Graphene-Based Metal-Organic Framework Hybrids for Applications in Catalysis, Environmental, and Energy Technologies.

Current energy and environmental challenges demand the development and design of multifunctional porous materials with tunable properties for catalysis, water purification, and energy conversion and storage. Because of their amenability to de novo reticular chemistry, metal-organic frameworks (MOFs) have become key materials in this area. However, their usefulness is often limited by low chemical stability, conductivity and inappropriate pore sizes.

B-Cu-Zn Gas Diffusion Electrodes for CO Electroreduction to C Products at High Current Densities.

Electroreduction of CO to multi-carbon products has attracted considerable attention as it provides an avenue to high-density renewable energy storage. However, the selectivity and stability under high current densities are rarely reported. Herein, B-doped Cu (B-Cu) and B-Cu-Zn gas diffusion electrodes (GDE) were developed for highly selective and stable CO conversion to C  products at industrially relevant current densities.

Electrocatalysis as the Nexus for Sustainable Renewable Energy: The Gordian Knot of Activity, Stability, and Selectivity.

The use of renewable energy by means of electrochemical techniques by converting H O, CO and N into chemical energy sources and raw materials, is the basis for securing a future sustainable "green" energy supply. Some weaknesses and inconsistencies in the practice of determining the electrocatalytic performance, which prevents a rational bottom-up catalyst design, are discussed. Large discrepancies in material properties as well as in electrocatalytic activity and stability become obvious when materials are tested under the conditions of their intended use as opposed to the usual laboratory conditions.

Online Monitoring of Electrochemical Carbon Corrosion in Alkaline Electrolytes by Differential Electrochemical Mass Spectrometry.

Carbon corrosion at high anodic potentials is a major source of instability, especially in acidic electrolytes and impairs the long-term functionality of electrodes. In-depth investigation of carbon corrosion in alkaline environment by means of differential electrochemical mass spectrometry (DEMS) is prevented by the conversion of CO into CO . We report the adaptation of a DEMS system for online CO detection as the product of carbon corrosion in alkaline electrolytes.

Synergistic catalysis of CuO/InO composites for highly selective electrochemical CO reduction to CO.

The development of low-cost, selective, and active catalysts for electrochemical CO2 reduction (ECR) remains an ongoing challenge. Here, we demonstrate for the first time, efficient ECR by exploiting interaction of CuO and In2O3. The catalytic properties of the composite catalysts can be readily tuned by manipulation of the metal oxide composition and interface, enabling remarkably high CO2-to-CO conversion with a CO faradaic efficiency of about 93.

Oxidative Deposition of Manganese Oxide Nanosheets on Nitrogen-Functionalized Carbon Nanotubes Applied in the Alkaline Oxygen Evolution Reaction.

The development of nonprecious catalysts for water splitting into hydrogen and oxygen is one of the major challenges to meet future sustainable fuel demand. Herein, thin layers of manganese oxide nanosheets supported on nitrogen-functionalized carbon nanotubes (NCNTs) were formed by the treatment of NCNTs dispersed in aqueous solutions of KMnO or CsMnO under reflux or under hydrothermal (HT) conditions and used as electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. The samples were characterized by X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy.

Oxygen Evolution Electrocatalysis of a Single MOF-Derived Composite Nanoparticle on the Tip of a Nanoelectrode.

Determination of the intrinsic electrocatalytic activity of nanomaterials by means of macroelectrode techniques is compromised by ensemble and film effects. Here, a unique "particle on a stick" approach is used to grow a single metal-organic framework (MOF; ZIF-67) nanoparticle on a nanoelectrode surface which is pyrolyzed to generate a cobalt/nitrogen-doped carbon (CoN/C) composite nanoparticle that exhibits very high catalytic activity towards the oxygen evolution reaction (OER) with a current density of up to 230 mA cm at 1.77 V (vs.

Ultrathin 2D Cobalt Zeolite-Imidazole Framework Nanosheets for Electrocatalytic Oxygen Evolution.

2D layered materials, including metal-di-chalcogenides and transition metal layered double hydroxides, among others, are intensively studied because of new properties that emerge from their 2D confinement, which are attractive for advanced applications. Herein, 2D cobalt ion (Co) and benzimidazole (bIm) based zeolite-imidazole framework nanosheets, ZIF-9(III), are reported as exceptionally efficient electrocatalysts for the oxygen evolution reaction (OER). Specifically, liquid-phase ultrasonication is applied to exfoliate a [Co(bIm)] zeolite-imidazole framework (ZIF), named as ZIF-9(III) phase, into nanoscale sheets.

On the Theory of Electrolytic Dissociation, the Greenhouse Effect, and Activation Energy in (Electro)Catalysis: A Tribute to Svante Augustus Arrhenius.

Svante Augustus Arrhenius (1859, Vik - 1927, Stockholm) received the Nobel Prize for Chemistry in 1903 "in recognition of the extraordinary services he rendered to the advancement of chemistry by his electrolytic theory of dissociation". Arrhenius was a physicist, and he received his PhD from the University of Uppsala, where he later became a professor for phyiscal chemistry, the first in the country for this subject. He was offered several positions as professor abroad, but decided to remain in Sweden and to build a Nobel Institute for physical chemistry using the Nobel funds.

Electrocatalytic Oxidation of 5-(Hydroxymethyl)furfural Using High-Surface-Area Nickel Boride.

The electrochemical oxidation of the biorefinery product 5-(hydroxymethyl)furfural (HMF) to 2,5-furandicarboxylic acid (FDCA), an important platform chemical for the polymer industry, is receiving increasing interest. FDCA-based polymers such as polyethylene 2,5-furandicarboxylate (PEF) are sustainable candidates for replacing polyethylene terephthalate (PET). Herein, we report the highly efficient electrocatalytic oxidation of HMF to FDCA, using Ni foam modified with high-surface-area nickel boride (Ni B) as the electrode.

Cobalt-metalloid alloys for electrochemical oxidation of 5-hydroxymethylfurfural as an alternative anode reaction in lieu of oxygen evolution during water splitting.

The electrochemical water splitting commonly involves the cathodic hydrogen and anodic oxygen evolution reactions (OER). The oxygen evolution reaction is more energetically demanding and kinetically sluggish and represents the bottleneck for a commercial competitiveness of electrochemical hydrogen production from water. Moreover, oxygen is essentially a waste product of low commercial value since the primary interest is to convert electrical energy into hydrogen as a storable energy carrier.

Influence of Temperature and Electrolyte Concentration on the Structure and Catalytic Oxygen Evolution Activity of Nickel-Iron Layered Double Hydroxide.

NiFe layered double hydroxide (LDH) is inarguably the most active contemporary catalyst for the oxygen evolution reaction under alkaline conditions. However, the ability to sustain unattenuated performance under challenging industrial conditions entailing high corrosivity of the electrolyte (≈30 wt. % KOH), high temperature (>80 °C) and high current densities (>500 mA cm ) is the ultimate criterion for practical viability.

Bifunctional Oxygen Reduction/Oxygen Evolution Activity of Mixed Fe/Co Oxide Nanoparticles with Variable Fe/Co Ratios Supported on Multiwalled Carbon Nanotubes.

A facile strategy is reported for the synthesis of Fe/Co mixed metal oxide nanoparticles supported on, and embedded inside, high purity oxidized multiwalled carbon nanotubes (MWCNTs) of narrow diameter distribution as effective bifunctional catalysts able to reversibly drive the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) in alkaline solutions. Variation of the Fe/Co ratio resulted in a pronounced trend in the bifunctional ORR/OER activity. Controlled synthesis and in-depth characterization enabled the identification of an optimal Fe/Co composition, which afforded a low OER/OER reversible overvoltage of only 0.

Co O @Co/NCNT Nanostructure Derived from a Dicyanamide-Based Metal-Organic Framework as an Efficient Bi-functional Electrocatalyst for Oxygen Reduction and Evolution Reactions.

There has been growing interest in the synthesis of efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reactions (OER), for their potential use in a variety of renewable energy technologies, such as regenerative fuel cells and metal-air batteries. Here, a bi-functional electrocatalyst, derived from a novel dicyanamide based nitrogen rich MOF {[Co(bpe) (N(CN) )]⋅(N(CN) )⋅(5 H O)} [Co-MOF-1, bpe=1,2-bis(4-pyridyl)ethane, N(CN) =dicyanamide] under different pyrolysis conditions is reported. Pyrolysis of the Co-MOF-1 under Ar atmosphere (at 800 °C) yielded a Co nanoparticle-embedded N-doped carbon nanotube matrix (Co/NCNT-Ar) while pyrolysis under a reductive H /Ar atmosphere (at 800 °C) and further mild calcination yielded Co O @Co core-shell nanoparticle-encapsulated N-doped carbon nanotubes (Co O @Co/NCNT).

Tuning the oxidation state of manganese oxide nanoparticles on oxygen- and nitrogen-functionalized carbon nanotubes for the electrocatalytic oxygen evolution reaction.

Manganese oxides are promising electrocatalysts for the oxygen evolution reaction due to their versatile redox properties. Manganese oxide (MnO) nanoparticles were synthesized on oxygen- and nitrogen-functionalized carbon nanotubes (OCNTs and NCNTs) by calcination in air of Mn-impregnated CNTs with a loading of 10 wt% Mn. The calcined samples were exposed to reducing conditions by thermal treatment in H or NH, and to strongly oxidizing conditions using HNO vapor, which enabled us to flexibly tune the oxidation state of Mn from 2+ in MnO to 4+ in MnO.

Powder Catalyst Fixation for Post-Electrolysis Structural Characterization of NiFe Layered Double Hydroxide Based Oxygen Evolution Reaction Electrocatalysts.

Highly active electrocatalysts for the oxygen evolution (OER) reaction are in most cases powder nanomaterials, which undergo substantial changes upon applying the high potentials required for high-current-density oxygen evolution. Owing to the vigorous gas evolution, the durability under OER conditions is disappointingly low for most powder electrocatalysts as there are no strategies to securely fix powder catalysts onto electrode surfaces. Thus reliable studies of catalysts during or after the OER are often impaired.

Overcoming the Instability of Nanoparticle-Based Catalyst Films in Alkaline Electrolyzers by using Self-Assembling and Self-Healing Films.

Engineering stable electrodes using highly active catalyst nanopowders for electrochemical water splitting remains a challenge. We report an innovative and general approach for attaining highly stable catalyst films with self-healing capability based on the in situ self-assembly of catalyst particles during electrolysis. The catalyst particles are added to the electrolyte forming a suspension that is pumped through the electrolyzer.

Polybenzoxazine-Derived N-doped Carbon as Matrix for Powder-Based Electrocatalysts.

In addition to catalytic activity, intrinsic stability, tight immobilization on a suitable electrode surface, and sufficient electronic conductivity are fundamental prerequisites for the long-term operation of particle- and especially powder-based electrocatalysts. We present a novel approach to concurrently address these challenges by using the unique properties of polybenzoxazine (pBO) polymers, namely near-zero shrinkage and high residual-char yield even after pyrolysis at high temperatures. Pyrolysis of a nanocubic prussian blue analogue precursor (K Mn [Co(CN) ] ⋅n H O) embedded in a bisphenol A and aniline-based pBO led to the formation of a N-doped carbon matrix modified with Mn Co O nanocubes.

MOF-Templated Assembly Approach for Fe C Nanoparticles Encapsulated in Bamboo-Like N-Doped CNTs: Highly Efficient Oxygen Reduction under Acidic and Basic Conditions.

Developing high-performance non-precious metal catalysts (NPMCs) for the oxygen-reduction reaction (ORR) is of critical importance for sustainable energy conversion. We report a novel NPMC consisting of iron carbide (Fe C) nanoparticles encapsulated in N-doped bamboo-like carbon nanotubes (b-NCNTs), synthesized by a new metal-organic framework (MOF)-templated assembly approach. The electrocatalyst exhibits excellent ORR activity in 0.

Micrometer-Precise Determination of the Thin Electrolyte Layer of a Spectroelectrochemical Cell by Microelectrode Approach Curves.

A spectroelectrochemical cell is presented that allows investigations of electrochemical reactions by means of attenuated total reflection infrared (ATR-IR) spectroscopy. The electrode holder for the working (WE), counter and reference electrode as mounted in the IR spectrometer cause the formation of a thin electrolyte layer between the internal reflection element (IRE) and the surface of the WE. The thickness of this thin electrolyte layer (d) was estimated by performing a scanning electrochemical microscopy-(SECM) like approach of a Pt microelectrode (ME), which was leveled with the WE toward the IRE surface.

Synergistic Effect of Cobalt and Iron in Layered Double Hydroxide Catalysts for the Oxygen Evolution Reaction.

Co-based layered double hydroxide (LDH) catalysts with Fe and Al contents in the range of 15 to 45 at % were synthesized by an efficient coprecipitation method. In these catalysts, Fe or Al ions play an essential role as trivalent species to stabilize the LDH structure. The obtained catalysts were characterized by a comprehensive combination of surface- and bulk-sensitive techniques and were evaluated for the oxygen evolution reaction (OER) on rotating disk electrodes.

Bipolar Electrochemistry for Concurrently Evaluating the Stability of Anode and Cathode Electrocatalysts and the Overall Cell Performance during Long-Term Water Electrolysis.

Electrochemical efficiency and stability are among the most important characteristics of electrocatalysts. These parameters are usually evaluated separately for the anodic and cathodic half-cell reactions in a three-electrode system or by measuring the overall cell voltage between the anode and cathode as a function of current or time. Here, we demonstrate how bipolar electrochemistry can be exploited to evaluate the efficiency of electrocatalysts for full electrochemical water splitting while simultaneously and independently monitoring the individual performance and stability of the half-cell electrocatalysts.

Co@Co3O4 Encapsulated in Carbon Nanotube-Grafted Nitrogen-Doped Carbon Polyhedra as an Advanced Bifunctional Oxygen Electrode.

Efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are vitally important for various energy conversion devices, such as regenerative fuel cells and metal-air batteries. However, realization of such electrodes is impeded by insufficient activity and instability of electrocatalysts for both water splitting and oxygen reduction. We report highly active bifunctional electrocatalysts for oxygen electrodes comprising core-shell Co@Co3O4 nanoparticles embedded in CNT-grafted N-doped carbon-polyhedra obtained by the pyrolysis of cobalt metal-organic framework (ZIF-67) in a reductive H2 atmosphere and subsequent controlled oxidative calcination.

Nanoelectrodes reveal the electrochemistry of single nickelhydroxide nanoparticles.

Individual Ni(OH)2 nanoparticles deposited on carbon nanoelectrodes are investigated in non-ensemble measurements with respect to their energy storage properties and electrocatalysis for the oxygen evolution reaction (OER). Charging by oxidation of Ni(OH)2 is limited by the diffusion of protons into the particle bulk and the OER activity is independent of the particle size.