Electrode Surface Structure Research Articles

Tailoring electrochemical CO2 reduction selectivity over CuSn by modulating surface oxidation state with infrared laser treatment

Infrared laser treatment was used to precisely modify the surface structure of CuSn electrodes, effectively fine-tuning the selectivity of reduction products. With increasing laser power, the metallic Cu and Sn surfaces became more oxidized, and the Sn/Cu composition ratio varied with depth and further changed post-EC reaction. The diversity of reduction products, including C1 (CO, CH4, and formate), C2 (C2H4, ethanol, acetate, acetaldehyde, and glycolaldehyde), and C3 (propanol and isopropanol) compounds, shifted towards a more selective production of C1 (CO and formate) products. These tailored behaviors are attributed to variations in interfacial electronic structures, oxidation states, composition ratios, and the interaction between CO2 and the density of states (Cu, O, and Sn) near the Fermi level. The laser treatment method enables precise tuning of electrode surfaces, modulation of reduction products, and enhancement of selectivity. Moreover, this technique presents a novel approach for electrode design in the field of CO2 reduction, offering new avenues for optimizing catalytic performance.

Optimizing Surface Texture Through Ion Induction for High Areal Capacitance and Enhanced Stability in MXene Electrodes

AbstractTo make supercapacitors a viable commercial product, it is necessary to increase the mass loading (ML) of the electrodes. However, current research on high ML MXene electrodes mainly focuses on internal structure optimization, often neglecting the importance of surface texture in the electrodes, which plays a crucial role in mediating interactions between the internal structure and the electrolyte. This study reports on a simple ion‐intercalation process that can reduce charge transfer resistance and improve cycling stability. Through the integration of 3D visualization models and wide‐angle X‐ray scattering techniques, a comprehensive investigation of the electrode's surface structure and MXene flake arrangement is conducted. The results showed that pre‐oriented aggregates induced by ion‐intercalation create a sophisticated surface structure with rich hills and valleys, promoting electrolyte permeation and ion exchange. This work highlights the significance of surface texture in films and electrodes, guiding the design of high‐performance materials.

Controlled Electrode-Electrolyte Interphases (EEI) Formation Via Ex-Situ Interfacial Synthesis

The stability and electrochemical performance of energy storage systems are heavily influenced by their interfaces. The electrode-electrolyte interphases (EEIs) present at these interfaces are typically formed in-situ through the electrochemically induced complex interactions involving the electrode surface and bulk electronic structure, functional groups and chemical species present at the interface, and electrolyte. Given the importance of interface stability in energy storage, herein, multiple ex-situ approaches (electrochemical fluorination, ion-exchange metathesis, layer-by-layer coating) have been explored to form stable and controlled EEI that allow ion transport and limit the electron leakage. Such controlled EEI via ex-situ interfacial synthesis demonstrated significantly improved cycling stability compared to in-situ EEI formation.

Proton Transfer Kinetics at a Defect-Free Liquid-Liquid Interface

Proton transfer at electrochemical interfaces is fundamentally important for many areas of science and technology, yet kinetic measurements of this elementary step are often convoluted by inhomogeneous electrode surface structures. We show that facilitated proton transfer at the interface between two immiscible electrolyte solutions (ITIES) can serve as a model system to study proton transfer kinetics in the absence of defects found at solid|electrolyte interfaces. Diffusion-controlled micropipette voltammetry revealed that 2,6-diphenylpyridine (DPP) facilitated direct proton transfer across the liquid|liquid interface and voltammetry at nanopipette-supported interfaces yielded activation-controlled ion transfer currents. The exchange current density for proton transfer at the ITIES is comparable to exchange current densities recently reported for H-UPD on Pt (111) and provides the first direct means of comparing ion transfer kinetics between solid|liquid and liquid|liquid interfaces, supporting the development of a general theory of ion transfer kinetics.

Mechanism of overscreening breakdown by molecular-scale electrode surface morphology in asymmetric ionic liquids

The interfacial nature of the electric double layer (EDL) assumes that electrode surface morphology significantly impacts the EDL properties. Since molecular-scale roughness modifies the structure of EDL, it is expected to disturb the overscreening effect and alter differential capacitance (DC). In this paper, we present a model that describes EDL near atomically rough electrodes with account for short-range electrostatic correlations. We provide numerical and analytical solutions for the analysis of conditions for the overscreening breakdown and DC shift estimation. Our findings reveal that electrode surface structure leads to DC decrease and can both break or enhance overscreening depending on the relation of surface roughness to electrostatic correlation length and ion size asymmetry.

Simple processing via thermal treatment and catalyst infiltration to enhance nickel electrode performance for liquid alkaline water electrolyzers

Two simple processes for enhancing liquid alkaline water electrolyzer performance are demonstrated. Both enhance 3D Ni electrodes by introducing a micron-scale rough structure throughout the bulk of the electrode. Oxidation/reduction relies on a simple thermal treatment cycle to create surface roughening through the volumetric expansion during NiO formation and volume contraction during reduction back to Ni metal. Catalyst infiltration introduces a washcoat of additional metal particles throughout the electrode, by flooding the electrode with catalyst precursor and converting it to micron-scale particles via a reducing thermal treatment. The largest improvement in performance (211 mV at 1.8 A cm−2) is observed for infiltrated NiFe-3x catalyst. For Fe-free Ni-only electrodes, oxidation/reduction provides a larger improvement (157 mV at 1.8 A cm−2) than infiltrated Ni-3X (106 mV at 1.8 A cm−2). For both processes, the observed electrode surface structure and performance is quite sensitive to the thermal treatment temperature.

Understanding Performance Limitation of Liquid Alkaline Water Electrolyzers

Liquid alkaline water electrolyzers (LAWEs), being the most commercially mature electrolysis technology, play a pivotal role in large-scale hydrogen production. However, LAWEs suffer from low operational efficiency, primarily due to un-optimized electrode structure and chemical compositions. Thus, we investigated how various electrode configurations could impact LAWE performance. Our results show that Ni felt electrodes outperform the conventional Ni foam thanks to improved electrochemical active surface area (ECSA) and preferred electrode surface structure that minimizes the micro-gaps in between the electrode and separator. By comparing the stainless steel (SS) felt electrodes with Ni felt electrodes, SS not only shows better oxygen evolution reaction activity but also improved hydrogen evolution reaction activity, which is less studied in the literature. We also show that a bilayer structure with small pore radius facing the separator could further improve LAWE performance by further optimizing interfacial contact between electrode and separator. These findings enable LAWEs to sustain 2 A cm−2 at 2.2 V and operate steadily at 1 A cm−2 for nearly 600 h with negligible performance decay. Our studies establish criteria for selecting electrodes to achieve high-performance LAWE and, in turn, expedite the adoption of LAWEs in hydrogen production and the transition towards low-carbon economies.

Size-dependent electrochemistry of laser-induced graphene electrodes

Laser-induced graphene (LIG) electrodes have become popular for electrochemical sensor fabrication due to their simplicity for batch production without the use of reagents. The high surface area and favorable electrocatalytic properties also enable the design of small electrochemical devices while retaining the desired electrochemical performance. In this work, we systematically investigated the effect of LIG working electrode size, from 0.8 mm to 4.0 mm diameter, on their electrochemical properties, since it has been widely assumed that the electrochemistry of LIG electrodes is independent of size above the microelectrode size regime. The background and faradaic current from cyclic voltammetry (CV) of an outer-sphere redox probe [Ru(NH3)6]3+ showed that smaller LIG electrodes had a higher electrode roughness factor and electroactive surface ratio than those of the larger electrodes. Moreover, CV of the surface-sensitive redox probes [Fe(CN)6]3– and dopamine revealed that smaller electrodes exhibited better electrocatalytic properties, with enhanced electron transfer kinetics. Scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy showed that the physical and chemical surface structure were different at the electrode center versus the edges, so the electrochemical properties of the smaller electrodes were improved by having rougher surface, more density of the graphitic edge planes, and more oxide-containing groups. The difference could be explained by the different photothermal reaction time from the laser scribing process that causes different stable carbon morphology to form on the polymer surface. Our results give a new insight on relationships between surface structure and electrochemistry of LIG electrodes and are useful for designing miniaturized electrochemical devices.

High performance Al anode for Al-air battery enabled by coordinating In and Sb additions with discharge parameters

High performance of Al anode for Al-air battery was achieved via coordinating minor In and Sb additions with discharge parameters. The electrochemical behaviors, discharge performance and surface structures of aluminum electrodes are systematically investigated to understand the alloying chemistry coordination of indium and antimony. The results show that coordinating indium and antimony can significantly activate the Al electrode without aggravating the hydrogen evolution. The assembled Al-air cell with Al-0.05In-0.05Sb electrode exhibits a desirable specific capacity and energy density of 2638 Ah·kg−1 and 3166 Wh·kg−1, respectively. Furthermore, antimony has better activating effect than indium, especially at discharge current density over 40 mA·cm−2. The activating mechanisms are discussed in detail.

Fast and precise CoFe3O4/TiO2/MWCNT-based voltammetric sensor preparation for salbutamol determination

Salbutamol is an important drug that opens the medium and large air spaces in the lungs. In this study, CoFe3O4, CoFe3O4/MWCNT, and CoFe3O4/TiO2/MWCNT modified electrode structures are prepared separately to determine the effect of each modification agent on salbutamol responses. The prepared electrodes are firstly structurally characterized by the FT-IR technique. The surface morphology and structure of electrodes are then analyzed by SEM, and AFM techniques. EDX analyses were performed to clarify this structural change on the electrode surface. The salbutamol activity of the modified electrodes is determined by DPV in 0.1 M PBS. The modified electrode shows a linear response in the concentration range of 2-18 µM salbutamol, and an R2 value of 0.9587 is achieved. LOD and LOQ of the modified electrode are determined as 1.39 µM and 22.87 µM, respectively. Considering the reproducibility of the experimental results, non-interference of the interfering species, and the measurement range, it is determined that it can be successfully used to figure out the concentration of salbutamol in physiological fluids and commercial form.

Impact of Pt(hkl) Electrode Surface Structure on the Electrical Double Layer Capacitance.

The classical theory of the electrical double layer (EDL) does not consider the effects of the electrode surface structure on the EDL properties. Moreover, the best agreement between the traditional EDL theory and experiments has been achieved so far only for a very limited number of ideal systems, such as liquid metal mercury electrodes, for which it is challenging to operate with specific surface structures. In the case of solid electrodes, the predictive power of classical theory is often not acceptable for electrochemical energy applications, e.g., in supercapacitors, due to the effects of surface structure, electrode composition, and complex electrolyte contributions. In this work, we combine ab initio molecular dynamics (AIMD) simulations and electrochemical experiments to elucidate the relationship between the structure of Pt(hkl) surfaces and the double-layer capacitance as a key property of the EDL. Flat, stepped, and kinked Pt single crystal facets in contact with acidic HClO4 media are selected as our model systems. We demonstrate that introducing specific defects, such as steps, can substantially reduce the EDL capacitances close to the potential of zero charge (PZC). Our AIMD simulations reveal that different Pt facets are characterized by different net orientations of the water dipole moment at the interface. That allows us to rationalize the experimentally measured (inverse) volcano-shaped capacitance as a function of the surface step density.

Long-Range Uniform Deposition of Ag Nanoseed on Cu Current Collector for High-Performance Lithium Metal Batteries.

Uniform lithium deposition is essential to hinder dendritic growth. Achieving this demands even seed material distribution across the electrode, posing challenges in correlating the electrode's surface structure with the uniformity of seed material distribution. In this study, the effect of periodic surface and facet orientation on seed distribution is investigated using a model system consisting of a wrinkled copper (Cu)/graphene structure with a [100] facet orientation. A new methodology is developed for uniformly distributed silver (Ag) nanoparticles over a large area by controlling the surface features of Cu substrates. The regularly arranged Ag nanoparticles, with a diameter of 26.4nm, are fabricated by controlling the Cu surface condition as [100]-oriented wrinkled Cu. The wrinkled Cu guides a deposition site for spherical Ag nanoparticles, the [100] facet determines the Ag morphology, and the presence of graphene leads to spacings of Ag seeds. This patterned surface and high lithiophilicity, with homogeneously distributed Ag nanoparticles, lead to uniform Li+ flux and reduced nucleation energy barrier, resulting in excellent battery performance. The electrochemical measurements exhibit improved cyclic stability over 260 cycles at 0.5mAcm-2 and 100 cycles at 1.0mAcm-2 and enhanced kinetics even under a high current density of 5.0mAcm-2.

In Situ Surface X-Ray Diffraction Studies of the Electrochemical Double Layer on Pt(111)

The molecular structure of the electrochemical double layer is an important fundamental topic in interfacial electrochemistry. It has received renewed interest in the last years, because of its influence on many electrochemical reactions and the emergence of ab initio molecular dynamics simulations that allow a detailed description of the interface structure and dynamics [1,2]. In the measurements presented here, we investigated the properties of the electrochemical double layer on Pt(111) via in situ surface X-ray diffraction (SXRD), a technique that is well-established for single crystal studies [3-7].Platinum electrodes are widely used as electrocatalysts, for example as cathodes in proton exchange membrane fuel cells due to their high ORR reactivity. The single-crystalline Pt(111) surface, which is a well studied model system, is especially interesting for studies of the electrochemical double layer. Recent electrochemical measurements revisited this system and found evidence for a double layer structure that strongly deviated from the traditional Gouy-Chapman-Stern model and indicated a complex structural influence of water [8,9]. The water structure within the electrochemical double layer is also of major interest in computational studies. For non-adsorbing, aqueous electrolyte the electrode surface charge can be partly compensated by a layer of oriented water molecules due to their dipole moment. For potentials around the potential of zero charge (PZC), a potential-dependent orientation of water molecules with respect to the electrode surface was suggested [1,2,10].To investigate the arrangement and orientation of the water molecules near the Pt(111) surface we used in situ SXRD methods, focussing on X-ray reflectivity (XRR) and crystal truncation rod (CTR) analysis. These methods allow to acquire detailed information about the electrode surface structure as well as the electrochemical double layer. By measuring multiple CTR sets at different surface potentials, information on the potential-dependence of the interface processes can be obtained. The experiments were performed at beamline ID31 of the European Synchrotron Radiation Facility using high photon energies of 75 keV, which provide very large data sets. This allows significantly improved structural modeling as compared to conventional SXRD. The studies employed an electrochemical hanging-meniscus X-ray diffraction cell that allows for SXRD measurements of fast dynamic systems in a well-defined electrochemical environment. We will report results on the water structure in the double layer obtained in perchloric acid at potentials around the PZC.We gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft via project no. 418603497 and the BMBF via 05K19FK3 and 05K22FK1.

An Easy-to-Use 3D-Printed Electrochemical Cell for I n Situ Raman Spectroscopy

In energy conversion devices such as electrolyzers and batteries, the monitoring of electrode surfaces during electrochemical processes is essential to understand their operation mechanisms. One of the promising techniques is in situ Raman spectroscopy, which can analyze (i) electrode surface structure, (ii) surface species (reaction intermediate species), and (iii) localized electrolyte species.1 The bottleneck for using this technique is the high cost and complexity of commercially available electrochemical cells designed for in situ Raman spectroscopy. To solve these issues, a few research groups provided 3D-printed spectroelectrochemical cells with low cost and less complexity.2,3 However, the spectroelectrochemical cells so far reported require a specific sample type (i.e., particles). We need a low-cost and less-complex spectroelectrochemical cell that can be used for more varieties of samples.In this study, we will provide a new design of a spectroelectrochemical cell that has compatibility with various sample types [i.e., substrates (e.g., metal foil strips, fluorine-doped tin oxide-coated glass, indium tin oxide-coated glass, etc.) and particle]. Specifically, a versatile, low-cost, and less-complex electrochemical cell for in situ Raman spectroscopy will be fabricated using a stereolithography (SLA) 3D printer with resin as a printing material. Herein, using the SLA 3D-printed spectroelectrochemical cell, we will also demonstrate a few example studies for electrolyzer and battery applications. References W. Zheng, Chemistry–Methods, 3, e202200042 (2023).M. F. dos Santos et al., Anal. Chem., 91, 10386–10389 (2019).G. D. da Silveira et al., Anal. Chim. Acta, 1141, 57–62 (2021).

Outstanding oxygen evolution reaction properties released at the interface of NiMoO4 and FeNi layer double hydroxide heterostructures

For the alkaline oxygen evolution reaction (OER), FeNi layered double hydroxide (FeNi LDH) exhibits good activity and stability. For the sake of saving freshwater, the use of abundant seawater as an electrolyte poses new requirements for its OER performance. A novel method was designed based on a corrosion reaction to convert commercial Fe foam into a high-performance OER catalyst (FeNiM), which consisted of FeNi LDH layers and NiMoO4 nanoparticles modified on its surface. FeNiM exhibited excellent OER activity, only requiring an overpotential of 250 mV to achieve a current density of 100 mA cm−2. Experimental results indicated that the heterostructures formed by NiMoO4 and FeNi LDH was conducive to exposing active sites, promoting the adsorption of active intermediates, and generating highly active oxyhydroxides. In addition, the heterostructure was beneficial to stabilizing the electrode surface structure and inhibiting seawater corrosion. Therefore, FeNiM could maintain high current density activity in both alkaline freshwater and alkaline seawater, which only required low overpotentials of 326 mV and 304 mV to achieve a high current density of 1500 mA cm−2, respectively. This catalyst preparation method has the advantages of economic efficiency, industrial compatibility, and significantly promoting the development of green hydrogen economy and industrial seawater desalination.

Developing an Electrochemically Reversible Switch for Modulating the Optical Signal of Gold Nanoparticles.

Gold nanoparticles (AuNPs) possess remarkable optical properties and electrical conductivity, making them highly relevant in various fields such as medical diagnoses, biological imaging, and electronic sensors. However, the existing methods for modulating the optical properties of AuNPs are often under limitations such as a high cost, the complexity of detection, a narrow range of application settings, and irreversibility. In this study, we propose a novel approach to address these challenges by constructing a reversible electrochemical switch. The switch (ITO-OMAD) involves covalently linking nitroxide radicals and AuNPs (AuNPs-NO•), followed by tethering this nanocomposite to a siloxane-derived indium tin oxide (ITO) electrode. By simply electrochemically oxidizing/reducing the nitroxide units, one is able to reversibly modulate the optical properties of AuNPs at will. The surface morphology and structure of the as-prepared ITO-OMAD electrode were characterized through scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM imaging confirmed the successful anchoring of AuNPs on the ITO electrode. Electrochemical tests performed in the three-electrode system demonstrated that the local surface plasmon resonance (LSPR) of AuNPs can be reversibly regulated by alternatively imposing ± 0.5V (vs. Ag/AgCl) to the modified electrode. The development of this electrochemical switch presents a novel approach to effectively control the optical properties of AuNPs. The further exploration and utilization of this reversible electrochemical switch could significantly enhance the versatility and practicality of AuNPs in numerous applications.

Electrochemical Enhancement of Lithium-Ion Diffusion in Polypyrrole-Modified Sulfurized Polyacrylonitrile Nanotubes for Solid-to-Solid Free-Standing Lithium-Sulfur Cathodes.

The energy density of lithium-sulfurized polyacrylonitrile (Li-SPAN) batteries has chronically suffered from low sulfur content. Although a free-standing electrode can significantly reduce noncapacity mass contribution, the slow bulk reaction kinetics still constrain the electrochemical performance. In this regard, a novel electrochemically active additive, polypyrrole (PPy), is introduced to construct PAN nanotubes as a sulfur carrier. This hollow channel greatly facilitates charge transport within the electrode and increases the sulfur content. Both electrochemical tests and simulations show that the SPANPPy-1% cathode possesses a larger lithium-ion diffusion coefficient and a more homogeneous phase interface than the SPAN cathode. Consequently, significantly improved capabilities and rate properties are achieved, as well as decent exportations under high-sulfur-loading or lean-electrolyte conditions. In-situ and semi-situ characterizations are further performed to demonstrate the nucleation growth of lithium sulfide and the evolution of the electrode surface structure. This type of electrochemically active additive provides a well-supported implementation of high-energy-density Li-S batteries.

Investigation of the Influence of Electrode Surface Structures on Wettability after Electrolyte Filling Based on Experiments and a Lattice Boltzmann Simulation

The filling of the electrolyte and the subsequent wetting of the electrodes is a quality-critical and time-intensive process in manufacturing of lithium-ion batteries. The exact influencing factors are the subject of research through experiments and simulation tools. Previous studies have demonstrated that wetting occurs mainly in the transition between the materials but leads to gas entrapments. Therefore, this paper investigates the influence of the electrode surface structures, situated between anode and separator, on the wetting progress, through experimental capillary wetting and simulated with a lattice Boltzmann simulation. The results show that the simulations can identify the exact pore size distribution and determine the wetting rates of the entire materials. Furthermore, the experiments reveal a negative correlation between fast wetting and rougher surface properties. This enables a more precise determination of the wetting phenomena in lithium-ion cell manufacturing.

Tuning wettability of nickel-based electrode by micro-nano surface structure to boost OER catalysis

Electrolysis of water is a green and environmentally friendly hydrogen production method, but its low oxygen evolution reaction (OER) efficiency hinders its large-scale application. A major strategy to improve the catalytic performance of OER is constructing the micro-nano structure on the surface of the catalyst. However, the exact effects of micro-nano surface structure, such as roughness, morphology and hierarchical structure on the catalytic performance have not been systematically studied. Herein, Nickel-Cobalt-Cerium Oxide (Ni-Co-CeO2) catalytic electrodes with the different micro-nano surface structures are fabricated by magnetic field-induced scanning electrodeposition. The effects of the micro-nano surface structure on catalytic performance are investigated. The results show that the micro-nano surface structure of Ni-Co-CeO2 catalytic electrodes has a great influence on the wetting state, which may lead to the Wenzel-Cassie transition, resulting in severe degradation of catalytic performance. By optimizing the micro-nano surface structure, the Ni-Co-CeO2 catalytic electrode has the best catalytic performance with the overpotential of 309 mV for OER to achieve the current density of 10 mA/cm2 and the corresponding Tafel slopes of 39.52 mV/dec. The study also demonstrates that the magnetic field-induced scanning electrodeposition is an efficient and simple method for tuning the micro-nano surface structure of electrodes to boost the OER efficiency.

A Study of the Surface Structure of Electrodes during Discharge in an Electrolyte in a Magnetic Field

A Study of the Surface Structure of Electrodes during Discharge in an Electrolyte in a Magnetic Field