Activity Descriptor Identification for Oxygen Reduction on Platinum-Based Bimetallic Nanoparticles: <i>In Situ</i> Observation of the Linear Composition–Strain–Activity Relationship

Despite recent progress in developing active and durable oxygen reduction catalysts with reduced Pt content, lack of elegant bottom-up synthesis procedures with knowledge over the control of atomic arrangement and morphology of the Pt–alloy catalysts still hinders fuel cell commercialization. To follow a less empirical synthesis path for improved Pt-based catalysts, it is essential to correlate catalytic performance to properties that can be easily controlled and measured experimentally. Herein, using Pt–Co alloy nanoparticles (NPs) with varying atomic composition as an example, we show that the atomic distribution of Pt-based bimetallic NPs under operating conditions is strongly dependent on the initial atomic ratio by employing microscopic and <i>in situ</i> spectroscopic techniques. The Pt_<i>x</i>Co/C NPs with high Co content possess a Co concentration gradient such that Co is concentrated in the core and gradually depletes in the near-surface region, whereas the Pt_<i>x</i>Co/C NPs with low Co content possess a relatively uniform distribution of Co with low Co population in the near-surface region. Despite their different atomic structure, the oxygen reduction reaction (ORR) activity of Pt_<i>x</i>Co/C and Pt/C NPs is linearly related to the bulk average Pt–Pt bond length (<i>R</i>_Pt–Pt). The <i>R</i>_Pt–Pt is further shown to contract linearly with the increase in Co/Pt composition. These linear correlations together demonstrate that (i) the improved ORR activity of Pt_<i>x</i>Co/C NPs over pure Pt NPs originates predominantly from the compressive strain and (ii) the <i>R</i>_Pt–Pt is a valid strain descriptor that bridges the activity and atomic composition of Pt-based bimetallic NPs

Peptide-Decorated Tunable-Fluorescence Graphene Quantum Dots

We report here the synthesis of graphene quantum dots with tunable size, surface chemistry, and fluorescence properties. In the size regime 15–35 nm, these quantum dots maintain strong visible light fluorescence (mean quantum yield of 0.64) and a high two-photon absorption (TPA) cross section (6500 Göppert–Mayer units). Furthermore, through noncovalent tailoring of the chemistry of these quantum dots, we obtain water-stable quantum dots. For example, quantum dots with lysine groups bind strongly to DNA in solution and inhibit polymerase-based DNA strand synthesis. Finally, by virtue of their mesoscopic size, the quantum dots exhibit good cell permeability into living epithelial cells, but they do not enter the cell nucleus

BME increases lipid accumulation in F442A cells.

<p><b>A</b>: microphotograph of cells treated with control (left panel) and BME (1 mM, right panel) on day 6 after cells were induced to differentiated by insulin supplement. <b>B</b>: fluorescent microphotograph of cells after staining with BODIPY-C12 under otherwise the same conditions as those shown in A. bar = 5×10⁻⁵ m. <b>C</b>: quantitative fluorescent intensity of lipid staining on day 6. Results are mean +/− se from four independent cell cultures for each five different views were analyzed. Columns denoted with non-identical alphabets are statistically different (p<0.05, by Tukey’s test).</p

BME suppresses expression of inflammatory cytokines.

<p>Messenger RNA expression of selected cytokines on day 1, 4, and 10 after incubation with BME at graded concentration of BME. Results are means +/− SE (N = 3–6). Bars denoted with non-identical alphabets are statistically different (p<0.05, by Tukey’s test).</p

BME increases expression of adipogenic genes.

<p><b>A</b>: The time course of aP2 mRNA expression in F442A cells after being induced to differentiate by insulin and fetal bovine serum and graded concentration of BME. <b>B</b>: Messenger RNA for SCD-1, LPL, Glut4, and adiponectin on day 10 of differentiation after being co-treated with graded concentration of BME. Results are means +/− SE (N = 3–6). Columns denoted with non-identical alphabets are statistically different (p<0.05, by Tukey’s test).</p

Anion Resistant Oxygen Reduction Electrocatalyst in Phosphoric Acid Fuel Cell

Phosphoric acid fuel cells are successfully used as energy conversion technologies in stationary power applications. However, decreased proton conductivity and lower oxygen permeability of phosphoric-acid-imbibed membranes require prohibitive loadings of the traditional noble-metal-based electrocatalyst, such as platinum supported on carbon. Additionally, specific adsorption of phosphate anions on the catalyst results in a surface poisoning that further reduces electrocatalytic activity. Here we report a nonplatinum group metal (non-PGM) electrocatalyst as an alternative cathode electrocatalyst for oxygen reduction in phosphoric acid fuel cells. The non-PGM was prepared in a one-pot synthesis using a metal organic framework and iron salt precursor. Phosphate anion poisoning was monitored electrochemically and spectroscopically in reference to the current state-of-the-art Pt-based catalyst at room temperature. Unlike Pt-based catalysts that are prone to phosphate poisoning, the non-PGM electrocatalyst exhibits immunity to surface poisoning by phosphate anions at room temperature. Imaging with microscopy reveals that the iron particles are isolated from the electrolyte by graphitic layers, which ultimately protect the iron from phosphate anion adsorption. The non-PGM electrocatalyst represents the highest performance to date in a high-temperature phosphoric acid membrane system, which is likely attributed to its immunity to phosphate adsorption at the harsher fuel cell environments

BME and TNFalpha mutually inhibits each other for effects on inflammation and adipogenesis.

<p><b>A</b>: Phase-contrast microphotograph of F442A cells induced to differentiate by insulin for 9 days with or without co-treatment of BME and/or TNFalpha and indicated concentrations. <b>B</b>: Messenger RNA expression of selected marker genes for adipogenesis (PPARgamma, C/EBPalpha, aP2, and LPL), inflammation (iNOS and IL-6), and adipokines (adiponectin and leptin) in cells treated with TNFalpha at 0, 1 ng/ml, and 10 ng/ml without (T0, T1, T10) or with BME added at 1 mM (BT0, BT1, BT10). <b>C.</b> NFkappaB activity measured in HEK293 cells transfected with firefly reporter luciferase vector and control Renilla luciferase vector. Cells were treated with BME (1 mM) for 12 h before TNFalpha (10 ng/ml) was added without medium change and harvested after another 12 h of incubation (B: BME, T: TNFalpha, BT: BME plus TNFalpha). <b>D.</b> Western analysis for NFkappaB activation in response to TNFalpha (10 ng/ml) in differentiating preadipocytes. Cells were treated with differentiation medium with or without BME for 24 h. TNFalpha was then added directly to the culture and cells were harvested at different time points to perform Western analysis for p65^ser536 and IkappaB^ser32 and their corresponding total protein levels, using actin as the loading index. For A–C, results are means +/− SE (N = 3–6). For B, bars denoted with non-identical alphabets are statistically different, e.g. a ≠ b, etc. (p<0.05, by Tukey’s test). For D, results are representative of three independent repeated experiments.</p

Tough Germanium Nanoparticles under Electrochemical Cycling

Mechanical degradation of the electrode materials during electrochemical cycling remains a serious issue that critically limits the capacity retention and cyclability of rechargeable lithium-ion batteries. Here we report the highly reversible expansion and contraction of germanium nanoparticles under lithiation–delithiation cycling with <i>in situ</i> transmission electron microscopy (TEM). During multiple cycles to the full capacity, the germanium nanoparticles remained robust without any visible cracking despite ∼260% volume changes, in contrast to the size-dependent fracture of silicon nanoparticles upon the first lithiation. The comparative <i>in situ</i> TEM study of fragile silicon nanoparticles suggests that the tough behavior of germanium nanoparticles can be attributed to the weak anisotropy of the lithiation strain at the reaction front. The tough germanium nanoparticles offer substantial potential for the development of durable, high-capacity, and high-rate anodes for advanced lithium-ion batteries

Tough Germanium Nanoparticles under Electrochemical Cycling

Mechanical degradation of the electrode materials during electrochemical cycling remains a serious issue that critically limits the capacity retention and cyclability of rechargeable lithium-ion batteries. Here we report the highly reversible expansion and contraction of germanium nanoparticles under lithiation–delithiation cycling with <i>in situ</i> transmission electron microscopy (TEM). During multiple cycles to the full capacity, the germanium nanoparticles remained robust without any visible cracking despite ∼260% volume changes, in contrast to the size-dependent fracture of silicon nanoparticles upon the first lithiation. The comparative <i>in situ</i> TEM study of fragile silicon nanoparticles suggests that the tough behavior of germanium nanoparticles can be attributed to the weak anisotropy of the lithiation strain at the reaction front. The tough germanium nanoparticles offer substantial potential for the development of durable, high-capacity, and high-rate anodes for advanced lithium-ion batteries