Ir‐based binary and ternary alloys are effective catalysts for the electrochemical oxygen evolution reaction (OER) in acidic solutions. Nevertheless, decreasing the Ir content to less than 50 at% while maintaining or even enhancing the overall electrocatalytic activity and durability remains a grand challenge. Herein, by dealloying predesigned Al‐based precursor alloys, it is possible to controllably incorporate Ir with another four metal elements into one single nanostructured phase with merely ≈20 at% Ir. The obtained nanoporous quinary alloys, i.e., nanoporous high‐entropy alloys (np‐HEAs) provide infinite possibilities for tuning alloy's electronic properties and maximizing catalytic activities owing to the endless element combinations. Particularly, a record‐high OER activity is found for a quinary AlNiCoIrMo np‐HEA. Forming HEAs also greatly enhances the structural and catalytic durability regardless of the alloy compositions. With the advantages of low Ir loading and high activity, these np‐HEA catalysts are very promising and suitable for activity tailoring/maximization.

We describe an atomistic method for computing the viscosity of highly viscous liquids based on activated state kinetics. A basin-filling algorithm allowing the system to climb out of deep energy minima through a series of activation and relaxation is proposed and first benchmarked on the problem of adatom diffusion on a metal surface. It is then used to generate transition state pathway trajectories in the potential energy landscape of a binary Lennard-Jones system. Analysis of a sampled trajectory shows the system moves from one deep minimum to another by a process that involves high activation energy and the crossing of many local minima and saddle points. To use the trajectory data to compute the viscosity we derive a Markov Network model within the Green-Kubo formalism and show that it is capable of producing the temperature dependence in the low-viscosity regime described by molecular dynamics simulation, and in the high-viscosity regime (10(2)-10(12) Pa s) shown by experiments on fragile glass-forming liquids. We also derive a mean-field-like description involving a coarse-grained temperature-dependent activation barrier, and show it can account qualitatively for the fragile behavior. From the standpoint of molecular studies of transport phenomena this work provides access to long relaxation time processes beyond the reach of current molecular dynamics capabilities. In a companion paper we report a similar study of silica, a representative strong liquid. A comparison of the two systems gives insight into the fundamental difference between strong and fragile temperature variations. We describe an atomistic method for computing the viscosity of highly viscous liquids based on activated state kinetics. A basin-filling algorithm allowing the system to climb out of deep energy minima through a series of activation and relaxation is proposed and first benchmarked on the problem of adatom diffusion on a metal surface. It is then used to generate transition state pathway trajectories in the potential energy landscape of a binary Lennard-Jones system. Analysis of a sampled trajectory shows the system moves from one deep minimum to another by a process that involves high activation energy and the crossing of many local minima and saddle points. To use the trajectory data to compute the viscosity we derive a Markov Network model within the Green-Kubo formalism and show that it is capable of producing the temperature dependence in the low-viscosity regime described by molecular dynamics simulation, and in the high-viscosity regime ͑10 2 -10 12 Pa s͒ shown by experiments on fragile glass-forming liquids. We also derive a mean-field-like description involving a coarse-grained temperature-dependent activation barrier, and show it can account qualitatively for the fragile behavior. From the standpoint of molecular studies of transport phenomena this work provides access to long relaxation time processes beyond the reach of current molecular dynamics capabilities. In a companion paper we report a similar study of ...

Thermoelectric properties are heavily dependent on the carrier concentration, and therefore the optimization of carrier concentration plays a central role in achieving high thermoelectric performance.

An extensive search for stable chemisorbed SO 2 configurations on the Pt(111) surface has been performed using first-principles DFT-GGA calculations. The most energetically stable configurations, η 2 -S b ,O a and η 3 -S a ,O a ,O a at fcc sites, where η 2 and η 3 mean that the number of atoms of the adsorbate coordinated to surface atoms are two and three, respectively, and the subscripts a and b stand for the atoms on atop sites and bridge sites, respectively, are consistent with experimental observations. It is found that strong sulfur-metal bonds are essential in stabilizing the molecular SO 2 binding to the Pt(111) surface. The lateral dipole-dipole interactions among chemisorbed SO 2 moieties are shown to be responsible for the strong coverage effect of the SO 2 binding energy to the surface. These strong lateral interactions do not greatly affect the molecular structures or relative binding energy differences among different binding configurations. The projected density of states and the induced density of states are studied in detail to explain binding effects.

Noble metal elements are the key to many high-performance heterogeneous catalytic processes; nevertheless, how to reduce the usage of such scarce and prohibitive materials while maintaining or even enhancing the desired catalytic performance has always been a grand challenge. In this work, we introduce a general dealloying procedure to synthesize a series of predesigned rugged high-entropy alloy (HEA) nanowires, including Al–Ni–Co–Ru–X, where X = Mo, Cu, V, Fe as the trifunctional electrocatalysts for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). These mechanically and chemically stable HEAs can not only significantly reduce the noble-metal contents but also effectively enhance the flexibility in their electronic structures suitable for broad catalytic functionalities. Specifically, our etched Al–Ni–Co–Ru–Mo nanowires exhibit a similarly high electrocatalytic activity as commercial Pt/C for HER. Its OER activity is much higher than the commercial RuO2 and among the highest ever-reported Ru-based OER catalysts. Its ORR catalytic activity is even higher than Pt/C, although Ru is not considered as a good ORR catalyst. Moreover, the oxidized surfaces of these HEAs are highly stable during continuous working conditions, which is crucial for overall water splitting and rechargeable Zn–air batteries.

Heteronuclear double-atom catalysts, unlike single atom catalysts, may change the charge density of active metal sites by introducing another metal single atom, thereby modifying the adsorption energies of reaction intermediates and increasing the catalytic activities. First, density functional theory calculations are used to figure out the best combination by modeling two transition-metal atoms from Fe, Co, and Ni onto N-doped graphene. Generally, Fe and Co sites are highly active for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER), respectively. The combination of Co and Fe to form CoFe–N–C not only further improves the Fe’s ORR and Co’s OER activities but also greatly enhances the Co site’s ORR and Fe site’s OER activities. Then, we synthesize the CoFe–N–C by a two-step pyrolysis process and find that the CoFe–N–C exhibits exceptional ORR and OER electrocatalytic activities in alkaline media, significantly superior to Fe–N–C and Co–N–C and even commercial catalysts.

A practical computational scheme based on time-dependent density functional theory (TDDFT) and ultrasoft pseudopotential (USPP) is developed to study electron dynamics in real time. A modified Crank-Nicolson time-stepping algorithm is adopted, under planewave basis. The scheme is validated by calculating the optical absorption spectra for sodium dimer and benzene molecule.As an application of this USPP-TDDFT formalism, we compute the time evolution of a test electron packet at the Fermi energy of the left metallic lead crossing a benzene-(1,4)-dithiolate junction. A transmission probability of 5-7%, corresponding to a conductance of 4.0-5.6 µS, is obtained. These results are consistent with complex band structure estimates, and Green's function calculation results at small bias voltages.

It is proved analytically that a one-dimensional half-filled polymer chain is subject to two coupled spontaneous conformational relaxations, the well-known Peierls bond length alternation and a uniform bond contraction. These two coupled relaxations work cooperatively against the lattice elastic energy penalty so that all bonds alternate and contract less than the case when these two relaxations are independent. When the fully relaxed neutral chain is taken as reference, creating self-localized charge carriers upon doping results in spontaneous bond contraction within the self-localized domain where the undimerization is enforced. Numeric results based on the Su-Schrieffer-Heeger and extended Peierls-Hubbard models and ab initio calculations resolve a long-lasting puzzle observed by x-ray scatterings concerning of the initial zero slope and accompanied sharp knee in the strain response of trans-polyacetylene to the Na + dopant concentration. The demonstrated doping-induced polymer chain length variation mechanism has implications for ultrafast artificial muscle designs.A one-dimensional ͑1D͒ equally spaced metallic polymer chain of one electron per ionic site is unstable with respect to the spontaneous relaxation via optical phonons with the double Fermi wave vector, resulting in a dimerized insulating polymer chain. This is the Peierls instability, originally derived using the free-electron energy dispersion relation. 1 A more rigorous proof was given by Kennedy and Lieb 2 stating that such a dimerization is exact without additional symmetry breakdown, at least for the Su-Schrieffer-Heeger ͑SSH͒ type of Hamiltonians 3 in which the nearest-neighbor electron hopping integrals vary linearly with the distance. This work points to the existence of a ubiquitously coupled twin of the Peierls distortion, with validations from previously unresolved puzzling x-ray scattering data on Na + doped trans-polyacetylene. [4][5][6][7][8][9] Without loss of generality, 10 we follow Kennedy and Lieb 2 to focus on the SSH Hamiltonian. It is well recognized that the SSH Hamiltonian is subject to a spontaneous contraction. Explicitly, Su proposed a constant tension of 4␣ / to compensate such a undesired global contraction. 11 Later, Stafstrom and Chao 12 suggested a 2% correction to Su's term and attributed such a difference to the discrete energy spectrum of using a finite system. Vos et al. expressed the contraction as a function of the electron-phonon coupling coefficient for the perfectly dimerized case and obtained the sound speeds of acoustic and optical modes. 13 Nevertheless, we note that the chain length variation in the above mentioned arguments is independent of the polymer charge state; namely, if the neutral dimerized chain is taken as reference, no further chain length variations would be expected upon charge injections. In addition, Bishop et al. 14 observed local contractions at the soliton center via adiabatic exciton dynamics and attributed such local contractions to the coupling between moving solitons and acoustic ...