Ag Electrocatalysts Research Articles

The AUREX cell: a versatile operando electrochemical cell for studying catalytic materials using X-ray diffraction, total scattering and X-ray absorption spectroscopy under working conditions.

Understanding the structure-property relationship in electrocatalysts under working conditions is crucial for the rational design of novel and improved catalytic materials. This paper presents the Aarhus University reactor for electrochemical studies using X-rays (AUREX) operando electrocatalytic flow cell, designed as an easy-to-use versatile setup with a minimal background contribution and a uniform flow field to limit concentration polarization and handle gas formation. The cell has been employed to measure operando total scattering, diffraction and absorption spectroscopy as well as simultaneous combinations thereof on a commercial silver electrocatalyst for proof of concept. This combination of operando techniques allows for monitoring of the short-, medium- and long-range structure under working conditions, including an applied potential, liquid electrolyte and local reaction environment. The structural transformations of the Ag electrocatalyst are monitored with non-negative matrix factorization, linear combination analysis, the Pearson correlation coefficient matrix, and refinements in both real and reciprocal space. Upon application of an oxidative potential in an Ar-saturated aqueous 0.1 M KHCO3/K2CO3 electrolyte, the face-centered cubic (f.c.c.) Ag gradually transforms first to a trigonal Ag2CO3 phase, followed by the formation of a monoclinic Ag2CO3 phase. A reducing potential immediately reverts the structure to the Ag (f.c.c.) phase. Following the electrochemical-reaction-induced phase transitions is of fundamental interest and necessary for understanding and improving the stability of electrocatalysts, and the operando cell proves a versatile setup for probing this. In addition, it is demonstrated that, when studying electrochemical reactions, a high energy or short exposure time is needed to circumvent beam-induced effects.

Uncovering Photoelectronic and Photothermal Effects in Plasmon-Mediated Electrocatalytic CO2 Reduction.

Plasmon-mediated electrocatalysis that rests on the ability of coupling localized surface plasmon resonance (LSPR) and electrochemical activation, emerges as an intriguing and booming area. However, its development seriously suffers from the entanglement between the photoelectronic and photothermal effects induced by the decay of plasmons, especially under the influence of applied potential. Herein, using LSPR-mediated CO2 reduction on Ag electrocatalyst as a model system, we quantitatively uncover the dominant photoelectronic effect on CO2 reduction reaction over a wide potential window, in contrast to the leading photothermal effect on H2 evolution reaction at relatively negative potentials. The excitation of LSPR selectively enhances the CO faradaic efficiency (17-fold at -0.6 VRHE ) and partial current density (100-fold at -0.6 VRHE ), suppressing the undesired H2 faradaic efficiency. Furthermore, in situ attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) reveals a plasmon-promoted formation of the bridge-bonded CO on Ag surface via a carbonyl-containing C1 intermediate. The present work demonstrates a deep mechanistic understanding of selective regulation of interfacial reactions by coupling plasmons and electrochemistry.

Uncovering Photoelectronic and Photothermal Effects in Plasmon‐Mediated Electrocatalytic CO2 Reduction

AbstractPlasmon‐mediated electrocatalysis that rests on the ability of coupling localized surface plasmon resonance (LSPR) and electrochemical activation, emerges as an intriguing and booming area. However, its development seriously suffers from the entanglement between the photoelectronic and photothermal effects induced by the decay of plasmons, especially under the influence of applied potential. Herein, using LSPR‐mediated CO2 reduction on Ag electrocatalyst as a model system, we quantitatively uncover the dominant photoelectronic effect on CO2 reduction reaction over a wide potential window, in contrast to the leading photothermal effect on H2 evolution reaction at relatively negative potentials. The excitation of LSPR selectively enhances the CO faradaic efficiency (17‐fold at −0.6 VRHE) and partial current density (100‐fold at −0.6 VRHE), suppressing the undesired H2 faradaic efficiency. Furthermore, in situ attenuated total reflection‐surface enhanced infrared absorption spectroscopy (ATR‐SEIRAS) reveals a plasmon‐promoted formation of the bridge‐bonded CO on Ag surface via a carbonyl‐containing C1 intermediate. The present work demonstrates a deep mechanistic understanding of selective regulation of interfacial reactions by coupling plasmons and electrochemistry.

Silver-M-Phathalocyanine (M= Co,Fe,Cu) Electrocatalysts for Oxygen Reduction Reaction in H2/O2 Anion Exchange Membrane Fuel Cells

In the transition from fossil fuels to clean energy sources, H2 plays a key role due to its high energy density, and direct conversion to electricity in fuel cells (FCs). FCs are devices that allow the clean conversion of chemical energy into electrical energy. In H2/O2 fuel cell the hydrogen oxidation reaction (HOR) occurs at the anodic electrode, while at the cathodic side oxygen is reduced into water (ORR). The electrodes are separated by a conductive membrane, that could exchange protons (Proton Exchange Membrane, PEM) or anions (Anion Exchange Membrane, AEM) to maintain the electro-neutrality of the system. AEMFCs are an attractive alternative to PEMFCs, thanks to the alkaline noncorrosive enviroment that allows the use of cheaper structural materials such as non-noble metal electrocatalysts. This work is centred on the study of silver (Ag) nanostructured electrocatalysts in ORR for the realization of a platinum-free AEMFCs. Ag nanoparticles promote, in alkaline media, a 4e- pathway of the ORR, optimizing the conversion of oxygen into water at the expense of hydrogen peroxide.1 However, the activity of Ag is limited by the strong hydroxide anion (OH-) binding energy, which reduces the free active sites destined to oxygen adsorption.1 To overcome this, Ag electrocatalysts were modified with metal-phthalocyanines (M-Pc M=Co, Fe, Cu) and supported on Ketjen-black carbon and on Ceria/Ketjen black (CeO2/C) supports. The synergistic effect between M-Pc and Ag NPs optimizes the OH- binding energy enhancing the ORR performances.2,3 The employment of ceria, thanks to its high oxophylicity, improves the transfer of OH- to the metal surface.4,5 The dispersion and size of nanoparticles (5-15 nm) was controlled through the Turkevich synthesis method, in order to maximize the interaction between Ag and Me-Pc. Physical characterization has been realized by High Resolution Trasmission Electron Microscopy (HR-TEM), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) while electrochemical behaviour has been explored in half cells and in complete AEMFCs. References Erikson, H., Sarapuu, A., & Tammeveski, K. (2019). Oxygen reduction reaction on silver catalysts in alkaline media: a minireview. ChemElectroChem, 6(1), 73-86.. Miller, H. A., Bevilacqua, M., Filippi, J., Lavacchi, A., Marchionni, A., Marelli, M., ... & Vizza, F. (2013). Nanostructured Fe–Ag electrocatalysts for the oxygen reduction reaction in alkaline media. Journal of Materials Chemistry A, 1(42), 13337-13347. Miller, H. A., Bellini, M., Oberhauser, W., Deng, X., Chen, H., He, Q., ... & Vizza, F. (2016). Heat treated carbon supported iron (ii) phthalocyanine oxygen reduction catalysts: elucidation of the structure–activity relationship using X-ray absorption spectroscopy. Physical Chemistry Chemical Physics, 18(48), 33142-33151. Miller, H. A., Bellini, M., Dekel, D. R., & Vizza, F. (2022). Recent developments in Pd-CeO2 nano-composite electrocatalysts for anodic reactions in anion exchange membrane fuel cells. Electrochemistry Communications, 135, 107219. Bellini, M., Pagliaro, M. V., Marchionni, A., Filippi, J., Miller, H. A., Bevilacqua, M., ... & Vizza, F. (2021). Hydrogen and chemicals from alcohols through electrochemical reforming by Pd-CeO2/C electrocatalyst. Inorganica Chimica Acta, 518, 120245. Figure 1

(Invited) Coupling of Electrochemistry with Surface Science and Computational Modeling to Understand Nanoparticle Electrocatalysts

We investigated nanoparticle electrocatalysts in oxygen evolution reaction (OER) and CO2 reduction reaction (CO2RR) via an approach coupling electrochemistry with ultra-high vacuum (UHV) surface science and computational modeling. Well-defined nanoparticle electrocatalysts such as Fe2O3, NiFeOx, and Ag, were prepared in the UHV chamber via physical vapor deposition (PVD) and characterized with surface science techniques including X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), followed by electrochemistry measurements to establish the structure-property relationships in OER and CO2RR. Calculations based on density functional theory (DFT) and microkinetic modeling (MKM) were then implemented to gain fundamental insight into these systems. We observed the edge-enhanced OER activity of Au-supported, ultra-thin Fe2O3 electrocatalysts and revealed incorporation of Ni at the edge sites (NiFeOx) further boosting their OER activity. We also resolved the size-dependent transition between CO2RR and H2 evolution reaction (HER) selectivity in sub-5 nm Ag electrocatalysts and identified an effective minimum size limit of ∼4 nm for active and selective Ag catalysts: particle diameters below this range experienced increased H2 evolutions due to a high population of Ag edge sites; and larger diameter particles favored CO2RR as the population of Ag(100) surface sites grew but will begin to lose catalyst utilization based on total metal masses.

Origin of surface-bonded oxygen on dendritic Ag particles towards 3D-nanocrystalline carbon formation during CO2 electrochemical reduction reaction

Formation of nanocrystalline carbon allotropes under the electrocatalytic reduction reaction of CO2 (CO2RR) on the dendritic Ag electrocatalysts was investigated at the applied potential −1.6 V vs. Ag/AgCl under the electrolyte system containing [BMIM]+[BF4]-, propylene carbonate, and water. The surface Ag − O bonds play an important role in developing the N+ stabilized highly energetic negatively charged Ag nanoclusters on which the nanocrystalline solid carbon was formed. Herein, the surface-bonded oxygen on dendritic Ag particles was originated from (i) the ultrathin natural silver oxide layers (unmodified Ag), (ii) anodization treatment (AD), and (iii) cyclic voltammetry treatments at a scan rate 1 (CV1) or 200 mV/s (CV200) for 5 cycles. Their capability to catalyze CO2RR towards solid carbon products depends on the stabilization of the active state of negatively charged nascent Ag nanoclusters under [BMIM]+[BF4]-. Even though each catalytic system yielded a major crystalline solid carbon product, a slight shift towards gaseous CO formation was noted in the case of AD compared to the unmodified Ag, CV200, and CV1, respectively. The increased intricacy in the three-dimensional structure of dendritic Ag particles following CV1 post-treatment, coupled with a stronger Ag − O bond could hinder agglomeration of anion Ag clusters. The crystalline solid carbon films containing sp2 − sp3 hybridization were grown on the facets of Ag nanocrystals as the building blocks and were matched with graphite and Diamond-C structures. The discoveries have significance in propelling the progress of electrocatalysts containing oxides, aiming to attain enhanced yields of higher value nanocrystalline carbon products through CO2RR.

Stability of Carbon Supported Silver Electrocatalysts for Alkaline Oxygen Reduction and Evolution Reactions.

Ag-based electrocatalysts are promising candidates to catalyze the sluggish oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFC) and oxygen evolution reaction (OER) in unitized regenerative fuel cells. However, to be competitive with existing technologies, the AEMFC with Ag electrocatalyst must demonstrate superior performance and long-term durability. The latter implies that the catalyst must be stable, withstanding harsh oxidizing conditions. Moreover, since Ag is typically supported by carbon, the strict stability requirements extend to the whole Ag/C catalyst. In this work, Ag supported on Vulcan carbon (Ag/VC) and mesoporous carbon (Ag/MC) materials is synthesized, and their electrochemical stability is studied using a family of complementary techniques. We first employ an online scanning flow cell combined with inductively coupled plasma mass spectrometry (SFC-ICP-MS) to estimate the kinetic dissolution stability window of Ag. Strong correlations between voltammetric features and the dissolution processes are discovered. Very high silver dissolution during the OER renders this material impractical for regenerative fuel cell applications. To address Ag stability during AEMFC load cycles, accelerated stress tests (ASTs) in O2-saturated solutions are carried out in rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) setups. Besides tracking the ORR performance evolution, an ex situ long-term Ag dissolution study is performed. Moreover, morphological changes in the catalyst/support are tracked by identical-location transmission electron microscopy (RDE-IL-TEM). Voltammetry analysis before and after AST reveals a smaller change in ORR activity for Ag/MC, confirming its higher stability. RRDE results reveal a higher increase in the H2O2 yield for Ag/VC after the ASTs. The RDE-IL-TEM measurements demonstrate different degradation processes that can explain the changes in the long term performance. The results in this work point out that the stability of carbon-supported Ag catalysts depends strongly on the morphology of the Ag nanoparticles, which, in turn, can be tuned depending on the chosen carbon support and synthesis method.

Preparation of thiol-decorated Ag nanoparticles on N-doped carbon through resonant acoustic mixing for electrochemical CO2 reduction

The development of electrocatalysts with high selectivity and low overpotentials has been a prominent area of focus in electrochemical CO2 reduction (ECR) research. Supported metal nanoparticle (NP) has been received considerable interest due to the immense potential of remarkable activity, stability, and recyclability in ECR applications. However, the practical production of these supported metal NPs necessitates a facile and scalable approach. Addressing this challenge, the present study introduces a novel method for solid-state synthesis of Ag/C using resonant acoustic mixing (RAM). The RAM technique successfully facilitated the deposition of Ag nanoparticles onto n-doped carbon support, forming Ag/N-C catalysts. The as-prepared Ag electrocatalysts exhibited excellent dispersion and uniformity in terms of particle size. A thiol-decorated Ag electrocatalyst (Ag-Th/N-C) was prepared using a simple soaking method to establish an Ag-thiol interface enhancing catalytic activity caused by promoted electron transfer from Ag to CO2. Significantly, the Ag-Th/N-C catalyst demonstrated an improved Faradaic efficiency of 87.26% for the reduction of CO2 to CO at − 1.1 V versus RHE compared to the pristine Ag/C catalyst (55.45%).

(Invited) Bipolar Membrane Electrolysis for CO2 to Ethylene

Carbon dioxide conversion systems are important to drive down the cost of carbon capture through the creation of valuable products. However, how to integrate carbon capture with carbon conversion devices is not yet clear. Bipolar membrane electrolyzers have attracted significant interest as a device which is compatible with carbon capture, as these systems can operate with bicarbonate and carbonate-based solutions. In a bipolar membrane electrolyzer, carbonate is converted to carbon dioxide through a pH swing process driven by water dissociation within the bipolar membrane. However, balancing the rate of water dissociation, carbon dioxide production, and carbon dioxide electrocatalysis remains a critical challenge. Furthermore, steering carbon dioxide electrocatalysis toward a specific high value product such as ethylene is unclear.Here, we set out to examine the activity of Cu, Ag and CuAg catalyst in a carbonate electrolysis system. Cu is a unique metal catalyst and has previously shown the capacity to generate multi-carbon products such as C2H4 and C2H5OH within gas phase anion exchange membrane electrochemical cell. Cu-based catalysts are however known to suffer sluggish C–C coupling kinetics which is a requirement for C2+ product formation. To overcome this challenge, bimetallic are used. For instance, through introducing a known CO-producing catalyst such as Au and Ag with Cu one can perform a cascade reaction. This tandem strategy can enhance performance of multi-carbon products by increasing the coverage of *CO intermediates, known as an important intermediate for C–C coupling, on the Cu surface. Thus, here we will detail a set of experiments aimed at discerning the selectivity of a bipolar-membrane electrode assembly cell which contains Cu, Ag, and Cu-Ag bimetallic electrocatalyst. We examine the impact of temperature, catalyst loading, and system operations. We also will briefly discuss technoeconomic considerations.

High-Performance Hydroxide Exchange Membrane Fuel Cell Comprising an Atomic Layer-Deposited Silver Cathode.

Atomic layer deposition (ALD) is emerging as an efficient tool for the precise manufacture of catalysts, owing to its sophisticated surface tailoring capabilities. To overcome the techno-economic limitations of fuel cell electric vehicles (FCEVs), which are considered suitable alternatives to battery electric vehicles (BEVs), the development of cost-efficient high-performance catalysts is essential. In this study, we successfully fabricated a Pt-free cathode for a hydroxide exchange membrane fuel cell (HEMFC) with excellent oxygen reduction activity under extremely low loading of Ag electrocatalysts using ALD. Microstructural analysis confirmed that the surface modification by ALD-Ag nanoparticles exhibited excellent step coverage characteristics on porous carbon nanotubes (CNTs). An HEMFC comprising a CNT cathode surface-decorated with ALD-Ag nanoparticles delivered a high peak power density of 2154 mW mgAg-1 in an alkaline environment at 65 °C. This study demonstrates the applicability of ALD for the manufacture of highly active low-cost electrocatalysts for high-performance HEMFCs.

Development of a Zn-Mn aqueous redox-flow battery operable at 2.4 V of discharging potential in a hybrid cell with an Ag-decorated carbon-felt electrode

The Zn-Mn redox pair has great potential as a next-generation redox flow battery (RFB) because of its economic strength and capability to conduct safe reactions. However, because of the potential window restriction of the aqueous system, maximizing the performance of the system with a Zn-Mn redox pair is difficult. Hence, in this study, a hybrid RFB cell with three-electrolyte chambers is designed to expand the potential window using different electrolytes with varying pH values in the anolyte and catholyte. In the three-electrolyte chamber cell, a buffer electrolyte is utilized between the anolyte and catholyte, and the system exhibits a high discharge potential of approximately 2.4 V. Despite this success, stability problems still arise because of MnO2 precipitation in the electrolyte. Therefore, the cathode is further modified using an Ag-based metal-organic framework (MOF). The stability of the carbon-felt electrode is also improved when the cathode is decorated with an Ag electrocatalyst. The potential plateau during the discharge sustained at 2.3–2.4 V, while the cell is maintained over 550 mAh/gMnO₂ of specific capacity. Accordingly, the system design with a three-electrolyte chamber cell and cathode modification can enable the Zn-Mn redox reaction to provide stable and superior cell performance during charge-discharge cycles.

Selective electrochemical reductive amination of benzaldehyde at heterogeneous metal surfaces

Ammonia is one of the largest-volume commodity chemicals, and electrochemical routes to ammonia utilization are appealing due to increasingly available renewable electricity. In this work, we demonstrate an electrochemical analog to reductive amination for the synthesis of benzylamine from benzaldehyde and ammonia. Previous works on electrochemical reductive amination have generally focused on proof-of-concept outer-sphere routes. In our system, imine hydrogenation proceeds via an inner-sphere route on an Ag electrocatalyst at ambient conditions with an initial Faradaic efficiency toward the primary amine product of ∼80% and partial current greater than 4 mA/cm2 at −1.96 V versus Fc/Fc+ (−1.36 V versus the normal hydrogen electrode). Ag was selected after evaluating diverse transition metal electrocatalysts, and the rate-determining step was the initial electron transfer to the imine. Overall, this work represents a step toward inner-sphere electrochemical reductive amination systems, opening a large phase space of heterogeneous electrocatalysts for reactions that currently rely on thermochemical routes.

Influence of Headgroups in Ethylene-Tetrafluoroethylene-Based Radiation-Grafted Anion Exchange Membranes for CO2 Electrolysis.

The performance of zero-gap CO2 electrolysis (CO2E) is significantly influenced by the membrane's chemical structure and physical properties due to its effects on the local reaction environment and water/ion transport. Radiation-grafted anion-exchange membranes (RG-AEM) have demonstrated high ionic conductivity and durability, making them a promising alternative for CO2E. These membranes were fabricated using two different thicknesses of ethylene-tetrafluoroethylene polymer substrates (25 and 50 μm) and three different headgroup chemistries: benzyl-trimethylammonium, benzyl-N-methylpyrrolidinium, and benzyl-N-methylpiperidinium (MPIP). Our membrane characterization and testing in zero-gap cells over Ag electrocatalysts under commercially relevant conditions showed correlations between the water uptake, ionic conductivity, hydration, and cationic-head groups with the CO2E efficiency. The thinner 25 μm-based AEM with the MPIP-headgroup (ion-exchange capacities of 2.1 ± 0.1 mmol g-1) provided balanced in situ test characteristics with lower cell potentials, high CO selectivity, reduced liquid product crossover, and enhanced water management while maintaining stable operation compared to the commercial AEMs. The CO2 electrolyzer with an MPIP-AEM operated for over 200 h at 150 mA cm-2 with CO selectivities up to 80% and low cell potentials (around 3.1 V) while also demonstrating high conductivities and chemical stability during performance at elevated temperatures (above 60 °C).

Dendritic Ag Electrocatalyst with High Mass-Specific Activity for Zero-Gap Gas-Fed CO2 Electroreduction

Dendritic Ag Electrocatalyst with High Mass-Specific Activity for Zero-Gap Gas-Fed CO₂ Electroreduction

Pd, Ag and Bi carbon-supported electrocatalysts as electrochemical multifunctional materials for ethanol oxidation and dopamine determination

This manuscript describes the investigation towards the multifunctional synthesis, characterization, and application of different Pd, Ag and Bi-carbon black supported electrocatalysts in two different fields in electrochemistry: fuel cells and electrochemical sensors. Throughout morphological and electrochemical characterizations, comprising scanning and transmission electron microscopies, X-ray powder diffraction, electrochemical impedance spectroscopy, and cyclic voltammetry techniques, the materials were characterized to better understand their properties towards proposed applications. Afterward, the materials were employed for ethanol oxidation in alkaline media, with investigations by chronoamperometry, cyclic voltammetry, and by closing a direct alkaline fuel cell, which the Pd50Ag45Bi05/C composite presented attractive ethanol catalysis behavior, with a maximum power density of 19.70 mW cm−2, at 30.59 mA cm−2. Also, the proposed device was applied for dopamine determination by square wave voltammetry. In this sense, two linear behaviors, respectively ranging from 0.2 to 1.0 and 4.0 to 40 μmol L−1 were obtained, due to two distinctive mechanisms. This higher activity has been attributed to the synergism among the used metals and proportions contributing to the bifunctional and electronic effects. As synthetic samples investigations were accomplished, data reinforces the proposed material as a possible interfacing composite in electrochemistry.

Tandem Electrochemical Conversion of CO2 to Liquid Fuels and Chemical Feedstocks

Increasing demand for energy has led to a high dependence on fossil fuels, which are limited and have been closely associated with major environmental issues such as groundwater pollution and imbalances in the carbon cycle. A more sustainable and cleaner method of producing chemicals and fuels is the electrochemical CO2 reduction reaction (CO2RR). When coupled with renewable electricity, CO2 can be converted to high energy density fuels and commodity chemicals, such as ethanol, propanol, and ethylene, in an environmentally friendly way.Recently, the use of CO feedstocks, instead of CO2, was shown to enhance the selectivity toward multi-carbon products on copper-based electrocatalysts. Technoeconomic analyses have also demonstrated that CO can be produced from CO2RR cost-effectively. This has led to increased efforts in developing tandem electrocatalytic systems. However, state-of-the-art CO2-to-CO electrocatalysts are based on expensive noble metals such as Ag and Au, while earth-abundant Zn displays relatively poorer selectivity and activity. Herein, we show that oxide-derived Zn with high surface area can reduce CO2 to CO with a Faradaic efficiency of 86% and a partial current density (j CO) of −201 mA cm-2. While oxygen vacancies were previously implicated for CO2RR to CO, we pinpointed by detailed experiments and density functional theory calculations that highly undercoordinated Zn sites provide even higher activity, in view of their nearly optimal *COOH adsorption energies. These findings indicate that suitably engineered ZnO-derived materials can potentially be an alternative to the more costly Ag and Au electrocatalysts, and that the main guideline for their design is to increase the undercoordination of the catalytic sites.We also investigate the electrochemical CO reduction reaction (CORR) to liquid fuels and industrial feedstocks on copper-based and mixed copper-silver catalysts. To further enhance the CORR activity and product selectivities, a systematic optimization of the experimental environment, such as the use of various supports, catalyst binder and electrolytes, was done. We develop a set of experimental conditions for optimal CORR performance to value-added products.

Ag/C composite catalysts derived from spray pyrolysis for efficient electrochemical CO2 reduction

• Ag/C composite and Ag electrocatalysts were synthesized by spray pyrolysis. • Composites had higher CO productivity and stability than Ag particles did. • Ag reaction sites on and within the carbon black support were used efficiently. • Carbon black support is a superior choice for CO 2 reduction by electrocatalyst. In this study, Ag/C composite catalysts with different weight ratios (20, 50, and 75 wt% Ag) were synthesized by spray pyrolysis to improve the performance of electrochemical CO 2 reduction for CO production. Among the electrocatalysts tested, the Ag75/C composite catalyst (75 wt% of Ag nanoparticles dispersed in carbon black support) showed the highest electrochemical CO 2 reduction performance, along with high stability that surpassed that of pure Ag particles. Above all, this is because Ag nanoparticles were dispersed on the surface of (and inside) the carbon black support. This enlarged the Ag surface area, thereby increasing the number of electrochemical CO 2 reduction sites. Additionally, the carbon black support has a hierarchically porous structure that improved the transport of the catholyte, reactant, and products, enabling enhanced electrochemical CO 2 reduction to CO. Furthermore, the use of carbon black support in the Ag/C composite catalysts allows the binder to bind more carbon microspheres than Ag nanoparticles, reducing the Ag surface area covered by the binder in comparison with that for pure Ag particles. Thus, the charge transfer resistance of a Ag/C composite catalyst was much lower than that of pure Ag particles due to the improved interconnection, contact, and number of electrochemical reaction sites provided by the combination of carbon black support and Ag nanoparticles. All of these interpretations imply that carbon black is an appropriate support able to play a key role in improving CO productivity via electrochemical CO 2 reduction.

Pd, Ag and Bi Carbon-Supported Electrocatalysts as Electrochemical Multifunctional Materials for Ethanol Oxidation and Dopamine Determination

Pd, Ag and Bi Carbon-Supported Electrocatalysts as Electrochemical Multifunctional Materials for Ethanol Oxidation and Dopamine Determination

Microenvironment Effects on Electrocatalytic Oxygen Reduction: The Role of Acid Electrolyte Anions

The surface-electrolyte microenvironment plays an important role in the performance of electrochemical systems. Better understanding the role that electrolyte ions play at or near the surface is an avenue to optimizing the local electrocatalyst reaction microenvironment in renewable electrochemical energy technologies such as fuel cells, electrolyzers, and batteries. Focusing on the oxygen reduction reaction (ORR), as one of the key half reactions often involved in these electrochemical technologies, better understanding acid electrolyte anion effects may help facilitate the design of non-Pt catalyst material alternatives for proton exchange membrane fuel cells (PEMFCs) and/or engineer better electrolyte-electrode interfaces with tuned local microenvironments. Previous work has focused on studying anion effects in acidic media using Pt electrocatalysts, and changes in performance as a function of anion species have been generally attributed to competitive adsorption. In addition to acid electrolyte anion effects not being widely studied outside of on Pt materials, possible anion effects outside competitive adsorption on the ORR have, in general, not been investigated in detail. Therefore, to better understand acid electrolyte anion effects on the ORR activity and selectivity of both strong and weak oxygen-binding materials, smooth Pd and Ag thin films specifically, we employed cyclic voltammetry with a rotating (ring) disk electrode to investigate the ORR performance response of these metals in various electrolytes (HClO4, HNO3, H2SO4, H3PO4, HCl, and HBr) at pH 1. Moreover, we employ extensive physical characterization methods to measure exposed electrocatalyst surface area (atomic force microscopy, AFM), composition & electronic structure (x-ray photoelectron spectroscopy, XPS), and mass/thickness (inductively coupled plasma optical emission spectrometry, ICP-OES) of the thin films before and after ORR testing in each electrolyte. In this work, we demonstrate anion identity plays a significant role in modifying ORR activity and selectivity on both smooth thin film Ag and Pd polycrystalline electrocatalysts; notably including decreased hydrogen peroxide selectivity in nitric acid compared to in the other investigated electrolytes. Moreover, we combine physics-based modeling and data science to gain insight into the fundamental nature of anion interactions in the electrochemical double layer microenvironment that result in the observed performance changes as a function of anion species. These insights provide guidance on opportunities to improve performance for ORR catalysts in PEMFCs and related applications.

Surface Oxidized Ag Nanofilms Towards Highly Effective CO2 Reduction

AbstractThe electrocatalytic CO2 reduction (converting redundant CO2 into carbon‐neutral fuels) holds a great potential to battle the energy and environmental crisis. The Ag‐based materials stand out from the pool of catalysts because of its high Faradic efficiencies for CO formation. In this work, thin Ag polycrystalline film was synthesized on carbon papers by a simple vacuum evaporation method. After 15 minutes of O3 treatment under ambient temperature, the Ag electrocatalysts can produce CO with a Faradic efficiency of up to 93.3 % at −0.9 V versus reversible hydrogen electrode (vs. RHE), which is higher than that of pristine Ag. In addition, the Ag electrode retained ∼90 % catalytic selectivity for CO after a 10‐hour test. The characterizations show that the surface AgxO layer on Ag was reduced to Ag0, which not only reduces the activation energy barrier of the initial electron transfer but also provides an increased number of active sites for the reduction of CO2 to CO.