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Thin‐film materials libraries (MLs) in the system Cr–Al–B are synthesized on 100 mm diameter Al2O3 sapphire substrates by combinatorial co‐sputtering from elemental targets at substrate temperatures of 600 and 700 °C to study phase formation of MAB phases (M = transition metal, A = A‐group element, B = boron). The formation of a mixture of two MAB phases Cr2AlB2 and Cr3AlB4 on the larger part of the ML prepared at 700 °C is observed by X‐ray diffraction and cross‐sectional transmission electron microscopy (TEM). Anisotropic growth of large grains of the MAB phases extending throughout the entire film thickness is revealed. Depending on the composition, the microstructure shows different levels of porosity and grain interlinkage. Imaging in the high‐resolution TEM mode identifies regions with Cr2AlB2, Cr3AlB4, and intermixed Cr2AlB2 and Cr3AlB4 atomic stacking sequences. Additional to the structural properties, electrocatalytic activity toward the alkaline hydrogen evolution reaction is measured. Higher activities are linked to crystalline MAB‐phase areas, further enhanced by increased porosity of the film which enlarges the surface area and the exposure of the active (010) planes. [ABSTRACT FROM AUTHOR]

As ammonia continues to gain more and more interest as a promising hydrogen carrier compound, so does the electrochemical ammonia oxidation reaction (AmOR). To avoid the liberation of H2 in a reverse Haber–Bosch reaction under release of the energetically more favorable N2, we propose the oxidation of ammonia to value‐added nitrite (NO2−), which is usually obtained during the Ostwald process. We investigated the anodic oxidation of gaseous ammonia directly supplied to a gas diffusion electrode (GDE) using a variety of compositionally different multi‐metal catalysts coated on Ni foam under the simultaneous formation of H2 at the cathode. This will double the amount of H2 per ammonia molecule while applying a lower overpotential than that required for water electrolysis (1.4–1.8 V vs. RHE at 50 mA ⋅ cm−2). A selectivity study demonstrated that some of the catalyst compositions were able to produce significant amounts of NO2−, and further investigations using the most promising catalyst composition Nif_AlCoCrCuFe integrated within a GDE demonstrated up to 88 % Faradaic efficiency for NO2− at the anode coupled to close to 100 % Faradaic efficiency for the cathodic H2 production. [ABSTRACT FROM AUTHOR]

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Room temperature ionic liquids (RT-ILs) are promising electrolytes for electrocatalysis. Understanding the effects of the electrode–electrolyte interface structure on electrocatalysis in RT-ILs is important. Ultrafast mass transport of redox species in N-methyl-N-ethyl-pyrrolidinium polybromide (MEPBr2n+1) enabled evaluation of the reorganization energy (λ), which reflects the solvation structure in the inner Helmholtz plane (IHP). λ was achieved by fitting the electron transfer rate-limited voltammogram at a Pt ultramicroelectrode (UME) to the Marcus–Hush–Chidsey model for heterogeneous electron transfer kinetics. However, it is time-consuming or even impossible to prepare electrode materials, including alloys of numerous compositions in the form of UME, for each experiment. Herein, we report a method to evaluate the λ of MEPBr2n+1 by scanning electrochemical cell microscopy (SECCM), which allows high throughput electrochemical measurements using a single electrode with high spatial resolution. Fast mass transport in the nanosized SECCM tip is critical for achieving heterogeneous electron transfer-limited voltammograms. Furthermore, investigating λ on a high-entropy alloy materials library composed of Pt, Pd, Ru, Ir, and Ag suggests a negative correlation between λ and the work function. Given that the potential of zero charge correlates with the work function of electrodes, this can be attributed to the surface-charge sensitive ionic structure in the IHP of MEPBr2n+1, modulating the solvation energy of the redox-active species in the IHP. [ABSTRACT FROM AUTHOR]

Finding strategies to enhance catalysts' electrochemical activity is based on controlling the material design. Bidimensional materials (2DM) such as MoS2 are explored as catalysts for the hydrogen evolution reaction (HER). A comprehensive study of the effects of doping 2D materials with transition metals based on theoretical predictions in tandem with experimental investigation correlates the doping type to the changes in the electronic and electrochemical activity. Localized electrochemical maps obtained by scanning electrochemical cell microscopy (SECCM) reveal that Ti‐doping induces a heterogeneous increase in 2H‐MoS2 basal plane electrochemical activity, while Ni‐doping induces a homogeneous decrease. Additionally, Kelvin probe microscopy provides insight into Ti‐doping, showcasing a decline in the 2H‐MoS2 work function, therefore confirming the predictions from density functional theory simulations. In essence, the findings underscore the potential of transition metal coordination on the 2H‐MoS2 surface as an attractive method for locally doping 2D materials with minimal damage to the crystalline lattice, consequently enhancing the electrochemical activity on the material's basal plane. [ABSTRACT FROM AUTHOR]

Mediated processes using a solid material, often called "solid booster", have been proposed to increase the energy density in redox flow batteries (RFB). The strategy alters the energy storage in the dissolved redox species to a solid active material placed in a compartment of the device. Understanding the reaction kinetics of the dissolved redox mediator and the solid booster is crucial for proposing feasible pairs of solid boosters and dissolved redox mediators. We demonstrate a nanoelectrochemical methodology to monitor the reaction between the dissolved species in solution and the solid active material electrodeposited in recessed carbon nanoelectrodes. Our strategy overcomes issues inherent to standard methodologies, such as mass transport limitation, and evaluation of the intrinsic reactivity of the solid material. As a proof of concept, Prussian blue was electrodeposited in a recessed carbon nanoelectrode and used as a confined‐solid material platform to evaluate the reaction between the reduced form of Prussian blue and triiodide, I3- ${{{\rm I}}_{3}^{-}}$. A high conversion rate of the solid booster was observed in the presence of μM concentrations of the dissolved redox species. The proposed nanoelectrode was successfully employed as a potentiometric sensor to monitor the evolution of the reaction with the dissolved active species. [ABSTRACT FROM AUTHOR]

For the anodic H2O2 generation, it has been shown that the electrolyte composition can steer the reaction pathway toward increased H2O2 generation. Previous efforts made on composition optimization found that the impact of the molar fraction of carbonate species varies for different anodes, and therefore, controversies remain concerning the reaction pathways as well as the species involved in H2O2 formation. Considering that water oxidation results in the liberation of protons within the anode microenvironment, the corresponding acidification would cause an equilibrium shift between carbonate species, which in turn may modulate the reaction pathway. We determined the changes in the fraction of carbonate species in the vicinity of an anode by performing local pH measurements using a Au nanoelectrode positioned in close proximity to an operating anode by shear‐force scanning electrochemical microscopy (SECM). It could be confirmed that the main anionic species at the interface is HCO3−, at potentials where H2O2 is preferentially formed, regardless of the pH value in the bulk. The simultaneous use of a Au−Pt double barrel microelectrode in generator‐collector SECM measurements demonstrates that the local HCO3− concentration is collectively determined by the oxidation current, buffer capacity, and bulk pH of the electrolyte. [ABSTRACT FROM AUTHOR]

Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Tuning the activity, selectivity, and stability of electrocatalysts for the electrochemical CO2 reduction reaction (eCO2RR) is of high interest. Among the multitude of possible eCO2RR products, formic acid/formate is not only of high industrial importance but even more importantly it can be obtained at nearly 100 % Faradaic efficiency if suitable catalysts are employed for the eCO2RR. Recently, two distinct strategies to modulate the eCO2RR over Bi‐based catalysts, namely phase modulation and functionalization with organic ligands, have come to the fore. This concept paper aims to string them together to accelerate their exploitation to design sophisticated electrocatalysts for the eCO2RR. [ABSTRACT FROM AUTHOR]

Efficient and selective oxidation of ethylene glycol is challenging due to uncontrollable C–C bond cleavage. We propose an electrochemical strategy for the selective electrooxidation of ethylene glycol to sythesise lactic acid on a Ni-based electrocatalyst by controlling the pH value of the electrolyte solution. [ABSTRACT FROM AUTHOR]

Nanoparticles that catalyze biochemically relevant reactions are promoted as alternative enzymes. The application of such artificial enzymes is severely restricted by poor selectivity in biological fluids; mainly because the reactions occur at active sites on the exterior surface of the nanoparticle. Enzymes in contrast typically have their active sites down a nanoconfined substrate channel where the reaction occurs in different solution conditions to bulk solution which aids in achieving selectivity for the substrate. Herein the same 3D structure of enzymes is mimicked in nanoparticles to allow selective reactions in biological fluids. This is achieved using a gold nanoparticle coated in a conducting mesoporous carbon shell where isolated nanochannels lead to the gold surface. It can detect glucose in whole blood with no interference from other species. This is achieved by electrochemically pulsing the artificial enzymes to generate the locally required alkalinity for an effective electrocatalytic reaction in the nanochannels, as well as expelling fouling agents that will otherwise passivate the electrocatalytic reaction. The artificial enzymes are shown to be capable of detecting glucose in biological fluids, without loss of signal, for several months. This study shows how nanoconfinement in nanoparticles can be exploited to potentially allow a broad range of species to be selectively detected in biological fluids with stability that can exceed that of enzymes. [ABSTRACT FROM AUTHOR]

High‐entropy alloys (HEAs), especially in the form of compositional complex solid solutions (CCSS), have gained attention in the field of electrocatalysis. However, exploring their vast composition space concerning their electrocatalytic properties imposes significant challenges. Scanning electrochemical cell microscopy (SECCM) offers high‐speed electrochemical analysis on surface areas with a lateral resolution down to tens of nm. However, high‐precision piezo positioners often used for the motion of the tip limit the area of SECCM scans to the motion range of the piezo positioners which is typically a few tens of microns. To bridge this experimental gap, the study proposes a long‐range SECCM system with a rapid gas‐exchange environmental cell for high‐throughput electrochemical characterization of 100 mm diameter HEA thin‐film material libraries (ML) obtained by combinatorial co‐sputtering. Due to the gas–liquid interface at the positioned SECCM droplet on the sample, high‐throughput evaluation under industrial current density conditions becomes feasible. This allows the direct correlation between electrocatalytic activity and material composition with high statistical reliability. The multidimensional data obtained accelerates materials discovery, development, and optimization. [ABSTRACT FROM AUTHOR]