Screening Of Electrocatalysts Research Articles

Electrocatalysis of Lithium (Poly-) Sulfides in Organic Ether-Based Electrolytes

This work aims at identifying an effective electrocatalyst for polysulfide reactions to improve the electrode kinetics of the sulfur half-cell in liquid organic electrolytes for alkali-sulfur cells. To increase the charge and discharge rates and energy efficiency of the cell, functionalized electrocatalytic coatings have been prepared and their electrode kinetics have been measured. To the best of our knowledge, there is no extensive screening of electrocatalysts for the sulfur electrode in dimethoxyethane:1,3-dioxolane (DME:DOL) electrolytes. In order to identify a suitable electrocatalyst, apparent exchange current densities at various materials (Al, Co, Cr, Cu, Fe, Steel, glassy carbon, ITO, Ni, Pt, Ti, TiN, Zn) are evaluated in a polysulfide electrolyte using potentiodynamic measurements with a Butler-Volmer fit. The chemical stability and surface morphology changes after electrochemical measurements are assessed with X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The results show that cobalt is a promising candidate with appropriate electrocatalytic properties for polysulfide reactions while being stable in the electrochemical environment, followed by chromium in terms of catalytic activity and stability. Sputtered TiN was found to be a very stable material with very low catalytic activity, a possible current collector for the cell.

Hidden in plain sight: unlocking the full potential of cyclic voltammetry with the thin-film rotating (ring) disk electrode studies for the investigation of oxygen reduction reaction electrocatalysts

Cyclic voltammetry conducted with a thin-film rotating disk electrode, or ring-disk electrode (CV-TF-R(R)DE) is a very popular ‘ex situ’ tool for the rapid screening of electrocatalysts for their activity in oxygen reduction reaction. Despite its popularity and broad use, in most instances only a small part of the information that could be accessed by CV-TF-R(R)DE is actually used by scientists in their research. This work outlines both innovative and more traditional (but half-forgotten) ways of using CV-TF-R(R)DE to its optimal or full potential in the ongoing quest to study the most relevant features of oxygen reduction reaction electrocatalysts and quickly identify the most promising candidates for their applications in fuel cells or other electrochemical devices.

Screening of electrocatalysts for hydrogen evolution reaction using bipolar electrodes fabricated by composition gradient magnetron sputtering

This paper reports the facile fabrication of bipolar electrodes using composition gradient magnetron sputtering and subsequent activity screening of the prepared electrodes for hydrogen evolution reaction using bipolar electrochemistry. The electrocatalysts layers based on Ni–Mo, Au–Mo and Au–Ni alloys were deposited in form of compositional gradients on the bipolar electrodes. Concentration of the elements in the gradients varies from 40 to 60 at. % across the bipolar electrodes depending on the deposition conditions. The results of the screening experiments for the hydrogen evolution activity were also confirmed by conventional voltammetry measurements. We find that optimal compositions of the electrocatalyst for hydrogen evolution reaction are Au2Ni, AuMo2, Ni2Mo and Ni2Mo alloy has the highest catalytic activity. Mechanisms of HER on selected alloy compositions was also studied in more detail using voltammetry experiments.

Scanning Electrochemical Flow Cell with Online Mass Spectroscopy for Accelerated Screening of Carbon Dioxide Reduction Electrocatalysts.

Electrochemical conversion of carbon dioxide into valuable chemicals or fuels is an increasingly important strategy for achieving carbon neutral technologies. The lack of a sufficiently active and selective electrocatalyst, particularly for synthesizing highly reduced products, motivates accelerated screening to evaluate new catalyst spaces. Traditional techniques, which couple electrocatalyst operation with analytical techniques to measure product distributions, enable screening throughput at 1-10 catalysts per day. In this paper, a combinatorial screening instrument is designed for MS detection of hydrogen, methane, and ethylene in quasi-real-time during catalyst operation experiments in an electrochemical flow cell. Coupled with experiment modeling, product detection during cyclic voltammetry (CV) enables modeling of the voltage-dependent partial current density for each detected product. We demonstrate the technique by using the well-established thin film Cu catalysts and by screening a Pd-Zn composition library in carbonate-buffered aqueous electrolyte. The rapid product distribution characterization over a large range of overpotential makes the instrument uniquely suited for accelerating screening of electrocatalysts for the carbon dioxide reduction reaction.

Recent Progress in First Principle Calculation and High-Throughput Screening of Electrocatalysts: A Review

There are many ongoing efforts to develop sustainable, clean, efficient, and economical pathways to produce renewable energy sources to satisfy worldwide energy demands. Electrochemical conversion processes, such as water splitting, CO2 conversion and N2 electroreduction, have been considered as successful approaches to solve these energy issues. Over the past decade, combining of theory and experiment has proven to be an innovative strategy, providing a framework for the design of high-performance catalysts and to investigate their mechanisms. This review introduces recent progress in theoretical strategies for state-of-the-art heterogeneous electrocatalysts. Theoretical approaches are essential for grasping the intrinsic nature of the catalytic materials. Various levels of model system, with corresponding descriptions to capture the realistic environment, are addressed. Meanwhile, machine learning using data obtained by high-throughput screening, exploited as a new scientific approach, is discussed. Based on this review, it is expected that theoretical approaches will shed light on the future design of electrocatalysts, allowing for the development of sustainable energy sources. Key words: electrocatalysts, density functional theory, first principle calculation, high-throughput screening, machine learning

Reactor design and integration with product detection to accelerate screening of electrocatalysts for carbon dioxide reduction.

Identifying new catalyst materials for complex reactions such as the electrochemical reduction of CO2 poses substantial instrumentation challenges due to the need to integrate reactor control with electrochemical and analytical instrumentation. Performing accelerated screening to enable exploration of a broad span of catalyst materials poses additional challenges due to the long time scales associated with accumulation of reaction products and the detection of the reaction products with traditional separation-based analytical methods. The catalyst screening techniques that have been reported for combinatorial studies of (photo)electrocatalysts do not meet the needs of CO2 reduction catalyst research, prompting our development of a new electrochemical cell design and its integration to gas and liquid chromatography instruments. To enable rapid chromatography measurements while maintaining sensitivity to minor products, the electrochemical cell features low electrolyte and head space volumes compared to the catalyst surface area. Additionally, the cell is operated as a batch reactor with electrolyte recirculation to rapidly concentrate reaction products, which serves the present needs for rapidly detecting minor products and has additional implications for enabling product separations in industrial CO2 electrolysis systems. To maintain near-saturation of CO2 in aqueous electrolytes, we employ electrolyte nebulization through a CO2-rich headspace, achieving similar gas-liquid equilibration as vigorous CO2 bubbling but without gas flow. The instrument is demonstrated with a series of electrochemical experiments on an Au-Pd combinatorial library, revealing non-monotonic variations in product distribution with respect to catalyst composition. The highly integrated analytical electrochemistry system is engineered to enable automation for rapid catalyst screening as well as deployment for a broad range of electrochemical reactions where product distribution is critical to the assessment of catalyst performance.

High-efficient preparation and screening of electrocatalysts using a closed bipolar electrode array system

High-efficient preparation and screening of electrocatalysts for oxygen reduction reaction (ORR) was realized by a three electrode driving closed bipolar electrode (BPE) array system. As high concentrations of Fe(CN)63−/4− (both 200 mM) existed in the anodic cell of the BPE system and same electrode material was adopted by the BPE anodic pole and driving electrode in anodic cell, the anodic cell performed similar to “good conductor” and the electrochemical behavior of the closed BPE system approximately equal to that of the three-electrode system in cathodic cell. Based on the above property and the parallel array, electrocatalysts containing bimetallic Pt Au and reduced graphene oxide (PtAu-rGO) with varying metal proportion were successfully prepared on the cathodic BPE poles by a two-step reduction process. Graphene oxide was firstly reduced to reduced graphene oxide (rGO) in each cathodic pole by cyclic voltammetry, and then Pt Au with different metal proportion were electrodeposited on the surface of rGO. Afterward, in-situ and high-throughput screening of these electrocatalysts for ORR was carried out based on the electrochemiluminescence (ECL) imaging on the corresponding anodic BPE poles. The screening results were consistent with those of the conventional electrochemical method by testing the catalytic performance one by one very well. This closed BPE array system with one potentiostat not only can prepare multiple catalyst candidates at the same time, but also can evaluate them, simultaneously, which is of great immediate significance to the field of fuel cell.

Extracting Kinetic Information from Bipolar Electrochemistry

Bipolar electrodes (BPEs) hold enormous promise for rapid screening of electrocatalysts owing to their ability to be operated wirelessly – without direct ohmic contact to a power source – and in parallel. A BPE is a conductor, immersed in an ionically conducting phase, that facilitates coupled oxidation and reduction reactions at opposing ends when exposed to an electric field. The current arising from these coupled processes can be monitored if one of the reactions leads to a visible change, such as chemiluminescence or anodic stripping of a metal film. Therefore, an array of BPEs operated with a single pair of driving electrodes can facilitate many electrochemical measurements simultaneously. Several reports have clearly demonstrated the utility of BPEs to obtain relative catalytic activity. However, to date, the extraction of specific activity and kinetic rate constants from these measurements remains challenging. We discuss here the experimental factors that contribute to this challenge and we present initial results demonstrating alternative approaches to extract this valuable information from BPE-based screens.

Perspectives on Computational Analysis of Electrocatalysis: Stability and Activity Considerations in Catalyst Screening

Advances in the theoretical understanding of interfacial electrochemistry have, over the past decade, permitted the extension of periodic Density Functional Theory studies, which have traditionally been applied to probe chemistry at gas/solid interfaces, to electrochemical systems where potential-dependent structural and chemical phase transformations occur at liquid/solid interfaces. Indeed, such techniques have been employed to study a surprisingly wide class of electrochemical processes, ranging from electrocatalysis to corrosion, and are now being used to identify promising candidates for new electrocatalytic materials. In this talk, I will provide a brief overview of current approaches to computational screening of electrocatalysts, focusing in particular on the need to couple predictions of catalyst stability with traditional analyses of rates and activities. I will begin with a discussion of recent results in the computational screening of oxygen reduction (ORR) electrocatalysts, focusing on the large number of materials “tuning knobs” that have been explored via calculations for this chemistry. I will then describe very recent efforts to computationally probe catalytic properties of more structurally complex electrocatalysts, including bifunctional catalysts and mixed metal/oxide systems. For such catalysts, which are relevant for chemistries ranging from CO oxidation in acidic solutions to hydrogen evolution in alkaline solutions, prediction of materials structure and stability is an essential prerequisite to determination of rates and currents, and I will therefore focus on how techniques to effect stability predictions are being combined with traditional screening methods for these systems. I will close with a few perspectives on future directions for electrocatalyst screening efforts.

High-Throughput Optical Screening of Electrocatalysts for Fuel Cell Applications – Review and Present Developments

Abstract In this paper on high-throughput optical screening for the discovery and optimization of electrocalatysts for potential application in polymer electrolyte membrane and direct methanol fuel cells the present state-of-the-art in literature is reviewed focussing on non-optical and optical fast serial, semi-parallel or truly parallel screening techniques as well as actual improvements of the fluorescence based testing method to a semi-quantitative or even quantitative method are described. The modifications of the method are concerning hindrance of fluorescing colorant interdiffusion, optimization of system parameters concerning colorant, electrolyte and other measurement components, and application of correction procedures. With fluorescence based setups especially adapted to both anodic and cathodic half-cell reactions methanol oxidation as well as oxygen reduction reaction electrocatalysts have been screened. By iteratively passing through high-throughput optimization workflows several hundreds of precious metal-free as well as Pt containing compositions were synthesized, tested and validated by conventional cyclovoltammetric measurements. For electrocatalysts to oxidize methanol on the anodic side of the fuel cell a small amount of Pt seems to be indispensable to result in stable catalysts. For the oxygen reduction reaction active compositions performing comparable or even better than the reference PtOx catalyst contained the elements Co and Mn, which correspond to primary activity descriptors already specified in literature.

Electrochemiluminescence Imaging-Based High-Throughput Screening Platform for Electrocatalysts Used in Fuel Cells

High throughput screening is very important for accelerating the discovery of fuel cell catalysts. In this paper, a novel electrochemiluminescence (ECL, a technology changing electric current into light) imaging-based screening platform for electrocatalysts used in fuel cells has been developed. The ECL imaging-based screening platform consists of bipolar electrode array-bridged electrochemical (EC)/ECL twin cells, by which electrocatalytic reduction currents of O(2) can be imaged directly by ECL. The ECL imaging-based screening platform is simple in instrumentation, can image the "current-voltage" dependence directly, reversibly, and sensitively, and may enable the activities of electrocatalysts to be evaluated in a high-throughput way. The developed ECL imaging-based screening platform is envisioned to have promising applications in high throughput combinatorial screening of electrocatalysts for fuel cells.

Bipolar Electrodes for Rapid Screening of Electrocatalysts

We report a method for rapid screening of arrays of electrocatalyst candidates. The approach is based on simultaneous activation of the oxygen reduction reaction (ORR) and Ag electrodissolution at the cathodic and anodic poles, respectively, of bipolar electrodes (BPEs). Because the electrochemical activity of the two poles is directly coupled via the BPE, the extent of Ag electrodissolution is directly related to the ORR activity. The screening process lasts ~12 min. Because Ag dissolution provides a permanent record of catalyst activity, the screening results can be determined by simple optical microscopy after the electrochemical experiment. The method has the potential to provide quantitative information about electrocatalyst activity.

Screening of Electrocatalysts for Photoelectrochemical Water Oxidation on W-Doped BiVO4 Photocatalysts by Scanning Electrochemical Microscopy

Oxygen evolution reaction (OER) electrocatalyst arrays for photoelectrochemical (PEC) water oxidation were fabricated on a metal oxide semiconductor photoelectrode, W-doped BiVO4 (BiVW-O). The electrocatalysts (IrOx, Pt, Co3O4) were prepared on a drop cast film of BiVW-O on fluorine-doped tin oxide (FTO) with a picoliter solution dispenser or photodeposition with light irradiation through an optical fiber. The prepared arrays were tested for PEC water oxidation in 0.2 M sodium phosphate buffer (pH 6.8) using scanning electrochemical microscopy modified with an optical fiber. Pt and Co oxide electrocatalysts showed an enhanced photocurrent for PEC water oxidation, while the other metal oxide catalysts including IrOx, which is known as an excellent water oxidation electrocatalyst on a metal substrate, were not effective. These results were confirmed with bulk film studies. A cobalt phosphate (Co-Pi) electrocatalyst was also tested as a bulk film on BiVW-O and showed improvement for PEC water oxidation. Preliminary characterization (X-ray diffraction and X-ray photoelectron spectroscopy) was also performed for these catalysts. The results indicate that considerations of the semiconductor photocatalyst/electrocatalyst interface are important in determining the effectiveness of materials for the photodriven OER.

The imaging ammeter

A method for measuring local current density, not requiring segmentation of the electrode or spatial scanning, is presented. The motion of colloidal particles in response to local current density, characterized by the intensity of the light they scatter, is the fundamental phenomenon of the technique. The scattering was produced and measured with the electrochemical total internal reflection microscope, a tool that places an electrochemical cell within a total internal reflection apparatus. The electrolysis of water and the oxidation of ferrocene monocarboxylic acid were used as test reactions. Light scattered by a probe particle produced an “image” of current density; scattered light was converted to local current density by a function derived herein. Numerical simulations supplemented experimental evidence that local current density controlled the probe particle’s vertical motion. The spatial resolution of the method was approximately the length scale of the probe particle, in this case 5.7 μm. The resolution of current density was better than 100 nA cm −2. The method might find use in high throughput screening of electrocatalysts.

Screening of electrocatalytic materials for hydrogen evolution

A general scheme for high-throughput screening of electrocatalysts is presented. By systematically exploiting a collection of theoretical and experimental materials databases, supplemented with quantum mechanical calculations, it locates systems that meet a set of pre-imposed selection criteria. As an example, the scheme is used to identify a binary "substrate-overlayer" electrocatalytic system for the hydrogen evolution reaction. The best catalysts found in this screening are based on Cu and W. The hydrogen evolution activity of W-Cu catalysts is evaluated by means of cyclic voltammetry. It turns out to be considerably more active than any of its constituents, pure W and Cu.

Micropipet Delivery−Substrate Collection Mode of Scanning Electrochemical Microscopy for the Imaging of Electrochemical Reactions and the Screening of Methanol Oxidation Electrocatalysts

The micropipet delivery-substrate collection (MD-SC) mode of scanning electrochemical microscopy (SECM) is demonstrated. This new mode is intended for the study and imaging of electrochemical as well as electrocatalytic reactions of neutral species that cannot be generated electrochemically. The spontaneous transfer of the analyte from an organic solvent across an interface between two immiscible electrolyte solutions (ITIES) and its diffusion into the aqueous solution served as the mechanism to deliver it to the substrate, where the corresponding electrochemical or electrocatalytic reaction is carried out. High-resolution SECM images of ferrocenemethanol (FcMeOH) oxidation, benzoquinone (BQ) reduction, and the formic acid oxidation reaction (FAOR) at a Pt microelectrode substrate were successfully acquired. Furthermore, this new mode was used for the screening of electrocatalyst arrays for the methanol oxidation reaction (MOR), with the optimization of an efficient candidate, Pt(80)Ce(20). Digital simulations produced quantitative information about the expected current response at the substrate in the proposed MD-SC mode of SECM.

Screening of Oxygen Evolution Electrocatalysts by Scanning Electrochemical Microscopy Using a Shielded Tip Approach

Oxygen evolution electrocatalysts in acidic media were studied by scanning electrochemical microscopy (SECM) in the substrate generation-tip collection (SG-TC) imaging mode with a 100 microm diam tip. Pure IrO2 and Sn(1-x)Ir(x)O2 combinatorial mixtures were prepared by a sol-gel route to form arrays of electrocatalyst spots. The experimental setup has been developed to optimize screening of electrocatalyst libraries under conditions where the entire array is capable of the oxygen evolution reaction (OER). The activity of individual spots was determined by reducing the interference from the reaction products of neighboring spots diffusing to the tip over the spot of interest. A gold layer deposited on the external wall of the SECM tip was used as a tip shield. In this study the shield was kept at a constant potential to reduce oxygen under mass transfer controlled conditions. The tip shield consumes oxygen coming from the neighbor spots in the array and enables the tip to correctly detect the activity of the spot below the tip. Simulations and experimental results are shown, demonstrating the effectiveness of the tip shield with the SG-TC setup in determining the properties of the composite materials and imaging arrays.

Screening of electrocatalysts for direct ammonia fuel cell: Ammonia oxidation on PtMe (Me: Ir, Rh, Pd, Ru) and preferentially oriented Pt(1 0 0) nanoparticles

Ammonia has attracted attention as a possible fuel for direct fuel cells since it is easy to handle and to transport as liquid or as concentrated aqueous solution. However, on noble metal electrodes ammonia oxidation is a sluggish reaction and the electrocatalyst needs to be improved for developing efficient ammonia fuel cells. In this work, ammonia electrooxidation reaction on 3–4-nm bimetallic PtMe (Ir, Rh, Pd, Ru) and on preferentially oriented Pt(1 0 0) nanoparticles is reported. PtMe nanoparticles have been prepared by using water-in-oil microemulsions to obtain a narrow size distribution whereas preferentially oriented Pt nanoparticles have been prepared through colloidal routes. Among all the bimetallic samples tested, only Pt 75Ir 25 and Pt 75Rh 25 nanoparticles show, at the low potential range, an enhancement of the oxidation density current with respect to the behaviour found for pure platinum nanoparticles prepared by the same method. In addition, two Pt(1 0 0) preferentially oriented nanoparticles of different particle size (4 and 9 nm) have been also studied. These oriented nanoparticles show higher current densities than polycrystalline Pt nanoparticles due to the sensitivity of ammonia oxidation toward the presence of surface sites with square symmetry. The reactivity of the different 4-nm nanoparticles parallels well with that expected from bulk PtMe alloys and Pt single crystal electrodes.

High throughput screening of electrocatalysts for fuel cell applications

We describe methodologies for the generation and screening of combinatorial libraries of electrocatalyst materials for fuel cell applications, generated by cosputtering of three elements onto a Si substrate coated with a Ta adhesion underlayer. Screening was carried out via a fluorescence assay as well as by scanning electrochemical microscopy. Whereas the former provided rapid qualitative screening with limited spatial resolution, the latter provided high spatial resolution. The fluorescence screening method was tested on Pt, PtBi, PtPb, and PtRu nanoparticles, while both methods were tested on a film containing a Pt–Bi–Pb ternary composition spread.