Gold nanoparticles represent an important class of functional nanomaterials for optoelectronics, biomedical applications, and catalysis. Therefore, controllable synthesis of nanoparticles with specified size and shape is important. Though reduction of gold ions is quite a simple process and may be performed with many different protocols, the reproducibility of the results and transfer of protocols between independent research groups remains a challenging task. Machine learning analysis based on statistical approaches is hardly applicable to the published data, since most of the researchers report only successful syntheses. In this work, we apply uniform sampling of the reaction parameter space. The concentrations of gold precursor, reducing agent, and surfactant were varied via an improved Latin hypercube sampling, and each run was performed under in situ UV−vis control. Based on the resulting set of optical spectra, we address the relevant chemical questions about nanoparticle formation, their shape, and period of growth. Our work demonstrates a data driven approach applied to the space of reaction parameters in a limited available set of experiments.

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Electrical energy storage becomes increasingly important to extend the range of electric vehicles and to buffer the electricity generated by intermittent energy sources. Recently a lot of effort has been put into finding novel materials with higher energy density and longer cycle life. Especially conversion materials based on fluorides offer a 3-5 fold increase of capacity compared to current state-of-the-art Li-ion batteries based on Li-intercalation [1]. Fluorides have the advantage of a high cell voltage vs. Li due to a large band gap compared to other conversion materials such as oxides and nitrides. For example, FeF3converts reversibly to Fe and LiF upon discharge transferring up to 3 electrons according to FeF3 + 3Li ↔ Fe + 3LiF E0 = 2.96 V (weighted average), Cth= 712 mAh/g The traditional approach to enable metal fluorides as cathode materials for Li-ion batteries is to coat the insulating fluoride particles with a conducting carbon shell by high-energy ball milling [2]. The FeF3/C nanocomposites show a very high capacity up to the theoretical maximum in the first few cycles, but cyclic stability is poor due to a pulverisation of the core-shell FeF3/C particles upon prolonged cycling. We recently prepared an improved LiF/Fe(V2O5) nanocomposite by high-energy ball milling, which shows a high reversible capacity of 420 mAh/g in the first 20 cycles and 270 mAh/g after 50 cycles [3]. The cyclic stability was much improved compared to FeF3/C composites due the addition of V2O5. We used in situ XAS, Mössbauer spectroscopy, ab initio calculation of model XANES spectra and principle component analysis to identify highly amorphous V[FeV]O4 nanograins, which form during ball milling [4]. From the calculations we also identified LixVO2-xFx. Both phases have open crystal structures and the ability to reversibly store lithium in interstitial lattice sites. As the V[FeV]O4 and LixVO2-xFx nanograins are in close contact with LiF and Fe particles, they help to maintain electrical and ionic contact upon prolonged cycling. J. Cabana, L. Monconduit, D. Larcher, M.R. Palacín, Adv. Mater. 22 (2010), E170. F. Badway, F. Cosandey, N. Pereira, G.G. Amatucci, J. Electrochem. Soc. 150 (2003), A1318. B. Das, A. Pohl, K. Chakravadhanula and M. Fichtner (2014), submitted. H. Pohl, A. A. Guda, V. V. Shapovalov, R. Witte, B. Das, F. Scheiba, J. Rothe, A. V. Soldatov and M. Fichtner, Acta Materialia 68 (2014), 179.

A facile water based synthesis method for HTB-FeF 3 /rGO and r-FeF 3 /rGO composites was developed using FeF 3 nanoparticles prepared by ball-milling and aqueous graphene oxide precursor. Electrodes of HTB-FeF 3 /rGO were cast in ambient air and the calendared electrode showed a stable specific energy of 470 Wh kg -1 (210 mAh g -1 , 12 mA g -1 ) after 100 cycles in the range 4.3-1.3 V with very little capacity fading. The good cycle stability is attributed to the intimate contact of FeF 3 nanoparticles with reduced graphene oxide carbon surrounding. We show using a combination of in situ XRD, XAS and ex situ Mössbauer spectroscopy that during discharge of HTB-FeF 3 /rGO composite Li is intercalated fast into the tunnels of the HTB-FeF 3 structure up to x = 0.95 Li followed by slow conversion to LiF and Fe nanoparticles below 2.0 V. During charge, the LiF and Fe phases are slowly transformed to amorphous FeF 2 and FeF 3 phases without reformation of the HTB-FeF 3 framework structure. At an elevated temperature of 55 °C a much higher specific energy of 780 Wh kg -1 was obtained.