Activity In Acidic Media Research Articles

Oxygen Reduction Reaction Activity of Carbon-Support-Free Titanium Oxynitride with Reduced Catalyst Loading

Energy storage and conversion devices attracted growing interests to reduce emissions from vehicles by replacing conventional combustion engines to electric motors. Recent analyses on the system cost and performance for both current/post lithium ion batteries and polymer electrolyte fuel cells (PEFCs) indicate that PEFCs are suitable to drive vehicles which operate over 200 miles or need high loads such as buses and tracks.1,2 Several minutes of refuelling time also makes this energy conversion technology promising; however, current usage of platinum in 114 kW-PEFC stack for a generic sedan is estimated in the range of 22–38 g,2 which is unacceptably high considering the world reserve of platinum-group-metals (PGMs), 67,000 tons.3 Further, corrosion of carbon, which is currently used to support platinum-based nanoparticle catalysts, is known to more severe to degrade the performance of PEFC than platinum dissolution.4 Most non-PGM catalysts developed in the last decade is a so-called Fe/N/C catalysts, which utilize graphitic carbon materials originated from carbonized polymers,5 carbonized metal organic frameworks6 or both.7,8 All these carbons are conductive as they contained graphitic layers with edges terminated by pyriginic nitrogen atoms. Another non-PGM catalyst type is oxide/oxynitride containing group IV or V metals. As these catalysts are not conductive, they have mostly been supported on carbon materials.9 – 11 Therefore, both these non-PGM catalyst types should be protected from corrosion of carbon supports accelerated during the startup/shutdown of the cell. Develompment of carbon-support-free non-PGM catalysts is a challenging, attractive option to replace conventional carbon-supported platinum-based catalysts. We therefore recently reported titanium oxynitride (TiO x N y ) catalyst free from carbon-supports.12 The activity in acidic media was the highest among the ever reported carbon-support-free oxide based catalysts, whereas the minimum catalyst loading to uniformly coat the grassy carbon disk electrode was also the highest, 2 mg cm–2 due to the high density. In this study, various attempts have been made to lower the density and thus decrease the catalyst loading. The minimum catalyst loading was successfully reduced to 0.6 mg cm–2, same as the standard of Fe/N/C catalysts. Effect of the loading on activity and visual reaction mechanism will be discussed at the meeting. Acknowledgments The authors gratefully acknowledge Mr. Yusei Tsushima for his help with acquisition of transmission/scanning electron microscopy images. This work was partially supported by a Grant-in-Aid for Scientific Research (C) (17K06180) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan; a research grant from Nippon Sheet Glass Foundation for Materials Science and Engineering in Japan; a research grant, KJ-2539, from the Kato Foundation for Promotion of Science in Japan, a research grant from Nippon Life Insurance Foundation in Japan and a research grant from Yashima Environment Technology Foundation. The X-ray photoelectron spectra were acquired with the support by Nanotechnology Platform of the MEXT of Japan. References (1) U. Eberle and R. von Helmolt, Energy Environ. Sci., 3, 689–699 (2010). (2) O. Gröger, H. A. Gasteiger and J. P. Suchsland, J. Electrochem. Soc., 162, A2605–A2622 (2015). (3) U.S. Department of the Interior, Mineral Commodity Summaries 2017, p. 126 https://minerals.usgs.gov/minerals/pubs/mcs/2017/mcs2017.pdf (4) J. Parrondo, T. Han, E. Niangar, C. Wang, N. Dale, K. Adjemian and V. Ramani, Proc. Natl Acad. Sci., 111, 45–50 (2014). (5) Y. C. Wang, Y. J. Lai, L. Song, Z. Y. Zhou, J. G. Liu, Q. Wang, X. D. Yang, C. Chen, W. Shi, Y. P. Zheng, M. Rauf and S. G. Sun, Angew. Chem. Int. Ed. 54, 9907–9910 (2015). (6) E. Proietti, F. Jaouen, M. Lefevre, N. Larouche, J. Tian, J. Herranz and J. P. Dodelet, Nature Commun. 2, 416-1–416-9 (2011). (7) J. Shuia, C. Chen, L. Grabstanowicz, D. Zhao and D. J. Liua,, Proc. Nat. Acad. Sci., 112, 10629 (2015). (8) X. Fu, P. Zamani, J. Y. Choi, F. M. Hassan, G. Jiang, D. C. Higgins, Y. Zhang, M. A. Hoque and Z. Chen, Adv. Mater., 29, 1604456-1–1604456-8 (2017). (9) M. Chisaka, A. Ishihara, N. Uehara, M. Matsumoto and K. Ota, J. Mater Chem. A, 3, 16414–16418 (2015). (10) M. Chisaka, Y. Ando and N. Itagaki, J. Mater Chem. A 4, 2501–2508 (2016). (11) M. Chisaka, A. Ishihara, H. Morioka, T. Nagai, S. Yin, Y. Ohgi, K. Matsuzawa, S. Mitsushima and K. Ota, ACS Omega, 2, 678–684 (2017). (12) M. Chisaka, Y. Ando, Y. Yamamoto and N. Itagaki, Electrochim. Acta, 214, 165–172 (2016).

Electronic metal-support interaction enhanced oxygen reduction activity and stability of boron carbide supported platinum

Catalysing the reduction of oxygen in acidic media is a standing challenge. Although activity of platinum, the most active metal, can be substantially improved by alloying, alloy stability remains a concern. Here we report that platinum nanoparticles supported on graphite-rich boron carbide show a 50–100% increase in activity in acidic media and improved cycle stability compared to commercial carbon supported platinum nanoparticles. Transmission electron microscopy and x-ray absorption fine structure analysis confirm similar platinum nanoparticle shapes, sizes, lattice parameters, and cluster packing on both supports, while x-ray photoelectron and absorption spectroscopy demonstrate a change in electronic structure. This shows that purely electronic metal-support interactions can significantly improve oxygen reduction activity without inducing shape, alloying or strain effects and without compromising stability. Optimizing the electronic interaction between the catalyst and support is, therefore, a promising approach for advanced electrocatalysts where optimizing the catalytic nanoparticles themselves is constrained by other concerns.

Facile charge transport in $$\hbox {FeN}_{\mathrm{x}}/\hbox {Mo}_{2}\hbox {N/CNT}$$ FeN x / Mo 2 N/CNT nanocomposites for efficient hydrogen evolution reactions

Molybdenum based materials are gaining importance as electrocatalysts for hydrogen evolution reaction because of their low cost and good electrocatalytic efficiency. Introducing iron nitride with molybdenum nitride as a composite results in efficient hydrogen evolution activity with current density of $${\sim }120$$ $$\hbox {mA/cm}^{2}$$ at $$-400 \hbox { mV}$$ vs. RHE. The nanocomposites were characterized using powder XRD, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Electron Diffraction, Thermogravimetric Analysis and FTIR Spectroscopy. The electrochemical investigations suggest that the electrocatalytic activity of the composite increases with iron nitride content. The composite exhibits good electrochemical stability upto 42 hours in acidic medium. The hydrogen evolution reaction (HER) follows Volmer-Heyrovsky mechanism where Volmer reaction is the rate determing step. SYNOPSIS Introducing iron nitride in composite with molybdenum nitride leads to higher HER activity in acidic media. The in-situ growth of CNTs in the composites enhances the conductivity and decreases the charge transfer resistance.

Growth of iron diselenide nanorods on graphene oxide nanosheets as advanced electrocatalyst for hydrogen evolution reaction

Advanced electrocatalysts for the fabrication of sustainable hydrogen from water splitting are innermost to energy research. Herein, we report the growth of iron diselenide (FeSe2) nanorods on graphene oxide (GO) sheets using two-step process viz., simple hydrothermal reduction and followed by wet chemical process. The orthorhombic phase of FeSe2 incorporated GO nanosheet was developed as a low-cost and efficient electrocatalyst for hydrogen evolution reaction (HER) by water splitting. The phase purity, crystalline structure, surface morphology and elemental composition of the synthesized samples have been investigated by UV–visible absorption spectroscopy (UV–vis), fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDS). Voltammetry and Tafel polarization methods have been utilized to assess the performance of various weight ratio of GO nanosheet in FeSe2 nanorods towards H2 evolution. Detailed electrochemical investigations revealed that the 30% FeSe2/GO composite showed a tremendous electrocatalytic HER activity in acidic medium with high cathodic current density of 9.68 mA/cm2 at η = 250 mV overpotential and with a Tafel slope of 64 mV/dec. The 30% FeSe2/GO composite offers a high synergistic effect towards HER activity, which is mainly due to high electrochemical active catalytic sites, low charge-transfer resistance and enhanced electrocatalytic performances of H2 production. The present analysis revealed the possible application of FeSe2/GO composite as a promising low-cost alternative to platinum based electrocatalysts for H2 production.

Pharmacodynamics of Finafloxacin, Ciprofloxacin, and Levofloxacin in Serum and Urine against TEM- and SHV-Type Extended-Spectrum-β-Lactamase-Producing Enterobacteriaceae Isolates from Patients with Urinary Tract Infections.

ABSTRACTThe pharmacodynamics of finafloxacin, ciprofloxacin, and levofloxacin against extended-spectrum-β-lactamase (ESBL)-producing Enterobacteriaceae isolates were compared. Since quinolones lose activity in acidic media, and particularly in urine, their activities were tested in parallel under conventional conditions and in acidic artificial urine. For this purpose, TEM- and SHV-type ESBL-producing Escherichia coli and Klebsiella pneumoniae strains and their wild-type counterparts were exposed in a modified Grasso model to simulated concentrations of drugs in serum and urine following oral doses of either finafloxacin at 800 mg once a day (q.d.), immediate-release ciprofloxacin at 500 mg twice a day (b.i.d.), extended-release ciprofloxacin at 1,000 mg q.d., or levofloxacin at 500 or 750 mg q.d. The concentrations of the drugs in urine were fitted by compartmental modeling. Bacteria were cultivated in Mueller-Hinton broth (MHB) at pH 7.2 or 5.8 or in artificial urine at pH 5.8. Bacteria were counted every 2 h until 10 h and at 24 h; the areas under the bacterial-count–versus–time curves were calculated. It was found that finafloxacin eliminated all strains within 2 h under all the conditions studied. At all doses studied, ciprofloxacin and levofloxacin were highly active against wild-type strains in MHB at pH 7.2 but lost activity in MHB, and particularly in urine, at pH 5.8. Viable counts of ESBL producers were reduced for 6 to 8 h by 3 log10 titers, but the bacteria regrew thereafter. Ciprofloxacin and levofloxacin were almost inactive against the SHV producer grown in artificial urine. We conclude that pharmacodynamic models using artificial urine may mirror the physiology of urinary tract infections more closely than those using conventional media. In contrast to ciprofloxacin and levofloxacin, finafloxacin gained activity in this model at an acidic pH, maintained activity in artificial urine, and was active against TEM and SHV producers.

In-situ activation of self-supported 3D hierarchically porous Ni3S2 films grown on nanoporous copper as excellent pH-universal electrocatalysts for hydrogen evolution reaction

The exploitation of low-cost, stable, and highly active electrocatalysts based on earth-abundant metals for hydrogen evolution reaction (HER) is crucial for developing renewable energy techniques. In this work, we report a facile synthesis strategy for in-situ fabrication of 3D hierarchically porous Ni3S2 films on a nanoporous copper substrate (Ni3S2@NPC) by unusual galvanic replacement reaction in the Ethaline-based deep eutectic solvent (DES) under a normal atmosphere. The self-supported nanoporous Ni3S2@NPC electrode is binder- free and exhibits good structural integrity with high conductivity. A mild evolution of bulk gas bubbles (H2-O2 gas mixture) is proved to drive an in-situ structure rearrangement process of the Ni3S2@NPC and results in substantial increases in the HER activity. The activated Ni3S2@NPC (a-Ni3S2@NPC) electrode can serve as a highly efficient and stable electrocatalyst for the HER in water over a wide pH range. Significantly, it displays high-performance HER catalytic activity in acidic media with robust durability over 111h and functions well under alkaline and neutral conditions. Such a superior catalytic performance of the a-Ni3S2@NPC is mainly due to the unique hierarchically nanoporous architectures and the synergetic effects in it caused by the restructuring NPC skeletons and active components. Our work offers a generic strategy for design and fabrication of many other self-supported transition metal sulfide and phosphide based HER electrocatalysts, and uncovers a new O2-induced electrochemical self-activation mechanism for improving the activity of catalysts.

Insights on the extraordinary tolerance to alcohols of Fe-N-C cathode catalysts in highly performing direct alcohol fuel cells

Direct alcohol fuel cells (DAFCs) represent the best alternative to batteries for portable and auxiliary power units application due to the high energy density of short chain alcohols. Currently, the utilization of the best platinum group metal (PGM) cathode catalysts is limited, not only by a high cost and scarce resources, but also by the inefficient oxygen reduction reaction (ORR) when permeated alcohols adsorb on the catalytic active sites. In this work, a highly active Fe-N-C catalyst derived from the pyrolysis of nicarbazin (a nitrogen charge transfer organic salt) and an iron precursor has been investigated to get insights on the extraordinary tolerance to the presence of alcohols (methanol and ethanol) of such a PGM-free catalyst. Density functional theory (DFT) calculations demonstrate for the first time that Fe-N4 and Fe-N2C2 active sites preferentially adsorb oxygen with much higher energy than methanol, ethanol and products of partial ethanol oxidation (0.73–1.16eV stronger adsorption), while nitrogen-carbon related sites (pyridinic and graphitic nitrogen) are much less selective towards ORR. Half-cell electrochemical characterization showed that the Fe-N-C catalyst overcomes Pt ORR activity in acidic medium with methanol or ethanol concentrations as low as 0.01M. The feasibility of DAFCs operation based on high methanol (up to 17M) and ethanol (up to 5M) concentration thanks to the utilization of Fe-N-C cathode catalyst is demonstrated. A new strategy is proposed for DAFCs where using Pt only at the anode and Fe-N-C at the cathode allows extending the device energy density compared to PGM-based catalysts at both electrodes.

In vitro characterization of pH-sensitive azithromycin-loaded methoxy poly (ethylene glycol)-block-poly (aspartic acid-graft-imidazole) micelles

In order to improve azithromycin’s antibacterial activity in acidic medium, monomethoxy poly (ethylene glycol)-block-poly (aspartic acid-graft-imidazole) copolymer was synthesized through allylation, free radical addition, ring-opening polymerization and amidation reactions with methoxy poly (ethylene glycol) as raw material. Drug loading capacity and encapsulation efficiency of azithromycin-loaded micelles prepared via thin film hydration method were 11.58±0.86% and 96.06±1.93%, respectively. The drug-loaded micelles showed pH-dependent property in the respects of particle size, zeta potential at the range of pH 5.5–7.8. It could control drug in vitro release and demonstrate higher release rate at pH 6.0 than that at pH 7.4. In vitro antibacterial experiment indicated that the activity of azithromycin-loaded micelles against S. aureus was superior to free azithromycin in medium at both pH 6.0 and pH 7.4. Using fluorescein as substitute with pH-dependent fluorescence decrease property, laser confocal fluorescence microscopy analysis confirmed that cellular uptake of micelles was improved due to protonation of copolymer’s imidazole groups at pH 6.0. The enhanced cellular uptake and release of drug caused its activity enhancement in acidic medium when compared with free drug. The micellar drug delivery system should be potential application in the field of bacterial infection treatment.

Hybrid carbon nanowire networks with Fe–P bond active site for efficient oxygen/hydrogen-based electrocatalysis

Exploring inexpensive, universal, highly active and stable electrocatalysts toward the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) is critical for developing high-performance energy conversion and storage devices. Herein, we report the synthesis of three-dimensional (3D) hybrid carbon nanowire (i.e., Fe/P/C) networks with superior ORR, OER and HER activities and stabilities, and further experimentally confirm the Fe–P bond in the networks is one of the main active sites for ORR, OER and HER for the first time. Under the optimized condition, the resultant Fe/P/C networks show better ORR electrocatalytic activity in alkaline media/comparable activity in acidic media, better durability and stronger methanol tolerance compared to those of 20wt.% Pt/C. The Fe/P/C networks also exhibit high activity with a potential of 1.56V (vs. reversible hydrogen electrode) to achieve 10mAcm−2 and a small Tafel slope of 67.1mV dec−1 for OER in 1.0M KOH. Furthermore, as HER electrocatalyst, the Fe/P/C networks need a low overpotential of 256mV to drive 10mAcm−2 in 0.5MH2SO4. These make Fe/P/C nanowire networks to be among the best non-precious metal based carbonaceous electrocatalysts for ORR, OER and HER to date.

Electrocatalytic nitrate reduction on well-defined surfaces of tin-modified platinum, palladium and platinum-palladium single crystalline electrodes in acidic and neutral media

Nitrate anion is one of the main nitrogen-containing-pollutants in groundwater and can be removed using denitrification systems including electrocatalytic systems. Herein we report on electrocatalytic nitrate reduction catalyzed on tin-modified single crystalline electrodes of palladium, platinum and palladium-platinum alloy in acidic and neutral media. We have prepared electrodes with the (111) surface or the (100) surface and modified their surface with tin. Cyclic voltammetry of the electrodes has revealed that the tin-modified alloy (trimetallic) electrodes show higher electrocatalytic activity than the tin-modified platinum or palladium (bimetallic) electrodes, and the catalytic reaction is more efficiently catalyzed on the (100) surface rather than the (111) surface. The tin-modified PdPt(100) electrode shows the highest catalytic activity in acidic media as well as in neutral media. X-ray photoelectron spectroscopy suggests that metallic tin forms on the (100) surface, but divalent tin species on the (111) surface, indicating that a surface alloy of tin may form on the (100) surface, resulting in enhancement of the electrocatalytic activity. Our findings suggest that design and preparation of ternary metallic electrodes with the (100) surface will pave the way to the development of practical systems on electrocatalytic denitrification.

Probing the electro-catalytic ORR activity of cobalt-incorporated nitrogen-doped CNTs

Catalysts for oxygen reduction reaction (ORR) are crucial for fuel cells. However, the rarity and poor durability of Pt-based catalysts have prohibited its commercialization. Herein, we report cobalt-incorporated nitrogen-doped CNT (Co-NCNT) as a Pt-free, efficient and low-cost catalyst for ORR, which is synthesized by the pyrolysis of melamine formaldehyde in which cobalt nitrate is homogeneously dispersed. The electro-catalyst exhibits reasonable activity for ORR in both acidic and alkaline media. Moreover, its activity remains almost unchanged in 1000 electrochemical cycles in both acidic and alkaline media due to the protection by dense graphite layers. More specifically, detailed electron energy loss spectroscopy investigations show that the doped nitrogen species tend to co-accumulate with cobalt at the arch areas of carbon nanotubes where catalytically active Co-Nx species are proposed to form. Combined with probe tests upon ligating, Co-Nx species enriched at the arches has found to be mainly responsible for the ORR activity in acidic medium, while in alkaline medium, nitrogen doped carbon species (N-C) of Co-NCNTs are proposed to serve as dominant active sites for ORR. The ratio of Co-Nx site density to N-C site density plays a significant role in determining ORR activity.

Iridium-based double perovskites for efficient water oxidation in acid media.

The development of active, cost-effective and stable oxygen-evolving catalysts is one of the major challenges for solar-to-fuel conversion towards sustainable energy generation. Iridium oxide exhibits the best available compromise between catalytic activity and stability in acid media, but it is prohibitively expensive for large-scale applications. Therefore, preparing oxygen-evolving catalysts with lower amounts of the scarce but active and stable iridium is an attractive avenue to overcome this economical constraint. Here we report on a class of oxygen-evolving catalysts based on iridium double perovskites which contain 32 wt% less iridium than IrO2 and yet exhibit a more than threefold higher activity in acid media. According to recently suggested benchmarking criteria, the iridium double perovskites are the most active catalysts for oxygen evolution in acid media reported until now, to the best of our knowledge, and exhibit similar stability to IrO2.

Iron polyphthalocyanine sheathed multiwalled carbon nanotubes: A high-performance electrocatalyst for oxygen reduction reaction

The past decade has witnessed a rapid surge of interest in the research and development of non-precious metal-based electrocatalysts for the oxygen reduction reaction (ORR). Until now, the best catalysts in acidic electrolytes have exclusively been Fe-N-C-type materials from high-temperature pyrolysis. Despite the ORR activities of metal phthalocyanine or porphyrin macrocycles having long been known, their durability remains poor. In this work, we use these macrocycles as a basis to develop a novel organic-carbon hybrid material from in-situ polymerization of iron phthalocyanine on conductive multiwalled carbon nanotube scaffolds using a low-temperature microwave heating method. At an optimal polymerto- carbon ratio, the hybrid electrocatalyst exhibits excellent ORR activity with a positive half-wave potential (0.80 V), large mass activity (up to 18.0 A/g at 0.80 V), and a low peroxide yield (<3%). In addition, strong electronic coupling between the polymer and carbon nanotubes is believed to suppress demetallization of the macrocycles, significantly improving cycling stability in acids. Our study represents a rare example of non-precious metal-based electrocatalysts prepared without high-temperature pyrolysis, while having ORR activity in acidic media with potential for practical applications.

Bulk Production of Nonprecious Metal Catalysts from Cheap Starch as Precursor and Their Excellent Electrochemical Activity

Development of a high-performance electrocatalyst for an oxygen reduction reaction with a low-cost bulk production method is crucial for practical applications of metal–air batteries, oxygen sensors, fuel cells, and so on. Here, we developed a bulk production method for nitrogen- and ferrum-doped nanoporous carbon microspheres as a high-performance ORR catalyst. The process involved hydrothermal carbonization of starch with iron ions as catalysts to catalyze the formation of carbon spheres and annealing the carbon spheres in an NH3 atmosphere. NH3 was used not only as the nitrogen source to form the N-doped carbon material but also to etch the carbon to produce a nanoporous carbon material, which has high surface area and pore volume. As a highly available, accessible, and recyclable biomass, starch can be used to achieve a cheap electrocatalyst. The proposed approach is simple and scalable. The typical product has excellent activity in alkaline media and high activity in acidic media. The typical product...

Group 4 Metal Oxynitride Nanocatalysts for Oxygen Reduction Reaction in Acidic Media

Titanium dioxide (TiO2) has attracted significant attention for the use in various applications; photocatalysts, dye-sensitized solar cells, lithium/sodium ion batteries, sensors, etc. Since the discovery of high visible-light photocatalytic activity by Asahi et al. in 2001,1 substitution of oxygen atoms in TiO2 by heteroatoms has been the hot topic in these fields. Recent work of Ota et al. opened a new application of TiO2: oxygen deficient TiO x showed the oxygen reduction reaction (ORR) activity in acidic media that simulate polymer electrolyte fuel cell (PEFC) cathodes.2 Other oxide catalysts containing group 4 or 5 metals also showed ORR activity in acidic media, whereas TiO2 is the most promising from the viewpoint of natural abundance. The oxygen defects in oxide catalysts have been acknowledged as active sites for ORR and they have been incorporated using various routes such as the pyrolysis under reductive atmosphere containing hydrogen,2 so-called carbothermal-reduction3 and nitrogen-doping.4-8 Rutile is more active for ORR than anatase,3,6,7 and this trend is opposite to that in photocatalytic activity. In this work, oxygen defects were incorporated into nanoparticles of rutile TiO2 and other group 4 metal oxides by substitutional nitrogen-doping using a recently developed solution phase combustion route.7,8 X-ray photoelectron spectroscopy analyses on TiO2 catalysts revealed that (1) charge imbalance caused by doped nitrogen atoms were compensated by the incorporation of oxygen defects, not the decrease in the valence of titanium on the surface and (2) the surface rutile was formed on TiN, yielding a core-shell structure. Many transition metal nitrides are well known to be unstable in water or even in air moisture, except for Ta3N5;9,10 however, the surface rutile successfully protected the TiN-core in 0.1 mol dm–3 H2SO4 solution not to change the ORR mechanism represented by Tafel slope after 20,000 potential cycles between 0.6 and 1.0 V versus the reversible hydrogen electrode. The active sites will be discussed at the meeting by comparing the activity of TiO2 and other group 4 metal oxides. Acknowledgments The authors gratefully acknowledge Mr. Yusei Tsushima for his help with acquisition of transmission electron microscopy images. This work was partially supported by a Grant-in-Aid for Scientific Research (C) (26420132) from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan; an Adaptable and Seamless Technology Transfer Program through Target-driven R&D grant (AS262Z02037) from the Japan Science and Technology Agency; a research grant from the Takahashi Industrial and Economic Research Foundation of Japan; a research grant from the Naoji Iwatani Foundation of Japan; and a grant for chemical research from the Foundation for Japanese Chemical Research. The X-ray photoelectron spectra were acquired with the support by Nanotechnology Platform, 12024046 of the MEXT of Japan. References (1) R. Asahi, T. Morikawa, T. Ohwaki, K. Aoki, and Y. Taga, Science, 293, 269 (2001). (2) J. H. Kim, A. Ishihara, S. Mitsushima, N. Kamiya, and K. Ota, Electrochim. Acta, 52, 2492 (2007). (3) M. Chisaka and N. Itagaki, Electrochim. Acta, in press. Doi:10.1016/j.electacta.2015.10.184. (4) M. Chisaka, H. Sasaki and H. Muramoto, Phys. Chem. Chem. Phys., 16, 20419 (2014). (5) M. Chisaka, A. Ishihara, K. Suito, K. Ota and H. Muramoto, Electrochim. Acta, 88, 697 (2013). (6) M. Chisaka and H. Muramoto, ChemElectroChem, 1, 544 (2014). (7) M. Chisaka, Y. Ando and H. Muramoto, Electrochim. Acta, 183, 100 (2015) (8) M. Chisaka, Y. Ando and N. Itagaki, J. Mater Chem. A, in press. Doi:10.1039/C5TA08235H (9) M. Hara, E. Chiba, A. Ishikawa, T. Takata, J. N. Kondo and K. Domen, J. Phys. Chem. B, 107, 13441 (2003). (10) M. Chisaka, A. Ishihara, N. Uehara, M. Matsumoto and K. Ota, J. Mater Chem. A, 3, 16414 (2015).

High Performance Fe- and N- Doped Hierarchically Porous Carbons Catalyst Derived from Polyquaternium for Oxygen Reduction

The heteroatom (N, S, Cl, B, P, Fe, Co, Mn or Ni)-doped carbon materials, such as carbon nanotubes (CNTs)1, graphene2, graphitic arrays3, and amorphous carbon4, have drawn great attention due to their excellent electrocatalytic performance for ORR. However, among all these non-precious carbon-based catalysts, very few are on a competitive level with platinum in acidic media. One family of these most promising alternatives to Pt are mainly the Fe/N co-doped carbon materials. Transition metal was found to be indispensable to catalyze the graphitization of nitrogen−carbon precursor to form the highly graphitized carbon. In addition, Some studies argued that metals could not only help the formation of active sites, but could be an integral active part of the catalytic site5. Based on the above conceptions, we studied the effect of Fe content on the catalyst performance by varying initial FeSO4 7H2O/Polyquaternium weight ratio to tune the final Fe content in the catalyst. The obtained optimal catalyst (N/Fe-PAD) showed a comparable ORR activity in acidic media with commercial Pt/C. The N/Fe-doped porous carbon electrode materials(N/Fe-PAD) were prepared by homogeneously dispersion of polyquaternium (PAD) and ferrous sulfate (FeSO4 7H2O) precursors onto the surface of silica (which was firstly dispersed in hydrochloric acid solution by ultrasonication, the FeSO4 7H2O/Polyquaternium weight ratio is 0.04 and 1.0, respectively). After dried overnight, the resulting solid was ground to a fine powder, and then calcined at 800oC for 1h in nitrogen atmosphere. The excess amount of sodium hydroxide (NaOH) was added to vacate the silica and the resulting powder was acid-leached using 0.5 M H2SO4 at 85oC to remove the unreacted metallic Fe. Then, the catalytic graphitization of the impregnated carbon was subjected heat treatment at 800oC for 1h pyrolyzation time again. The catalysts as-prepared are thus designated as N/FeX-PAD(X=0.04 and 1.0, respectively). The electrocatalytic activity on the N/FeX-PAD and Pt/C was investigated using cyclic voltammetry (CV) and linear sweep voltammetry (LSV) employing rotating disk electrode (RDE) technique in 0.1M HClO4. Fig. 1 shows CV responses of N/Fe1.0-PAD in N2/O2 saturated 0.1 M HClO4 solution. In the case of a N2-saturated solution, the cyclic voltammogram only presents a featureless quasi-rectangular trace. However, when O2 is introduced into the solution, a distinct ORR response with the peak potential (Ep) at 0.61 V vs. RHE, and the peak current density (Ip) of 2.64 mA cm-2 can be clearly observed, indicating that this N/Fe1.0-PAD catalyst has a profound catalytic ORR activity. Figure 2 shows the polarization curves of the N/Fe1.0-PAD, N/Fe0.04-PAD and Pt/C catalysts. It can be seen that the high activity of N/Fe1.0-PAD for oxygen reduction was clearly demonstrated by onset potential of 0.80V, half-wave potential of 0.68V, which are positively shifted more than 25 and 80 mV, respectively, compared to N/Fe0.04-PAD. In addition, the limiting current densities for N/Fe1.0-PAD are improved greatly (～7.5 mA cm-2 at 0.30 V), much higher than Pt/C catalyst. Reference 1. S.Y. Wang, E. Iyyamperumal, A. Roy, Y.H. Xue, D.S. Yu, L.M. Dai, Angew. Chem. Int. Ed. 50, 11756 (2011). 2. Y. Li, Y. Zhao, H.H. Cheng, Y. Hu, G.Q. Shi, L.M. Dai, and L.T Qu, J. Am. Chem. Soc. 134, 15(2012). Electrochem. Acta, 80, 213 (2012) 3. J. Liang, Y. Zheng, J. Chen, J. Liu, D. Hulicova-Jurcakova, M. Jaroniec, S.Z. Qiao, Angew. Chem. Int. Ed. 51, 3892 (2012). 4. W. Yang, T.P. Fellinger, M. Antonietti, J. Am. Chem. Soc. 133, 206 (2011). 5. X.J. Zhou, Z.Y. Bai, M.J. Wu, J.L. Qiao, Z.W. Chen, J. mater. Chem. 3, 3343-3350 (2015).­ Figure 1

N/S-Me (Fe, Co, Ni) doped hierarchical porous carbons for fuel cell oxygen reduction reaction with high catalytic activity and long-term stability

A series of novel and high-performing oxygen reduction reaction (ORR) catalysts based on N/S-Me-doped (Me=Fe, Co, Ni) hierarchical porous carbons (N/S-Fe-HPC, N/S-Co-HPC and N/S-Ni-HPC) have been synthesized by a green and cost-effective method combining a simple silicate templated two-step graphitization of the impregnated carbon. After optimization of the porous structures and enlargement of the BET specific surface area by combining the silicate template and the Fe-, Co- and Ni-metal sulfates, the obtained N/S-Me-HPC catalysts exhibit excellent ORR performance in both alkaline and acidic media. In particular, N/S-Fe-HPC shows superior catalytic ORR performance compared to commercially available 20% Pt/C in alkaline medium reflected by the onset potential of 0.98V and half-wave potential of 0.86V, and comparable ORR activity in acidic media with the onset potential of 0.84V and half-wave potential of 0.73V. In addition, the N/S-Fe-HPC catalyst exhibits excellent long-term stability and a high methanol tolerance. The outstanding electrochemical performance of such catalysts thereby makes it possible for these non-noble catalysts to replace the commercial Pt/C in both fuel cell and metal–air battery applications.

Co-N Decorated Hierarchically Porous Graphene Aerogel for Efficient Oxygen Reduction Reaction in Acid.

Nitrogen-functionalized graphene materials have been demonstrated as promising electrocatalyst for the oxygen reduction reaction (ORR), owning to their respectable activity and excellent stability in alkaline electrolyte. However, they exhibit unacceptable catalytic activity in acid medium. Here, a hierarchically porous Co-N functionalized graphene aerogel is prepared as an efficient catalyst for the ORR in acid electrolyte. In the preparation process, polyaniline (PANI) is introduced as a pore-forming agent to aid in the self-assembly of graphene species into a porous aerogel networks, and a nitrogen precursor to induce in situ nitrogen doping. Therefore, a Co-N decorated graphene aerogel framework with a large surface area (485 m(2) g(-1)) and an abundance of meso/macropores is effectively formed after heat treatment. Such highly desired structures can not only expose sufficient active sites for the ORR but also guarantee the fast mass transfer in the catalytic process, which provides significant catalytic activity with positive onset and half wave potentials, low hydrogen peroxide yield, high resistance to methanol crossover, and remarkable stability that is comparable to commercial Pt/C in acid medium.

Using nitrogen-rich polymeric network and iron(II) acetate as precursors to synthesize highly efficient electrocatalyst for oxygen reduction reaction in alkaline media

Carbon-supported transition metal/nitrogen (M–N/C) materials are considered as one of the most promising electrocatalysts for the oxygen reduction reaction (ORR) owing to their high ORR electrocatalytic activity, long-term stability, and excellent methanol tolerance. So far only a few examples of such catalysts are prepared from N-containing polymers. Herein, we report a novel Fe–N/C catalyst using a nitrogen-rich polymeric network and iron(II) acetate as the precursors. The porous polymeric network is fabricated by one-step Friedel–Crafts reaction of a low-cost cross-linker, formaldehyde dimethyl acetal, with 2,4,6-tripyrrol-1,3,5-triazine. Compared to commercial Pt/C catalyst, the as-prepared Fe–N/C electrocatalyst exhibits superior ORR activity in alkaline electrolyte, and comparable ORR activity in acidic medium. The results obtained are significant for the development of new Fe–N/C electrocatalysts for fuel cells.

A highly active molybdenum multisulfide electrocatalyst for the hydrogen evolution reaction

We prepared a molybdenum multisulfide electrocatalyst, which exhibits superior activity in acid media, surpassing most existing molybdenum-sulfide-based catalysts.