Rechargeable lithium ion batteries are integral to today's information-rich, mobile society. Currently they are one of the most popular types of battery used in portable electronics because of their high energy density and flexible design. Despite their increasing use at the present time, there is great continued commercial interest in developing new and improved electrode materials for lithium ion batteries that would lead to dramatically higher energy capacity and longer cycle life. Silicon is one of the most promising anode materials because it has the highest known theoretical charge capacity and is the second most abundant element on earth. However, silicon anodes have limited applications because of the huge volume change associated with the insertion and extraction of lithium. This causes cracking and pulverization of the anode, which leads to a loss of electrical contact and eventual fading of capacity. Nanostructured silicon anodes, as compared to the previously tested silicon film anodes, can help overcome the above issues. As arrays of silicon nanowires or nanorods, which help accommodate the volume changes, or as nanoscale compliant layers, which increase the stress resilience of silicon films, nanoengineered silicon anodes show potential to enable a new generation of lithium ion batteries with significantly higher reversible charge capacity and longer cycle life.

Chalcogenide nanostructures offer promise for obtaining nanomaterials with high electrical conductivity, low thermal conductivity, and high Seebeck coefficient. Here, we demonstrate a new approach of tuning the Seebeck coefficient of nanoplate assemblies of single-crystal pnictogen chalcogenides by heterostructuring the nanoplates with tellurium nanocrystals. We synthesized bismuth telluride and antimony telluride nanoplates decorated with tellurium nanorods and nanofins using a rapid, scalable, microwave-stimulated organic surfactant-directed technique. Heterostructuring permits two- to three-fold factorial tuning of the Seebeck coefficient, and yields a 40% higher value than the highest reported for bulk antimony telluride. Microscopy and spectroscopy analyses of the nanostructures suggest that Seebeck tunability arises from carrier-energy filtration effects at the Te-chalcogenide heterointerfaces. Our approach of heterostructuring nanoscale building blocks is attractive for realizing high figure-of-merit thermoelectric nanomaterials.

Platinum catalyst layers with Pt loadings w = 0.05-0.40 mg/cm 2 were deposited by magnetron sputtering from a variable deposition angle ␣ onto gas diffusion layer ͑GDL͒ substrates and tested as cathode electrodes in proton exchange membrane ͑PEM͒ fuel cells using Nafion 1135 membranes and Teflon-bonded Pt-black electrode ͑TBPBE͒ anodes. Layers deposited at normal incidence ͑␣ = 0°͒ are continuous and approximately replicate the rough surface morphology of the underlying GDL. In contrast, glancing angle deposition ͑GLAD͒ with ␣ = 87°and continuous substrate rotation yields highly porous layers consisting of vertically oriented Pt particles, 100-500 nm high and 100-300 nm wide, that are separated by 20-100 nm. The particle electrodes exhibit a higher ͑lower͒ mass-specific performance than the continuous-layer electrodes for a high ͑low͒ current density i. This is attributed to a higher porosity but lower overall electrochemically active surface area for the particles compared to the continuous layer. Increasing w in particle cells from 0.05 to 0.10 to 0.18 mg/cm 2 yields increasing potentials, but w = 0.40 mg/cm 2 causes a voltage drop at i Ͼ 0.4 A/cm 2 , associated with the reduced pore density at large w. Comparison cells with a TBPBE cathode exhibit comparatively low Tafel slopes but a lower Pt mass specific performance than the sputtered catalysts. Quantitative analyses of kinetic and mass-transport losses in the polarization curves suggest a competing microstructural effect, favoring mass-transport performance and an efficient oxygen reduction reaction for particle and continuous layer electrodes, respectively. The overall results suggest that in addition to the well-known promise of sputter-deposited Pt catalysts as an approach to increase Pt utilization at low loading, GLAD provides the unique ability to control Pt porosity and to achieve efficient reactant flow for high-currentdensity operation.

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