Precious Metal Oxides Research Articles

Enhanced arsenic removal from water by mechanochemical synthesis of Ca–Al–Fe ternary composites

To date, there have been many studies on arsenic removal by the multi-metal Fe/Al oxide compound adsorbents. The various precious metal oxides were usually incorporated to enhance the removal efficiency while increasing the cost of the complex adsorbents remarkably. In this work, the traditional method of adding rare or precious metal oxides was abandoned, high efficiency and low-cost Ca–Al–Fe ternary composite was synthesized through mechanochemical processing and low temperature calcination for the efficient removal of As(III). The SEM-EDS, BET, XPS and TG-DSC were employed to characterize the Ca–Al–Fe ternary composite before and after As(III) adsorption. Moreover, the As(III) removal mechanism and the composition and physical properties of the Ca–Al–Fe ternary composite were also studied. The kinetics study fitted the pseudo-second-order model, and the adsorption isotherm followed the Freundlich model, of which the maximum adsorption capacity up to 56.86 mg/g. The Ca–Al–Fe ternary composite is of high activity and amorphous type, which can be attributed to the Al(III) and freshly generated Fe(III) to generate Fe–Al hydroxide enhancing the high adsorption capacity. The excellent As(III) removal efficiency and reusability of the Ca–Al–Fe ternary composite suggested its vast application prospects as a competitive candidate for As(III) pollution remediation in water.

Metal oxides supported cobalt nanoparticles: Active electrocatalysts for oxygen evolution reaction

Besides precious metal oxides, non-noble metal oxides are found to be promising materials especially, in the alkaline medium for OER. In this work, Co/MO2 (M = Ti, Zr, and Ce) catalysts were synthesized without using any harsh steps such as pyrolization, annealing, calcination, and carbonization. Cobalt nanoparticles with ∼2.6 nm particle size were loaded on metal oxides by simple impregnation and reduction method. Considering the low onset and overpotential values, low Tafel slopes, high exchange current densities, high TOF values, as well as high Faradaic efficiency, Co/CeO2, Co/ZrO2, and Co/TiO2 nanocatalysts show the remarkable electrocatalytic performance in 1 M KOH for OER. Moreover, no noticeable change in the performance of Co/MO2 (M = Ti, Zr, and Ce) catalysts were observed after the stability test at 10 mA.cm−2. This work will also shed light on other studies, in the preparation of inexpensive, earth abundant, and highly active OER electrocatalysts via changing impregnated metals or metal oxides supports.

Nickel-Iron nitrides and alloy heterojunction with amorphous N-doped carbon Shell: High-efficiency synergistic electrocatalysts for oxygen evolution reaction

Transition metal nitrides have received a great deal of attention as highly efficient OER catalysts due to their excellent electrical conductivity, which grants them lower overpotential values than precious metal oxide catalysts (RuO2, IrO2, etc.). Herein, we report the characteristics of Nickel-Iron nitrides, alloy heterogeneous nanostructures (Ni2Fe2N, Ni2Fe2N/Ni3Fe, Ni3Fe/Ni2Fe2N), and amorphous N-doped carbon shells differing only in nitridation temperature. Heterogeneous Nickel-Iron nitrides and alloy with amorphous N-doped carbon shells showed superior OER performance such as a low overpotential value of 251 mV at current density of 10 mA/cm2, Tafel slope of 35.0 mV/dec, and great stability even after 24 h. Additionally, this study accurately identified that the heterogeneous nanostructure and amorphous N-doped carbon shell improve the catalytic properties and durability of the Nickel-Iron nitrides and alloy nanoparticles. The morphological control strategy used to produce the heterogeneous nanostructure and amorphous N-doped carbon shell can be applied to improve electrochemical properties or encapsulation in strong alkaline solution.

(Invited) Slurry of Transition Metal Chalcogenides for Multifaceted Electrochemical Applications: Energy Conversion, Storage, Sensing & Catalysis

Transition metal chalcogenides has been at the center of attraction for materials chemistry for decades owing to their novel and interesting optoelectronic properties that can be tuned with anion composition, coordination and doping. Recently these transition metal chalcogenides have also been explored for energy-related applications with primary focus on sustainable energy conversion. Energy harvesting from solar and water has created ripples in sustainable energy research for the last several decades, complemented by the rise of Hydrogen as a clean fuel. It has become very apparent that hydrogen-on-demand technology needs to be developed to complement the growth of hydrogen fuel economy without adding on to the process cost by storing hydrogen in pressurized tanks or non-reactive framework. In this regard, water electrolysis leading to generation of oxygen and hydrogen, has been one of the most promising routes towards sustainable alternative energy generation and storage without depleting fossil-fuel based natural resources. However, the efficiency and practical feasibility of water electrolysis is limited by the anodic oxygen evolution reaction (OER), which is a kinetically sluggish, electron-intensive uphill reaction and designing efficient catalysts for OER process from earth-abundant resources has been one of the primary concerns for advancing solar water splitting. In the Nath group we have been successful in producing transition metal chalcogenide-based highly efficient OER electrocatalysts which surpasses efficiency of state-of-the-art precious metal oxides by several orders of magnitude. Our main design principle if based on the concept that chalcogenides, specifically, selenides and tellurides will show much better OER catalytic activity due to increasing covalency around the catalytically active transition metal site, compared to the oxides caused by decreasing electronegativity of the anion, which in turn leads to variation of chemical potential around the transition metal center, [e.g. lowering the Ni2+ --> Ni3+ oxidation potential in Ni-based catalysts where Ni3+ is the actually catalytically active species]. Based on such hypothesis, we have synthesized a plethora of transition metal selenides including those based on Ni, Ni-Fe, Co, Ni-Co, Cu, and Cu-Co which show high catalytic efficiency characterized by low onset potential and overpotential at 10 mA/cm2 [Ni3Se2 - 200 - 290 mV; Co7Se8 - 260 mV; FeNi2Se4-NrGO - 170 mV (NrGO - N-doped reduced graphene oxide); NiFe2Se4 - 210 mV; CoNi2Se4 - 190 mV; Ni3Te2 – 180 mV]. In this presentation we will highlight the importance of this increasing covalency in enhancing OER catalytic activity and illustrate with examples recently discovered examples of selenide and telluride compositions ranging from binary chalcogenides (Ni3Se2, NiSe2, NiSe, Cu2Se), to ternary and quaternary mixed metal selenides (Ni-Co-Se, Ni-Fe-Se) as well as seleno-based molecular complex containing NiSe4 tetrahedral core. We will illustrate how the Ni(II) --> Ni(III) oxidation potential is indeed lowered within the chalcogenide coordination compared to the oxide leading to the formation of mixed anionic (hydroxy)chalcogenide surface which enhances surface reactivity through preferential intermediate adsorption. Another aspect that has become more relevant is the electroreduction of atmospheric carbon dioxide into fuel or other value-added chemicals, thereby offering environmental remediation without the need to store large amounts of pressurized CO2. The electrochemical tunability of transition metal chalcogenide surfaces along with their increased lattice covalency has led to development of the concept that some of these compositions can enhance carbon dioxideCO2 reduction. Specifically, we have focused on Cu and Ni-based chalcogenides based on the hypothesis that higher d-electron occupancy of the transition metal within a covalent lattice will lead to better adsorption of intermediate CO on the surface through enhanced metal-to-ligand back-bonding, which in turn leads to longer dwell time and subsequent reduction of the CO to higher carbon content products. The Nath group has recently discovered copper and nickel chalcogenides as highly active electrocatalysts for CO2 reduction to C2 and C3 products with high selectivity. Interestingly it was observed that product composition could be controlled by tuning the applied potential with ethanol and acetic acid forming predominantly at low applied potential while formic acid was obtained exclusively at higher applied potential. Lastly, we will discuss the electrocatalytic activity of the transition metal chalcogenides towards biomolecule conversion enhancing their applicability as biosensors for detecting potentially life-threatening disorders. Detailed studies of the chemical reactivity, electrochemical activity, interfacial chemistry, and functional stability of the transition metal chalcogenides that makes all these applications feasible will be discussed in depth.

Carbon Nanotube Encapsulated Metal Selenide Eelectrocatalyst for Oxygen Evolution Reaction

The oxygen evaluation represents an important reaction in electrochemical water splitting and metal-air batteries. To deal with the increasing energy crisis, production of low-cost, high-efficiency, and robust oxygen evolution reaction (OER) electrocatalysts is urgently needed. Recently, transition metal chalcogenides (TMCs) have been used as active electrocatalysts for OER because of their high electric conductivity and enriched redox chemistry. These chalcogenide based electrocatalysts show unprecedented high activity surpassing state-of-the-art precious metal oxides or hydroxide-based catalysts. In the present work, nickel selenide nanorods (NRs) were grown inside carbon nanotubes (NiSe@CNT) through chemical vapor deposition (CVD) wherein, the carbon nanostructure formed in-situ wrapping around the growing nickel selenide nanorods. Electrocatalytic behavior was explored by various electrochemical studies, including linear sweep voltammetry (LSV), chronoamperometric experiments, electrochemical surface area determination, and Tafel slope calculation, under highly alkaline condition. It was observed that this NiSe@CNT composites showed enhanced electrocatalytic activity for OER. Our results indicate that the self-grown CNT around Nickel selenide increases catalytic activity of this hybrid due to an increased number of catalytic sites and electronic conductivity of the nanocomposite. The overpotential at 10 mA cm-2 current density for the as-synthesized NiSe@CNT catalyst is 270 mV which is much better than precious metal based electrocatalysts for OER, such as RuO2 and IrO2. In addition, before and after the 40 h chronoamperometry stability test, the LSV curves were almost similar confirming that the as-synthesized catalyst could give stable electrocatalytic OER activity in 1 M KOH medium for the extended time period. The as-synthesized catalyst was characterized by XRD, Raman spectroscopy, XPS and TEM for morphology, elemental and chemical compositions.

Thermally templated cobalt oxide nanobubbles on crumpled graphene sheets: A promising non-precious metal catalysts for acidic oxygen evolution

Ru- or Ir-based precious metal oxides are typically applied as oxygen evolution reaction (OER) catalysts, owing to their high activity in acidic media and at high operating potentials. However, their expense and unsatisfactory durability prevent their application as anode catalysts in proton exchange membrane water electrolyzer stacks. This study presents the synthesis of various noble metal-free cobalt oxides supported on reduced graphene oxide catalysts using ultrasonic spray pyrolysis following different heat treatment processes. The catalyst prepared through additional thermal reduction and subsequent oxidation exhibits highly dispersed and Co3+ ion-rich hollow Co3O4 spheres on crumpled reduced graphene oxide sheets, thereby providing additional catalytically active sites for the OER. Under severe potential cycling, this catalyst exhibits acid-stability and a robust nanostructure, thereby demonstrating an extraordinarily superior stability in comparison to that of a commercially available Ir black catalyst.

Recent Progress in Advanced Electrocatalyst Design for Acidic Oxygen Evolution Reaction.

Proton exchange membrane (PEM) water electrolyzers hold great significance for renewable energy storage and conversion. The acidic oxygen evolution reaction (OER) is one of the main roadblocks that hinder the practical application of PEM water electrolyzers. Highly active, cost-effective, and durable electrocatalysts are indispensable for lowering the high kinetic barrier of OER to achieve boosted reaction kinetics. To date, a wide spectrum of advanced electrocatalysts has been designed and synthesized for enhanced acidic OER performance, though Ir and Ru based nanostructures still represent the state-of-the-art catalysts. In this Progress Report, recent research progress in advanced electrocatalysts for improved acidic OER performance is summarized. First, fundamental understanding about acidic OER including reaction mechanisms and atomic understanding to acidic OER for rational design of efficient electrocatalysts are discussed. Thereafter, an overview of the progress in the design and synthesis of advanced acidic OER electrocatalysts is provided in terms of catalyst category, i.e., metallic nanostructures (Ir and Ru based), precious metal oxides, nonprecious metal oxides, and carbon based nanomaterials. Finally, perspectives to the future development of acidic OER are provided from the aspects of reaction mechanism investigation and more efficient electrocatalyst design.

Ab Initio Multiscale Process Modeling of Ethane, Propane and Butane Dehydrogenation Reactions: A Review

Olefins are among the most important structural building blocks for a plethora of chemical reaction products, including petrochemicals, biomaterials and pharmaceuticals. An ever-increasing economic demand has urged scientists, engineers and industry to develop novel technical methods for the dehydrogenation of parent alkane molecules. In particular, the catalysis over precious metal or metal oxide catalysts has been put forward as an alternative way route to thermal-, steam- and fluid catalytic cracking (FCC). Multiscale system modeling as a tool to theoretically understand processes has in the past decade period evolved from a rudimentary measurement-complementing approach to a useful engineering environment. Not only can it predict various experimentally obtained parameters, such as conversion, activity, and selectivity, but it can help us to simulate trends, when changing applicative operating conditions, such as surface gas temperature or pressure, or even support us in the search for the type of materials, their geometrical properties and phases for a better functional performance. An overview of the current set state of the art for saturated organic short chain hydrocarbons (ethane, propane and butane) is presented. Studies that combine at least two different dimensional scales, ranging from atomistic-, bridging across mechanistic mesoscale kinetics, towards reactor- or macroscale, are focused on. Insights considering reactivity are compared.

Oxygen Evolution Reaction of Mo Oxide-Based Electocatalysts Doped with Different Metals in Acid Solution

At end of February in 2020, Fukushima Hydrogen Energy Research Field (FH2R) has started to operate with a renewable energy-powered 10MW-class hydrogen production unit, which is the largest-class in the world. These kinds of “Green Hydrogen” [1] production technologies will be accelerated not only in Japan but also all over the world because “Global Action Agenda” was released and many presentations were also given by international organizations in Hydrogen energy ministerial meeting (H2 EM 2019) which was held in Tokyo, last year with cabinet members and officials from 35 countries, regions, and organizations.In FH2R, the newest system of water electrolysis has installed. In Japan, not only alkaline water electrolysis (AWE) but also polymer electrolyte water electrolysis (PEWE) have been developed. Compared with AWE, PEWE is partly commercialized procedure to produce the hydrogen with high purity. However, one of the issue of PEWE is iridium oxide (IrO2) anode that is one of the precious metal oxide with poor resources. In order to utilize the PEWE system applying for green hydrogen production in large scale with low cost, we focused on the molybdenum-oxide based electrocatalyst (MoOx) as alternative anode materials because of its low cost compared with precious metal oxide [2-4]. In this study, we have investigated the catalytic activity of oxygen evolution reaction (OER) on MoOx with and without doping.Ti rod was used as substarate. Mo oxide-based electrocatalyst was prepared by RF magnetron sputtering method. Mo disc was used as the sputtering target. In the case of fabrication for Zr- and Ta-MoOx, Zr or Ta piece for 10% surface area was set on the Mo disc as doping material. Each partial pressure of Ar and O2 gas was adjusted to 0.23 Pa in fabrication of MoOx, Zr-MoOx and Ta-TiOx. The substrate heating temperature was constant at 673 K during sputtering. We used conventional three electrode cell with each sample as working electrode while the reversible hydrogen electrode (RHE) and carbon plate were used as reference and counter electrode to demonstrate the electrochemical measurement. In order to evaluate the OER activity of samples, the slow scan voltammetry was performed from 1.2 to 2.5 V vs. RHE in 1 M H2SO4 solution at 303 K. We also carried out electrochemical impedance spectroscopy (EIS) to obtain resistance components and semiconducting properties.Figure 1 shows the slow scan voltammograms of OER on Zr-MoOx, Ta-MoOx, and MoOx. The Zr-MoOx in this study have larger current densities than that of Ta-MoOx and MoOx. It was found that that Zr doping was effective for enhancing the OER activity of MoOx. According to Mott-Schottky plots, all samples whether doping or non-doping showed n-type semiconductor while flat band potential of Zr-MoOx was smaller than that of Ta-MoOx and MoOx.Acknowledgement: This work is partially supported by Toyota Mobility Foundation.Reference K. Ota, A. Ishihara, K. Matsuzawa, and S. Mitsushima, Electrochemistry, 78, 970 (2010).S. Hirayama, A. Ishihara, K. Sumi, K. Ota, and K. Matsuzawa, Proc. 39th Symp. Hydrogen Ener. Syst Soc Jpn (HESS), p.99 (2019) (in Japanese).K. Matsuzawa, K. Sumi, S. Hirayama, Y. Kuroda, S. Mitsushima, K. Ota and A. Ishihara, Abst. 237th ECS Meeting, I02-1551 (2020).S. Hirayama, A. Ishihara, K. Sumi, and K. Matsuzawa, Proc. 27th FCDIC Fuel Cell Symp., P9 (2020) (in Japanese). Figure 1

Ex-Situ Investigation of Activated Stainless Steel As Oxygen Evolution Reaction Electrode in Alkaline Media

Transition metal mixed oxides have been considered as promising catalysts for OER in alkaline media due to high catalytic activity, possible long lifetime and cheap alternatives to precious metal oxides [1-3]. Increasing research interest has been dedicated to Ni-based OER catalysts in particular, which possesses all desired qualities for a catalyst including being earth-abundant and have theoretically high catalytic activity [1]. Iron impurities in nickel hydroxide was found to lower OER overpotential in Ni-based alkaline batteries [4, 5], which paved the way for NiFe catalysts as active OER electrocatalysts in water electrolysis [5-9]. Large use of Ni-rich materials is becoming an increasing difficulty in alkaline electrolysis, and the search for cheaper bulk materials has recently been intensified. In particular, cheaper stainless steels being a source of both Fe and Ni have shown promise as OER electrode. However, the as-received stainless steel has low OER activity and some surface treatment, enriching the surface with nickel is necessary.In this work, we activate as-received 316 stainless steel bulk material by electrooxidation at 1.72 V vs RHE in KOH electrolyte at room temperature. We study the effect of electrolyte pH during activation as well as oxidation time. The electrode surface layer is studied using XPS, GDOES and SEM, while the surface activity is studied electrochemically using potential step and linear sweep voltammetry in a three-electrode Teflon cell. The active surface area was assessed using cyclic voltammetry. Reaction order and Tafel slope are determined to specify the reaction mechanism.We show that surface treatment of 316 stainless steel in the highest concentration of KOH (7.5 M) gives the highest activity for a minimum of 240 minutes oxidation time. Longer oxidation times did not improve electrochemical activity. Surface analysis by XPS, SEM and GDOES show a significant increase in surface Ni after activation, which was correlated to the improved activity. The surface content of Ni increased in general with increasing electrolyte pH during activation. SEM indicates small crystals on the surface, which could be due to precipitation of dissolved species on the activated samples. The best pretreatment performed in this study leads to an overvoltage of 320 mV at 10 mA cm-2. Krasil’shchikov reaction pathway is assigned as the OER reaction mechanism corresponding to the measured reaction order and Tafel slope. All the samples have the same Tafel slope. Repetitive polarization curves after 24h chronoamperometry indicate negligible change in performance with time. This indicates that the activated stainless steel is a promising electrode material for oxygen evolution. Han, L., S. Dong, and E. Wang, Transition‐metal (Co, Ni, and Fe)‐based electrocatalysts for the water oxidation reaction. Advanced materials, 2016. 28(42): p. 9266-9291. Singh, R., J. Singh, and A. Singh, Electrocatalytic properties of new spinel-type MMoO4 (M= Fe, Co and Ni) electrodes for oxygen evolution in alkaline solutions. international journal of hydrogen energy, 2008. 33(16): p. 4260-4264. Song, F., et al., Transition metal oxides as electrocatalysts for the oxygen evolution reaction in alkaline solutions: an application-inspired renaissance. Journal of the American Chemical Society, 2018. 140(25): p. 7748-7759. Conway, B. and P. Bourgault, The electrochemical behavior of the nickel–nickel oxide electrode: Part I. Kinetics of self-discharge. Canadian Journal of Chemistry, 1959. 37(1): p. 292-307. Lyons, M.E. and M.P. Brandon, The oxygen evolution reaction on passive oxide covered transition metal electrodes in aqueous alkaline solution. Part 1-Nickel. Int. J. Electrochem. Sci, 2008. 3(12): p. 1386-1424.

A selective and efficient precious metal-free electrocatalyst for chlorine evolution reaction: An experimental and computational study

Chlor-Alkali (CA) process benefits from chlorine evolution reaction (ClER) over various precious metal oxides electrocatalysts. This study introduces a novel precious metal-free Ti 0:35 V 0:35 Sn 0:25 Sb 0.05 -oxide electrocatalyst which selectively conducts the reaction pathway towards ClER with a high faradaic current efficiency of ~88%. The electrocatalyst and its electrochemical activity were scrutinized by various techniques such as field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and linear scanning voltammetry (LSV). A decent overpotential difference (DE) between oxygen evolution reaction (OER) and chlorine evolution reactions (ClER) was attributed to the reasonable design of the electrocatalyst composite. Namely, the geometric structure and surface properties of the synthesized electrocatalyst, as well as the associated electrochemical selectivity was tuned by incorporation of vanadium pentoxide, antimony and tin oxide in the electrocatalyst material. In addition, the electronic properties of the synthesized electrocatalysts including band structure and the corresponding electron density were studied by density functional theory (DFT) calculations. • A cost-effective Ti 0:35 V 0:35 Sn 0:25 Sb 0.05 -oxide electrocatalyst was synthesized. • The developed electrocatalyst was tuned towards chlorine evolution reaction. • Preferred chlorine evolution was resulted rather than oxygen evolution reaction. • The electronic structure of the developed electrocatalysts was explored by DFT. • The presence of vanadium oxide could lower the band gap of the electrocatalyst.

Development and performance of A-site rich perovskite-type material for enhanced oxygen evolution reaction in alkaline electrolyte

A-site rich perovskites Ba2xCoMoO6 (x = 1, 1.1, 1.2, and 1.3) were synthesised by a solid-state reaction method. The as-prepared Ba2.4CoMoO6 catalyst showed good catalytic activity towards oxygen evolution reaction (OER) activity with an overpotential of 420 mV at 10 mA cm−2, which was enhanced by 100 mV compared with that of Ba2CoMoO6, with a low Tafel slope of 79 mV dec−1, an obviously enhanced electrochemical active surface area value, and sharply improved mass and specific activities. The enhanced OER activity even surpassed the precious metal oxide IrO2 and perovskite benchmark Ba0.5Sr0.5Co0.8Fe0.2O3-δ activities.

Selective dissolution of A-site cations of La0.6Sr0.4Co0.8Fe0.2O3 perovskite catalysts to enhance the oxygen evolution reaction

Perovskite oxide is a potential alternative to precious metal oxides like IrO2 and RuO2 as electrocatalysts in the oxygen evolution reaction (OER), mostly for its cost-effectiveness and adequate stability. However, the low catalytic activity in the OER limits its practical application. This paper deals with the preparation of perovskite oxides (by the sol-gel method) with enhanced electrocatalytic activity through selective dissolution of A-site cations of La0.6Sr0.4Co0.8Fe0.2O3 (LSCF) in order to tune the A-site cation deficiency. Additionally, a thorough investigation of the catalysts’ OER performance was performed in a 0.1 mol⋅L−1 KOH solution. Based on the results of XRD, SEM, TEM, XPS and ICP-AES, it can be concluded that selective dissolution of Sr cations on A-sites can be achieved using a HNO3 etching remaining the perovskite structure. The OER catalytic activity of LSCF can be effectively promoted after acid etching for 6 h, which can be attributed to the higher surface area (BET result) and ratio of the high oxidative oxygen species (O2−/O−) and surface oxygen species (OH−/O2). Moreover, the LSCF catalysts maintains an appropriate electrochemical stability after acid etching. Our work offers a simple but effective way to modify the perovskite surface so as to boost the OER performance.

Iridium nanostructured metal oxide, its inclusion in silica matrix and their activity toward photodegradation of methylene blue

Precious metal oxides of IrO2 were prepared by thermal treatment of the macromolecular Chitosan●(IrCl3)X and PSP-4-PVP●(IrCl3)X precursors. Using this procedure, pure IrO2, phases were formed. The nature of the polymeric precursor is acting as a solid state template and influences the size of the iridium dioxide but not significantly the morphology, and the obtained IrO2 nanoparticles are about 15 nm. For the first time, the photocatalytic degradation of methylene blue using IrO2 was measured founding a moderated activity. The inclusion of IrO2 into SiO2 was performed using a combined solution of the Chitosan and PVP precursors by the sol-gel method. Subsequent pyrolysis of the isolated solid-state Chitosan●(IrCl3)x(SiO2)y and PSP-4-PVP●(IrCl3)x(SiO2)y give rise to the IrO2//SiO2 nanocomposites. The IrO2 particles are distributed uniformly inside the matrix of SiO2 leading to stable semi porous materials appropriate for high temperature catalytic applications. The IrO2 nanoparticles formed from the PVP precursor are mainly nanobars of 10 nm width, while that for the chitosan precursor are around 25 nm. The IrO2/SiO2 composites exhibit a moderate photocatalytic activity toward the degradation of methylene blue and similar to that of IrO2.

Oxygen Evolution Reaction of Ti and Mo Oxide-Based Electocatalysts in Acid Solution

On Oct. 25, 2019, Hydrogen energy ministerial meeting (H2 EM 2019) was held in Tokyo, Japan with cabinet members and officials from 35 countries, regions, and organizations. In the meeting, “Global Action Agenda” was released as the chairman’s summary, and many presentations were also given by international organizations. In the sector-integration workshop in this meeting, several presenters from industrial company of water electrolysis expected to improve its technologies for producing hydrogen from renewable energies. In our research center, the hydrogen producing from renewable energies is called as “Green Hydrogen” [1].Polymer electrolyte water electrolysis (PEWE) is partly commercialization procedure to produce the hydrogen with high purity. Recently, it has been developed to be large scale for applying the Power-to-Gas (PtG) in Europe. However, the conventional anode uses an iridium oxide that is one of the precious metal oxide with poor resources. In order to utilize the PEWE system applying for PtG and "Hreen hydrogen" production in large scale with low cost, we focused on the titanium- and molybdenum-oxide based electrocatalyst (TiOx and MoOx) as alternative anode materials because of its low cost with abundant resources compared with precious metal oxide. In addition, it is reported that the overpotential of oxygen evolution reaction (OER) on molybdenum (Mo) doped TiOx (Mo-TiOx) was predicted to be similar to that of IrO2 from the density functional theory calculation [2-3]. In this study, we have investigated the catalytic activity of TiOx and MoOx with and without doping for the OER.Ti rod was used as substarate. Ti and Mo oxide-based electrocatalyst was prepared by RF magnetron sputtering method. Ti or Mo disc was used as the sputtering target. In the case of fabrication for Mo-TiOx, a piece of Mo metal as 10% surface area for Ti metal was set on the Ti disc as doping material. Each partial pressure of Ar and O2 gas was adjusted to 0.23 Pa in fabrication of TiOx and Mo-TiOx. In the case of fabrication MoOx, partial pressure of O2 was fix at 0.10 Pa. The substrate heating temperature was constant at 373 K during sputtering. The output was set on 150 W, and sputtering time was constant for 20 minutes. We used conventional three electrode cell with each sample as working electrode while the reversible hydrogen electrode (RHE) and carbon plate were used as reference and counter electrode to demonstrate the electrochemical measurement. In order to evaluate the OER activity of samples, the slow scan voltammetry was performed from 1.2 to 2.0 V vs. RHE in 1 M H2SO4 solution at 303 K.Figure 1 shows the slow scan voltammograms of OER on Ti and Mo oxide-based electrocatalysts. The result of ZrO2 on conductive oxide (ZrO2/ConOx) [4] is also shown in this figure. The Mo-TiOx/Ti and MoOx/Ti in this study have obviously larger current densities than that of ZrO2/ConOx and TiOx/Ti. The Tafel slope of OER on Mo-TiOx/Ti was 91 mV dec-1 the while the that on the ZrO2/ConOx, MoOx/Ti and TiOx/Ti were larger than 180 mV dec-1. Because of the smallest Tafel slope and the largest current density on Mo-TiOx/Ti in this study, the Mo doping is effective for enhancing OER activities. According to Mott-Schottky plots, the Mo-TiOx/Ti seemed to have higher carrier concentration than that of TiOx/Ti while both materials showed as n-type semiconductors. Above all, the Mo-TiOx/Ti has higher activity for the OER than other materials in this study.Acknowledgement: This work is partially supported by Toyota Mobility Foundation.Reference 1. K. Ota, A. Ishihara, K. Matsuzawa, and S. Mitsushima, Electrochemistry, 78, 970 (2010).2. M. Garca-Mota, A. Vojvodic, H. Metiu, I. C. Man, H-Y. Su, J. Rossmeisl, and J. K. Norskov, ChemCatChem, 3, 1607 (2011).3. X. Huang, J. Wang, H. B. Tao, H. Tiana and H. Xu, Chem. Sci., 10, 3340 (2019).4. K. Matsuzawa, K. Sumi, Y. Kuroda, S. Mitsushima, and A. Ishihara, Abst. 16th Annual Meeting of Soc. Nano Sci. Tech., #O-33, Tokyo, Jpn (2018) (in Japanese). Figure 1

Formation of glyco-functionalized interfaces for protein binding using polyphenolic glycoside

In this study, a polyphenolic glycoside (α-glucosyl rutin) was used to form glyco-functionalized interfaces for protein binding. α-Glucosyl rutin was coated onto precious metals, metal oxides, and synthetic polymers, including polyethylene and polytetrafluoroethylene with poor surface modifiability. The glyco-functionalized interfaces bound strongly and specifically to concanavalin A and Bauhinia purpurea lectin, which have different carbohydrate specificities. Competitive adsorption tests demonstrated that the binding sites for the abovementioned lectins were glucosyl and rhamnosyl residues, respectively. The glyco-functionalized interfaces maintained the protein binding ability after being stored in aqueous solution for 1 day and in air for 160 days. Once the glyco-functionalized interfaces were formed on gold, silicon dioxide, polystyrene, and polytetrafluoroethylene using α-glucosyl rutin, all the glyco-functionalized interfaces bound to concanavalin A rather than peanut agglutinin.

Atomically dispersed Pt\u2013N4 sites as efficient and selective electrocatalysts for the chlorine evolution reaction

Chlorine evolution reaction (CER) is a critical anode reaction in chlor-alkali electrolysis. Although precious metal-based mixed metal oxides (MMOs) have been widely used as CER catalysts, they suffer from the concomitant generation of oxygen during the CER. Herein, we demonstrate that atomically dispersed Pt−N4 sites doped on a carbon nanotube (Pt1/CNT) can catalyse the CER with excellent activity and selectivity. The Pt1/CNT catalyst shows superior CER activity to a Pt nanoparticle-based catalyst and a commercial Ru/Ir-based MMO catalyst. Notably, Pt1/CNT exhibits near 100% CER selectivity even in acidic media, with low Cl− concentrations (0.1 M), as well as in neutral media, whereas the MMO catalyst shows substantially lower CER selectivity. In situ electrochemical X-ray absorption spectroscopy reveals the direct adsorption of Cl− on Pt−N4 sites during the CER. Density functional theory calculations suggest the PtN4C12 site as the most plausible active site structure for the CER.

General anion-exchange reaction derived amorphous mixed-metal oxides hollow nanoprisms for highly efficient water oxidation electrocatalysis

High cost precious metal oxides (RuO2 and IrO2) electrocatalysts are required to overcome the sluggish kinetics of the oxygen evolution reaction (OER), which severely restricts the scalable application. Herein, we present a versatile anion-exchange based strategy to fabricate various amorphous transition metal oxide hollow nanoprisms with FeCo-MIL-88B template, which exhibit highly efficient OER catalysis in alkaline media. Impressively, a low overpotential of 294 mV at 10 mA cm−2 with an ultrasmall Tafel slope of 45.1 mV dec-1 and decent durability can be achieved. More importantly, the underlying origin is unraveled using the in-situ Raman spectroscopy measurement combined with the ex-situ X-ray photoelectron spectroscopy anlysis, where the electrochemically transformed metal hydroxide and oxyhydroxide species could be the real active species. This work provides a universal strategy to construct transition metal oxide hollow nanostructures with enhanced OER activity, which could push forward the advance of noble metal free electrocatalytic water splitting.

Reduced graphene oxide supported nitrogen-doped porous carbon-coated NiFe alloy composite with excellent electrocatalytic activity for oxygen evolution reaction

Designing of cost-effective electrocatalysts for efficient oxygen evolution reaction (OER) is highly desired for the practical production of clean hydrogen energy. Herein, reduced graphene oxide (RGO) supported N-doped porous carbon-coated NiFe alloy composite (NiFe@NC/RGO) was synthesized via a facile pyrolysis route. The introduction of RGO effectively protects the active NiFe component from agglomeration and largely promotes charge transfer. Meanwhile, the formation of porous N-doped carbon shell provides sufficient contact between active species and electrolyte, thus exposing plenty of accessible active sites. Specifically, the optimized NiFe@NC/RGO composite shows superior electrocatalytic performance, delivering an overpotential as low as 223 mV at current density of 10 mA cm−2, and a small Tafel slope of 48.7 mV dec−1 in 1 M KOH solution, which outperforms commercial precious metal oxide catalysts such as RuO2 and a vast majority of electrocatalysts reported so far. Long-term cycling test demonstrates that the overpotential at current density of 10 mA cm−2 has almost no change after 1000 cycles at a scan rate of 50 mV s−1, indicating its quite good stability. The low-cost and high-performance electrocatalyst developed in this work shows great potential for practical hydrogen production from electrolysis of water.

Chlorine doped graphitic carbon nitride nanorings as an efficient photoresponsive catalyst for water oxidation and organic decomposition

Rationally engineering the microstructure and electronic structure of catalysts to induce high activity for versatile applications remains a challenge. Herein, chlorine doped graphitic carbon nitride (Cl-doped g-C3N4) nanorings have been designed as a superior photocatalyst for pollutant degradation and oxygen evolution reaction (OER). Remarkably, Cl-doped g-C3N4 nanorings display enhanced OER performance with a small overpotential of approximately 290 mV at current density of 10 mA cm−2 and Tafel slope of 83 mV dec-1, possessing comparable OER activity to precious metal oxides RuO2 and IrO2/C. The excellent catalytic performance of Cl-doped g-C3N4 nanorings originates from the strong oxidation capability, abundant active sites exposed and efficient charge transfer. More importantly, visible light irradiation gives rise to a prominent improvement of the OER performance, reducing the OER overpotential and Tafel slope by 140 mV and 28 mV dec-1, respectively, demonstrating the striking photo-responsive OER activity of Cl-doped g-C3N4 nanorings. The great photo-induced improvement in OER activity would be related to the efficient charge transfer and the OH radicals arising spontaneously on CN-Cl100 catalyst upon light irradiation. This work establishes Cl-doped g-C3N4 nanorings as a highly competitive metal-free candidate for photoelectrochemical energy conversion and environmental cleaning application.