ACS electrochemistry最新文献

Water electrolysis, including seawater splitting to produce hydrogen and oxygen, stands as a promising approach for the efficient storage of intermittent energy. However, the half-reactions of water splitting, the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), are known to be very sensitive toward the quality of water employed and are susceptible to contaminants originating from various sources, including the electrolyte or the electrodes. Those contaminants have a profound impact on the activity of these reactions of water splitting by modifying the electronic and physical structures of electrocatalysts as well as electrode-electrolyte interfaces. For seawater electrolysis, the unintentional presence of impurities, such as anions, cations, and organic compounds, affects the catalyst stability, selectivity, and activity. Despite the existence of numerous comprehensive reviews that delve into various aspects of catalysts and their structure-property relationships for several electrocatalytic reactions, the impact of contaminants has often been ignored. This critical review endeavors to address this issue by providing an overview of the diverse sources of contaminants influencing electrocatalytic water splitting and seawater splitting reactions, delineating the trends in electrochemical parameters and detailing different characterization methods for elucidating the physical and electronic changes of the electrode and electrolyte.

In organic electrosynthesis, the hydrogen evolution reaction (HER) is a parasitic process that significantly diminishes the faradaic efficiency (FE) of aqueous electrochemical reductions and contributes to the cathodic corrosion of widely used metals such as lead and tin. Developing strategies that selectively suppress HER without hindering desired electrochemical transformations is therefore crucial. In this study, we demonstrate that various quaternary ammonium salts (QAS) suppress HER on lead cathodes even under acidic conditions (pH 1). These QAS electrostatically self-assemble at the negatively charged lead surface, forming a cationic barrier that hinders hydronium ion (H₃O⁺) diffusion to the surface, thereby mitigating HER. Chronoamperometry (CA) at -1.8 V vs Ag/AgCl for 1 h revealed stark differences in QAS performance depending on molecular structure. H12MS (N,N,N,N',N',N'-hexamethyl-1,12-dodecanediammonium methyl sulfate) was the most effective salt, suppressing hydrogen evolution from ∼0.76 to ∼0.11 mmol cm^-2 (an 85% decrease), even at concentrations as low as 1 μM. CA also showed that the monotonic increase in current over time for blank lead electrodes, which is due to corrosion and surface roughening, was also suppressed in the presence of QAS, underscoring their dual role as inhibitors of both HER and cathodic corrosion. Moreover, during the electrochemical hydrogenation of fumaric acid at -1.7 V vs Ag/AgCl, the addition of 1 mM H12MS enhanced the faradaic efficiency from 7.3% to 38.5% (a 5.3-fold increase) without affecting the yield of succinic acid. These findings highlight the effectiveness of QAS additives in tailoring the boundary layer to improve the efficiency and durability of electrochemical processes.

Scanning electrochemical probe microscopy (SEPM) maps and investigates the chemical and physical properties of surfaces and interfaces using a micro- or nanoscale electrochemical probe, e.g., a microelectrode or a nanopipette, positioned close to an interface of interest. SEPM instruments share a common general architecture but are distinct from each other through the choice of probe and in the different physicochemical properties of the sample that can be investigated, including, among others, interfacial charge transfer rates, topography, permeability, or surface charge. Thus, a single instrument, with an appropriately flexible control system, can facilitate widespread access to the family of SEPM techniquesscanning electrochemical microscopy (SECM), scanning ion conductance microscopy (SICM), scanning electrochemical cell microscopy (SECCM), the scanning micropipette contact method (SMCM), and hybrid varieties of these techniques. Herein, we describe in detail a flexible open-source SEPM instrument that can perform common and widely applicable SEPM techniques and experimenter-defined methodologies, with minimal programming from the user. The instrument makes use of a field programmable gate array (FPGA)-based data acquisition card, and this contribution further illustrates the benefits of adopting FPGA architecture generally in electrochemical instrumentation. We describe the software and hardware for the instrument, using examples from the literature to illustrate how common SEPM operation modes and hyphenated techniques are readily implemented. Additionally, to demonstrate the application of custom-developed scanning protocols, we briefly present some further experimental examples. This Tutorial seeks to serve the needs of expert users of SEPMs and encourage new entrants alike. To this end, to encourage those who are interested in either setting up their own instruments or making optimal use of commercially available instruments, we also briefly include some more basic and general information on SEPM techniques and uses, to put the more advanced work and instrumental aspects in context.

Modification of ultramicroelectrode sensors with electroactive nanomaterials is key to enhancing their microscale sensing performance for advanced applications in cellular biology, disease diagnostics, or scanning electrochemical microscopy (SECM). This work employs a modern design-of-experiment (DoE) approach to develop a systematic, multiple-parameter methodology for the development of robust ultramicroelectrode modification protocols. Specifically, platinum ultramicroelectrode sensors are coated with platinum/nanocarbon nanocomposites through electrophoretic deposition (EPD), using 2 ^k factorial screening designs to systematically investigate the ultramicroelectrode modification process. The steady state current is employed as a quantitative DoE target metric, enabling us to map and model optimum ultramicroelectrode modification conditions. DoE-optimized modification conditions are shown to achieve substantial improvements in coating quality and limit of detection in a model H₂O₂ sensing study. The DoE-optimized conditions are also successfully translated to the modification of carbon-fiber ultramicroelectrodes (CFM), achieving effective modification in a single experiment. This systematic DoE approach provides a versatile, robust, and highly effective method for developing ultramicroelectrode modification across multiple parameters through a minimal number of experiments. Importantly, the DoE methodology also readily identifies tolerances and limiting conditions for the modification process, vital for broader adoption and future technology translation of functionalized ultramicroelectrodes.

Electrochemical impedance spectroscopy (EIS) is widely used to probe the solid electrolyte interphase (SEI) under realistic conditions, without causing damage to its structure. However, the models and experimental conditions often raise concerns about the reliability of the results. In this work, we present an extensive EIS study of lithium metal in the model electrolyte lithium bis-(fluorosulfonyl)-imide in tetraglyme, analyzing the system at equilibrium as a function of time, temperature, and salt concentration using a setup designed to minimize artifacts. We apply information theory to determine the number of independent degrees of freedom and constrain the number of Voigt elements used in fitting. Our analysis reveals strong correlations among processes, warranting caution when assigning physical meaning. X-ray photoelectron spectroscopy and 4D-scanning transmission electron microscopy measurements are used to support the interpretation and provide complementary insights into the chemical nature of the interphase. The unique and extensive dataset we have collected, comprising over 12000 highly reproducible impedance spectra, will serve as a valuable resource to the community for further analysis and for supporting additional modeling and experimental efforts.

The Li-N₂ cell represents a fascinating device that opens a new pathway for ammonia electrosynthesis. It combines the unique property of lithium, which can spontaneously react with N₂ under mild conditions, with an energy-efficient solution to the challenging N₂ fixation reaction. However, such a battery-inspired setup may be susceptible to false-positive results and present some pitfalls. This work elucidates some critical aspects of Li-N₂ cells, aiming at identifying a reliable methodology to assess the electrochemical reduction of N₂ at the cathodic surface, avoiding misleading pathways. Despite the spontaneous nature of the reaction between lithium and N₂, it remains uncertain whether it is feasible to promote the electrochemical fixation of N₂ before reaching the lithium plating potential. This would involve lithium as an ion in the electrolyte, which should activate and enable N₂ reduction on the carbonaceous surface before any Li⁺ reduction occurs, i.e., at a potential higher than the lithium plating potential (-3.04 V vs SHE). This study discusses this possibility, searching for setup limitations, such as the presence of metallic lithium at the anode, and pitfalls, such as the use of cyclic voltammetry in different testing environments as a methodology to evaluate the formation of Li₃N before lithium plating occurs.

Hydrophobic surface modification of porous carbon materials is critical for the performance and durability of polymer electrolyte membrane fuel cells and many other electrochemical technologies. However, conventional treatments rely on dip coating approaches using polymer dispersions containing fluorinated compounds (i.e., polytetrafluoroethylene), which pose environmental hazards and yield heterogeneous surfaces with limited control over wetting behavior and poor durability. Here, we introduce a facile method that exploits the facile electroreduction of 4-nitrobenzodiazonium tetrafluoroborate to generate aryl radicals and initiate a radical chain reaction that enables the grafting of vinyl-terminated organosilicon compounds. This method proceeds under ambient conditions and at milder potentials than traditional vinylic electrografting. We investigate three organosilicon derivativesallyltriisopropylsilane, acryloxymethyl-trimethylsilane, and monomethacryl-oxypropyl-terminated polydimethylsiloxaneas electrografted coatings to tailor surface wettability. We perform microscopic, spectroscopic, and contact angle measurements and electrochemical characterization to correlate chemical moieties with the resulting wettability and electrochemical performance in fuel cells. We find that the electrografted coatings form a covalently bonded, thin layer that significantly reduces the solid surface energy of the carbonaceous substrate, reaching values close to those of polytetrafluoroethylene. Additionally, we find a correlation between surface energy and fuel cell performance, where the less hydrophobic coatings show cell flooding under more humid conditions. Polydimethylsiloxane-based coating outperforms the commercial baseline (polytetrafluoroethylene) in operando fuel cells, which paves a promising pathway for this class of materials. Importantly, this study highlights the potential of fluorine-free alternatives to traditional fluorinated hydrophobic treatments, offering a more sustainable and environmentally friendly approach without compromising performance.

Over the past two decades, the pollution lexicon has expanded beyond nutrients, hydrocarbons, and heavy metals to include emerging pollutants (EPs) and emerging contaminants (ECs), which now pose a critical challenge to environmental monitoring. Although, the conventional techniques are accurate and sensitive but often impractical for rapid, on-site monitoring. In response, a new wave of innovation has emerged to redefine environmental sensing through the development of paper-based electrochemical analytical devices (ePADs) which is a convergence of green chemistry, flexible electronics, and smart design. At the heart of their effectiveness lies in cellulose materials which depends on renewability, biodegradability, capillarity, and flexibility enable effective, low impact ePADs for passive fluid handling and microfluidics. Advances in 3D origami-based ePADs enable multi-analyte sensing, and, when paired with green manufacturing and smartphone-linked, low-power electronics, deliver real-time, cloud-ready data. Achieving widespread, sustainable deployment for decentralized pollution monitoring will require standardized validation, scalable manufacturing, and collaboration across scientific, technological, and policy domains. Looking forward, more than a replacement for conventional techniques, ePADs invite us to rethink our relationship with the environment. It signals a new contract between innovation and the planet-one in which analytical performance is inseparable from ecological responsibility. Each cellulose channel and fold demonstrates that high-precision sensing can be lightweight, biodegradable, and accessible. In this vision, smarter technology is also gentler, delivering cleaner water, healthier communities, and a more resilient Earth.

3D-printed electrochemical devices have gained tremendous attention recently because they are highly customizable platforms for analysis and energy storage that can be produced using simple, inexpensive components in a wide variety of settings. 3D-printed electrochemical sensors, fabricated from carbon-loaded conductive thermoplastics, enable decentralized production of electrochemical devices that, if optimized, could be widely distributed. Achieving this goal requires a comprehensive understanding of the electrochemical behavior of these filaments. Here, we investigated how the electrochemical behavior of three commercial filaments was affected by alumina polishing, electrochemical activation in 0.5 M NaOH, and electrodepositing Au nanoparticles (NPs). The goal of this study is to characterize if/how these commonly used pretreatments affect different filaments. The study is not an exhaustive combination of all filaments and pretreatment options. We characterized the physical properties of each filament/pretreatment using thermogravimetric analysis, scanning electron microscopy, and Raman microscopy measurements. We then benchmarked the background electrochemical processes (capacitance and solvent window), the peak current response versus scan rate, and the peak potential separation of two common outer-sphere redox species (ruthenium hexamine and ferrocene methanol) for each filament under each pretreatment (i.e., nine total conditions). We subsequently investigated how the filaments responded to inner-sphere redox couples that were surface sensitive (ferrocyanide oxidation), dependent on surface adsorption (dopamine oxidation), and sensitive to surface oxides (Fe²⁺ oxidation). The data collectively underline the complexity of electrodes fabricated from conductive 3D printing filaments and highlight several important considerations that should be addressed when interpreting the electrochemistry of such materials. First, we present evidence that these materials behave as partially blocked electrodes, which complicates interpretations of electrochemical data. We also found that the outer-sphere electrochemical reactivity on a given filament was largely consistent regardless of pretreatment. The important variable for assessing outer-sphere electron transfer was the uncompensated resistance (R _u), which varies depending on the filament material, electrode size, and contact method. Finally, we observed that the selected filaments do not respond to pretreatments identically when tested against inner-sphere redox species, suggesting that a variety of treatments should be evaluated when assessing conductive 3D-printed filament electrodes.

Ni-based electrocatalysts are among the most active materials for the hydrogen evolution reaction (HER) in alkaline media. In this work, we demonstrate the ability to use films of boron-doped diamond (BDD), a stable and corrosion-resistant electrode material, as a support for highly textured Ni films. Our approach is based on the electrodeposition of NiCu alloy thin-films, followed by electrochemical dealloying. The structure and composition of the electrocatalysts were characterized using scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. In pH 13 KOH, a dealloyed Ni catalyst corresponding to an initial NiCu composition of 68% Ni, gave a HER overpotential at 10 mA cm^-2 of 152 mV. With further analysis, we show that the rate of HER is 2^nd order with respect to the number of Ni active sites, and that the kinetics are limited by the surface diffusion of adsorbed intermediates. Two Tafel slopes are additionally observed, suggesting a change in HER mechanism and intrinsic activity at dealloyed Ni catalysts.