Chronopotentiometric Measurements Research Articles

Transfer of Sodium Ion across Interface between Na+-Selective Electrode Membrane and Aqueous Electrolyte Solution: Can We Use Nernst Equation If Current Flows through Electrode?

Electrochemical impedance and chronopotentiometric measurements with Na+-selective solvent polymeric (PVC) membranes containing a neutral ionophore and a cation exchanger revealed low-frequency resistance, which is ascribed to Na+ ion transfer across the interface between the membrane and aqueous solution. The attribution is based on the observed regular dependence of this resistance on the concentration of Na+ in solutions. The respective values of the exchange current densities were found to be significantly larger than the currents flowing through ion-selective electrodes (ISEs) during an analysis in non-zero-current mode. This fact suggests that the interfacial electrochemical equilibrium is not violated by the current flow and implies that the Nernst equation can be applied to interpret the data obtained in non-zero-current mode, e.g., constant potential coulometry.

Cation-Selective Actuator-Sensor Response of Microcrystalline Cellulose Multi-Walled Carbon Nanotubes of Different Electrolytes Using Propylene Carbonate Solvent.

Microcrystalline cellulose (MC) with 50 wt.% multi-walled carbon nanotube (MCNT) composites is obtained through extrusion, forming MC-MCNT fiber. In this study, we concentrate on three different electrolytes in propylene carbonate (PC) which have the same anions (TF-, trifluoro-methanesulfonate CF3SO3-) but different cations, EDMI+ (1-ethyl-2,3-dimethylimidazolium), Li+ (lithium ion), and TBA+ (tetrabutylammonium). Cyclic voltammetry and square wave potential steps, in combination with linear actuation measurements in a potential range of 0.7 V to -0.2 V, were conducted. Our goal in this work was to establish a cation-selective actuator-sensor device capable of distinguishing different cations. The linear actuation of MC-MCNT fiber had its main expansion at discharge due to the incorporation of TF- in the MC-MCNT fiber with the cations. In the following order, TBA+ > EDMI+ > Li+ had the best stress, strain, charge density, diffusion coefficients, and long-term stability. Chronopotentiometric measurements revealed that the cations in the PC solvent can be differentiated by their ion sizes. Further characterization of the MC-MCNT fiber was completed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and FTIR and Raman spectroscopy.

INFLUENCE OF THE POSITIVE ELECTRODE PROPERTIES ON THE ACTIVATION TIME OF THE RESERVE CHEMICAL POWER SOURCES OF THE SYSTEM LEAD – PERCHLORIC ACID – LEAD DIOXIDE

The influence of the positive electrode properties on the activation time of the reserve chemical power sources of the system lead – perchloric acid – lead dioxide has been studied. Coatings of cathodes with lead dioxide obtained under various conditions are characterized by scanning electron spectroscopy, X-ray spectral microanalysis, X-ray photoelectron spectroscopy, standard contact porosimetry. The improvement of the performance characteristics of power sources including the ensuring of a short time of their activation at a low temperature has been shown to be possible with the use of a nanoporous coating of lead dioxide. To estimate the applicability of cathodes for the manufacture of power sources having minimal activation time a diagnostic principle has been used that it based on testing of cathodes by the method of chronopotentiometric measurements during galvanostatic discharge. Pilot industrial samples of small-sized reserve power sources of the mentioned electrochemical system with unprecedented short activation time (less than 30 ms at temperarure –50°С) were manufactured and tested.

Enhanced Hydrogen Evolution Performance of Ni−Mo-Based Electrocatalysts in Seawater by Controlling Surface Wettability

Environmental pollution and global warming have become enormous problems all over the world. At the United Nations Climate Change Conference, carbon neutrality was proposed as a way to solve this problem through the Paris Agreement in 2015. To achieve zero net carbon dioxide emissions, research on how to obtain energy from renewable energy resources has been intensively conducted. Among various candidates of renewable chemical fuels, green H2, produced by water electrolysis is considered as one of the promising, next generation chemical fuels.Almost 97% of earth’s water resources exist as seawater. Moreover, seawater has an advantage that it can be used as an electrolyte owing to the various ions, existing naturally. Therefore, one of the ultimate goals in green H2 generation is to directly utilize seawater as the electrolyte source.Although Pt-group materials (PGMs) are well known catalysts in hydrogen evolution reaction (HER) but one of the main challenges for wide commercialization with PGMs is its high cost and scarcity. In order to overcome this issue, research on HER catalysts using non-PGM (NPGM) has been intensively performed. Among various NPGM elements, Ni−Mo has great potential for electrocatalysts in HER owing to its cost effectiveness as well as their high electrocatalytic activities in wide pH range of electrolytes. It is well known that not only the electrocatalytic activity in HER, mainly originating from chemical compositions at the surface, but also the physical surface properties, especially the surface wettability, play an important role to regulate the electrocatalytic performance. The evolved bubbles by the HER form the solid−gas−liquid interfaces, which results in the turn-off of the active sites toward electrochemical reactions until the gas bubbles remove from the electrocatalytic surface. Previous studies reveal that this dynamic, evolutionary behavior of surface active sites by the bubble growth/departure significantly influence the electrocatalytic performance.Herein, we demonstrate the Ni−Mo-based material as the electrocatalyst toward HER in simulated seawater, which is 0.5 M phosphate buffer with 0.6 M NaCl. The electrocatalytic layers are deposited by simple electrodeposition with the aminated graphene oxide (aGO) to form composites (aGO/NiMo). The addition of aGO in Ni−Mo does not influence the electrocatalytic activity in HER, exhibiting nearly the same cyclic voltammograms with pure NiMo. Interestingly, the long-term performance of aGO/NiMo, however, is observed when compared to the pure NiMo. The enhanced durability by chronopotentiometric measurements in the aGO/NiMo is ascribed to the improved surface wettability, originating from added aGO. The images taken by high-speed camera clearly show that the H2 bubbles with smaller sizes at the surface of aGO/NiMo but much larger density than the ones at pure NiMo are observed. These phenomena denotes that the regeneration rate of active sites by bubbles departure from the surface is much higher in the aGO/NiMo than NiMo without aGO, indicating that the aGO is beneficial for improving the surface wettability. The longer residence of H2 bubbles at the pure NiMo increases the actual overpotential applied in the single active site under constant current density, leading to the faster degradation of electrocatalytic activity in HER. The physical properties of surface between aGO/NiMo and NiMo for surface wettability is also supported by surface roughness measurements in atomic force microscope and contact angles. Our study contributes to the fundamental design of the physical properties of electrocatalytic surfaces physical properties, thereby simply improving the electrochemical performance in HER.

A novel Ni3S2/MnO2@N,F-CQDs composite with spherical-chain-like morphology for efficient oxygen evolution reaction in aqueous alkaline solutions

Developing earth-abundant transition metal-based oxygen evolution reaction (OER) electrocatalysts is extremely essential for accomplishing efficient electrocatalytic overall water splitting. Herein, we synthesized a Ni3S2/MnO2@N,F-CQDs catalyst with a microstructure composed of interlaced nanowires in a spherical-chain shape by treating a nickel foam substrate with sulfur and co-regulating the morphology and properties of manganese dioxide with carbon dots. The catalyst exhibited excellent OER electrocatalytic performance and stability under alkaline conditions, requiring only a low overpotential of 226 mV at 10 mA cm-2 and a Tafel slope of 105.76 mV dec-1. Furthermore, the catalyst remained stable after 3000 cycles of Cyclic Voltammetry (CV) testing and multistep chronopotentiometric (CP) measurements at the current density of 10, 50 and 100 mA cm−2 for 12 h, respectively. The enhanced performance of Ni3S2/MnO2@N,F-CQDs catalyst was mainly attributed to the practical improvement of charge interface transport performance induced by carbon dots and interface layer Ni3S2 which increased active catalytic sites of the electrode and reduced charge transfer resistance. These results suggest a promising approach for developing efficient OER electrocatalysts.

Bridging Colloidal and Electrochemical Nanoparticle Growth with In Situ Electrochemical Measurements.

ConspectusProspective applications involving the electrification of industrial chemical processes and electrical energy to chemical fuels interconversion as part of the energy transition to renewable energy sources have led to an increasing need for highly tailored nanostructures immobilized on electrode surfaces. Control of surface facet structure across material compositions is of particular importance for ensuring performance in such applications. Colloidal methods for producing shaped nanoparticles in solution are abundant, particularly for noble metals. However, significant technical challenges remain with respect to rationally designing syntheses for the novel compositions and morphologies required to sustainably enable the above technological advances as well as in developing methods for uniformly and reproducibly dispersing colloidally synthesized nanostructures on electrode surfaces. The direct synthesis of nanoparticles on electrodes using chemical reduction approaches remains challenging, though recent advances have been made for certain materials and structures. Electrochemical nanoparticle synthesis─where an applied current or potential instead of a chemical reducing agent drives the redox chemistry of nanoparticle growth─is poised to play an important role in advancing the fabrication of nanostructured electrodes. Specifically, this Account focuses on the colloidal-inspired design of electrochemical syntheses and the interplay between colloidal and electrochemical approaches in terms of understanding the fundamental chemical reaction mechanisms of nanoparticle growth. An initial discussion of the development of electrochemical particle syntheses that incorporate colloidal synthetic tools highlights the promising emergent capabilities that result from blending these two approaches. Furthermore, it demonstrates how existing colloidal syntheses can be directly translated to electrochemical growth on a conductive surface using real-time electrochemical measurements of the chemistry of the growth solution. Measuring the open circuit potential of a colloidal synthesis over time and then replicating that measured potential during electrochemical deposition leads to the formation of the same nanoparticle shape. These in situ open circuit and chronopotentiometric measurements also give fundamental insight about the changing chemical environment during particle growth. We highlight how these time-resolved electrochemical measurements, as well as correlated spectroelectrochemical monitoring of particle formation kinetics, enable the extraction of information regarding mechanisms of particle formation that is difficult to obtain using other approaches. This information can be translated back into colloidal synthesis design via a directed, intentional approach to synthetic development. We additionally explore the added flexibility of synthetic design for methods involving electrochemically driven reduction as compared to the use of chemical reducing agents. The Account concludes with a brief perspective on potential future directions in both fundamental studies and synthetic development enabled by this emerging integrated electrochemical approach.

Ion‐selectivity of polypyrrole carbide‐derived carbon films in aqueous electrolytes

AbstractIn this work, we have combined polypyrrole (PPy) doped with dodecylbenzene sulfonate (DBS−) and carbide‐derived carbon (CDC), forming PPyCDC (PPy/DBS‐CDC) composites. Scanning electron microscopy revealed for PPyCDC that most CDC particles are located on the surface of the films. This work's main goal is to investigate the ion‐selectivity of the novel PPyCDC composite by linear actuation studies, with primary actuation taking place at discharging. Four different aqueous electrolytes are applied with hydrophobic cations, such as TMA+ (tetramethylammonium ion) and EDMI+ (1‐ethyl‐2,3‐dimethyl imidazolium ion). They are hydrophilic with Li+ (lithium‐ion) and Na+ (sodium ion). It was possible to distinguish each cation from linear actuation studies, either cyclic voltammetry or square wave potential steps. In the case of pristine PPy/DBS, that ion differentiation could not separate. Chronopotentiometric measurements of both films (PPyCDC and PPy/DBS) were performed. It could control (read) the strain for PPyCDC films and the potential at constant current density. The electrical energy adapts to exchange cations, forming a sensor device with ion‐selectivity of the applied cations considering their hydrophilic and hydrophobic characteristics. The best specific capacitance (energy storage) is found for EDMI+ cations in PPyCDC films with 193 F g−1, enabling this composite in multifunctional applications.

Electrolyte contribution to the multifunctional response of cellulose carbon nanotube fibers

Flexible wearable multifunctional devices such as cellulose loaded with electroactive components are in the focus of modern research for electrochemical energy storage, sensors and actuators. In this report, the multifunctional response of cellulose with 50 wt% MWCNT formed into Cell-CNT composite fibers is demonstrated. The effect of (aqueous) electrolyte choice on the electro-mechanical response of Cell-CNT was studied. Aqueous electrolytes such as tetramethylammonium chloride (TMACl), sodium perchlorate (NaClO4), and 1-ethyl-2,3-dimethylimidazolium trifluoromethanesulfonate (EDMITF) were considered, with the resulting stress and strain decreasing in the order Cl− > ClO4− > TF−, matching the order of the size of the ions. Upon negative charging, the cations of the electrolytes showed electromechanical response in the order: TMA+ > EDMI+ > Na+, where the solvation strength of the cations had stronger influence than their size without solvation shell. The highest specific capacitance was shown by TMACl in the range of 74 mF cm−2 upon positive charging, with also the best retention of capacitance of 86% in long-term measurements. Chronopotentiometric measurements of Cell-CNT fibers where conducted to evaluate if the composites can also act as sensors for different electrolytes. The Cell-CNT fibers were characterized with scanning electron microscopy, energy dispersive X-ray, FTIR and Raman spectroscopy.

Carbon composite thermoplastic electrodes integrated with mini-printed circuit board for wireless detection of calcium ions.

Here, a smartphone-based portable sensing system is developed for real-time detection of Ca2+ ions in a variety of biofluids. A solid-contact calcium-selective electrode (Ca2+-ISE) consisting of anion-selective membrane (ISM), carbon black nanomaterial and polystyrene-graphite nanoplatelets as a solid contact was fabricated. The polyvinylchloride (PVC)-based ISM was optimized using different plasticizers and ion-exchangers. Under optimized conditions, the solid contacts were electrochemically characterized byelectrochemical impedance spectroscopy(EIS), chronopotentiometric andpotentiometric measurements. The Ca2+-ISE showed a Nernst response with a slope of 31.2 ± 0.6mV/decade in the concentration range from 0.1M to 10-4M Ca2+ with a limit of detection (LOD) of 1.0 × 10-5M. In addition, the ISEs exhibited good selectivity to Ca2+ ions over various interfering electrolytes and metabolites. The Ca2+-ISEs were applied in human urine and, artificial serum and cerebrospinal fluid samples. The ISEs showed good recoveries between 90 and 105%, indicating potential applicability of these electrodes in biological fluids. The portable lab-made potentiometer provides wireless data signaling and transmission to a smartphone and final Ca2+ concentration display due to its customized software. Therefore, the developed smartphone-based sensing platform offers low cost (< $25), rapid, user-friendly detection of Ca2+ especially in resource-limited areas.

Tuning the linear actuation of multiwall carbon nanotube fibers with carbide-derived carbon

Fibers made from carbon nanotubes (CNT) have received a lot of attention, including for the intended applications in “artificial muscles”. Combination of CNT fibers with high capacitance particles such as carbide-derived carbon (CDC) is the focus of this research. A dielectrophoretic method was used to form novel CNT-CDC fibers with different wt% of CDC from 25% to 75%. The CNT-CDC fibers were compared to pristine CNT fibers in their electromechanical response to different electrochemical driving regimes (cyclic voltammetry, square wave potential steps) in an organic electrolyte. The best performance in strain and stress was achieved by CNT-CDC(50%) with nearly double charge density and 1.5 times higher electronic conductivity in comparison to pristine CNT fibers. The determination of the specific capacitance over chronopotentiometric measurements revealed 175 F g−1 (0.54 A g−1) for CNT-CDC(75%) fibers, while the best stability and charging durability was shown by CNT-CDC(50%). The CNT-CDC fibers demonstrated consistent dual functionality for potential applications in linear actuators, supercapacitors or in multifunctional designs.

Role of Polyoxometalate Contents in Polypyrrole: Linear Actuation and Energy Storage.

A combination of polyoxometalates with polypyrrole is introduced in this work. Our goal was to include phosphotungstic acid (PTA) in different molar concentrations (0.005, 0.01, and 0.05 M) in the electropolymerization of pyrrole doped with dodecylbenzene sulfonate (DBS) and phosphotungstinates (PT), forming PPy/DBS-PT films. Scanning electron microscopy (SEM) revealed that the PPy/DBS-PT films became denser and more compact with increasing PTA concentrations. The incorporation of PT in PPy/DBS was analyzed using Fourier-transform infrared (FTIR) and energy dispersive X-ray (EDX) spectroscopy. The linear actuation in cyclic voltammetry and potential square wave steps in an organic electrolyte revealed increasing mixed actuation, with major expansion upon oxidation found for PPy/DBS-PT films with a PTA concentration of 0.005 M. Best results of a strain of 12.8% and stress at 0.68 MPa were obtained for PPy/DBS-PT (0.01 M). The PPy/DBS-PT films polymerized in the presence of 0.05 M of PTA and showed main expansion upon reduction, changing the actuation direction. Chronopotentiometric measurements of PPy/DBS-PT samples were conducted to determine the specific capacitance optimal for a 0.01 M PTA concentration in the range of 80 F g−1 (±0.22 A g−1).

Enhancing catalytic activity of NdFeO3 perovskite by tuning A-site cation deficiency for oxygen evolution reaction

Electrochemical water splitting got much attention because of its great promising electrochemical technology to generate sustainable and renewable energy resources. In this aim, we have prepared a novel series of electrocatalysts Nd1-xFeO3 (x = 0.0, 0.05, 0.1, 0.15) by sol-gel method. The effect of the deficiency in the A-site on the structure, morphology, surface and electrocatalytic activity of these perovskites were studied by means of XRD, XPS, MEB, LSV, EIS and chronopotentiometric measurements. Among all the samples, Nd0.9FeO3 (denoted NF10) exhibits the higher catalytic activity with a low overpotential of 370 mV at a current density of 10 mA cm−2, a small Tafel slope of 79 mV dec−1 and a good electrochemical stability in 1 M KOH solution. The OER performance of NF10 can be effectively enhanced by optimizing iron valence and highly oxidative oxygen species (O22−/O−) based on the surface of catalyst. The results of this study indicate that the NF10 electrocatalyst can be considered as a good candidate for the OER in alkaline media.

Dual function composite fibers of cellulose with activated carbon aerogel and carbide derived carbon

AbstractPolymers of natural origin, especially cellulose, have risen to the focus of smart materials, and also energy storage materials' research as sustainable matrix alternatives. In this work, novel composites of cellulose with activated carbon aerogel (ACA) and carbide‐derived carbon (CDC) are demonstrated. The composites were formulated as fibers from regenerated cellulose (Cell). The electromechanical response as linear actuation in stress and strain of the fibers was studied in an organic electrolyte at low applied potentials in range of 0.55 to −0.8 V. Cyclic voltammetry and square wave potential steps were performed revealing for both composite fibers expansion at positive charging. The Cell‐ACA fibers showed a stronger response compared with Cell‐CDC, largely due to the particle structure, reflected in higher electronic conductivity. The chronopotentiometric measurements showed that Cell‐ACA also had the higher specific capacitance of the two of 47.5 F g−1. The dual‐function of Cell‐ACA and Cell‐CDC of electromechanical activity and energy storage capability can have potential in smart clothing applications.

Polypyrrole with Phosphor Tungsten Acid and Carbide-Derived Carbon: Change of Solvent in Electropolymerization and Linear Actuation.

Linear actuators based on polypyrrole (PPy) are envisaged to have only one ion that triggers the actuation direction, either at oxidation (anion-driven) or at reduction (cation-driven). PPy doped with dodecylbenzenesulfonate (PPy/DBS) is the most common applied conducting polymer having cation-driven actuation in aqueous solvent and mainly anion-driven actuation in an organic electrolyte. It is somehow desired to have an actuator that is independent of the applied solvent in the same actuation direction. In this research we made PPy/DBS with the addition of phosphorus tungsten acid, forming PPyPT films, as well with included carbide derived carbon (CDC) resulting in PPyCDC films. The solvent in electropolymerization was changed from an aqueous ethylene glycol mixture to pure EG forming PPyPT-EG and PPyCDC-EG composites. Our goal in this study was to investigate the linear actuation properties of PPy composites applying sodium perchlorate in aqueous (NaClO4-aq) and propylene carbonate (NaClO4-PC) electrolytes. Cyclic voltammetry and square potential steps in combination with electro-chemo-mechanical-deformation (ECMD) measurements of PPy composite films were performed. The PPyPT and PPyCDC had mixed ion-actuation in NaClO4-PC while in NaClO4-aq expansion at reduction (cation-driven) was observed. Those novel PPy composites electropolymerized in EG solvent showed independently which solvent applied mainly expansion at reduction (cation-driven actuator). Chronopotentiometric measurements were performed on all composites, revealing excellent specific capacitance up to 190 F g−1 for PPyCDC-EG (best capacitance retention of 90 % after 1000 cycles) and 130 F g−1 for PPyPT-EG in aqueous electrolyte. The films were characterized by scanning electron microscopy (SEM), Raman, Fourier-transform infrared (FTIR) and energy dispersive X-ray spectroscopy (EDX).

Solvent Effect in Imidazole-Based Poly(Ionic liquid) Membranes: Energy Storage and Sensing.

Polymerized ionic liquids (PILs) are interesting new materials in sustainable technologies for energy storage and for gas sensor devices, and they provide high ion conductivity as solid polymer electrolytes in batteries. We introduce here the effect of polar protic (aqueous) and polar aprotic (propylene carbonate, PC) electrolytes, with the same concentration of lithium bis(trifluoromethane) sulfonimide (LiTFSI) on hydrophobic PIL films. Cyclic voltammetry, scanning ionic conductance microscopy and square wave voltammetry were performed, revealing that the PIL films had better electroactivity in the aqueous electrolyte and three times higher ion conductivity was obtained from electrochemical impedance spectroscopy measurements. Their energy storage capability was investigated with chronopotentiometric measurements, and it revealed 1.6 times higher specific capacitance in the aqueous electrolyte as well as novel sensor properties regarding the applied solvents. The PIL films were characterized with scanning electron microscopy, energy dispersive X-ray, FTIR and solid state nuclear magnetic resonance spectroscopy.

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Synchronization Patterns of Two Coupled Oscillators in a Closed Electrochemical Bipolar Cell

We investigate the dynamical behavior of the oscillatory electrodissolution of two nickel and hydrogen reduction reaction in a closed electrochemical bipolar cell. In the bipolar setup, two half U cells are separated by an epoxy plate with two embedded nickel wires; the oxidation and reduction reactions take place at the two ends of the same wire. By tuning the concentration of electrolyte in the anode and cathode compartments, the current level and the dynamics of the oscillatory range can be varied without any external resistance. Phase analysis of the chronopotentiometric measurements showed that the potential oscillations of the two nickel anodes are completely in-phase synchronized, and thus strongly coupled, when 1.00 mm diameter electrodes were employed. The complete in-phase synchronization and strong coupling effect was lost as the electrode diameter was decreased from 1.00 mm to 0.25 mm. The synchronization effects were interpreted by the charge transfer resistance of the hydrogen reduction reaction as the main coupling element in the cell. The experiments demonstrate the use of bipolar electrochemical cells for the investigation of coupling and synchronization in chemical oscillatory processes.

The Origin of the Non-Constancy of the Bulk Resistance of Ion-Selective Electrode Membranes within the Nernstian Response Range.

The dependence of the bulk resistance of membranes of ionophore-based ion-selective electrodes (ISEs) on the composition of mixed electrolyte solutions, within the range of the Nernstian potentiometric response, is studied by chronopotentiometric and impedance measurements. In parallel to the resistance, water uptake by the membranes is also studied gravimetrically. The similarity of the respective curves is registered and explained in terms of heterogeneity of the membranes due to the presence of dispersed aqueous phase (water droplets). It is concluded that the electrochemical equilibrium is established between aqueous solution and the continuous organic phase, while the resistance refers to the membrane as whole, and water droplets hamper the charge transfer across the membranes. In this way, it is explained why the membrane bulk resistance is not constant within the range of the Nernstian potentiometric response of ISEs.

Membrane-Less Ethanol Electrooxidation over Pd-M (M: Sn, Mo and Re) Bimetallic Catalysts

The effect of the addition of three oxophilic co-metals (Sn, Mo and Re) on the electrochemical performance of Pd in the ethanol oxidation reaction (EOR) was investigated by performing half-cell and membrane-less electrolysis cell experiments. While the additions of Sn and Re were found to improve significantly the EOR performance of Pd, Mo produced no significant promotional effect. When added in significant amounts (50:50 ratio), Sn and Re produced a 3–4 fold increase in the mass-normalized oxidation peak current as compared to the monometallic Pd/C material. Both the electrochemical surface area and the onset potential also improved upon addition of Sn and Re, although this effect was more evident for Sn. Cyclic voltammetry (CV) measurements revealed a higher ability of Sn for accommodating OH- species as compared to Re, which could explain these results. Additional tests were carried out in a membrane-less electrolysis system. Pd50Re50/C and Pd50Sn50/C both showed higher activity than Pd/C in this system. Chronopotentiometric measurements at constant current were carried out to test the stability of both catalysts in the absence of a membrane. Pd50Sn50/C was significantly more stable than Pd50Re50/C, which showed a rapid increase in the potential with time. Despite operating in the absence of a membrane, both catalysts generated a high-purity (e.g., 99.99%) hydrogen stream at high intensities and low voltages. These conditions could lead to significant energy consumption savings compared to commercial water electrolyzers.

Interfacial Leveler-Accelerator Interactions in Cu Electrodeposition

We investigate the effect of amine-based leveler additives on the catalytic function of the accelerator at the Cu-electrolyte interface. In the presence of the bis-(sodium sulfopropyl)-disulfide (SPS) accelerator, chronopotentiometric measurements show the potential changes from inhibition of the levelers increased with molecular weight and were greater to those of glycol-based suppressors. In situ surface-enhanced Raman spectroscopy (SERS) revealed significant conformational changes of the surface-adsorbed SPS in the presence of the amine-based levelers. This leveler-induced conformational perturbation of SPS diminishes the activity of SPS. SERS also revealed decreased coverages of surface-adsorbed SPS in the presence of the high molecular weight amine-based levelers at negative potentials, indicating that the leveler limits direct contact of SPS with the surface. Decreased coverages were also found for adsorbed chloride in the presence of all levelers considered, likely contributing to the deactivation of the accelerative effect of SPS. Secondary-ion mass spectrometry (SIMS) analysis of Cu electrodeposited from solutions comprised of a linear polyethyleneimine (PEI), SPS, and Cl– show increased S, Cl, and C content in the deposit relative to solutions absent PEI, indicating the presence of PEI results in co-incorporation of these additives. This leveler-assisted incorporation of SPS and Cl– also serves to mitigate SPS acceleration.