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Correlating the current/voltage response of an electrode to the intrinsic properties of the active material requires knowledge of the electrochemically active surface area (ECSA), a parameter that is often unknown and overlooked, particularly for highly nanostructured electrodes. Here we demonstrate the power of nonaqueous electrochemical double layer capacitance (DLC) to provide reasonable estimates of the ECSA across 17 diverse materials spanning metals, conductive oxides, and chalcogenides. Whereas data recorded in aqueous electrolytes generate a wide range of areal specific capacitance values (7-63 μF/real cm), nearly all materials examined display an areal specific capacitance of 11 ± 5 μF/real cm when measured in weakly coordinating KPF/MeCN electrolytes. By minimizing ion transfer reactions that convolute accurate DLC measurements, we establish a robust methodology for quantifying ECSA, enabling more accurate structure-function correlations.

The photocatalytic degradation mechanism of an azo dye, C.I. Reactive Black 5 (RB5), has been investigated in an aqueous suspension of SrTiO3/CeO2 composite under 250 W UV irradiation at pH 12.0. The process was studied by monitoring the change in RB5 concentration and the intermediate products employing UV-visible spectrophotometry, ion chromatography (IC), and gas chromatography/ mass spectrometry (GC/MS) techniques and depletion in total organic carbon (TOC) content as a function of irradiation time. The adsorption peaks at wavelengths of 600, 312, and 254 nm were identified as the chromophore structure, and the naphthalene and benzene components of RB5, respectively. Little influence of iodide ion, tert-butyl alcohol, fluoride ion, or persulfate ion as h(vb)+, *OH, or e(cb)- scavengers on the decolorization proved that the decolorization of RB5 primarily proceeded by photolysis and/or O2*- in the bulk solution. After the decolorization, the process could shift progressively from the bulk solution to the surface of the catalysts and cleavage of the naphthalene and benzene rings was mainly attributed to the h(vb)+ pathway and *OH(ads) reactions, which was further verified by the effect of scavengers.

ABSTRACT:Electrodeposited thin films and nanoparticles of Ni 3 S 2 are highly active, poison and corrosion resistant catalysts for oxygen reduction to water at neutral pH. In pH 7 phosphate buffer, Ni 3 S 2 displays catalytic onset at 0.8 V vs the reversible hydrogen electrode, a Tafel slope of 109 mV/decade, and high Faradaic efficiency for four--electron reduction of O 2 to water. Under these conditions, the activity and stability of Ni 3 S 2 exceeds that of polycrystalline platinum and manganese, nickel, and cobalt oxides illustrating the catalytic potential of pairing labile first row transition metal active sites with a more covalent sulfide host lattice.The interconversion of water and O 2 is an essential chemistry underlying a future renewable energy economy. 1 Nature exe--cutes this kinetically demanding multi--proton, multi--electron interconversion with remarkable selectivity and efficiency. Oxygen evolution is carried out at the Mn 4 Ca co--factor of the oxygen evolving complex of photosystem II 2 whereas oxygen reduction is carried out at the heme/Cu ac--tive site of cytochrome C oxidase 3 and Cu 3 cluster active sites of multicopper oxidases. 4 While these catalysts operate effi--ciently and selectively under benign conditions of neutral pH and ambient temperature and pressure, precious and base metal containing heterogeneous catalysts typically require highly alkaline or acidic electrolytes ( Figure 1).The paucity of heterogeneous electrocatalysts capable of efficient oxygen reduction at neutral pH 5 arises from two seemingly divergent kinetic/materials requirements: 1) the catalyst must remain active in the presence of buffering elec--trolytes that are required to maintain neutral pH stability and deliver protons to drive the proton--coupled electron transfer (PCET) activation of O 2 6 and 2) the catalyst must resist protolytic corrosion under reducing conditions. Pre--cious metal catalysts such as Pt and Au meet the latter re--quirement but also strongly adsorb buffering electrolyte ions such as phosphate, degrading their catalytic efficiency. 7 In contrast, low valent mid to late first row transition metal ions are substitutionally labile, 8 allowing them to meet the first requirement, but this very property makes their corre--sponding oxides unstable with respect to corrosion in all but highly alkaline environments. 9Unlike metal oxides, bonding in transition metal sulfides is more covalent, inhibiting their corrosion under similar con--ditions. 10 Thus, we envisioned that both of the above re--quirements could be met if a labile first row transition metal active site ion can be exposed at the surface of a sulfide host lattice. Here, we illustrate the effectiveness of this design strategy by uncovering a novel earth abundant catalyst for oxygen reduction at neutral pH, the heazlewoodite phase of nickel sulfide, Ni 3 S 2 . Under phosphate buffered neutral pH conditions, Ni 3 S 2 outperforms state of the art ORR catalysts including MnO x and platinum owing to its unique combina--tion of labile ...

ABSTRACT:Starting from d,l-acid and SnCl 2 as catalyst, poly(d,l-lactic acid) (PDLLA) was directly synthesized by melt polycondensation. Under the appropriate conditions such as 0.5 wt % SnCl 2 , 170 -180°C, 70 Pa, and 10 h, the viscosity-average molecular weight (M ) of PDLLA was 4100 Da. PDLLA produced by the most practical method was used as the drug-delivery material for erythromycin and ciprofloxacin. The optimal conditions for the preparation of erythromycin-poly(d,l-lactic acid)-microsphere (ERY-PDLLA-MS) for lung targeting was investigated, and further confirmed by good reappearance tests. DSC and SEM demonstrated that ERY-PDLLA-MS had good spherical shape. The release in vitro of ERY-PDLLA-MS was effective and the half-time (T 1/2 ) was 51.0 h. After 175 h, the accumulated release percentage was 80.0%. The test in vivo showed that ERY-PDLLA-MS was more easily distributed in rabbit lung tissue. When PDLLA was applied in an antibacterial ciprofloxacin drug-delivery microsphere (CIP-P-DLLA-MS), CIP-PDLLA-MS was also characterized with DSC and SEM, and the release T 1/2 in vitro was 24.9 h. After 53.2 h, the accumulated release percentage reached 84.0%, which indicated that CIP-PDLLA-MS was advantageous to long-term release.

First-row transition metal oxides and chalcogenides have been found to rival or exceed the performance of precious metal-based catalysts for the interconversion of water and O2, central reactions that underlie renewable electricity storage and utilization. However, the high lability of the first-row transition metal ions leads to surface dynamics under the conditions of catalysis and results in active site structures distinct from those expected by surface termination of the bulk lattice. While these surface transformations have been well-characterized on many metal oxides, the surface dynamics of heavier chalcogenides under electrocatalytic conditions are largely unknown. We recently reported that the heazlewoodite Ni3S2 bulk phase supports efficient ORR catalysis under benign aqueous conditions and exhibits excellent tolerance to electrolyte anions such as phosphate which poison Pt. Herein, we combine electrochemistry, surface spectroscopy and high resolution microscopy to characterize the surface dynamics of Ni3S2 under ORR catalytic conditions. We show that Ni3S2 undergoes self-limiting oxidative surface restructuring to form an approximately 2 nm amorphous surface film conformally coating the Ni3S2 crystallites. The surface film has a nominal NiS stoichiometry and is highly active for ORR catalysis. Using DFT simulations we show that, to a first approximation, the catalytic activity of nickel sulfides is determined by the Ni-S coordination numbers at surface exposed sites through a simple geometric descriptor. In particular, we find that the surface sites formed dynamically on the surface of amorphous NiS during surface restructuring provide an optimal energetic landscape for ORR catalysis. This work provides a systematic framework for characterizing the rich surface chemistry of metal-chalcogenides and provides principles for the development of structure-energy-activity descriptors leading to a broader understanding of electrocatalysis mediated by amorphous materials.The interconversion of water and oxygen is a central chemistry underlying the storage of renewable electricity in energy-dense chemical bonds (Lewis and Nocera, 2006). The oxidation of H2O to O2 is the efficiency limiting half reaction for the splitting of water to generate H2 fuel, whereas the reduction of O2 to H2O is the efficiency limiting cathode reaction in low temperature fuel cells (Katsounaros et al., 2014). Platinum group metals and their corresponding oxides and chalcogenides are well-known catalysts for these reactions(Matsumoto and Sato, 1986) - (Gasteiger et al., 2005), but recent studies have uncovered a diversity of earth abundant first-row transition metal oxides(Kanan and Nocera, 2008) - (Long et al., 2014) and chalcogenides (Gao et al., 2012) , (Gao et al., 2013) that, depending on the reaction conditions, rival the activity of their precious metal analogs.Unlike their precious metal congeners, first-row transition metal ions are labile, Merbach, 1999, 2005) and as a result, the surfaces of these materials are expected to ...

A series of photocatalysts was synthesized by codoping TiO 2 with lanthanum and iodine (La-I-TiO 2 ). The structure and properties of the catalysts were studied by X-ray diffraction (XRD), the Brunauer-Emmett-Teller (BET) method, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectra. The prepared anatase-phase La-I-TiO 2 (molar ratio 20:20:100) calcined at 400 °C had a BET surface area of 92.9 m 2 g -1 , and the crystallite size calculated from XRD data was ∼3.57 nm, and it had a remarkable absorption in the visible light range of 400-550 nm. The catalytic efficiency was tested by monitoring the photocatalytic degradation of oxalic acid under visible light irradiation. An optimum molar ratio of 20:100 La/TiO 2 was determined for the most efficient inhibition of the recombination of electron-hole pairs and the photocatalytic activity of La-I-TiO 2 calcined at 400 °C was significantly higher than that calcined at 500 or 600 °C in aqueous oxalic acid solution. The probable process of oxalic acid degradation was that it was first adsorbed onto the surface of the catalysts, where it reacted with valence band holes (h vb + ) and the surface-bound or adsorbed • OH radicals ( • OH ads ) as well as reactive oxygen species (ROS) derived from oxygen reduction by photogenerated electrons, and finally converted into CO 2 and H 2 O without any stable intermediate.

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