Journal Article

# Ab Initio Thermodynamics and Kinetics of the Lattice Oxygen Evolution Reaction in Iridium Oxides

02 Mar 2021-ACS energy letters (American Chemical Society (ACS))-Vol. 6, Iss: 3, pp 1124-1133
Abstract: Iridium-oxide-based catalysts are among the most active and stable materials for the anodic oxygen evolution reaction (OER) in acidic media, but even their longevity represents an important issue. ...

Topics: Oxygen evolution (59%), Ab initio (58%), Catalysis (51%) ... read more
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Open accessJournal Article
Kai S. Exner1Institutions (1)
15 Jul 2021-
Abstract: Summary In the last decade, tremendous efforts have been dedicated to the breaking of the OOH versus OH scaling relation, which is recognized as the bottleneck for electrocatalysts in the oxygen evolution reaction (OER), the anodic process in water electrolyzers. Breaking the OER scaling relation is seen as a universal remedy to enhance electrocatalytic activity, yet no major progress has so far been achieved in the design of improved OER materials according to this strategy. Introducing kinetics into the thermodynamics-based concept of scaling relations illustrates that the breaking of the OER scaling relation could be accompanied by decreased electrocatalytic activity. As a consequence, it appears imperative to progress the theoretical description of the OER in different directions other than the breaking of this scaling relation. This could include the investigation of competing mechanistic pathways, concerted and decoupled proton-electron transfer steps, or microkinetic considerations in conjunction with machine-learning approaches.

6 Citations

Open accessJournal Article
06 Aug 2021-ACS Catalysis
Abstract: The structure of IrO$_{2}$ during the oxygen evolution reaction (OER) was studied by operando X-ray absorption spectroscopy (XAS) at the Ir L$_{3}$-edge to gain insight into the processes that occur during the electrocatalytic reaction at the anode during water electrolysis. For this purpose, calcined and uncalcined IrO$_{2}$ nanoparticles were tested in an operando spectroelectrochemical cell. In situ XAS under different applied potentials uncovered strong structural changes when changing the potential. Modulation excitation spectroscopy combined with XAS enhanced the information on the dynamic changes significantly. Principal component analysis (PCA) of the resulting spectra as well as FEFF9 calculations uncovered that both the Ir L$_{3}$-edge energy and the white line intensity changed due to the formation of oxygen vacancies and lower oxidation state of iridium at higher potentials, respectively. The deconvoluted spectra and their components lead to two different OER modes. It was observed that at higher OER potentials, the well-known OER mechanisms need to be modified, which is also associated with the stabilization of the catalyst, as confirmed by in situ inductively coupled plasma mass spectrometry (ICP-MS). At these elevated OER potentials above 1.5 V, stronger Ir–Ir interactions were observed. They were more dominant in the calcined IrO$_{2}$ samples than in the uncalcined ones. The stronger Ir–Ir interaction upon vacancy formation is also supported by theoretical studies. We propose that this may be a crucial factor in the increased dissolution stability of the IrO$_{2}$ catalyst after calcination. The results presented here provide additional insights into the OER in acid media and demonstrate a powerful technique for quantifying the differences in mechanisms on different OER electrocatalysts. Furthermore, insights into the OER at a fundamental level are provided, which will contribute to further understanding of the reaction mechanisms in water electrolysis.

Topics: , , Oxygen evolution (51%)

4 Citations

Journal Article
Jing-Yi Xie1, Bin Dong1Institutions (1)
Abstract: To meet the current energy needs of society, the highly efficient and continuous production of clean energy is required. One of the key issues facing the green hydrogen evolution is the construction of efficient, low-cost electrocatalysts. Prussian blue (PB), Prussian blue analogs (PBAs), and their derivatives have tunable metal centers and have attracted significant interest as novel photo- and electrochemical catalysts. In this review, recent research progress into PB/PBA-based hollow structures, substrate-supported nanostructures, and their derivatives for green water splitting is discussed and summarized. First, several remarkable examples of nanostructured PB/PBAs supported on substrates (copper foil, carbon cloth, and nickel foam) and hollow structures (such as single-shelled hollow boxes, open hollow cages, and intricate hollow structures (multi–shell and yolk–shell)) are discussed in detail, including their synthesis and formation mechanisms. Subsequently, the applications of PB/PBA derivatives ((hydr)oxides, phosphides, chalcogenides, and carbides) for water splitting are discussed. Finally, the limitations in this research area and the most urgent challenges are summarized. We hope that this review will stimulate more researchers to develop technologies based on these intricate PB/PBA structures and their derivatives for highly efficient, green water splitting.

Topics: Prussian blue (52%), Water splitting (51%)

1 Citations

Open accessJournal Article
Kai S. Exner1Institutions (1)
07 Oct 2021-Chemcatchem
Topics: Oxygen evolution (56%)

1 Citations

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62 results found

Journal Article
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif

Topics: , ,  ... read more

117,932 Citations

Journal Article
Georg Kresse1, Jürgen Furthmüller2Institutions (2)
15 Oct 1996-Physical Review B
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.

Topics: DIIS (51%)

64,484 Citations

Journal Article
Georg Kresse1, Jürgen Furthmüller2Institutions (2)
Abstract: We present a detailed description and comparison of algorithms for performing ab-initio quantum-mechanical calculations using pseudopotentials and a plane-wave basis set. We will discuss: (a) partial occupancies within the framework of the linear tetrahedron method and the finite temperature density-functional theory, (b) iterative methods for the diagonalization of the Kohn-Sham Hamiltonian and a discussion of an efficient iterative method based on the ideas of Pulay's residual minimization, which is close to an order Natoms2 scaling even for relatively large systems, (c) efficient Broyden-like and Pulay-like mixing methods for the charge density including a new special ‘preconditioning’ optimized for a plane-wave basis set, (d) conjugate gradient methods for minimizing the electronic free energy with respect to all degrees of freedom simultaneously. We have implemented these algorithms within a powerful package called VAMP (Vienna ab-initio molecular-dynamics 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 semi-conducting surfaces, phonons in simple metals, transition metals and semiconductors) and turned out to be very reliable.

Topics: , , Iterative method (54%) ... read more

40,008 Citations

Journal Article
Abstract: We present a method for calculating the stability of reaction intermediates of electrochemical processes on the basis of electronic structure calculations. We used that method in combination with detailed density functional calculations to develop a detailed description of the free-energy landscape of the electrochemical oxygen reduction reaction over Pt(111) as a function of applied bias. This allowed us to identify the origin of the overpotential found for this reaction. Adsorbed oxygen and hydroxyl are found to be very stable intermediates at potentials close to equilibrium, and the calculated rate constant for the activated proton/electron transfer to adsorbed oxygen or hydroxyl can account quantitatively for the observed kinetics. On the basis of a database of calculated oxygen and hydroxyl adsorption energies, the trends in the oxygen reduction rate for a large number of different transition and noble metals can be accounted for. Alternative reaction mechanisms involving proton/electron transfer to ...

Topics: Overpotential (59%), , Oxygen (53%) ... read more

5,473 Citations

Journal Article
Abstract: Objective comparisons of electrocatalyst activity and stability using standard methods under identical conditions are necessary to evaluate the viability of existing electrocatalysts for integration into solar-fuel devices as well as to help inform the development of new catalytic systems. Herein, we use a standard protocol as a primary screen for evaluating the activity, short-term (2 h) stability, and electrochemically active surface area (ECSA) of 18 electrocatalysts for the hydrogen evolution reaction (HER) and 26 electrocatalysts for the oxygen evolution reaction (OER) under conditions relevant to an integrated solar water-splitting device in aqueous acidic or alkaline solution. Our primary figure of merit is the overpotential necessary to achieve a magnitude current density of 10 mA cm–2 per geometric area, the approximate current density expected for a 10% efficient solar-to-fuels conversion device under 1 sun illumination. The specific activity per ECSA of each material is also reported. Among HER...