
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Journal ArticleDOI
TL;DR: RuO2/(Co,Mn)3O4 nanocomposite with low Ru loading (2.51 wt%) as a highly efficient OER catalyst in acidic media (0.5 M H2SO4) is presented in this article.
Abstract: Oxygen evolution reaction (OER) in acidic media usually requires a catalyst with high content of noble Ir or Ru, becoming a bottleneck for the electrochemical water splitting. To address this issue, here we report the fabrication of a RuO2/(Co,Mn)3O4 nanocomposite with low Ru loading (2.51 wt%) as a highly efficient OER catalyst in acidic media (0.5 M H2SO4). Spectroscopic and theoretical studies demonstrate that the introduction of Mn in Co3O4 results in redistribution of electrons and the generation of electron-rich Ru species of the RuO2/(Co,Mn)3O4 catalyst. With modulated electronic properties, the adsorption of O on RuO2/(Co,Mn)3O4 is weakened and the rate determining step, formation of OOH*, of the OER process is therefore accelerated. At such a low Ru loading, RuO2/(Co,Mn)3O4 exhibits superior acidic OER activity (η =270 mV at 10 mA/cm2) and long‐term stability to the benchmark RuO2 catalyst. This work provides a new strategy for the design of cost-effective acidic OER electrocatalysts for energy conversion applications.

82 citations

Journal ArticleDOI
TL;DR: In this paper , the authors discuss the correlation between OER activity and stability, methodologies and experimental techniques to study the stability and deactivation as well as the deactivation mechanisms, together with factors influencing stability.

78 citations

Journal ArticleDOI
TL;DR: In this article , single-atom Ir and Ru anchored on mesoporous graphitic carbon nitride (g-CN) were used as electrocatalysts and photocatalysts for the hydrogen evolution reaction (HER), which achieved a high turnover frequency of 12.9 and 5.1 s−1 at an overpotential (η) of 100 mV in 0.5 M H2SO4 and 1.0 M KOH, respectively.
Abstract: Renewable energy-powered water electrolysis and photocatalytic water splitting are two promising approaches to green hydrogen production. Electrocatalysts and photocatalysts are essential components determining the performance of water electrolyzers and photocatalytic reactors, respectively. Currently, there is a pressing need to develop efficient and stable electrocatalysts and photocatalysts for large-scale deployment of these devices to reach carbon neutrality. Herein, we report the synthesis of single-atom Ir and Ru anchored on mesoporous graphitic carbon nitride (Ir-g-CN and Ru-g-CN), which can be used as electrocatalysts and photocatalysts for the hydrogen evolution reaction (HER). Remarkably, Ru-g-CN shows a high turnover frequency (TOF) of 12.9 and 5.1 s−1 at an overpotential (η) of 100 mV in 0.5 M H2SO4 and 1.0 M KOH, respectively, outperforming Ir-g-CN, commercial Pt/C benchmark and many other advanced HER catalysts reported recently. Moreover, Ru-g-CN can deliver an exceptionally high mass activity of 24.55 and 8.78 A mg−1 at η = 100 mV in acidic and alkaline solutions, meanwhile exhibiting a high apparent current density, which is favorable for practical applications. Additionally, both Ru-g-CN and Ir-g-CN show outstanding catalytic stability, continuously catalyzing the HER in acidic and alkaline conditions for 120 h with minimal degradation. Besides, when used for photocatalytic water splitting, Ru-g-CN can achieve a high hydrogen production rate of 489.7 mmol H2 gRu−1 h−1, and shows good photocatalytic stability. Our density functional theory (DFT) calculations demonstrate that loading Ir and Ru single-atoms on g-CN alters the electronic structure, resulting in a reduced bandgap and improved electrical conductivity, facilitating electron transfer during the catalysis. Moreover, the Gibbs free energy of hydrogen adsorption on Ru-g-CN and Ir-g-CN is also substantially lowered, enhancing HER performance.

35 citations

Journal ArticleDOI
TL;DR: In this article , the fundamental catalytic mechanisms and key evaluation parameters of OER in acidic and alkaline media are presented first, design strategies for metal-organic framework (MOF)-based OER catalysts and research progress in the study of the structure-performance relationship are summarized.
Abstract: Oxygen evolution reaction (OER) is an energy‐determined half‐reaction for water splitting and many other energy conversion processes, such as rechargeable metal–air batteries and CO2 reduction, due to its four‐electron sluggish process. To reduce the energy consumption and cost of these advanced technologies, various transition metal‐based nanomaterials, like metal oxides/hydroxides, nitride, and phosphide are synthesized. Among these, metal–organic framework (MOF)‐based materials are considered as the ideal candidate for the fabrication of efficient OER electrocatalysts owing to their unique physicochemical properties. In this review, the fundamental catalytic mechanisms and key evaluation parameters of OER in acidic and alkaline media are presented first. Then, design strategies for MOF‐based OER catalysts and research progress in the study of the structure–performance relationship are summarized. Subsequently, the recent research advances of MOF‐based OER electrocatalysts in alkaline, acidic, and neutral electrolytes are overviewed. Finally, current challenges and future opportunities are provided under the frame of materials design, theoretical understanding, advanced characterization techniques, and industrial applications.

32 citations

Journal ArticleDOI
TL;DR: In this paper , the authors provide a summary and highlight the in situ studies of crystal nucleation and growth, with a particular emphasis on the state-of-the-art research progress since the year 2016, and include technological advances, atomic-scale observations, substrate-and temperature-dependent nucleation, and the progress achieved in the various materials: metals, alloys, metallic compounds, colloids, and proteins.
Abstract: Nucleation and growth are critical steps in crystallization, which plays an important role in determining crystal structure, size, morphology, and purity. Therefore, understanding the mechanisms of nucleation and growth is crucial to realize the controllable fabrication of crystalline products with desired and reproducible properties. Based on classical models, the initial crystal nucleus is formed by the spontaneous aggregation of ions, atoms, or molecules, and crystal growth is dependent on the monomer's diffusion and the surface reaction. Recently, numerous in situ investigations on crystallization dynamics have uncovered the existence of nonclassical mechanisms. This review provides a summary and highlights the in situ studies of crystal nucleation and growth, with a particular emphasis on the state-of-the-art research progress since the year 2016, and includes technological advances, atomic-scale observations, substrate- and temperature-dependent nucleation and growth, and the progress achieved in the various materials: metals, alloys, metallic compounds, colloids, and proteins. Finally, the forthcoming opportunities and challenges in this fascinating field are discussed.

29 citations

References
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Journal ArticleDOI
TL;DR: An efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set is presented and the application of Pulay's DIIS method to the iterative diagonalization of large matrices will be discussed.
Abstract: We present an efficient scheme for calculating the Kohn-Sham ground state of metallic systems using pseudopotentials and a plane-wave basis set. In the first part the application of Pulay's DIIS method (direct inversion in the iterative subspace) to the iterative diagonalization of large matrices will be discussed. Our approach is stable, reliable, and minimizes the number of order ${\mathit{N}}_{\mathrm{atoms}}^{3}$ operations. In the second part, we will discuss an efficient mixing scheme also based on Pulay's scheme. A special ``metric'' and a special ``preconditioning'' optimized for a plane-wave basis set will be introduced. Scaling of the method will be discussed in detail for non-self-consistent and self-consistent calculations. It will be shown that the number of iterations required to obtain a specific precision is almost independent of the system size. Altogether an order ${\mathit{N}}_{\mathrm{atoms}}^{2}$ scaling is found for systems containing up to 1000 electrons. If we take into account that the number of k points can be decreased linearly with the system size, the overall scaling can approach ${\mathit{N}}_{\mathrm{atoms}}$. We have implemented these algorithms within a powerful package called VASP (Vienna ab initio simulation package). The program and the techniques have been used successfully for a large number of different systems (liquid and amorphous semiconductors, liquid simple and transition metals, metallic and semiconducting surfaces, phonons in simple metals, transition metals, and semiconductors) and turned out to be very reliable. \textcopyright{} 1996 The American Physical Society.

81,985 citations

Journal ArticleDOI
Peter E. Blöchl1
TL;DR: An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way and can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function.
Abstract: An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way. The method allows high-quality first-principles molecular-dynamics calculations to be performed using the original fictitious Lagrangian approach of Car and Parrinello. Like the LAPW method it can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function. The augmentation procedure is generalized in that partial-wave expansions are not determined by the value and the derivative of the envelope function at some muffin-tin radius, but rather by the overlap with localized projector functions. The pseudopotential approach based on generalized separable pseudopotentials can be regained by a simple approximation.

61,450 citations

Journal ArticleDOI
TL;DR: In this paper, the formal relationship between US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived and the Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional.
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.

57,691 citations

Journal ArticleDOI
TL;DR: A detailed description and comparison of algorithms for performing ab-initio quantum-mechanical calculations using pseudopotentials and a plane-wave basis set is presented in this article. But this is not a comparison of our algorithm with the one presented in this paper.

47,666 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present an ab initio quantum-mechanical molecular-dynamics calculations based on the calculation of the electronic ground state and of the Hellmann-Feynman forces in the local density approximation.
Abstract: We present ab initio quantum-mechanical molecular-dynamics calculations based on the calculation of the electronic ground state and of the Hellmann-Feynman forces in the local-density approximation at each molecular-dynamics step. This is possible using conjugate-gradient techniques for energy minimization, and predicting the wave functions for new ionic positions using subspace alignment. This approach avoids the instabilities inherent in quantum-mechanical molecular-dynamics calculations for metals based on the use of a fictitious Newtonian dynamics for the electronic degrees of freedom. This method gives perfect control of the adiabaticity and allows us to perform simulations over several picoseconds.

32,798 citations

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