N2-saturated Solution Research Articles

In-MOF derived In2S3-X@ZnS heterojunction with rich sulfur vacancies for enhanced performance in photocatalytic nitrogen fixation

Photocatalytic nitrogen fixation has the characteristics of green, energy-saving and environment-friendly. Herein, the hollow microtube-flower In2S3-X@ZnS with rich sulfur vacancies was synthesized by the one-step solvothermal method of sulfurization from the precursor MIL-68(In). In-MOF derived sulfur-vacancy modulation and the construction of the In2S3-X@ZnS heterojunction had been proved to be the desirable strategies to dramatically enhance the ammonia production rate. One the one hand, the characterizations of HRTEM, ESR and the transient photocurrent responses (TPR) in N2, Air and Ar saturated solution directly and indirectly proved the existence of rich sulfur-vacancy, which could be the active sites for the chemisorption and activation of N2. On the other hand, the results of EIS, PL and band analysis demonstrated that the established Type-п heterojunction promoted the photogenerated carriers to separate and clarified the enhanced photocatalytic mechanism, the corresponding nitrogen fixation performance had been greatly improved with a high yield rate of 58.988 µmol∙gcat−1∙h−1, which was evidently much higher than that of pristine In2S3-X and pure ZnS. This work provided a new insight for developing functional photocatalysts with the synergy effect of sulfur-vacancy and heterojunction for highly efficient nitrogen fixation.

Mechanism of electrochemical carbon dioxide reduction to formate on tin electrode

Carbon dioxide can be electrochemically reduced to formate on tin electrodes. Formate is one of the most economically viable products of CO2 reduction reaction (CO2RR). While CO2 is reduced to formate, hydrogen evolution reaction (HER) occurs concomitantly. The kinetics of CO2RR and HER on the tin electrode was investigated. Potentiodynamic polarization studies were conducted in CO2 saturated and N2 saturated 0.1 M KHCO3 solutions, in the potential range from −0.014 V to −1.59 V vs. RHE. A faradaic efficiency of 93.95 % towards formate production was obtained at −1.09 V vs. RHE. The mass transfer effects and bicarbonate dissociation equilibrium were used to estimate the concentration of the reactants at the electrode surface. Density functional theory calculations indicate that –OCHO intermediate species is thermodynamically favoured, and a four-step reaction with two intermediates is proposed. The proposed mechanism captures the major features of the polarization data. CO2 reduction occurs via two intermediate species, viz. adsorbed H and OCHO species, while HER occurs via Volmer-Heyrovsky steps. The model predicts that in N2 saturated solutions, the fractional surface coverage of adsorbed H reaches a maximum of ∼0.48 at a potential of −0.82 V vs. RHE while in CO2 saturated solutions, the corresponding value is ∼0.29. In addition, the maximum fractional surface coverage of adsorbed OCHO is predicted to be ∼0.12 in CO2 saturated solutions.

In-Situ Observation of Adsorption Species on Platinum Catalyst in Oxygen Reduction Reaction Using High Energy Resolution XAFS

The oxygen reduction reaction (ORR) on Pt surfaces, for examples, Pt single crystals, polycrystalline Pt electrodes, Pt nanoparticles (NPs), Pt-based alloys, and core–shell Pt nanostructures, has been discussed in the last few decades.In polymer electrolyte fuel cells (PEFCs), hydrogen peroxide and its radicals are known to be fatal attacking species not only for electrode catalysts but also for carbon materials and polymer membranes.A thorough understanding of ORR schemes has led to the development of seamless four-electron reduction cathodes, contributing to improved endurance reliability of both anion-exchange membrane (AEM) and proton-exchange membrane (PEM) fuel cells.In this study, the reaction pathway, and intermediate species such as molecular oxygen, in the ORR were investigated in alkaline and acidic environments, respectively.In this work, High Energy Resolution Fluorescence Detection X-ray Absorption Spectroscopy (HERFD-XAS) at the Pt L III-edge, which enhances resolution by partially collecting fluorescent X-ray was employed.X-ray absorption fine structure (XAFS) can detect the electronic structure of Pt, and its high energy resolution makes it possible to distinguish between different adsorption species on the surface of Pt nanoparticles.In addition, photon-in photon-out experiments using hard X-ray with high penetrating ability make it relatively easy to perform in-situ/operando measurements in potential controlled solutions.Carbon-supported Pt nanoparticles as powder catalysts were used for measurement as more realistic conditions, and the species adsorbed on the Pt nanoparticles were analyzed while controlling under the potentials both in acidic and basic electrolyte solutions with N2 or O2 gas bubbling.In N2-saturated solutions, the XANES spectra of the Pt LIII-edge reflected the presence of the adsorption species such as Pt-O (*O), Pt-OH (*OH), Pt-H (*H), as well as PtO2 oxide and Pt metallic states without any adsorption, during the ORR with the potential change.In O2-saturated solutions, one additional adsorption species of molecular oxygen was observed in both acidic and basic electrolyte solutions. It was analyzed that the intermediate species adsorbed to platinum in a side-on configuration as a superoxide anion in an alkaline environment.This intermediate species is identified as hydrogen superoxide, also known as hydroperoxyl radical, with the chemical formula HO2 by being protonated in an acidic environment.The results of research on adsorption species using HERFD-XAS have provided important knowledge for designing catalysts that enable seamless four-electron reduction.The preferred cathode catalyst design will be discussed in detail in an oral presentation at the 244th ECS Meeting. Acknowledgments: The synchrotron radiation experiments were performed at the BL11XU in the SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Numbers of 2012B3506, 2013A3506, 2014A3506, 2014B3506, 2015B3506, 2016A3556 2019A3508, 2019B3508, 2020A3508, 2021A3508, 2021B3508, 2022A3508 and 2022B3597 at BL11XU). This work was supported by JSPS KAKENHI Grant Number JP22H02188). Figure 1

Promoting photocatalytic nitrogen reduction for aqueous nitrogenous fertilizer from organic wastewater over p-BiOBr/n-Bi2MoO6 hetero-nanofibers

Photocatalytic nitrogen reduction (PNR) is a potential routine for producing aqueous nitrogenous fertilizer via a green chemistry process but is still limited by a relatively poor efficiency. Considering the dynamic coupling of excited electrons and holes, we introduced organic wastewater oxidation process to substitute the sluggish water oxidation for promoting the PNR reaction. We developed p-BiOBr/n-Bi2MoO6 Z-scheme hetero-nanofibers and experimentally studied their interface charge transfer mechanism in detail. Their strong redox ability and high charge separation efficiency enabled efficient PNR with simultaneous organic pollutant degradation. They have exhibited a PNR rate of up to 911.6 µmol g−1 h−1 L−1 in Rhodamine B (RhB) solution, about 2.5 times higher than that in pure water. Meanwhile, their RhB removal rate reached ∼91.2% in the PNR process (i.e., in N2 saturated solution), close to that in the air (∼96.6%) due to the strong oxidation ability of valence band holes. The proper loading ratio of BiOBr on the hetero-nanofibers and their super-long one-dimensional structures were essential for tuning the charge separation and photocatalytic activity. Moreover, the dual-functional system exhibited efficient photocatalytic performance in a natural water matrix and simulated flowing wastewater scene. Based on a comparative plant cultivation study, the system could effectively convert pollutant solutions into aqueous nitrogenous fertilizers that could promote the healthy growth of nitrogenous sensitive plants. The green and sustainable strategy of PNR for aqueous nitrogenous fertilizer from organic wastewater would have broad applications in energy conservation and environmental remediation.

Research on direct electron transfer of native glucose oxidase at PEDOT:PSS hydrogels modified electrode

Direct electron transfer (DET) is the critical issue in developing the third-generation glucose biosensor. However, the DET of glucose oxidase (GOx) is hard to realize because the redox center of GOx is located deeply within the enzyme molecule. Here, we have studied DET of GOx on a poly(3,4-ethylene dioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) hydrogels decorated carbon nanotube fiber (CNTF) electrode with oxygen-independence glucose determination performance. PEDOT:PSS hydrogels modified on carbon nanotube fiber by electrogelation might play a key role in keeping the catalytic activity and DET for GOx simultaneously. The cyclic voltammetric result of the biosensor shows a pair of well-defined and quasi-reversible redox peaks with a formal potential of −0.431 V and a peak-to-peak separation of 69 mV. The constructed biosensor shows a linear range from 0.05 to 0.5 mM and a sensitivity of 43.52 μA mM−1 cm−2 toward glucose via a constant potential of −0.3 V in an N2-saturated solution. Three GOx models on the electrode surface are proposed to explain these DET-related electrochemical performances of the biosensor. We demonstrate the DET for the native GOx with catalytic activity in PEDOT:PSS hydrogels, which takes a step towards developing the third-generation glucose biosensor with conductive hydrogels.

ELECTROCHEMICAL CO2 REDUCTION OF RHENIUM TRICARBONYL COMPLEX

Carbon dioxide is considered as a primary reason for global climate change, thus CO2 needs to be urgently reduced. Catalytic conversion of CO2 into chemical fuels is one of the most crucial technologies that can address both global warming and the depletion of fossil fuels. Rhenium tricarbonyl complex [Re(bpy)(CO)3Cl] (bpy: 2,2’ bipyridine) possesses a great potential of capturing and highly selective converting CO2 to carbon monoxide. In the current study, we synthesized and characterized the structure of [Re(bpy)(CO)3Cl] by 1H NMR, ESI-MS, FITR, and PL spectroscopy. The electrochemical properties and the electrochemical CO2 reduction of [Re(bpy)(CO)3Cl] in the absence and presence of an electron donor source were carried out using cyclic voltammetric measurements. The cyclic voltammogram of [Re(bpy)(CO)3Cl] in N2-saturated DMF solution displayed one irreversible reduction wave at -1.33 V. [Re(bpy)(CO)3Cl] expressed its electrocatalytic behavior in CO2 atmosphere by the enhancement of the cathodic current density. The current increased approximately twofold in CO2-saturated DMF solution (from 0.15 to 0.32 mA/cm2) and more enhancement when adding TEOA solvent. With the presence of an electron donor, the CO2 reduction efficiency of [Re(bpy)(CO)3Cl] was improved and represented by an approximately fourfold increase in cathodic current from 0.32 to 1.12 mA/cm2. One-electron reduced species of [Re(bpy)(CO)3Cl] observed at 1.33 V in N2 and CO2-saturated electrolytes contributed to the reaction with CO2.

Effect of Hydrogen Pressure on the Intrinsic Kinetics of Hydrogen Evolution Reaction at Pt(111) Electrode

Many kinetic studies on hydrogen evolution reaction (HER) were done in N2 saturated solutions in order to avoid possible H2 leakage, which results in a variation of H2 concentration at the electrode/electrolyte interface (). It will induce the drift of equilibrium potential (Eeq) and applied activation overpotential (η act) for HER. Consequently, it may result in errors for estimating the kinetic parameters for HER. By taking HER at Pt(111) under RDE configuration as a model reaction, quantitative relation among and the reaction current density (j) is established based on the mass transport equations. From the j–η act plots, our results reveal that i) with the increase of HER current, the equivalent increases, which accompanies with a drift of thermodynamic equilibrium potential (Eeq) for HER decreases; ii) when η act is negative of −50 mV, the j–η act plot for HER is the same in N2 and H2 saturated solution, with a slope of 30 mV Dec−1; Our results suggest that HER activity should be compared in solutions with the same composition and at the same activation overpotential instead of at the same applied potential. Proper experimental methods for post data analysis are proposed in order to derive the intrinsic HER kinetics.

Supramolecular semiquinone radicals confined with DNAzymes for dissipative ROS generation and therapy

Current reactive oxygen species (ROS)-regulating materials for disease treatments are always at turn-on state, leading to long-lasting inflammation and chronic wound healing. Inspired by the process of Coenzyme Q (CoQ)-mediated ROS formation in the mitochondrial electron transport chain (ETC), a dissipative ROS nanogenerator possessing energy storage function and horseradish peroxidase (HRP)-mimicking activity was realized by a type of ternary composite nanosheets. Specifically, semiquinone radicals generated from polydopamine polymerization were captured and stabilized by supramolecular DNA scaffolds hosts, i.e. G-quadruplexes/hemin (GH) complexes with large π-planes of bases and interplane spaces. As a consequence, semiquinone radicals served as electron donor to oxygen for generating H2O2 which could be utilized by the neighboring GH to generate hydroxyl radicals (•OH) at weakly acidic conditions. The cascade catalytic activity remained above 93% and 45% after 20, 60 days of storage in N2 saturated solution. However, it was consumptively attenuated (~22 h of dissipation duration) due to the electron depletion/exhaustion of semiquinone radicals at pathological conditions. Thereby, effective inhibition of tumor recurrence and wound infection, as well as accelerated tissue repair were achieved in tumor postoperative treatments. This system significantly advances ROS regulators for integrative therapy.

Oxidative electropolymerization films of a styrene-appending ruthenium complex with highly performed electrochemical, solar photoelectric conversion and photoelectrochemical oxygen reduction properties

Vinyl or styrene-containing ruthenium complexes were previously reported to be reductively electropolymerized, which needed to be carried out under strict deoxygenation conditions. Here, we present the first example of an oxidatively electropolymerized thin film of a styrenyl-containing ruthenium complex, Ru1 under ambient condition. As revealed by UV–visible absorption spectroscopy, emission spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, electrochemical impedance spectroscopy, cyclic voltammetry, and photoelectrochemical measurements, the electropolymerized films, poly(Ru1)n, exhibited good adherence and chemical stability, porous structure, strong photoluminescence, well reversible and surface-controlled RuIII/II redox behavior. More interestingly, at a -0.4 V external bias potential, a significant cathodic photocurrent density of 8.04 μA/cm2 was observed for poly(Ru1)3-modified ITO electrode irradiated by 100 mW•cm−2 white light in an air-equilibrated 0.1 M Na2SO4 aqueous solution. Furthermore, the photo-current polarity could be switched from cathodic to anodic up to a photocurrent density of 9.22 μA/cm2 for poly(Ru1)3-modified ITO electrode as the electron donor of quinhydrone was added under external bias potential-free conditions. More interestingly, poly(Ru1)3 exhibited impressively strong photoelectrochemical oxygen reduction properties with a O2-induced 4.7-fold cathodic photo-current enhancement relative to a N2-saturated electrolyte solution condition. This work offers an efficient way to fabricate highly stabilized Ru(II) complex-based modified electrodes by facile oxidative electropolymerization of the styrenyl-containing ruthenium complex, offering poly(Ru1) films with intriguing applications in electrochemical, photoluminescence, photoelectrochemical O2 reduction and solar photoelectric conversion, molecular switching devices.

Increased production of H2 under visible light by packing CdS in a Ti, Zr-Based metal organic framework

Metal organic frameworks (MOFs) are crystalline porous materials, and some of them have been used as photocatalysts for H2 production in the presence of Pt and sacrificial reagents. Herein we report a significantly enhanced production of H2 on mixed CdS and MOF, measured under a 420 nm LED lamp in a N2-saturated aqueous solution containing Na2S and Na2SO3. MIL-125-NH2, UiO-66-NH2, and PCN-415-NH2, which are Ti-, Zr-, and Ti, Zr-based MOFs, respectively, were prepared, followed by a two-step precipitation of CdS. All MOFs were nearly not active, but CdS-loaded MOFs were not only active, but also more active than either CdS or Pt/CdS. Moreover, at 40% CdS loading, the MOF activity was PCN-415-NH2 > MIL-125-NH2 > UiO-66-NH2. N2 adsorption showed that CdS nanoparticles were present in the micropores of MOFs. Then the solid photoluminescence, band parameters, and (photo)electrochemical reactions were measured. Accordingly, a possible mechanism is proposed, involving the electron transfer from CdS to PCN-415-NH2, and the hole transfer from PCN-415-NH2 to CdS. In the reaction process, both CdS and MOF act as photocatalysts, other than co-catalysts. This work shows a simply strategy for enhancing H2 production under visible light.

PEFC Cathode Catalysts of ZrO2/C Prepared By RF Magnetron Sputtering and Crosslinked Polymer Methods

Fuel cells are expected to be clean power generation devices in the future energy society. Various types of fuel cells, which are different in electrocatalysts, electrolytes, and operating temperatures, are available for practical use in various places depending on their characteristic. Among them polymer electrolyte fuel cells (PEFC) have been applied to fuel cell vehicles (FCV), household cogeneration systems and etc. PEFC uses large amounts of Pt for electrocatalysts, which is one of the serious problems for large scale commercialization. The worldwide production of Pt is about 180 ton/year, and about 60 g of platinum is practically used in one FCV. If all of the world production of Pt is used for FCV, only 3 million of FCV can be manufactured in a year, although the annual production of cars in the world is about 100 million. Therefore, the development of electrocatalysts with non-Pt materials is indispensable for the broad spread of PEFC. The cathode catalysts significantly affect to the cell voltage, current density, and durability, so that the developments of alternative cathode materials to conventional Pt-based catalysts are expected. Compounds of oxides of group 4 and 5 elements transition metals such as Zr, Ta, Nb, and Ti, chalcogenides such as Ru and Mo, and carbon materials with N-containing complexes of Fe and Co, carbon materials doped with B and N are intensively investigated in the past decade. In this study, ZrO2/C catalysts were investigated for oxygen reduction reaction (ORR) activity in acidic media. Two types of preparation methods have been examined; radio-frequency magnetron sputtering and crosslinked polymer methods.In magnetron sputtering method, carbon black (CB) powders were stirred in a rotary drum chamber with milling balls and cubes. A Zr metal target was attached to a sputtering gun placed in the stirring drum. Sputtering was performed in 10 Pa of Ar. In crosslinked polymer method, ammonium zirconium carbonate (AZC) was used as a crosslink reagent for polyvinyl alcohol (PVA). Addition of citric acid (CA) was found to be effective. Mixture of AZC, PVA, and CA were well stirred at 80ºC, and CB was immersed in the mixture. The mixture was dried at 300ºC in air and them heat treated 600~1200ºC in N2 or H2. The catalyst ink was obtained by ultrasonically dispersing 300 µL of isopropanol (IPA), 4 mg of catalyst and 12 µL of 5% Nafion-dispersed solution. The sample electrode was prepared by dropping 150 µL of the catalyst ink on glassy carbon (GC) and drying. ORR activity was measured in 0.1 M H2SO4 with O2 bubbling.ORR activity of ZrO2/C catalysts which were prepared by sputtering method was shown in the attached figure. This figure shows ORR properties of ZrO2/C catalysts prepared at various sputtering times in 0.1 M H2SO4. ZrO2/C was pretreated in H2 flow at 1000˚C for 3 h. ORR current was difference between current in O2 and N2 saturated solutions. ORR Current appeared around 0.8 VR HE for the catalysts deposited longer than 40 min. This result indicate ZrO2/C have obvious ORR activity. X ray diffraction (XRD) of ZrO2/C showed the formation of both monoclinic and tetragonal ZrO2 crystals. ZrO2 particles with diameter in several nm scale were observed by transmission electron microscopic (TEM) images, and formation of these particles were concluded to contribute the obvious ORR activity. On the other hand, ZrO2/C catalysts which were prepared by crosslinked polymer methods also showed similar ORR activity to those by sputtering method. The details were discussed in the presentation.This work was supported by ESICB, Kyoto University and New Energy and Industrial Technology Development Organization (NEDO) of Japan. Figure 1

One-Pot Preparation of Pt Nanoparticle-Supported Graphene Nanoplatelets By Ionic Liquid-Pyrolysis Method

sp2-hybridized carbon materials, such as carbon nanotube and graphene nanoplatelet (GNP), have attracted a great deal of attention for their unique physicochemical properties. The carbon materials emerged as the promising candidates to replace carbon blacks as polymer membrane electrolyte fuel cell (PEMFC) catalyst supports, because those can prevent carbon oxidation and Pt nanoparticle catalyst agglomeration during start and stop cycling of the PEMFC.1 However, the problem is how to anchor Pt nanoparticles over the smooth chemical inert surface of these carbon materials. It has a big risk leading to a decrease in the desired stability of GNP by the commonly used method of grafting functional groups onto the destroyed honeycomb structure.2 Recently, based on the ionic liquid (IL)-based two-step method,3 we established a simple and mass-production available one-pot pyrolysis method with ionic liquid (IL one-pot process) for preparing Pt metal and PtNi alloy nanoparticle-supported multi-walled carbon nanotube composite electrocatalysts for oxygen reduction reaction (ORR).4 In the present study, this method was applied to two kinds of GNPs with different thicknesses, 20~30 layers (GNP-20) and 3 layers (GNP-3). The impacts of IL and GNP species on the catalytic performance to ORR were examined in detail. Two types of ILs, N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)amide ([N1,1,1,3][Tf2N]) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim][Tf2N]) were used as reaction media. These ILs were purified by an appropriate pretreatment process prior to use. 2.5 g L-1 of platinum(II) acetylacetonate was mixed with 1.25 g L-1 GNP-20 in the ILs. The Pt nanoparticle supported GNP-20 composite materials (Pt/GNP-20s) were prepared by agitating the IL mixtures at 573 K for 4 hrs under N2 atmosphere. Similarly, Pt/GNP-3s were prepared using GNP-3 instead of GNP-20. The resultant composites were washed with acetonitrile and water several times and dried in vacuum overnight. The final products were characterized by TEM, ICP, and XRD. Their electrocatalytic performances were evaluated by electrochemical measurements.3,4 Figure 1 shows TEM images of Pt nanoparticle supported GNPs prepared by the IL one-pot process method. Compared to the specimens prepared in [N1,1,1,3][Tf2N], those in [C4mim][Tf2N] have smaller Pt nanoparticle size and show better Pt nanoparticle dispersion, if carbon supports are the same. These results seem to be related to the molecular structures of organic cations in reaction media. [C4mim][Tf2N] contains a larger cation with an aromatic ring, which can form a π-π stacking structure on the GNPs,5 would confine the nucleation points for Pt nanoparticle deposition at the anchor points. Difference in the GNP species affected Pt nanoparticle size on the Pt/GNP-20s and Pt/GNP-3s. For example, when [N1,1,1,3] [Tf2N] was used, mean particle sizes for the Pt nanoparticle on GNP-20 and GNP-3 were 3.8 nm and 3.3 nm, respectively. This result is attributed to a difference in specific surface area, i.e., Pt nanoparticle growth is suppressed on the GNP-3 having a larger surface area and more nucleation points. As given in Table I, the similar tendency was also recognized in [C4mim][Tf2N]. Electrocatalytic performances for the obtained Pt/GNP-20s and Pt/GNP-3s were evaluated by commonly-used electrochemical approaches in N2 and O2 saturated HClO4 solutions along with a commercial catalyst (TEC10V30E). All the electrochemical data are summarized in Table I. The Pt/GNP-3 prepared in [C4mim][Tf2N] shows the highest mass activity (439.34 A g-1) among all Pt nanoparticle supported GNPs because of the smallest mean particle size. Considering oxygen accessibility, Pt nanoparticle density per unit area of the basal plane on GNPs may also affect the electrocatalytic performances. Interestingly, after 15000 cycle durability test, all the Pt/GNPs showed higher mass activity retention rates than TEC10V30E. This should be due to the chemically stable surface structure at the basal plane on the GNP. References X.Zhou, J. Qiao, L. Yang, and J. Zhang, Adv. Energy Mater., 4, 1301523 (2014).L.Xin, F. Yang, S. Rasouli, J. Xie, et al., ACS Catal., 6, 2642 (2016).K.Yoshii, T. Tsuda, T. Torimoto, S. Kuwabata, et al., J. Mater. Chem. A, 4, 12152 (2016).Y.Yao, R. Izumi, T. Tsuda, S. Kuwabata, et al., ACS Appl. Energy Mater., 2, 4865 (2019).T. Fukushima, A. Kosaka, Y. Ishimura, T. Yamamoto, T. Aida, et al., Science, 300, 2072 (2003).

Electrodeposited thiophene-containing organic small molecule-modified ITO electrode with highly efficient photoelectric conversion and photoelectrochemical oxygen reduction

An organic small molecule-based thin film on an indium-tin oxide (ITO) electrode was fabricated by anodic coupling of a novel thiophene unit-capping organic small molecule (L), and characterized by ultraviolet-visible absorption spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and photoelectrochemical measurements. The n cycles of anodic potential scanning produced red-colored electrodeposited films of Film(dimer-Ln) in minutes with visible light harvesting characteristics akin to those previously observed for ruthenium polypyridyl complex star dye-based films that were much more costly and difficultly accessible. Film(dimer-Ln) films were found to exhibit surface-controlled thiophene unit associated redox behaviors and significant cathodic photocurrent generation properties. As irradiated with white light at 100 mW cm−2 and biased at a zero potential, a Film(dimer-L2)-modified ITO electrod exhibited a high photo-to-current conversion efficiency of 0.90% at 450 nm, and a photocurrent density of 13.6 μA cm−2 in an N2-saturated electrolyte solution, which was greatly boosted by ~7 folds to 108.8 μA cm−2 in an O2-saturated electrolyte solution. The resulting modified electrodes offer great prospects for a wide range of applications ranging from photoelectric conversion to light detection devices to photoelectrocatalytic O2 reduction and sensing.

Iron Phthalocyanine-Knitted Polymers as Electrocatalysts for the Oxygen Reduction Reaction.

Knitted iron phthalocyanine-based porous polymer networks (K-FePcs) were prepared in a single step using solvent-knitting strategies with commercial iron phthalocyanine as a building monomer. The incorporation of different aryl comonomers (biphenyl and 1,2,4,5-tetraphenylbenzene) to FePc allowed quantitative yields, high porosities, and excellent ORR activity. The reversible Fe(III)/Fe(II) redox potential of FeN4 centers of the knitted polymer networks in N2-saturated electrolyte solution (i.e., ∼0.8 V vs RHE) were shown as good descriptors of their ORR activity. K-FePc2Ph presented the highest amount of FeN4 active sites and an adequate degree of steric hindrance to maintain the isolation between catalytically active sites. Moreover, it displayed comparable current density limits and superior mass activity and half-wave potential (i.e., 0.88 V vs RHE) than those of 20% Pt/C benchmark catalyst, while keeping higher stability toward methanol oxidation. K-FePc2Ph can be an interesting alternative to Pt-based ORR electrocatalysts.

The effect of carbon dioxide and nitrogen on pyrite surface properties and flotation response

In 1997 Newmont USA Ltd. introduced the N2TEC process for the flotation recovery of auriferous pyrite and other sulfide minerals in Carlin type ores, using nitrogen as the flotation gas, and low pH to prevent oxidation and hydrolysis of the pyrite surface. However, increased amounts of carbonate gangue minerals in certain Carlin type ores adversely affect the flotation recovery due to difficulties with pH control in the presence of carbonate minerals, i.e. calcite, dolomite, etc. Subsequently, it was discovered that by using CO2 for flotation, the pH of the system can be more effectively controlled, and consequently the recovery and rate of pyrite flotation can be improved significantly.In our current laboratory research on pyrite flotation chemistry these results were confirmed, as both fresh and oxidized pyrite particles exhibited an increased flotation response in CO2 saturated solution. It was found that the water contact angle at the pyrite surface increased in CO2 and N2 saturated solutions, while surface oxidation and bubble attachment time decreased. In addition to decreased surface oxidation and the influence of pH on surface hydrolysis, the significance of bubble attachment phenomena in these CO2 flotation systems helps to explain the improved flotation response.

A Spectroscopic Study on the Electrochemical Nitrogen and Nitrate Reduction Reactions on Rhodium and Ruthenium Surfaces

Ammonia is one of the most promising carbon-free alternative energy storage media for several reasons, including its high weight fraction of hydrogen (17.65%), ease of decomposition to produce high-purity hydrogen, ease of liquefaction at room temperature, and low transportation cost.1 The N2 reduction reaction (NRR) is an attractive approach to synthesizing ammonia with renewable electrical energy by using water and nitrogen as the reactants.2-3 Rh and Ru are promising N2 reduction reaction electrocatalysts, given their suitable nitrogen adsorption energy and low overpotential. However, the N2 reduction reaction pathway on these surfaces is still unclear, as there is a lack of information about the reaction intermediates. In this study, we employed surface-enhanced infrared absorption spectroscopy (SEIRAS) and differential electrochemical mass spectrometry (DEMS) to study the reaction mechanisms of nitrogen reduction on Rh and Ru. A Rh nanofilm deposited on the Si prism by a chemical deposition method was used as the working electrode. Figure 1a shows the IR spectra collected in the first CV segment in N2-saturated KOH solution with the spectrum at 0.4 V as the reference. The bands at 3250 and 1612 cm-1 attribute to the O-H stretching and H-O-H bending of water molecules. Those bands intensity increase significantly as a result of the change in the adsorption configuration of water molecules upon decreasing the potential. A weak band at 1865 cm−1 emerged below −0.2 V, and the band intensity increased as the potential became more negative, which was assigned to the adsorbed H atoms. An obvious band at ~2020 cm−1 was attributed to the N=N stretching of end-on adsorbed N2HX (1≤X≤2) on the Rh surface. These bands were clearly revealed in a single spectrum at 0 and −0.4 V, shown in Figure 1b. The potential dependence of the N=N stretching band absorption and frequency are given in Figure 1c, as well as the IR absorption potential dependence of hydrogen on the Rh surface. When the potential fell from 0.2 V to −0.05 V, the band intensity of N2HX was significantly enhanced, peaking at −0.05 V, which suggested that the coverage of the adsorbed N2HX species on the Rh surface was boosted in this potential range. Simultaneously, the frequency of the N=N stretching band was blue-shifted from 1997 cm−1 at 0.2 V to 2034 cm−1 at −0.05 V, due to the weakened adsorption strength of the N2HX species on the Rh surface. The highest N2HX coverage was achieved between 0 and −0.2 V. When the potential further decreased from −0.2 to −0.4 V, the N=N stretching band intensity decreased, indicating less coverage of the adsorbed N2HX species. Figure 1d presents the DEMS data collected during the NRR in an alkaline electrolyte with Rh/C as the electrocatalyst. As occurred during nitrate reduction, the pulse DEMS signal of H2 (m/e = 2) was detected at potentials below 0 V as the HER occurred on the Rh surface. The pulse DEMS signal of N2H2 (m/e = 29) was also detected with H2, but its intensity was much lower than that of H2 (m/e=2), and the signal of N2H2 (m/e = 30) was undetectable. Similar spectroscopic studies on Ru surface will be also discussed. Figure 1. (a) FTIR spectra during the first segment from 0.4 to −0.4 V on Rh film electrode in N2-saturated 0.1 M KOH solution. The reference spectrum was taken at 0.4 V. (b) Single spectrum at 0 V (black line) and −0.4 V (red line) in the range of 1250−3000 cm−1. (c) Potential dependence of the N=N stretching band IR absorption (black dot) and frequency (red triangle), derived from (a). The potential dependence of the hydrogen IR absorption magnified by a factor of two (pink dot) is also given. (d) DEMS of H2 (m/e = 2) and N2H2 (m/e = 29, 30) on Rh/C during a scan from 0.4 to −0.8 V in N2-saturated 1 M KOH solution. Potential scan rate: 5 mV s−1. References Lipman, T.; Shah, N., Ammonia as an Alternative Energy Storage Medium for Hydrogen Fuel Cells: Scientific and Technical Review for Near-Term Stationary Power Demonstration Projects, Final Report. UC Berkeley Transportation Sustainability Research Center 2007.Giddey, S.; Badwal, S. P. S.; Kulkarni, A., Int. J. Hydrogen. Energ. 2013, 38, 14576-14594.Guo, C. X.; Vasileff, A.; Qiao, S., Energ. Environ. Sci. 2017. Figure 1

First Assessments of the Influence of Oxygen Reduction on the Glycerol Electrooxidation Reaction on Pt

The electroactivity of new nanomaterials candidates to be used as anodes for glycerol fuel cells or electrolysers has been largely investigated, but most of the literature reports the use of O2-free solutions. However, the purging process to extract O2 from glycerol solution and the storage at similar condition is costly. Moreover, the lack of knowledge on the glycerol electrooxidation reaction (GEOR) in the presence of O2 prevents alternative applications, as that in single channel microfluidic fuel cells, when the anode must be selective for the alcohol oxidation in the presence of O2. Herein, we accessed the influence of the oxygen reduction reaction on the GEOR by using a flow system with an electrode in wall-jet configuration. The GEOR is investigated on Pt/C nanoparticles (NPs) in the presence of different amounts of O2 in solution as a proof of concept. We also used synthesized Pt@Au to apply the method for a new material candidate to be used as catalyst in glycerol technologies. The presence of oxygen in solution barely influences GEOR on Pt/C or Pt@Au whenever classic stationary measurements are used. We found comparable electrocatalytic parameters and the same carbonyl products, but at slightly different proportions, in the presence or absence of O2 after long-time electrolysis followed by chromatographic analysis. On the other hand, oxygen competes with glycerol by the active sites when the reactants are convectively forced towards the electrode surface, at flow configuration. The competition between GEOR and oxygen reduction results in a net cathodic current density when using O2-saturated glycerol solution at potentials suitable for the reduction reaction on Pt/C. Pt@Au shows remarkable activity for the oxygen reduction, producing high cathodic currents even in air-saturated glycerol solution. Moreover, the presence of O2 greatly decreases the stability of Pt@Au during GEOR, mainly due to the improved oxygen reduction and extended surface accessed by O2, while same material controversially displayed good stability in N2-saturated solution. The use of flow configuration shed a light on the influence of O2 on GEOR, providing new information non-accessible by other classic stationary methods.

(Invited) In Situ Structural Analysis of PtCo Alloy Catalysts with Stabilized Platinum-Skin Layers and Durability/Activity Towards Oxygen Reduction Reaction

For polymer electrolyte fuel cells, Pt-based alloy catalysts have been widely studied. We have developed the nanocapsule method1,2 for the synthesis of PtCo alloy nanoparticles (n-PtCo) with well-controlled size and composition. On n-PtCo subsequently treated in hydrogen gas at high temperature (n-PtCoH2-HT), additional Pt-skin layers were formed (PtxAL-PtCo).3 Figure 1 shows the area-specific activities j k for the oxygen reduction reaction (ORR) at carbon-supported n-PtCoH2-HT and PtxAL-PtCo (n-PtCoH2-HT/C and PtxAL-PtCo/C, respectively) and a commercial carbon-supported Pt catalyst (c-Pt/C) coated with Nafion in O2-saturated 0.1 M HClO4 solution at 65 oC and 0.85 V vs. RHE measured by a multi-channel flow double-electrode cell technique.2 Potential-step cycles were applied to the catalyst electrodes as the accelerated durability tests (ADTs) simulating load-change cycles of fuel cell vehicles4 in N2-saturated solution with no solution flow. Both the initial j k and the durability were the highest at Pt2AL-PtCo/C.3 Figure 2 shows changes in the electrochemically active areas (ECAs) of n-PtCoH2-HT/C and PtxAL-PtCo/C during the ADTs in a constant solution flow at 65 °C so that the re-deposition of Pt became negligible. The ECA values of the catalysts decreased as the number of potential-step cycles increased, and the losses of the ECA of n-PtCo/C and PtxAL-PtCo/C after 5000 cycles were 42% and 26%, respectively. Therefore, the ECA loss was much mitigated by the existence of Pt skins. Figure 3 shows the in-situ X-ray diffraction (XRD) pattern of the (111) peak of Pt-Co alloy of n-PtCo/C and PtxAL-PtCo/C measured during the ADT in a solution flow. For n-PtCo/C, the diffraction peak at ca. 27.6° was close to that for Pt (27.5°), suggesting that Co easily dissolved from n-PtCo into the hot acid electrolyte solution. The peak was small and broad even before the ADT, probably because of a low order of atoms in crystallite. In the XRD pattern of PtxAL-PtCo/C, a significantly large, distinct peak was observed before the potential cycles; the ordering of atoms in PtxAL-PtCo was very high. The peak was almost unchanged after the potential-step cycles, indicating that the crystallite structures of PtxAL-PtCo remained the same. The parameters of the Pt-Co alloy catalysts from the data obtained by the electrochemical measurements, transmission electron microscopy, and in-situ XRD are listed in Table 1. For n-PtCo/C, the crystallite size was approximately 2.3 nm during 5000 cycles. The number of crystallites per area and the metal retention ratio gradually decreased from 14 × 103 to 10 × 103 mm-2 and from 100% to 50%, respectively. Not only the dissolution but the migration/coalescence also played a role. For PtxAL-PtCo/C, the crystallite size was approximately 2.9 nm during 5000 cycles. No change was indicated in the shape and the number of the crystallites per area, as well as the loss of the metals. Interestingly, the ECA of PtxAL-PtCo/C gradually decreased during 5000 cycles by 26%. Therefore, it is assumed that the PtxAL-PtCo crystallites were aggregated into a larger particle consisting of multi-crystallites, while keeping the shape of each crystallite unchanged. The loss of ECA is explained by the loss of surface areas by a contact between crystallites. As shown in Fig. 1, the j k value at PtxAL-PtCo/C remained the same level during the potential-step cycles. The coalescence of alloy crystallites without any dissolution of Pt and Co clearly explains this constant value of j k. Analyzing an EXAFS of Pt in PtxAL-PtCo/C, the Debye-Waller factor for Pt–Pt in PtxAL-PtCo/C was even smaller than that of Pt nanoparticles with a similar size, revealing that the crystallinity of the outer Pt skin was extremely high.6 Thus, the existence of a rigid Pt skin realized the extensively high durability of PtxAL-PtCo/C. Further structural analyses of the Pt-Co catalyst at the atomic level are now in progress. Acknowledgements This work was carried out under the “SPer-FC” project, NEDO, Japan. The synchrotron radiation experiments were performed at BL14B2, BL16B2, BL19B2, and BL46XU of SPring-8 (No. 2015B3388, 2016A1760, 2016A1805, 2016A5390, 2016B1550, and 2016B1856, 2016B5390). References Yano, H.; Kataoka, M.; Yamashita, H.; Uchida, H.; Watanabe M. Langmuir, 2007, 23, 6438.Yano, H.; Song, J. M.; Uchida, H.; Watanabe, M. Phys. Chem. C, 2008, 112, 8372.Watanabe, M.; Yano, H.; Tryk, A.; Uchida, H. J. Electrochem. Soc., 2016, 163, F455.http://fccj.jp/pdf/23_01_kt.pdf in Japanese.Watanabe, M.; Tryk, D. A.; Wakisaka, M.; Yano, H; Uchida, H. Acta, 2012, 84, 187.Shi, G.; Yano, H; Tryk, D. A.; Matsumoto, M.; Tanida, H.; Arao, M.; Imai, H; Inukai, J.; Iiyama A.; Uchida H. Sci. Technol., 2017, 7, 6124. Figure 1

(Invited) A Surface Enhanced Infrared Absorption Spectroscopy Study on the Nitrogen Electrochemical Reduction Reaction on Gold Surfaces

Ammonia has received much attention as a potential energy storage medium and an alternative fuel for vehicles, in addition to its use as a kind of fertilizer. Recent studies showed that ammonia could be produced by N2 and H2O through an electrochemical method, with the advantages of zero CO2 emission and energy saving compared with the “Haber-Bosch” process.1-2 However, as the theoretical potentials of hydrogen evolution reaction (HER) and nitrogen reduction reaction (NRR) are very close, H2 is the dominant product due to the much fast reaction kinetics of the former. For this reason, the experimental studies on NRR mechanism are rather rare. In this study, the NRR mechanism on Au surfaces was first studied by surface enhanced infrared absorption spectroscopy (SEIRAS) technique. Au was selected as its excellent NRR activity but low HER activity.3-4 An Au nanofilm deposited on the Si prism by a chemical deposition method was used as the working electrode. Its cyclic voltammograms (CV) in a N2 saturated KOH solution is shown in Figure 1a. In the 1st segment (cathodic scan, solid red line), the reduction current resulting from the HER and NRR appeared at 0 V and arose sharply starting at -0.1 V. Figure 1b is the corresponding FTIR spectra of the 1st segment in Figure 1a. The bands at 3300 cm-1 and 1645 cm-1 attribute to the O-H stretching and H-O-H bending of water molecules. Those bands intensity increase significantly as a result of the change in the adsorption configuration of water molecules upon decreasing the potential. The bands at 1450 cm-1, 1298 cm-1 and 1109 cm-1 attribute to the H-N-H bending, -NH2 wagging and N-N stretching of adsorbed N2Hy species, respectively. Those bands started to appear at potentials below 0 V and increased with potential decreasing. This result indicates that the nitrogen reduction reaction on Au surfaces follows an associative mechanism, and the N≡N bonds in N2 tend to break simultaneously with the hydrogen addition. Similar spectroscopic studies on Pt surfaces will be also discussed. Figure 1. a) Cyclic voltammograms of an Au film electrode deposited on the Si prism in a N2-saturated 0.1M KOH aqueous solution; potential scan rate: 2.5 mV s-1. b) FTIR spectra during the 1st segment from 0.4 V to -0.5 V on the Au film electrode in a N2-saturaed 0.1 M KOH solution. The reference spectrum was taken at 0.4 V. References Lan, R.; Irvine, J. T. S.; Tao, S. W. Sci Rep 2013, 3, 1145..Renner, J. N., Greenlee, L. F., Ayres, K. E., Herring, A. M. The Electrochemical Society Interface 2015, 24, 7, 51-57.Bao, D.; Zhang, Q.; Meng, F. L.; Zhong, H. X.; Shi, M. M.; Zhang, Y.; Yan, J. M.; Jiang, Q.; Zhang, X. B. Adv. Mater. 2017, 29, 1604799.Shi, M. M.; Bao, D.; Wulan, B. R.; Li, Y. H.; Zhang, Y. F.; Yan, J. M.; Jiang, Q. Adv. Mater. 2017, 29, 1606550. Figure 1

Amperometric glucose biosensor based on immobilization of glucose oxidase on a magnetic glassy carbon electrode modified with a novel magnetic nanocomposite

We present a method to produce a magnetic glassy carbon electrode (MGCE) modified with multilayer nanocomposite (Ag@MWCNT-IL-Fe3O4) as an immobilization support to promote electron transfer reactions of glucose oxidase (GOx). The nanocomposite verified by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD) and a vibrating sample magnetometer (VSM). The direct electron transfer (DET) between GOx and Ag@MWCNT-IL-Fe3O4 nanocomposite was investigated using cyclic voltammetry which showed a pair of well-defined redox peaks corresponding to redox active center of GOx. Utilization of constructed electrode for detection of glucose was studied in N2 and air saturated solutions (pH 7.0). The GOx/Ag@MWCNT-IL-Fe3O4/MGCE showed excellent stability, a detection limit of 2.12μM, a linear range between 6μM and 2mM, and a dynamic range up to 2.7mM at the air saturated solutions. Also, in N2 saturated solutions (pH 7.0), determination of glucose was carried out by amperometry, and the proposed biosensor showed good reproducibility and stability with a detection limit of 3.8μM and a linear range between 10μM and 1mM. Such analytical performances confirm that the fabricated biosensor used in this work has potential to be applied for development of redox enzyme based biosensors.