Platinum Electro-dissolution in Acidic Media upon Potential Cycling

Enhancing Flexible Neural Probe Performance via Platinum Deposition: Impedance Stability under Various Conditions and In Vivo Neural Signal Monitoring

Monitoring neural activity in the central nervous system often utilizes silicon-based microelectromechanical system (MEMS) probes. Despite their effectiveness in monitoring, these probes have a fragility issue, limiting their application across various fields. This study introduces flexible printed circuit board (FPCB) neural probes characterized by robust mechanical and electrical properties. The probes demonstrate low impedance after platinum coating, making them suitable for multiunit recordings in awake animals. This capability allows for the simultaneous monitoring of a large population of neurons in the brain, including cluster data. Additionally, these probes exhibit no fractures, mechanical failures, or electrical issues during repeated-bending tests, both during handling and monitoring. Despite the possibility of using this neural probe for signal measurement in awake animals, simply applying a platinum coating may encounter difficulties in chronic tests and other applications. Furthermore, this suggests that FPCB probes can be advanced by any method and serve as an appropriate type of tailorable neural probes for monitoring neural systems in awake animals.

A Recyclable Standalone Microporous Layer with Interpenetrating Network for Sustainable Fuel Cells

The commercialization of fuel cells inevitably brings recycling problems. Therefore, achieving high recyclability of fuel cells is particularly important for their sustainable development. In this work, a recyclable standalone microporous layer (standalone MPL) with interpenetrating network that can significantly enhance the recyclability and sustainability of fuel cells is prepared. The interpenetrating network enables the standalone MPL to have high strength (17.7 MPa), gas permeability (1.55 × 10-13  m2 ), and fuel-cell performance (peak power density 1.35 W cm-2 ), providing the basic guarantee for its application in high-performance and highly recyclable fuel cells. Additionally, the standalone MPL is highly adaptable to various gas-diffusion backings (GDBs), providing high possibility to select highly recyclable GDBs. Outstandingly, anode standalone MPLs and GDBs can be easily detached from the spent membrane electrode assembly (MEA). This not only saves >90 vol% solvent in the recovery of the catalyst-coated membrane (CCM), but also extends the service life of the GDBs and the anode standalone MPL at least 138 times (2 760 000 h assuming 20 000 h of CCM) comparing to CCM. Therefore, the standalone MPL significantly enhances the recyclability and sustainability of fuel cells and is promising to be an indispensable component in the next-generation fuel cells.

Anodic and Cathodic Platinum Dissolution Processes Involve Different Oxide Species

The degradation of Pt-containing oxygen reduction catalysts for fuel cell applications is strongly linked to the electrochemical surface oxidation and reduction of Pt. Here, we study the surface restructuring and Pt dissolution mechanisms during oxidation/reduction for the case of Pt(100) in 0.1 M HClO4 by combining operando high-energy surface X-ray diffraction, online mass spectrometry, and density functional theory. Our atomic-scale structural studies reveal that anodic dissolution, detected during oxidation, and cathodic dissolution, observed during the subsequent reduction, are linked to two different oxide phases. Anodic dissolution occurs predominantly during nucleation and growth of the first, stripe-like oxide. Cathodic dissolution is linked to a second, amorphous Pt oxide phase that resembles bulk PtO2 and starts to grow when the coverage of the stripe-like oxide saturates. In addition, we find the amount of surface restructuring after an oxidation/reduction cycle to be potential-independent after the stripe-like oxide has reached its saturation coverage.

Towards a realistic prediction of catalyst durability from liquid half-cell tests

Liquid half-cell measurements provide a convenient laboratory method for determining relevant parameters of electro-catalysts applied in e.g. polymer electrolyte membrane fuel cells. While these measurements may be effective in certain contexts, their applicability to real-world systems, such as single-cells in a membrane electrode assembly (MEA) configuration, is not always clear. This is particularly true when assessing the stability of these systems through accelerated stress tests (ASTs). Due to different electrode compositions and operating conditions, nanoscale degradation proceeds differently. Nevertheless, given the high demands of MEA measurements in terms of time, testing equipment complexity, and amount of catalyst material, application-relevant predictions of catalyst durability from liquid half-cell tests are highly desirable. This study combines electrochemical and nanoparticle analysis based on transmission electron microscopy to conduct a typical voltage cycling AST for rotating disc electrode (RDE) measurements, showing that the loss of the electrochemically active surface area (ECSA) of the used Pt/Vulcan catalyst is strongly enhanced at 80 °C compared to room temperature, which goes along with increased nanoparticle coarsening. Additionally, a high ionomer/carbon mass ratio (I/C = 0.7) accelerates the ECSA loss, and further investigations of its influence suggest a combination of several factors, including the high local proton concentration and the presence of adsorbing anions. At the same temperature (80 °C) and I/C ratio (0.7), the ECSA loss vs. AST cycle number of the Pt/Vulcan catalyst is essentially identical for a voltage cycling AST conducted in either an RDE half-cell or an MEA configuration, suggesting that liquid electrolyte half-cell based ASTs can provide application-relevant results. Thus, our study points out a way for predicting the stability of electro-catalysts in MEAs based on RDE experiments that require less specialized equipment and only μg-quantities of catalysts.

Acid anion electrolyte effects on platinum for oxygen and hydrogen electrocatalysis

Platinum is an important material with applications in oxygen and hydrogen electrocatalysis. To better understand how its activity can be modulated through electrolyte effects in the double layer microenvironment, herein we investigate the effects of different acid anions on platinum for the oxygen reduction/evolution reaction (ORR/OER) and hydrogen evolution/oxidation reaction (HER/HOR) in pH 1 electrolytes. Experimentally, we see the ORR activity trend of HClO4 > HNO3 > H2SO4, and the OER activity trend of HClO4 [Formula: see text] HNO3 ∼ H2SO4. HER/HOR performance is similar across all three electrolytes. Notably, we demonstrate that ORR performance can be improved 4-fold in nitric acid compared to in sulfuric acid. Assessing the potential-dependent role of relative anion competitive adsorption with density functional theory, we calculate unfavorable adsorption on Pt(111) for all the anions at HER/HOR conditions while under ORR/OER conditions [Formula: see text] binds the weakest followed by [Formula: see text] and [Formula: see text]. Our combined experimental-theoretical work highlights the importance of understanding the role of anions across a large potential range and reveals nitrate-like electrolyte microenvironments as interesting possible sulfonate alternatives to mitigate the catalyst poisoning effects of polymer membranes/ionomers in electrochemical systems. These findings help inform rational design approaches to further enhance catalyst activity via microenvironment engineering.

Understanding the Crucial Significance of the Temperature and Potential Window on the Stability of Carbon Supported Pt-Alloy Nanoparticles as Oxygen Reduction Reaction Electrocatalysts

The present research provides a study of carbon-supported intermetallic Pt-alloy electrocatalysts and assesses their stability against metal dissolution in relation to the operating temperature and the potential window using two advanced electrochemical methodologies: (i) the in-house designed high-temperature disk electrode (HT-DE) methodology as well as (ii) a modification of the electrochemical flow cell coupled to an inductively coupled plasma mass spectrometer (EFC-ICP-MS) methodology, allowing for highly sensitive time- and potential-resolved measurements of metal dissolution. While the rate of carbon corrosion follows the Arrhenius law and increases exponentially with temperature, the findings of the present study contradict the generally accepted hypothesis that the kinetics of Pt and subsequently the less noble metal dissolution are supposed to be for the most part unaffected by temperature. On the contrary, clear evidence is presented that in addition to the importance of the voltage/potential window, the temperature is one of the most critical parameters governing the stability of Pt and thus, in the case of Pt-alloy electrocatalysts, also the ability of the nanoparticles (NPs) to retain the less noble metal. Lastly, but also very importantly, results indicate that the rate of Pt redeposition significantly increases with temperature, which has been the main reason why mechanistic interpretation of the temperature-dependent kinetics related to the stability of Pt remained highly speculative until now.

An electrochemical modification strategy to fabricate NiFeCuPt polymetallic carbon matrices on nickel foam as stable electrocatalysts for water splitting

Electrochemical modification is a mild and economical way to prepare electrocatalytic materials with abundant active sites and high atom efficiency. In this work, a stable NiFeCuPt carbon matrix deposited on nickel foam (NFFeCuPt) was fabricated with an extremely low Pt load (∼28 μg cm⁻²) using one-step electrochemical co-deposition modification, and it serves as a bifunctional catalyst for overall water splitting and achieves 100 mA cm⁻² current density at a low cell voltage of 1.54 V in acidic solution and 1.63 V in alkaline solution, respectively. In addition, a novel electrolyte was developed to stabilize the catalyst under acidic conditions, which provides inspiration for the development of highly efficient, highly stable, and cost-effective ways to synthesize electrocatalysts.

Multiple metal elements immobilized into a carbon matrix to fabricate an ultra-stable water splitting electrocatalyst by one-step electrochemical modification.

In situ electrochemical activation as a generic strategy for promoting the electrocatalytic hydrogen evolution reaction and alcohol electro-oxidation in alkaline medium

In situ electrochemical activation as a new pre-treatment method is extremely effective for enhanced electrocatalytic performances for different applications. With the help of this method, in situ surface modification of electrocatalyst is achieved without using pre-made seeds or complex synthesis procedure. Herein, with the purpose of finding an in situ and simple electrochemical activation protocol, the green synthesis of Au/Pd nanoparticles (AuPd) by means of polyoxometalate (POM) is reported. Structural analysis of the AuPd nanohybrid unveil the Au-core/Pd-shell structure which surrounded by POM. We propose a novel cathodic electrochemical activation in phosphate buffer solution which can greatly boost the electrocatalytic activity of the as-prepared AuPd and Pd electrocatalyst not only for hydrogen evolution reaction (HER) as a model of electro-reduction, but also for methanol and ethanol electro-oxidation reaction (MOR & EOR). For the HER in 1 M NaOH solution, after the electrochemical activation, the needed potential to drive a geometrical current density of 10 mA cm-2 significantly decreases from - 400 mV vs. the reversible hydrogen electrode (RHE) to -290 mV vs. RHE. For the EOR and MOR, electrochemically activated AuPd realized 3.4- and 2.9- fold increase in mass current density (mA mgPd -1) with respect to the pristine AuPd electrocatalyst, respectively.

Anisotropy of Pt nanoparticles on carbon- and oxide-support and their structural response to electrochemical oxidation probed by in situ techniques

Identifying the structural response of nanoparticle-support ensembles to the reaction conditions is essential to determine their structure in the catalytically active state as well as to unravel the possible degradation pathways. In this work, we investigate the (electronic) structure of carbon- and oxide-supported Pt nanoparticles during electrochemical oxidation by in situ X-ray diffraction, absorption spectroscopy as well as the Pt dissolution rate by in situ mass spectrometry. We prepared ellipsoidal Pt nanoparticles by impregnation of the carbon and titanium-based oxide support as well as spherical Pt nanoparticles on an indium-based oxide support by a surfactant-assisted synthesis route. During electrochemical oxidation, we show that the oxide-supported Pt nanoparticles resist (bulk) oxide formation and Pt dissolution. The lattice of smaller Pt nanoparticles exhibits a size-induced lattice contraction in the as-prepared state with respect to bulk Pt but it expands reversibly during electrochemical oxidation. This expansion is suppressed for the Pt nanoparticles with a bulk-like relaxed lattice. We could correlate the formation of d-band vacancies in the metallic Pt with Pt lattice expansion. PtOx formation is strongest for platelet-like nanoparticles and we explain this with a higher fraction of exposed Pt(100) facets. Of all investigated nanoparticle-support ensembles, the structural response of RuO2/TiO2-supported Pt nanoparticles is the most promising with respect to their morphological and structural integrity under electrochemical reaction conditions.

Platinum recycling through electroless dissolution under mild conditions using a surface activation assisted Pt-complexing approach

High industrial demand and limited global abundance of precious metals (PMs) make their recycling essential for industrial and societal sustainability. Owing to their high surface-to-volume ratio, recycling of nanoparticulate precious metals through dissolution in dilute acids at room temperature is quite relevant. However, their dissolution by approaches such as the cyclic oxidation-reduction of metal surfaces through surface potential manipulation may not be suitable for large-scale production. Here, we demonstrate fast dissolution of Pt-nanoparticles under mild conditions (normal temperature and pressure) in Cl- containing dilute acidic/neutral baths without using cyclic oxidation-reduction. We demonstrate that the dissolution of Pt nanoparticles through [PtClx]2- complexing is hindered by blockage of the Pt surface due to adsorption of non-oxide species (impurities), a phenomenon termed herein as non-oxide passivation (NOP). The nanoparticles can be kept active for the [PtClx]2- complexing through removal of the adsorbed species by surface activation, a process to remove the NOP layer by application of cyclic/continuous perturbation. As an example, average % dissolution rate (calculated on initial Pt loading) increases from ∼10% per h (∼30% dissolution in 3 h) for dissolution without NOP removal to ∼19% per h (∼55% dissolution in 3 h) for dissolution through cyclic activation of the Pt surface by HCl-water cycling. The approach may be implemented with a range of cost-efficient and non-toxic reagents for industrial-scale and environmentally friendly recycling of Pt.

Best Practice for Evaluating Electrocatalysts for Hydrogen Economy

Screening new electrocatalysts is key to the development of new materials for next-generation energy devices such as fuel cells and electrolyzers. The counter electrodes used in such tests are often made from materials such as Pt and Au, which can dissolve during testing and deposit onto test electrocatalysts, resulting in inaccurate results. The most common strategy for preventing this effect is to separate the counter electrode from the test material using an ion-transporting Nafion membrane. Here, we use X-ray photoelectron spectroscopy, energy-dispersive X-ray analysis, mass spectrometry, and voltammetry to demonstrate the limitations of this approach during constant-current, extended stability testing of electrocatalysts for H₂ evolution. We show that Nafion membranes cannot prevent contamination of carbon electrocatalysts by Pt and Au counter electrodes, leading to an apparent increase in the electrocatalytic activity of the carbon. We then demonstrate that carbon counter electrodes in undivided cells can contaminate and deactivate Pt and Au electrocatalysts for H₂ evolution. We show that use of a setup composed of a glass frit separating a carbon counter electrode from the test electrocatalyst can prevent these effects. Finally, we discuss these phenomena using H₂ evolution at MoS₂ and at a K₆[P₂W₁₈O₆₂](H₂O)₁₄/carbon nanotube composite as test reactions.

Electrocatalysis of Oxygen Reduction Reaction on Shape-Controlled Pt and Pd Nanoparticles-Importance of Surface Cleanliness and Reconstruction

Shape-controlled precious metal nanoparticles have attracted significant research interest in the recent past due to their fundamental and scientific importance. Because of their crystallographic-orientation-dependent properties, these metal nanoparticles have tremendous implications in electrocatalysis. This review aims to discuss the strategies for synthesis of shape-controlled platinum (Pt) and palladium (Pd) nanoparticles and procedures for the surfactant removal, without compromising their surface structural integrity. In particular, the electrocatalysis of oxygen reduction reaction (ORR) on shape-controlled nanoparticles (Pt and Pd) is discussed and the results are analyzed in the context of that reported with single crystal electrodes. Accepted theories on the stability of precious metal nanoparticle surfaces under electrochemical conditions are revisited. Dissolution, reconstruction, and comprehensive views on the factors that contribute to the loss of electrochemically active surface area (ESA) of nanoparticles leading to an inevitable decrease in ORR activity are presented. The contribution of adsorbed electrolyte anions, in-situ generated adsorbates and contaminants toward the ESA reduction are also discussed. Methods for the revival of activity of surfaces contaminated with adsorbed impurities without perturbing the surface structure and its implications to electrocatalysis are reviewed.

Pt-C Interfaces Based on Electronegativity-Functionalized Hollow Carbon Spheres for Highly Efficient Hydrogen Evolution

The hydrogen evolution reaction activity of carbon-supported Pt catalyst is highly dependent on Pt-C interfaces. Herein, we focus on the relationships between Pt activity and N/O-functionalized hollow carbon sphere (HCS) substrate in acidic media. The electrochemical dissolution of Pt counter electrode is performed to prepare Pt nanoparticles in low loading. The N groups are beneficial for homogeneously sized Pt nanoparticles, whereas the O groups lead to aggregated nanoparticles. Moreover, the proper electronegativity of the N groups may enable capturing of protons to create proton-rich Pt-C interfaces and transfer them onto the Pt sites. The O groups may also capture protons by hydrogen bonding, but the subsequent release of protons is more difficult due to a stronger electronegativity and result in an inferior Pt activity. Consequently, the N-doped HCS with a low Pt loading (1.7 μg cm^-2 and 0.05 wt %) possesses a higher intrinsic activity compared with Pt on O-doped HCS. Moreover, it outperforms the commercial 20% Pt/C with a stable operation for 12 h. This work may provide suggestions for constructing the advantageous Pt-C interfaces by proper functional groups for high catalytic efficiencies.

Environmentally and Industrially Friendly Recycling of Platinum Nanoparticles Through Electrochemical Dissolution-Electrodeposition in Acid-Free/Dilute Acidic Electrolytes

A process to recycle platinum from industrial waste, for example, spent catalysts from polymer fuel cells and electrolyzers, through potentiodynamic dissolution along with potentiostatic electrodeposition in dilute acidic/acid-free baths has been explored. During potentiodynamic dissolution, owing to Ostwald ripening, redeposition of the dissolved Pt species on source nanoparticles becomes significant, leading to lower overall dissolution efficiency. Alternatively, high concentrations of Pt-complexing agents (e.g., Cl^- ) are required to stabilize dissolved species through complex formation. The present process overcomes those limitations by removing the dissolved Pt species continuously through electrodepositing them in the form of Pt⁰ on another electrode. Such a process significantly promotes the overall reaction kinetics, and an increase in dissolution rate by a factor of two or more has been observed in non-complexing electrolytes. The process may be implemented for environmentally and industrially friendly recycling of Pt in dilute acidic/acid-free baths, thus eliminating the additional steps such as electrolyte upconcentration and post-dissolution reduction of dissolved Pt species.

In-situ electrochemical activation designed hybrid electrocatalysts for water electrolysis

Developing transition metal-based electrocatalysts with rich active sites for water electrolysis plays important roles in renewable energy fields. So far, some strategies including designing nanostructures, incorporating conductive support or foreign elements have been adopted to develop efficient electrocatalysts. Herein, we summarize recent progresses and propose in-situ electrochemical activation as a new pretreating technique for enhanced catalytic performances. The activation techniques mainly comprise facile electrochemical processes such as anodic oxidation, cathodic reduction, etching, lithium-assisted tuning and counter electrode electro-dissolution. During these electrochemical treatments, the catalyst surfaces are modified from bulk phase, which can tune local electronic structures, create more active species, enlarge surface area and thus improve the catalytic performances. Meanwhile, this technique can couple the atomic, electronic structures with electrocatalysis mechanisms for water splitting. Compared to traditional chemical treatment, the in-situ electrochemical activation techniques have superior advantages such as facile operation, mild environment, variable control, high efficiency and flexibility. This review may provide guidance for improving water electrolysis efficiencies and hold promising for application in many other energy-conversion fields such as supercapacitors, fuel cells and batteries.

Redox titration of gold and platinum surface oxides at porous microelectrodes

Cavity-microelectrodes were used to investigate surface oxides on supported platinum nanoparticles and nanoporous gold with the surface interrogation mode of scanning electrochemical microscopy.

Limits of Detection and Quantification of Electrochemical Quartz-Crystal Nanobalance in Platinum Electrochemistry and Electrocatalysis Research

The electrochemical quartz-crystal nanobalance has been used in electrochemistry research for over three decades. It provides an atomic/molecular level insight into the nature of interfacial electrochemical phenomena by measuring in situ mass changes on the nanogram scale. The sensitivity of this technique remains unknown because there have been no attempts to determine its limits of detection (LOD) or quantification (LOQ). We propose an experimental approach for determining the values of LOD and LOQ for Pt electrodes in aqueous H₂SO₄ solutions that employs cyclic voltammetry and frequency variation measurements. However, this methodology is also appropriate to other electrode materials and electrolytes. The LOD and LOQ values depend on the electrolyte concentration and decrease (i.e., the sensitivity increases) as the concentration decreases. Knowledge of the LOD and LOQ values determines the applicability of this technique in research on the oxidation and degradation of Pt catalysts employed in fuel cells.

In-Situ Platinum Deposition on Nitrogen-Doped Carbon Films as a Source of Catalytic Activity in a Hydrogen Evolution Reaction

Copolymer-templated nitrogen-doped carbon (CTNC) films deposited on glassy carbon were used as electrodes to study electrochemically driven hydrogen evolution reaction (HER) in 0.5 M H2SO4. The activity of these materials was extremely enhanced when a platinum counter electrode was used instead of a graphite rod and reached the level of commercial Pt/C electrodes. Postreaction scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) measurements of electrode surfaces revealed that incorporation of even extremely low amounts of Pt resulted in this considerable gain of HER activity. High resolution XPS analysis and density functional theory (DFT) calculations confirmed that pyridinic nitrogen atoms act as active sites for Pt coordination and deposition. The Pt can be incorporated in both molecular (Pt(2+)) and metallic (Pt(0)) form. This study shows that great caution must be taken when designing "metal-free" HER catalysts based on N-doped carbons.

Reconstruction and dissolution of shape-controlled Pt nanoparticles in acidic electrolytes

Reconstruction and dissolution of shape-controlled Pt nanoparticles in acidic electrolytes.

The Stability Challenge on the Pathway to Low and Ultra-Low Platinum Loading for Oxygen Reduction in Fuel Cells

We report the influence of catalyst loading on rates of platinum degradation in acidic electrolyte at room temperature. A piezoelectric printer is used to deposit spotted arrays of a commercially available catalyst comprised of Pt nanoparticles on a porous carbon support. The kinetically controlled oxygen reduction reaction (ORR) activity at different loadings is measured using an electrochemical scanning flow cell (SFC), and found to be quite stable over the range of loadings studied. This behaviour, however, contrasts sharply with rates of both transient and quasi‐steady‐state platinum dissolution. These are shown using downstream inductively coupled plasma mass spectrometry (ICP‐MS) analytics, to increase as loading becomes lower. This dichotomy between activity and stability has direct implications for the development of improved catalyst materials, as well as for the achievement of current targets for reduced loadings of noble metals for fuel cells and other energy storage devices.