The next generation of high-performance batteries should include alternative chemistries that are inherently safer to operate than nonaqueous lithium-based batteries. Aqueous zinc-based batteries can answer that challenge because monolithic zinc sponge anodes can be cycled in nickel-zinc alkaline cells hundreds to thousands of times without undergoing passivation or macroscale dendrite formation. We demonstrate that the three-dimensional (3D) zinc form-factor elevates the performance of nickel-zinc alkaline cells in three fields of use: (i) >90% theoretical depth of discharge (DOD) in primary (single-use) cells, (ii) >100 high-rate cycles at 40% DOD at lithium-ion-commensurate specific energy, and (iii) the tens of thousands of power-demanding duty cycles required for start-stop microhybrid vehicles.

Au nanoparticles (NPs) with protecting organothiolate ligands and core diameters smaller than 2 nm are interesting materials because their size-dependent properties range from metal-like to molecule-like. This Account focuses on the most thoroughly investigated of these NPs, Au(25)L(18). Future advances in nanocluster catalysis and electronic miniaturization and biological applications such as drug delivery will depend on a thorough understanding of nanoscale materials in which molecule-like characteristics appear. This Account tells the story of Au(25)L(18) and its associated synthetic, structural, mass spectrometric, electron transfer, optical spectroscopy, and magnetic resonance results. We also reference other Au NP studies to introduce helpful synthetic and measurement tools. Historically, nanoparticle sizes have been described by their diameters. Recently, researchers have reported actual molecular formulas for very small NPs, which is chemically preferable to solely reporting their size. Au(25)L(18) is a success story in this regard; however, researchers initially mislabeled this NP as Au(28)L(16) and as Au(38)L(24) before correctly identifying it by electrospray-ionization mass spectrometry. Because of its small size, this NP is amenable to theoretical investigations. In addition, Au(25)L(18)'s accessibility in pure form and molecule-like properties make it an attractive research target. The properties of this NP include a large energy gap readily seen in cyclic voltammetry (related to its HOMO-LUMO gap), a UV-vis absorbance spectrum with step-like fine structure, and NIR fluorescence emission. A single crystal structure and theoretical analysis have served as important steps in understanding the chemistry of Au(25)L(18). Researchers have determined the single crystal structure of both its "native" as-prepared form, a [N((CH(2))(7)CH(3))(4)(1+)][Au(25)(SCH(2)CH(2)Ph)(18)(1-)] salt, and of the neutral, oxidized form Au(25)(SCH(2)CH(2)Ph)(18)(0). A density functional theory (DFT) analysis correctly predicted essential elements of the structure. The NP is composed of a centered icosahedral Au(13) core stabilized by six Au(2)(SR)(3) semirings. These semirings present interesting implications regarding other small Au nanoparticle clusters. Many properties of the Au(25) NP result from these semiring structures. This overview of the identification, structure determination, and analytical properties of perhaps the best understood Au nanoparticle provides results that should be useful for further analyses and applications. We also hope that the story of this nanoparticle will be useful to those who teach about nanoparticle science.

Zinc-based replacements for Li-ion batteries are now feasible by using 3D-interconnected Zn sponges that suppress dendrite formation when cycled.

I. Technical aspects of transient grating experimentsFemtosecond spectroscopy experiments are based on a Quantronix Q-lite seeded Integra C Titanium Sapphire amplifier generating 130 fs, 800 nm, 2.0 mJ laser pulses at 1 kHz. The laser system pumps two home-built noncollinear optical parametric amplifiers (NOPA). 1,2 The NOPA used for pump pulse generation has a spectral bandwidth corresponding to transform limited 15 fs laser pulses, whereas the NOPA from which probe pulses are derived generates spectra spanning the full 500-750 nm wavelength range. Portions of the probe spectrum are filtered in a fused silica prism compressor for use in experiments. Pump and probe pulses are compressed to 15-20 fs with a time-bandwidth product of 0.5-0.6 where residual third-order dispersion prevents compression to the Fourier transform limit.Transient grating (TG) experiments are performed with the interferometer shown in Figure S1. The interferometer generates a trapezoidal laser beam geometry with diffractive-optics (DO) for passively phase-stabilized interferometric signal detection. [3][4][5][6][7][8][9] The TG interferometer uses a DO (Holoeye) producing an angle of 4.65 degrees between the +/-1 diffraction orders at 590 nm. The pump (pulses 1 and 2) and probe (pulses 3) beams are crossed at angle of approximately 4.6 degrees in the DO. Pulses 1 and 2 arrive at the sample at the same time, and are delayed with respect to pulses 3 and 4 with a motorized translation stage. The signal is phase-matched so that it is automatically collinear with the reference pulse after the sample.

New approaches to electrospray ionization mass spectrometry (ESI-MS)swith exact compositional assignmentssof small (Au25) nanoparticles with uniform and mixed protecting organothiolate monolayers are described. The results expand the scope of analysis and reveal a rich chemistry of ionization behavior. ESI-MS of solutions of phenylethanethiolate monolayer-protected gold clusters (MPCs), Au25(SC2Ph)18, containing alkali metal acetate salts (MOAc) produce spectra in which, for Na + , K + , Rb + , and Cs + acetates, the dominant species are MAu25(SC2Ph)18 2+ and M2Au25(SC2Ph)18 2+ . Li + acetates caused ligand loss. This method was extended to the analysis of Au25 MPCs with mixed monolayers, where thiophenolate (-SPh), hexanethiolate (-SC6), or biotinylated (-S-PEG-biotin) ligands had been introduced by ligand exchange. In negative-mode ESI-MS, no added reagents were needed in order to observe Au25(SC2Ph)18and to analyze mixed monolayer Au25 MPCs prepared by ligand exchange with 4-mercaptobenzoic acid, HSPhCOOH, which gave spectra through deprotonation of the carboxylic acids. Adducts of tetraoctylammonium (Oct4N + ) with -SPhCOOsites were also observed. Mass spectrometry is the only method that has demonstrated capacity for measuring the exact distribution of ligand-exchange products. The possible origins of the different Au25 core charges (1-, 0, 1+, 2+) observed during electrospray ionization are discussed.

Proton nuclear magnetic resonance (NMR) was used to measure the rate constant and activation energy barrier for electron self-exchanges of the phenylethanethiolate-protected nanoparticle couple [Au25(SC2Ph)18]0/1−. The thiolate ligand α-methylene proton resonances of electrolytically prepared CD2Cl2 solutions of the oxidized (Au25 0) and reduced (Au25 1−) nanoparticles exhibit characteristic chemical shifts and line-shapes. That for the α-CH2 protons in Au25 0 is shifted ∼2 ppm downfield from Au25 1− and has an increased line-width reflecting the odd electron count of the nanoparticle core. Solution mixtures of Au25 0 and Au25 1− exhibit further peak broadening and intermediate values of α-CH2 proton chemical shifts, effects quantitatively consistent with an electron self-exchange process in the fast-exchange regime. Analysis of changes in peak broadening at varied total nanoparticle concentration and at varied temperatures produces a rate constant for [Au25(SC2Ph)18]0/1− self-exchange of 3.0(±0.1) × 107 M−1s−1 at 22 °C and an activation barrier energy E A = 25.0 (±1.5) kJ/mol. This barrier energy is much larger than the calculated estimate of outer-sphere reorganization energy, implying the presence of a significant inner-sphere reorganization energy. The latter is confirmed by a detected difference in the Raman Au−S bond stretch energies of Au25 0 and Au25 1− nanoparticles.

Zinc-based batteries are experiencing a resurgence in interest owing to their promising energy and power metrics, and inherent safety advantages compared with lithium-ion batteries. As scientists worldwide address the remaining obstacles to realizing competitive performance across the family of zinc batteries, the enthusiasm to report new ''breakthroughs'' at the materials or small-device level must be tempered by a realistic understanding of how such improvements will translate to practical energy-storage devices. Framing early-stage results in such a context will advance the prospects of next-generation Zn batteries while avoiding the ''hype cycle'' that has plagued research and development for other energy-storage technologies. Herein, we present guidelines by which to evaluate and report data derived from new electrode formulations and cell components such that the results will directly inform which breakthroughs are technologically relevant to scale up.

A single phase (THF) synthesis of monodisperse [Oct(4)N(+)][Au(25)(SR)(18)(-)] nanoparticles is described that yields insights into pathways by which it is formed from initially produced larger nanoparticles. Including the Oct(4)N(+)Br(-) salt in a reported single phase synthetic procedure enables production of reduced nanoparticles having a fully occupied HOMO molecular energy level (Au(25)(SR)(18)(-), as opposed to a partially oxidized state, Au(25)(SR)(18)(0)). The revised synthesis accommodates several (but not all) different thiolate ligands. The importance of acidity, bromide, and dioxygen on Au(25) formation was also assessed. The presence of excess acid in the reaction mixture steers the reaction toward making Au(25)(SR)(18); while bromide does not seem to affect Au(25) formation, but it may play a role in maintaining the -1 oxidation state. Conducting the nanoparticle synthesis and "aging" period in the absence of dioxygen (under Ar) does not produce small nanoparticles, providing insights into the pathway of reaction product "aging" in the synthesis solvent, THF. The "aging" process favors the Au(25)(-) moiety as an end point and possibly involves degradation of larger nanoparticles by hydroperoxides formed from THF and oxygen.