The selective synthesis and in situ characterization of aqueous Alcontaining clusters is a long-standing challenge. We report a newly developed integrated platform that combines (i) a selective, atomeconomical, step-economical, scalable synthesis of Al-containing nanoclusters in water via precision electrolysis with strict pH control and (ii) an improved femtosecond stimulated Raman spectroscopic method covering a broad spectral range of ca. T he importance of Al (aluminum) in the biosphere and to human civilization is enormous. The scale of mining and production of Al compounds is second only to that of Fe (iron). Our lives are influenced by its use in electronics (1, 2), cooking and eating utensils, and food packaging, and as structural materials in the construction, automotive, and aircraft industries. Its deposition and migration as a mineral ore are controlled by its aqueous chemistry and speciation. Millions of tons of Al compounds are used worldwide each year for water treatment, and it is found in all drinking water (3). The behavior of Al in water plays significant roles in soil chemistry and plant growth (4, 5), for example, governing Al bioavailability, toxicity, and its overall impact in aquatic ecosystems (6). Meanwhile, aqueous Al clusters are gaining importance as solution precursors for the large-area deposition of Al 2 O 3 coatings with broad technological applications (7,8).Despite more than a century of study (9, 10), the complete portrait of aqueous Al chemistry remains unclear. Studies of aqueous Al chemistry are notoriously difficult because of the variety and complexity of the species that can be formed, encompassing monomeric, oligomeric, and polymeric hydroxides (11-17); colloidal solutions and gels; and precipitates. Synthesis is complicated by the fact that the counter-ions and the method and rate of pH change all have dramatic effects on product formation (18,19). Few methods exist for the in situ determination and assignment of molecular-level structures. For instance, 27 Al NMR can only identify certain Al aqueous species (15). Furthermore, unlike organic compounds, systematic spectroscopic signatures of metal hydroxide clusters are less accessible, making interpretation of experimental spectra challenging. We hereby report a combined synthesis, experiment, and theory platform for the study of aqueous metal clusters. Electrolysis is exploited to control the solution pH and counter-ion content precisely during cluster synthesis without using chemical reagents. The evolution of solution species is followed in situ by an improved femtosecond stimulated Raman (FSR) technique (20-22) that can detect weak signals associated with structure-defining vibrational modes. The resulting pHdependent Raman spectra are interpreted by juxtaposition to quantum mechanically computed vibrational modes to assign specific molecular structures. Through this integrated approach, we have discovered a speciation behavior for Al in water that has not previously been observed. We focus here on the synthesis an...

Flexible solid-state supercapacitors provide a promising energy-storage alternative for the rapidly growing flexible and wearable electronic industry. Further improving device energy density and developing a cheap flexible current collector are two major challenges in pushing the technology forward. In this work, we synthesize a nitrogen-doped graphene/MnO2 nanosheet (NGMn) composite by a simple hydrothermal method. Nitrogen-doped graphene acts as a template to induce the growth of layered δ-MnO2 and improves the electronic conductivity of the composite. The NGMn composite exhibits a large specific capacitance of about 305 F g(-1) at a scan rate of 5 mV s(-1). We also create a cheap and highly conductive flexible current collector using Scotch tape. Flexible solid-state asymmetric supercapacitors are fabricated with NGMn cathode, activated carbon anode, and PVA-LiCl gel electrolyte. The device can achieve a high operation voltage of 1.8 V and exhibits a maximum energy density of 3.5 mWh cm(-3) at a power density of 0.019 W cm(-3). Moreover, it retains >90% of its initial capacitance after 1500 cycles. Because of its flexibility, high energy density, and good cycle life, NGMn-based flexible solid state asymmetric supercapacitors have great potential for application in next-generation portable and wearable electronics.

This tutorial review surveys the wide variety of oligomeric hydroxide structures formed from aluminum, gallium, and indium. Both inorganic and ligand-supported structures are reviewed, providing a leading introduction to this research area. In addition to homometallic clusters comprising only one metal type, a series of heterometallic structures are described. This review highlights the synthesis and characterization of these nanoscale cluster compounds that have implications in a variety of fields, including catalysis, mineral mimicry, environmental chemistry, geochemistry, materials science, and semiconductors.