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Lupe
Lupe
2015
Rosa M. Arán-Ais, Fabio Dionigi, Thomas Merzdorf, Martin Gocyla, Marc Heggen, Rafal E. Dunin-Borkowski, Manuel Gliech, José Solla-Gullón, Enrique Herrero, Juan M. Feliu, and Peter Strasser

Elemental Anisotropic Growth and Atomic-Scale Structure of Shape-Controlled Octahedral Pt−Ni−Co Alloy Nanocatalysts

Nano Lett. 15, 7473−7480

DOI: 10.1021/acs.nanolett.5b03057

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Multimetallic shape-controlled nanoparticles offer great opportunities to tune the activity, selectivity, and stability of electrocatalytic surface reactions. However, in many
cases, our synthetic control over particle size, composition, and shape is limited requiring trial and error. Deeper atomic-scale insight in the particle formation process would enable more rational syntheses. Here we exemplify this using a family of trimetallic PtNiCo nanooctahedra obtained via a low-temperature, surfactant-free solvothermal synthesis. We analyze the competition between Ni and Co precursors under coreduction “one-step” conditions when the Ni reduction rates prevailed. To tune the Co reduction rate and final content, we develop a “two-step” route and track the evolution of the composition and morphology of the particles at the atomic scale. To achieve this,
scanning transmission electron microscopy and energy dispersive X-ray elemental mapping techniques are used. We provide evidence of a heterogeneous element distribution caused by element-specific anisotropic growth and create octahedral nanoparticles with tailored atomic composition like Pt1.5M, PtM, and PtM1.5 (M = Ni + Co). These trimetallic electrocatalysts have been tested toward the oxygen reduction reaction (ORR), showing a greatly enhanced mass activity related to commercial Pt/C and less activity loss than binary PtNi and PtCo after 4000 potential cycles.
Tran Ngo Huan, Eugen. S. Andreiadis, Jonathan Heidkamp, Philippe Simon, Etienne Derat, Saioa Cobo, Guy Royal, Arno Bergmann, Peter Strasser, Holger Dau, Vincent Artero and Marc Fontecave

From molecular copper complexes to composite electrocatalytic materials for selective reduction of CO2 to formic acid

J. Mater. Chem. A  3, 3901–3907

DOI: 10.1039/C4TA07022D

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The development of new energy storage technologies is central to solving the challenges facing the widespread use of renewable energies. An option is the reduction of carbon dioxide (CO2) into carbon-based products which can be achieved within an electrochemical cell. Future developments of such processes depend on the availability of cheap and selective catalysts at the electrode. Here we show that a unique well-characterized active electrode material can be simply prepared via electrodeposition from a molecular copper complex precursor. The best performances, namely activity (150 mV onset overpotential and 1 mA cm-2 current density at 540 mV overpotential), selectivity (90% faradaic yield) and stability for electrocatalytic reduction of CO2 into formic acid in DMF/H2O (97:3 v/v) have been obtained with the [Cu(cyclam)](ClO4)2 complex (cyclam = 1,4,8,11-tetraazacyclotetradecane) as the precursor. Remarkably the organic ligand of the Cu precursor remains part of the composite material and the electrocatalytic activity is greatly dependent on the nature of that organic component.
Erik Ortel, Jörg Polte, Denis Bernsmeier, Björn Eckhardt, Benjamin Paul, Arno Bergmann, Peter Strasser, Franziska Emmerling, Ralph Kraehnert

Pd/TiO2 coatings with template-controlled mesopore structure as highly active hydrogenation catalyst

Applied Catalysis A: General 493, 25–32

DOI: 10.1016/j.apcata.2014.12.044

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Micro-structured reactors offer excellent mass and heat transport capabilities and can therefore sustain very high reaction rates and space–time-yields also for highly exothermic catalytic reactions. However, such high rates cannot be reached when the reactors are coated or filled with conventional catalysts powders. We present a strategy for the direct synthesis of highly active wall-coated supported catalysts via co-deposition of a pore template (here micelles formed from PEO-b-PPO-b-PEO) and a precursors for the metal oxide (TiCl4) along with a compatible precursor for the active metal (PdCl2). The obtained catalytic coatings possess a template-controlled open pore structure and excellent mechanical stability. Moreover, the active metal is highly dispersed and well-distributed across the coating also at high Pd loadings. The corresponding high activity along with rapid mass transfer enabled by the open pore system results in the best space–time-yields in the gas-phase hydrogenation of butadiene reported so far in literature for a supported catalyst.
Guang-Ping Hao, Nastaran Ranjbar Sahraie, Qiang Zhang, Simon Krause, Martin Oschatz, Alicja Bachmatiuk, Peter Strasser and Stefan Kaskel

Hydrophilic non-precious metal nitrogen-doped carbon electrocatalysts for enhanced efficiency in oxygen reduction reaction

Chem. Commun. 51, 17285-17288

DOI: 10.1039/C5CC06256J

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Exploring the role of surface hydrophilicity of non-precious metal N-doped carbon electrocatalysts in electrocatalysis is challenging. Herein we discover an ultra-hydrophilic non-precious carbon electrocatalyst, showing enhanced catalysis efficiency on both gravimetric and areal basis for oxygen reduction reaction due to a high dispersion of active centres.
Xin Gong, Shanshan Liu, Chuying Ouyang, Peter Strasser, and Ruizhi Yang

Nitrogen- and Phosphorus-Doped Biocarbon with Enhanced Electrocatalytic Activity for Oxygen Reduction

ACS Catal. 5(2), 920–927

DOI: 10.1021/cs501632y

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The oxygen reduction reaction (ORR) at the cathode of fuel cells and metal–air batteries requires efficient electrocatalysts to accelerate its reaction rate due to its sluggish kinetics. Nitrogen- and phosphorus-doped biocarbon has been fabricated via a simple and low-cost biosynthesis method using yeast cells as a precursor. The as-prepared biocarbon exhibits excellent electrocatalytic activity for the ORR. An onset potential of −0.076 V (vs Ag/AgCl) and a negative shift of only about 29 mV in the half-wave potential of the biocarbon as compared to commercial Pt/C (20 wt % Pt on Vulcan XC-72, Johnson Matthey) is achieved. The biocarbon possesses enhanced electron poverty in carbon atoms and a decreasing amount of less electroactive nitrogen and phosphorus dopants due to the biomineralization during the synthesis. The surface gap layer along with the mesopores in the biocarbon increases accessible active sites and facilitates the mass transfer during the ORR. These factors correlate with the high ORR activity of the biocarbon. The results demonstrate that biomineralization plays a critical role in tailoring the structure and the electrocatalytic activity of the biocarbon for ORR. 
Xuecheng Cao, Jiao Wu, Chao Jin, Jinghua Tian, Peter Strasser, and Ruizhi Yang

MnCo2O4 Anchored on P‑Doped Hierarchical Porous Carbon as an Electrocatalyst for High-Performance Rechargeable Li−O2 Batteries

ACS Catal. 5 (8), 4890–4896

DOI: 10.1021/acscatal.5b00494

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The design and synthesis of MnCo2O4 anchored on P-doped hierarchical porous carbon (MCO/P-HPC) is reported. Without harsh oxidative treatment, creating anchoring sites for MnCo2O4 on the surface of carbon is realized by P-doping in carbon. The chemical coupling between P-HPC and MCO induced by P-doping provides pathways for fast charge transport. This hybrid with a hierarchical porous structure favors efficient electrolyte penetration, oxygen transport, and effective accommodation of insoluble discharge product Li2O2. When employed as an electrocatalyst in rechargeable Li–O2 batteries, the MCO/P-HPC hybrid delivers a high discharge capacity (13 150 mAh g–1 at 200 mA g–1), excellent rate capability (7028 mAh g–1 at 1000 mA g–1), and long cycle stability (200 cycles at a capacity of 1000 mAh g–1 under 200 mA g–1).
Arno Bergmann, Elias Martinez-Moreno, Detre Teschner, Petko Chernev, Manuel Gliech, Jorge Ferreira de Araújo, Tobias Reier, Holger Dau, and Peter Strasser

Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution

Nature Communications 6 (8625), 1-9

DOI:10.1038/ncomms9625

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Water splitting catalysed by earth-abundant materials is pivotal for global-scale production of non-fossil fuels, yet our understanding of the active catalyst structure and reactivity is still insufficient. Here we report on the structurally reversible evolution of crystalline Co3O4 electrocatalysts during oxygen evolution reaction identified using advanced in situ X-ray techniques. At electrode potentials facilitating oxygen evolution, a sub-nanometre shell of the Co3O4 is transformed into an X-ray amorphous CoOx(OH)y which comprises di-μ-oxo-bridged Co3+/4+ ions. Unlike irreversible amorphizations, here, the formation of the catalytically-active layer is reversed by re-crystallization upon return to non-catalytic electrode conditions. The Co3O4 material thus combines the stability advantages of a controlled, stable crystalline material with high catalytic activity, thanks to the structural flexibility of its active amorphous oxides.We propose that crystalline oxides may be tailored for generating reactive amorphous surface layers at catalytic potentials, just to return to their stable crystalline state under rest conditions.
Nastaran Ranjbar Sahraie, Ulrike I. Kramm, Julian Steinberg, Yuanjian Zhang, Arne Thomas, Tobias Reier, Jens-Peter Paraknowitsch, and Peter Strasser

Quantifying the density and utilization of active sites in non-precious metal oxygen electroreduction catalysts

Nature Communications 6 (8618), 1-9

DOI: 10.1038/ncomms9618

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Carbon materials doped with transition metal and nitrogen are highly active, non-precious metal catalysts for the electrochemical conversion of molecular oxygen in fuel cells, metal air batteries, and electrolytic processes. However, accurate measurement of their intrinsic turn-over frequency and active-site density based on metal centres in bulk and surface has remained difficult to date, which has hampered a more rational catalyst design. Here we report a successful quantification of bulk and surface-based active-site density and associated turn-over frequency values of mono- and bimetallic Fe/N-doped carbons using a combination of chemisorption, desorption and 57Fe Mossbauer spectroscopy techniques. Our general approach yields an experimental descriptor for the intrinsic activity and the active-site utilization, aiding in the catalyst development process and enabling a previously unachieved level of understanding of reactivity trends owing to a deconvolution of site density and intrinsic activity.
Rosa M. Arán-Ais, Fabio Dionigi, Thomas Merzdorf, Martin Gocyla, Marc Heggen, Rafal E. Dunin-Borkowski, Manuel Gliech, José Solla-Gullón, Enrique Herrero, Juan M. Feliu, and Peter Strasser

Elemental Anisotropic Growth and Atomic-Scale Structure of Shape-Controlled Octahedral Pt–Ni–Co Alloy Nanocatalysts

Nano Lett. 15 (11), 7473–7480

DOI: 10.1021/acs.nanolett.5b03057

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Multimetallic shape-controlled nanoparticles offer great opportunities to tune the activity, selectivity, and stability of electrocatalytic surface reactions. However, in many cases, our synthetic control over particle size, composition, and shape is limited requiring trial and error. Deeper atomic-scale insight in the particle formation process would enable more rational syntheses. Here we exemplify this using a family of trimetallic PtNiCo nanooctahedra obtained via a low-temperature, surfactant-free solvothermal synthesis. We analyze the competition between Ni and Co precursors under coreduction “one-step” conditions when the Ni reduction rates prevailed. To tune the Co reduction rate and final content, we develop a “two-step” route and track the evolution of the composition and morphology of the particles at the atomic scale. To achieve this, scanning transmission electron microscopy and energy dispersive X-ray elemental mapping techniques are used. We provide evidence of a heterogeneous element distribution caused by element-specific anisotropic growth and create octahedral nanoparticles with tailored atomic composition like Pt1.5M, PtM, and PtM1.5 (M = Ni + Co). These trimetallic electrocatalysts have been tested toward the oxygen reduction reaction (ORR), showing a greatly enhanced mass activity related to commercial Pt/C and less activity loss than binary PtNi and PtCo after 4000 potential cycles.
Mahdi Ahmadi, Chunhua Cui, Hemma Mistry, Peter Strasser, and Beatriz Roldan Cuenya

Carbon Monoxide-Induced Stability and Atomic Segregation Phenomena in Shape-Selected Octahedral PtNi Nanoparticles

ACS Nano 9 (11), 10686–10694

DOI: 10.1021/acsnano.5b01807

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The chemical and morphological stability of size- and shape-selected octahedral PtNi nanoparticles (NP) were investigated after different annealing treatments up to a maximum temperature of 700°C in vacuum and under 1 bar of CO. Atomic force microscopy (AFM) was used to examine the mobility of the NPs and their stability against coarsening, and X-ray photoelectron spectroscopy (XPS) to study the surface composition, chemical state of Pt and Ni in the NPs and thermally and CO-induced atomic segregation trends. Exposing the samples to 1 bar of CO at room temperature before annealing in vacuum was found to be effective at enhancing the stability of the NPs against coarsening. In contrast, significant coarsening was observed when the sample was annealed in 1 bar of CO, most likely as a result of Ni(CO)4 formation and their enhanced mobility on the support surface. Sample exposure to CO at room temperature prior to annealing lead to the segregation of Pt to the NP surface. Nevertheless, oxidic PtOx and NiOx species still remained at the NP surface, and, irrespective of the initial sample pretreatment, Ni surface segregation was observed upon annealing in vacuum at moderate temperature (T<300°C). Interestingly, a distinct atomic segregation trend was detected between 300°C-500°C for the sample pre-exposed to CO, namely, Ni surface segregation was partially hindered. This might be attributed to the higher bonding energy of CO to Pt as compared to Ni. Annealing in the presence of 1-bar CO also resulted in the initial surface segregation of Ni (T<400°C) as long as PtOx and NiOx species were
available on the surface as a result of the higher affinity of Ni for oxygen. Above 500°C, and regardless of the sample pretreatment, the diffusion of Pt atoms to the NP surface and the formation of a Ni-Pt alloy is observed.
Tobias Reier, Zarina Pawolek, Serhiy Cherevko, Michael Bruns, Travis Jones, Detre Teschner, Sören Selve, Arno Bergmann, Hong Nhan Nong, Robert Schlögl, Karl J. J. Mayrhofer, and Peter Strasser

Molecular Insight in Structure and Activity of Highly Efficient, Low-Ir
Ir−Ni Oxide Catalysts for Electrochemical Water Splitting (OER)

J. Am. Chem. Soc. 137 (40), 13031-13040

DOI: 10.1021/jacs.5b07788

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Mixed bimetallic oxides offer great opportunities for a systematic tuning of electrocatalytic activity and stability. Here, we demonstrate the power of this strategy using well-defined thermally prepared Ir–Ni mixed oxide thin film catalysts for the electrochemical oxygen evolution reaction (OER) under highly corrosive conditions such as in acidic proton exchange membrane (PEM) electrolyzers and photoelectrochemical cells (PEC). Variation of the Ir to Ni ratio resulted in a volcano type OER activity curve with an unprecedented 20-fold improvement in Ir mass-based activity over pure Ir oxide. In situ spectroscopic probing of metal dissolution indicated that, against common views, activity and stability are not directly anticorrelated. To uncover activity and stability controlling parameters, the Ir–Ni mixed thin oxide film catalysts were characterized by a wide array of spectroscopic, microscopic, scattering, and electrochemical techniques in conjunction with DFT theoretical computations. By means of an intuitive model for the formation of the catalytically active state of the bimetallic Ir–Ni oxide surface, we identify the coverage of reactive surface hydroxyl groups as a suitable descriptor for the OER activity and relate it to controllable synthetic parameters. Overall, our study highlights a novel, highly active oxygen evolution catalyst; moreover, it provides novel important insights into the structure and performance of bimetallic oxide OER electrocatalysts in corrosive acidic environments.
Amandine Guiet, Caren Göbel, Katharina Klingan, Michael Lublow, Tobias Reier, Ulla Vainio, Ralph Krähnert, Helmut Schlaad, Peter Strasser, Ivelina Zaharieva, Holger Dau, Matthias Driess, Jörg Polte, and Anna Fischer

Hydrophobic Nanoreactor Soft-Templating: A Supramolecular Approach to Yolk@Shell Materials

Adv. Func. Mater. 25, 6228–6240

DOI: 10.1002/adfm.201502388

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Due to their unique morphology-related properties, yolk@shell materials are promising materials for catalysis, drug delivery, energy conversion, and storage. Despite their proven potential, large-scale applications are however limited due to demanding synthesis protocols. Overcoming these limitations, a simple soft-templated approach for the one-pot synthesis of yolk@shell nanocomposites and in particular of multicore metal nanoparticle (NP)@metal oxide nanostructures (MNP@MOx) is introduced. The approach here, as demonstrated for AuNP@ITOTR (ITOTR standing for tin-rich ITO), relies on polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) inverse micelles as two compartment nanoreactor templates. While the hydrophilic P4VP core incorporates the hydrophilic metal precursor, the hydrophobic PS corona takes up the hydrophobic metal oxide precursor. As a result, interfacial reactions between the precursors can take placebetween the compartments, leading to the formation of yolk@shell structures in solution, which once calcined yield AuNP@ITOTR nanostructures, composed of multiple 6 nm sized Au NPs strongly anchored onto the inner surface of porous 35 nm ITOTR hollow spheres. Although of multicore nature, only limited sintering of the metal nanoparticles is observed at high temperatures (700 C). In addition, the as-synthesized yolk@shell structures exhibit high and stable activity toward CO electrooxidation, thus proving the functionality of this approach for the design of yolk@shell nanocatalysts.

Ana Sofia Varela, Nastaran Ranjbar Sahraie, Julian Steinberg, Wen Ju, Hyung-Suk Oh, and Peter Strasser

Metal-Doped Nitrogenated Carbon as Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons

Angew. Chem. Int. Ed. 54 (37), 10758-10762

DOI: 10.1002/anie.201502099

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This study explores the kinetics, mechanism, and active sites of the CO2 electroreduction reaction (CO2RR) to syngas and hydrocarbons on a class of functionalized solid carbon-based catalysts. Commercial carbon blacks were functionalized with nitrogen and Fe and/or Mn ions using pyrolysis and acid leaching. The resulting solid powder catalysts were found to be active and highly CO selective electrocatalysts in the electroreduction of CO2 to CO/H2 mixtures outperforming a low-area polycrystalline gold benchmark. Unspecific with respect to the nature of the metal, CO production is believed to occur on nitrogen functionalities in competition with hydrogen evolution. Evidence is provided that sufficiently strong interaction between CO and the metal enables the protonation of CO and the formation of hydrocarbons. Our results highlight a promising new class of low-cost, abundant electrocatalysts for synthetic fuel production from CO2.
Claudio Baldizzone, Lin Gan, Nejc Hodnik, Gareth Keeley, Aleksander Kostka, Marc Heggen, 3 Peter Strasser and Karl J. J. Mayrhofer

Stability of Dealloyed Porous Pt/Ni Nanoparticles

ACS Catal. 5, 5000-5007

DOI: 10.1021/acscatal.5b01151

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We provide a comprehensive durability assessment dedicated to a promising class of electrocatalysts for the oxygen reduction reaction (i.e., porous platinum nanoparticles). The stability of these nanoengineered open structures is tested under two accelerated degradation test conditions (ADT), particularly selected to mimic the potential regimes experienced by the catalyst during the operative life of a fuel cell (i.e., load cycles (up to 1.0 VRHE) and start-up cycles (up to 1.4 VRHE)). To understand the evolution of the electrochemical performance, the catalyst properties are investigated by means of fundamental rotating disc electrode studies, identical location transmission electron microscopy (IL-TEM) coupled with electron energy loss spectroscopy chemical mapping (IL-EELS), and post-use chemical analysis and online highly sensitive potential resolved dissolution concentration monitoring by scanning flow cell inductively coupled plasma-mass spectrometry (SFC-ICP-MS). The experimental results on the nanoporous Pt revealed distinctive degradation mechanisms that could potentially affect a wide range of other nanoengineered open structures. The study concludes that, although providing promising activity performance, under the relevant operational conditions of fuel cells, the nanoporosity is only metastable and subjected to a progressive reorganization toward the minimization of the nanoscale curvature. The rate and pathways of this specific degradation mechanism together with other well-known degradation mechanisms like carbon corrosion and platinum dissolution are strongly dependent on the selected upper limit potential, leading to distinctly different durability performance.
Peter Strasser

Catalysts by Platonic design

Science 349, 379

DOI: 10.1126/science.aac7861

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Sophisticated shape-controlled design is yielding ever more active nanocatalysts
Nina Erini, Paul Krause, Manuel Gliech, Ruizhi Yang, Yunhui Huang, Peter Strasser

Comparitive assessment of synthetic strategies toward active platinum-rhodium-tin electrocatalysts for efficient ethanol electro-oxidation

Journal of Power Sources 294, 299-304

DOI: 10.1016/j.jpowsour.2015.06.042

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The present work explores the effect of autoclave-based autogenous-pressure vs. ambient pressure conditions on the synthesis and properties of carbon-supported Pt–Rh–Sn nanoparticle electrocatalysts. The Pt–Rh–Sn nanoparticles were characterized by X-ray spectroscopy, electron microscopy and mass spectroscopy and deployed as catalysts for the electrocatalytic ethanol oxidation reaction. Pt–Rh–Sn catalysts precipitated with carbon already present showed narrow particle size distribution around 7 nm, while catalysts supported on carbon after particle formation showed broader size distribution ranging from 8 to 16 nm, similar metal loadings between 40 and 48 wt.% and similar atomic ratios of Pt:Rh:Sn of 30:10:60. The highest ethanol oxidation activity at low overpotentials associated with exceptionally early ethanol oxidation onset potential was observed for ambient-pressure catalysts with the active ternary alloy phase formed in presence of the carbon supports. In contrast, catalysts prepared under ambient pressure in a two-step approach, involving alloy particle formation followed by particle separation and subsequent deposition on the carbon support, yielded the highest overall mass activities. Based on the observed synthesis–activity correlations, a comparative assessment is provided of the synthetic techniques at high vs. low pressures, and in presence and absence of carbon support. Plausible hypotheses in terms of particle dispersion and interparticle distance accounting for these observed differences are discussed.
Michael Bernicke, Erik Ortel, Tobias Reier, Arno Bergmann, Jorge Ferreira de Araujo, Peter Strasser and Ralph Kraehnert

Iridium Oxide Coatings with Templated Porosity as Highly Active Oxygen Evolution Catalysts: Structure-Activity Relationships

ChemSusChem 8 (11), 1908-1915

DOI: 0.1002/cssc.201402988

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Iridium oxide is the catalytic material with the highest stability in the oxygen evolution reaction (OER) performed under acidic conditions. However, its high cost and limited availability demand that IrO2 is utilized as efficiently as possible. We report the synthesis and OER performance of highly active mesoporous IrO2 catalysts with optimized surface area, intrinsic activity, and pore accessibility. Catalytic layers with controlled pore size were obtained by soft-templating with micelles formed from amphiphilic block copolymers poly(ethylene oxide)-b-poly(butadiene)-b-poly(ethylene oxide). A systematic study on the influence of the calcination temperature and film thickness on the morphology, phase composition, accessible surface area, and OER activity reveals that the catalytic performance is controlled by at least two independent factors, that is, accessible surface area and intrinsic activity per accessible site. Catalysts with lower crystallinity show higher intrinsic activity. The catalyst surface area increases linearly with film thickness. As a result of the templated mesopores, the pore surface remains fully active and accessible even for thick IrO2 films. Even the most active multilayer catalyst does not show signs of transport limitations at current densities as high as 75 mA cm−2.
Lei Wang, Fabio Dionigi, Nhat Truong Nguyen, Robin Kirchgeorg, Manuel Gliech, Sabina Grigorescu, Peter Strasser and Patrik Schmuki

Tantalum Nitride Nanorod Arrays: Introducing Ni–Fe Layered Double Hydroxides as a Cocatalyst Strongly Stabilizing Photoanodes in Water Splitting

Chem. Mater. 27 (7), 2360-2366

DOI: 10.1021/cm503887t

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Ta3N5 nanostructures are widely explored as anodes for photoelectrochemical (PEC) water splitting. Although the material shows excellent semiconductive properties for this purpose, the key challenge is its severe photocorrosion when used in typical aqueous environments. In the present work we introduce a NiFe layered double hydroxide (LDH) cocatalyst that dramatically reduces photocorrosion effects. To fabricate the Ta3N5 electrode, we use through-template anodization of Ta and obtain oxide nanorod arrays that then are converted to Ta3N5 by high temperature nitridation. After modification with our cocatalyst system, we obtained solar photocurrents of 6.3 mA cm–2 at 1.23 VRHE in 1 M KOH, and an electrode maintains about 80% of the initial activity for extended irradiation times.
Hyung-Suk Oh, Hong Nhan Nong, Tobias Reier, Manuel Gliech and Peter Strasser

Oxide-supported Ir nanodendrites with high activity and durability for the oxygen evolution reaction in acid PEM water electrolyzers

Chem. Sci. 6, 3321-3328

DOI: 10.1039/C5SC00518C

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Reducing the noble-metal catalyst content of acid Polymer Electrolyte Membrane (PEM) water electrolyzers without compromising catalytic activity and stability is a goal of fundamental scientific interest and substantial technical importance for cost-effective hydrogen-based energy storage. This study presents nanostructured iridium nanodendrites (Ir-ND) supported on antimony doped tin oxide (ATO) as efficient and stable water splitting catalysts for PEM electrolyzers. The active Ir-ND structures exhibited superior structural and morphological properties, such as particle size and surface area compared to commercial state-of-art Ir catalysts. Supported on tailored corrosion-stable conductive oxides, the Ir-ND catalysts exhibited a more than 2-fold larger kinetic water splitting activity compared with supported Ir nanoparticles, and a more than 8-fold larger catalytic activity than commercial Ir blacks. In single-cell PEM electrolyzer tests, the Ir-ND/ATO outperformed commercial Ir catalysts more than 2-fold at technological current densities of 1.5 A cm−2 at a mere 1.80 V cell voltage, while showing excellent durability under constant current conditions. We conclude that Ir-ND/ATO catalysts have the potential to substantially reduce the required noble metal loading, while maintaining their catalytic performance, both in idealized three-electrode set ups and in the real electrolyzer device environments
Hyung-Suk Oh, Hong Nhan Nong and Peter Strasser

Preparation of Mesoporous Sb-, F-, and In-Doped SnO2 Bulk Powder with High Surface Area for Use as Catalyst Supports in Electrolytic Cells

Adv. Func. Mater. 25, 1074-1081

DOI: 10.1002/adfm.201401919

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The M-doped tin oxides (M = Sb, F, and In) to be used as catalyst support are synthesized by using templating process with tetradecylamine (TDA) as the template, combined with a hydrothermal (HT) method to improve its thermal stability. The obtained materials are characterized by XRD, SAXS, TEM, EDX, SEM, and BET to study microstructure and physical properties, which have a mesoporous structure, small particle size, and high surface area (125–263 m2 g–1). The materials show an overall conductivity of 0.102–0.295 S cm–1. Repetitive potential cycling is employed to characterize the electrochemical properties and stability. The M-doped tin oxides are highly electrochemical stable compared to carbon black. From the observed results, it can be concluded that the combination of TDA and HT treatment are an effective synthetic method for designing mesoporous M-doped tin oxide as catalyst supports.
Hong Nhan Nong, Hyung-Suk Oh, Tobias Reier, Elena Willinger, Marc-Georg Willinger, Valeri Petkov, Detre Teschner and Peter Strasser

Oxide-Supported IrNiOx Core–Shell Particles as Efficient, Cost-Effective, and Stable Catalysts for Electrochemical Water Splitting

Angew. Chem. 127, 3018-3022

DOI: 0.1002/ange.201411072

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Active and highly stable oxide-supported IrNiOx core–shell catalysts for electrochemical water splitting are presented. IrNix@IrOx nanoparticles supported on high-surface-area mesoporous antimony-doped tin oxide (IrNiOx / Meso-ATO) were synthesized from bimetallic IrNix precursor alloys (PA-IrNix/Meso-ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA-IrNix/Meso-ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core–shell particles. The core–shell IrNiOx/Meso-ATO catalyst displayed high water-splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.
Prashanth W. Menezes, Arindam Indra, Diego González‑Flores, Nastaran Ranjbar Sahraie, Ivelina Zaharieva, Michael Schwarze, Peter Strasser, Holger Dau and Matthias Driess 
 
High-Performance Oxygen Redox Catalysis with Multifunctional 2 Cobalt Oxide Nanochains: Morphology-Dependent Activity 
 
ACS Catal. 5, 2017-2027
 
DOI: 10.1021/cs501724v  
 
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Future advances in renewable and sustainable energy require advanced materials based on earth-abundant elements with multifunctional properties. The design and the development of cost-effective, robust, and high-performance catalysts that can convert oxygen to water, and vice versa, is a major challenge in energy conversion and storage technology. Here we report cobalt oxide nanochains as multifunctional catalysts for the electrochemical oxygen evolution reaction (OER) at both alkaline and neutral pH, oxidant-driven, photochemical water oxidation in various pH, and the electrochemical oxygen reduction reaction (ORR) in alkaline medium. The cobalt oxide nanochains are easily accessible on a multigram scale by low-temperature degradation of a cobalt oxalate precursor. What sets this study apart from earlier ones is its synoptical perspective of reversible oxygen redox catalysis in different chemical and electrochemical environments.
Nina Erini, Stefan Rudi, Vera Beermann, Paul Krause, Ruizhi Yang, Yunhui Huang and Peter Strasser

Exceptional Activity of a Pt–Rh–Ni Ternary Nanostructured Catalyst for the Electrochemical Oxidation of Ethanol

ChemElectroChem 2 (6), 903-908

DOI: 10.1002/celc.201402390

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Alloying Pt with highly oxophilic transition metals such as Rh, Ni, or Sn has been a promising strategy to modify the electrocatalytic surface properties of Pt in order to supply active
oxygen-containing species for ethanol electrooxidation. A new, highly active, ternary single-phased cubic PtRhNi/C nanoparticle electrocatalyst for the electrocatalytic oxidation of ethanol (EOR) is reported and its morphology (XRD and TEM), composition (inductively coupled plasma optical emission spectroscopy), and electrochemical activity are discussed in comparison with the state-of-art PtRhSn/C electrocatalyst. The EOR activity of the PtRhNi/C material outperformed the benchmark PtRhSn/ C material in acidic and alkaline media, showing high stability, especially in alkaline media. The higher intrinsic EOR activity of the Ni-containing electrocatalyst lends support to the notion that surface NiOx is an excellent oxygenate-supplying catalyst component for the oxidation of ethanol.
Prashanth W. Menezes, Arindam Indra, Nastaran Ranjbar Sahraie, Arno Bergmann, Peter Strasser and Matthias Driess 

Cobalt–Manganese-Based Spinels as Multifunctional Materials that Unify Catalytic Water Oxidation and Oxygen Reduction Reactions

ChemSusChem 8 (1), 164-171

DOI: 10.1002/cssc.201402699

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Recently, there has been much interest in the design and development of affordable and highly efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts that can resolve the pivotal issues that concern solar fuels, fuel cells, and rechargeable metal-air batteries. Here we present the synthesis and application of porous CoMn2O4 and MnCo2O4 spinel microspheres as highly efficient multifunctional catalysts that unify the electrochemical OER with oxidant-driven and photocatalytic water oxidation as well as the ORR. The porous materials were prepared by the thermal degradation of the respective carbonate precursors at 400 °C. The as-prepared spinels display excellent performances in electrochemical OER for the cubic MnCo2O4 phase in comparison to the tetragonal CoMn2O4 material in an alkaline medium. Moreover, the oxidant-driven and photocatalytic water oxidations were performed and they exhibited a similar trend in activity to that of the electrochemical OER. Remarkably, the situation is reversed in ORR catalysis, that is, the oxygen reduction activity and stability of the tetragonal CoMn2O4 catalyst outperformed that of cubic MnCo2O4 and rivals that of benchmark Pt catalysts. The superior catalytic performance and the remarkable stability of the unifying materials are attributed to their unique porous and robust microspherical morphology and the intrinsic structural features of the spinels. Moreover, the facile access to these high-performance materials enables a reliable and cost-effective production on a large scale for industrial applications.
Binghong Han, Christopher E. Carlton, Anusorn Kongkanand, Ratandeep S. Kukreja, Brian R. Theobald, Lin Gan, Rachel O’Malley, Peter Strasser, Frederick T. Wagner, Yang Shao-Horn

Record Activity and Stability of Dealloyed Bimetallic Catalysts for Proton Exchange Membrane Fuel Cells

Energy & Environmental Science 8, 258-266

DOI:10.1039/C4EE02144D

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We  demonstrate  unprecedented  Proton  exchange  membrane  fuel  cell  (PEMFC)  performance  durability  of  a  family  of dealloyed Pt-Ni nanoparticle catalysts for oxygen reduction reaction (ORR), exceeding scientific and technological state-of-art activity and stability targets. We provide atomic-scale insight in key factors controlling the stability of the cathode catalyst by studying the influence of particle size, dealloyingprotocol and post-acid-treatment annealing on nanoporosity and passivation of the alloy nanoparticles. Scanning transmission electron microscopy coupled to energy dispersive spectroscopy data revealed the compositional variations of Ni in the particle surface and core, which were combined with an analysis of the particle morphology evolution during PEMFC voltage cycling; together, this enabled the elucidation of alloy structure and compositions conducive to long-term PEMFC device stability. We found that smaller size, less-oxidative acid treatment and annealing significantly reduced Ni  leaching  and  nanoporosity  formation  while  encouraged  surface  passivation,  all  resulting  in  improved stability  and  higher catalytic ORR activity. This study demonstrates a successful example of how a translation of basic catalysis research into a reallife device technology may be done.
Stefan Rudi, Lin Gan, Chunhua Cui, Manuel Gliech and Peter Strasser

Electrochemical Dealloying of Bimetallic ORR Nanoparticle Catalysts at Constant Electrode Potentials

J. Electrochem. Soc. 162 (4), F403-F409

DOI:10.1149/2.0621504jes

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Dealloyed, that is, selectively leached Pt-based oxygen reduction reaction (ORR) nanoparticle catalysts have demonstrated previously unachieved initial reactivity and performance durability in single cell of PEM fuel cells. Dealloying is typically achieved using free corrosion in acid or electrochemical cycling. Here, we explore dealloying at constant electrode potentials of PtNi3 bimetallic alloy nanoparticles at 5–7 nm and >20 nm size ranges. We investigate how Ni dissolution at four distinct electrode potentials affects the composition, morphology, and surface roughness of the resulting dealloyed catalysts. The electrode potentials cover the hydrogenadsorption, the double layer region, and the oxygenate adsorption region to examine whether adlayers affect the characteristics of the dealloyed catalysts. We show that large alloy nanoparticles invariably dealloy into porous nanoparticles with a relatively low Ni molar ratio of 0.4, while the smaller size particles show non-porous solid core-shell structures with a monotonic dependence between Ni at% and potential.We provide evidence that the dealloyed catalyst surface is strongly influenced by the presence/absence of adsorbed adlayers of hydrogen or oxygenates. In particular, data suggest that adsorbate adlayers modify the balance between Ni dissolution and Pt surface diffusion during the dealloying process resulting in rougher catalyst surfaces with enhanced surface area values.

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