Prolonged Potential Cycling Research Articles

Differences in the electrochemical behavior of Vulcan XC-72 carbon black and glassy carbon after prolonged potential cycling

The electrochemical characteristics of a carbon carrier play an important role in catalyst investigations. The evolution of the electrochemical characteristics of Vulcan XC-72 carbon black and a glassy carbon disk electrode was studied under prolonged electrochemical action. The electrochemical action was performed by repeated application of a sawtooth periodic potential to the electrodes in the range from 0.05 to 1 V vs. RHE and back at a scan rate of 50 mV/s. The EDL charging current, the cyclic current–voltage curves, the equilibrium electrode potential, and the dissolved oxygen reduction current in potentiostatic mode at 0.05 V vs. RHE were recorded periodically. Carbon black was characterized by helium pycnometry, SEM, TEM, X-ray diffraction, and Raman spectroscopy. The currents on the carbon black were several orders of magnitude higher than those on the glassy carbon. The differences in the dynamics of electrochemical characteristics are discussed.

Comparing Different Nanoparticles Protecting Layers That Can Slow Down the Degradation of Pd-Ni Based Catalyst during Hydrogen Oxidation Reaction (HOR) in Alkaline Media

Alkaline fuel cell (AFC) technology has several advantages over the mature Proton exchange membrane fuel cell (PEMFC), notably its low cost, coming from the use of non-Pt catalysts. [1] Gencell Energy is one of the very few companies that invest in AFC, with a specialty on membraneless AFC that can be used at extreme weather condition without compromising their lifetime and efficiency, where it is impossible to use PEMFC. The 6.6 M KOH electrolyte of membraneless AFC drive is a key to its robustness [2,3], but it is a highly corrosive environment, in which the HOR catalyst on the anode side can deactivate. Based on previously reports, Pd-Ni is a good candidate for HOR in high pH compared to Pt-based catalysts [4,5]. Yet, after long-term operation, Pd-Ni still suffer severe particle detachment and passivation. To increase the durability of such catalyst, forming a protecting layer that covers the nanoparticle is necessary, without hindering the HOR activity. [6,7] This work presents a variety of protecting layers that cover the Pd-Ni particles to slow down the degradation. An example of HOR activity for one of the Pd-Ni capped is presented in Figure 1. The Pd-Ni capped generation 1 (G1)/ Vulcan XC72 needs an activation using prolonged potential cycling in Ar (typically 300 CVs from 0.1-1.23 V vs. RHE, 100 mV/s). Once the catalyst is fully activated, accelerated stress tests (AST) are performed up to 3300 cycles to track the durability of the catalyst. As shown, after 21 AST runs (which corresponds to 3150 CVs), the catalyst still maintains its HOR activity. It will be shown that different cover layers (varying in type and thickness of the cover) enable to modulate the materials’ activation and durability. In any case, the HOR activity and rate of degradation of Pd-Ni with different protecting layers is tracked using IL-TEM, XRD and XPS pre and post AST.(1) Simon, C.; Hanzlik, M.; Gasteiger, H. A.; Schuler, T.; Durst, J.; Siebel, A.; Hasche, F.; Herranz, J.; Rheinlander, P. J. Hydrogen Oxidation and Evolution Reaction (HOR/HER) on Pt Electrodes in Acid vs. Alkaline Electrolytes: Mechanism, Activity and Particle Size Effects. ECS Trans. 2014, 64 (3), 1069–1080.(2) Gülzow, E. Alkaline Fuel Cells. Fuel Cells 2004, 4 (4), 251–255.(3) Gouérec, P.; Poletto, L.; Denizot, J.; Sanchez-Cortezon, E.; Miners, J. H. The Evolution of the Performance of Alkaline Fuel Cells with Circulating Electrolyte. J. Power Sources 2004, 129 (2), 193–204.(4) Sankar, S.; Anilkumar, G. M.; Tamaki, T.; Yamaguchi, T. Binary Pd−Ni Nanoalloy Particles over Carbon Support with Superior Alkaline Formate Fuel Electrooxidation Performance. ChemCatChem 2019, 11 (19), 4731–4737.(5) Zhao, Y.; Wang, G.; Xiao, L.; Lu, J.; Zhuang, L. Hydrogen Oxidation Reaction on Pd-Ni(OH)2 Composite Electrocatalysts in an Alkaline Electrolyte. ChemistrySelect 2020, 5 (26), 7803–7807.(6) Yang, Y.; Sun, X.; Han, G.; Liu, X.; Zhang, X.; Sun, Y.; Zhang, M.; Cao, Z.; Sun, Y. Enhanced Electrocatalytic Hydrogen Oxidation on Ni/NiO/C Derived from a Nickel-Based Metal–Organic Framework. Angew. Chemie - Int. Ed. 2019, 58 (31), 10644–10649.(7) Gao, Y.; Peng, H.; Wang, Y.; Wang, G.; Xiao, L.; Lu, J.; Zhuang, L. Improving the Antioxidation Capability of the Ni Catalyst by Carbon Shell Coating for Alkaline Hydrogen Oxidation Reaction. ACS Appl. Mater. Interfaces 2020, 12 (28), 31575–31581. Figure 1

Interfacing perovskite strontium molybdate to molybdenum disulfide nanoplatelts for boosting HER from water

Due to low hydrogen adsorption free energy at the edges of 2D-MoS2 layered sheets, nanostructured MoS2 materials recently are assigned to prospective electrocatalysts for hydrogen evolution reaction (HER) from water. However, the efficiency and stability of HER onto the MoS2 designed on the conductive substrates are poor. To significantly increase the number of active sites and achieve a long-time working stability, the design of hybrid-type electrodes is crucial. Here, we report the synthesis of a new hybrid material composed of molybdenum disulfide and molybdenum oxides heterostructured with strontium molybdate. For this, a facile one-pot hydrothermal process was developed directly onto the TiO2 nanotube carpet substrate. The interfacing of strontium molybdate at the electrode substrate verified by X-ray photoelectron spectroscopy and Time of flight secondary ions mass spectrometry (ToF SIMS) techniques. Considerable higher catalytic activity at the surface of this hybrid film, with the onset potential of 190 mV vs RHE and a Tafel slope of 66 mV dec−1 attaining ~80 mA cm−2 at 0.35 V overvoltage was ascertained. Exciting HER stability in comparison with the pure synthetic MoS2 was verified by a prolonged potential cycling from 0.05 to −0.35 V versus RHE potential and 45 h continuous HER processing at a constant current density.

Differences in electrochemical response of prospective anticancer drugs IPBD and Cl-IPBD, doxorubicin and Vitamin C at plasmid modified glassy carbon

For the comparison of the DNA interactions with drugs, two newly synthesized prospective anticancer drugs, 6-(1H-imidazo[4,5-b]phenasine-2-yl)benzene-1,3-diol (IPBD) and, its -Cl derivative (Cl-IPBD) have been compared with doxorubicin, a drug widely used in medicine, and with Vitamin C. These compounds were accumulated at a supercoiled scpUC19 plasmid layer formed on a glassy carbon electrode (GCE). Stability of the drug-plasmid/GCE layer was achieved by initial plasmid accumulation using prolonged potential cycling for ca. 200 min. from highly diluted scpUC19 solutions (8 pg/mL), followed by accumulation of the drugs from 1 µM − 50 µM. Electrochemical properties in terms of the redox potentials of the compounds and capacitative/resistive characteristics of the layers have been tested using, in sequence, four voltammetric methods: Square Wave (SWV), Differential Pulse (DPV) and Alternating Current (ACV) with phase detection 0° and 90°. Importantly, with progressive drug accumulation in the plasmid, for Cl-IPBD, but not for IPBD, an increase in peak (I) at –0.42 V vs. SCE was observed, while biological tests revealed a higher cytotoxic activity for Cl-IPBD vs. IPBD. Moreover, an additional redox signal of Cl-IPBD was observed with the compound reductive accumulation at the plasmid layer in the presence of Vitamin C.

Graphitic Nitrogen Is Responsible for Oxygen Electroreduction on Nitrogen-Doped Carbons in Alkaline Electrolytes: Insights from Activity Attenuation Studies and Theoretical Calculations

To date, controversies remain in the unambiguous identification of the active sites in N-doped carbons for oxygen reduction reaction (ORR). In the present study, prolonged potential cycling was conducted on three N-doped carbons in O2-saturated 0.1 M KOH aqueous solution, where apparent attenuation of the ORR activity was observed, within the context of limiting current and onset potential. The attenuation trend of the limiting current was closely correlated with the diminishing content of graphitic N, as manifested in X-ray photoelectron spectroscopy measurements and Mott–Schottky analysis. In addition, the specific activity per graphitic N was found to be almost invariant within a wide range of potentials during prolonged potential cycling for all three model catalysts, in good agreement with theoretical prediction, whereas no such a correlation was observed with pyrrolic or pyridinic N. Density functional theory calculations showed that the first-electron reduction, which is a rate-determining step for...

Highly Conductive and Stable Graphene/PEDOT:PSS Composites As Metal Free Cathodes for Organic Dye-Sensitized Solar Cells

Graphene is a potential candidate as a counter electrode (CE) material to replace the Pt for long-term stability and low-cost fabrication of dye-sensitized solar cells (DSSC). Although the catalytic activity of graphene towards iodine-based redox mediator is not significantly high, it exhibited excellent electrocatalytic activity for cobalt-based redox mediators. However, the low adhesion capacity of graphene with FTO and low stability is the significant problems of graphene based CE for the development of long-term stable DSSCs. This research demonstrated the fabrication of highly stable with strong adhesion capacity based graphene nanoplatelets (GnP) CEs for organic DSSCs. We used conducting polymer (PEDOT:PSS) together with GnPs to improve the adhesion, stability, and catalytic activity. Different weight percent (%) of GnPs were mixed with PEDOT:PSS (PP), and subsequently dispersed by ultrasonication. The dispersed solutions were deposited on FTO by an electro spray (e-spray) method and their electro-catalytic properties were measured for Co(bpy)3 2+/3+ redox couple (bpy=2,2′-bipyridine). The optimal PP/GnP (PPG) CE with 1wt% GnP mixed PP exhibited the profound improvement in conductivity, eletrocatalytic activity, and electrochemical stability for the Co(bpy)3 2+/3+ redox couple compared to the Pt, GnP, and PP CEs. The charge transfer resistance (R CT) of the optimal PPG CE at the CE/electrolyte interface was 0.07 W.cm2, which is much lower than that of Pt CE (1.02 W.cm2). Moreover, the optimal PPG CEs showed better electrochemical stability under prolonged potential cycling. The DSSCs based on the Y123 sensitizer and optimal PPG CE showed a higher photovoltaic performance (J sc, FF, and h of 13.64 mA/cm2, 67.01%, and 8.33%, respectively) than those of Pt-CE (J sc, FF, and h of 13.27 mA/cm2, 65.52%, and 7.99%, respectively), GnP-CE (J sc, FF, and h of 12.74 mA/cm2, 65.69%, and 7.61%, respectively), and PP-CE (J sc, FF, and h of 12.27 mA/cm2, 60.72%, and 7.03%, respectively).

Pt-Pd Bimetal Popcorn Nanocrystals: Enhancing the Catalytic Performance by Combination Effect of Stable Multipetals Nanostructure and Highly Accessible Active Sites.

Exploration of highly efficient electrocatalysts is significantly urgent for the extensive adoption of the fuel cells. Because of their high activity and super stability, Pt-Pd bimetal nanocrystals have been widely recognized as one class of promising electrocatalysts for oxygen reduction. This article presents the synthesis of popcorn-shaped Pt-Pd bimetal nanoparticles with a wide composition range through a facile hydrothermal strategy. The hollow-centered nanoparticles are surrounded by several petals and concave surfaces. By exploring the oxygen reduction reaction on the carbon supported Pt-Pd popcorns in perchloric acid solution, it is found that compared with the commercial Pt/C catalyst the present catalysts display superior catalytic performances in aspects of catalytic activity and stability. More importantly, the Pt-Pd popcorns display minor performance degradations through prolonged potential cycling. The enhanced performances can be mainly attributed to the unique popcorn structure of the Pt-Pd components, which allows the appearance and long existence of the high active sites with more accessibility. The present work highlights the key roles of accessible high active sites in the oxygen reduction reaction, which will ultimately guide the design of highly durable Pt-Pd catalysts.

Electrochemical Formation of Gold Nanoparticles on Polycrystalline Gold Electrodes during Prolonged Potential Cycling

AbstractThe voltammetric behavior of polycrystalline gold electrodes in 0.1 M sulfuric acid and the influence of prolonged repetitions of oxidation and reduction cycles at different scan rates on the surface morphology was studied. Slow (0.1 V s−1) as well as fast (1.0 V s−1) scan rates lead to an intense roughening of the electrode surface and the formation of a variety of different crystalline particles on it. These crystallites, their formation, and the influence of surface pretreatment were investigated with electrochemical methods, X‐ray diffraction measurements, and scanning electron microscopy. Additionally, an interpretation of the changing electrochemical signals of polycrystalline gold during prolonged potential cycling is given.

Surface resistance change during nickel hydroxide phase transformations

Nickel hydroxide undergoes profound structural transformations under prolonged potential cycling in alkaline solutions. In this work, gold film electrodes modified with different nickel hydroxide coverages were subjected to continuous potentiodynamic cycling in alkaline medium, while the simultaneous evolution of voltammetric and surface resistance records was monitored until stable responses were obtained. A surface resistance (SR) increase proportional to the nickel hydroxide coverage was observed at potential values more negative than −0.3V (vs. SCE), which was attributed to the deposition of nickel adatoms from the reduction of nickel hydroxide layers. This SR change was analysed on the basis of the electron scattering theory, considering that nickel adatoms act as scatterers for the reflection of gold conduction electrons. The nickel adatom layer produced from the reduction of the nickel hydroxide structure formed during the first voltammetric scan potential cycles (<40) exhibits a more specular reflection than that generated after a larger number of potential cycles (>140). As the specularity of a layer for electron scattering can be associated with scatterer compactness, the distance between nickel atoms in the former nickel adatom structure is shorter than that in the last one.

Deactivation of poly(o-aminophenol) film electrodes by storage without use in the supporting electrolyte solution and its comparison with other deactivation processes. A study employing EIS

The effect of storage time without use (STWU) in the supporting electrolyte solution on the charge-transport parameters of poly(o-aminophenol) (POAP) film electrodes was studied by electrochemical impedance spectroscopy. STWU decreases the charge-transport rate of the polymer. This effect is herein called deactivation. Impedance diagrams of both nondeactivated and deactivated films in contact with a solution containing the p-benzoquinone/hydroquinone redox couple were interpreted on the basis of a model formulated for homogeneous conducting polymers, where the bathing electrolyte contains a redox pair that provides the possibility for electrons to leak from the film surface. Dependences of diffusion coefficients for electron (D e) and ion (D i) transport and interfacial resistances related to ion \(\left( {R_{\text{i}}^{{{\text{f}}|{\text{s}}}} } \right)\) and electron \(\left( {R_{{{\text{m}}|{\text{f}}}} ,R_{\text{e}}^{{{\text{f}}|{\text{s}}}} } \right)\) transfer across the polymer/solution and metal/polymer interfaces, respectively, on the degree of deactivation (θ d) of the polymer were obtained. These dependences were compared with those from previous work for POAP films deactivated by employing other procedures, such as high positive potential limits, soaking in a ferric ion solution, and prolonged potential cycling.

Earth-abundant Cu2SnSe3 thin film counter electrode for high-efficiency quantum dot-sensitized solar cells

We present herein a new facile solution-phase route to the growth of high crystalline quality Cu2SnSe3 (CTSe) thin film on a conductive substrate and demonstrate for the first time its promising application as an efficient counter electrode (CE) in liquid-junction quantum dot-sensitized solar cells (QDSCs). Dissolving Cu2Se and SnSe powders in the thiol-amine mixture forms a homogeneous CTSe molecular precursor solution. High-quality crystalline CTSe thin film electrode can be readily deposited from the above solution via a low-temperature heating step. Powder X-ray diffraction experiment combined with Raman spectroscopy revealed that the resulting CTSe has the monoclinic crystal structure. Electrochemical measurements, impedance spectroscopy, Tafel polarization, and cyclic voltammetry verified that CTSe possesses fascinating electrocatalytic activity for S2−/Sn2− redox couple in aqueous polysulfide electrolyte solution, and is superior to the traditional electrocatalyst, Pt, both in catalytic activity and in electrochemical stability under prolonged potential cycling, rationalizing the improved solar cell device performance, i.e., QDSCs employing CTSe CE showed more than a two-fold improvement in power conversion efficiency relative to that of Pt-based cells. The excellent catalytic performance along with the ease of solution processing of these earth-abundant CTSe materials make them a distinctive choice among the various CEs studied.

Deactivation of poly(o-aminophenol) film electrodes by storage without use in the supporting electrolyte solution and its comparison with other deactivation processes

The effect of storage time without use (STWU) in the supporting electrolyte solution on the conducting properties of poly(o-aminophenol) (POAP) film electrodes was studied. Cyclic voltammetry (CV), rotating disc electrode voltammetry (RDEV), and surface resistance (SR) were employed. The storage of a POAP film without use for time periods longer than 32h strongly reduces its electroactivity. Here, this effect is called deactivation. The attenuation of the voltammetric response of the polymer film with the increase of the storage time allows one to define a degree of deactivation (θd). A decrease of the electron transport rate (De) with the increase of the degree of deactivation of POAP films was obtained from RDEV measurements. This effect was attributed to the increase of the mean distance between active redox sites in the bulk of the POAP film. The relative surface resistance change (ΔR/R) of a gold film coated with POAP is also attenuated by the increase of the STWU. The attenuation was attributed to interfacial (gold/POAP) redox site distributions where the nearest neighbor distance between redox sites gradually increases as the degree of deactivation increases. The deactivation of POAP films by the STWU studied in this work was compared with deactivations caused by other electrochemical and chemical treatments, such as prolonged potential cycling (PPC), high positive potential limits (HPPL) and soaking in a ferric ion solution (SFeIS), described in previous work.

Catalytic activities of Pt thin films electrodeposited onto Bi coated glassy carbon substrate toward formic acid electrooxidation

Formic acid oxidation was studied on platinum-coated bismuth deposits on glassy carbon substrate. The catalyst was prepared by a two-step process using chronocoulometry, i.e. controlled amount of Bi was electrodeposited onto glassy carbon followed by electrodeposition of Pt layer. The amount of Pt was constant while the amount of Bi vary to correspond the molar ratio of Pt:Bi=1:0.1 or 1:1 or 1:10. AFM characterization of the electrode surface indicates that Pt is deposited preferentially on previously formed Bi particles, but cyclic voltammetry revealed Bi leaching meaning that Bi was not completely occluded by Pt. In order to obtain stable electrode surface, deposits were subjected to potential cycling up to 1.2V vs. SCE in supporting electrolyte, prior to use as catalysts for formic acid oxidation. On this way the electrodes composed of Bi core occluded by Pt and Bi-oxide surface layers were obtained. The Pt(Bi)/GC electrodes exhibit enhanced electrocatalytic activity in comparison to Pt/GC for formic acid oxidation which depends on composition and surface morphology. High currents and onset potential shifted to negative values indicate a significant increase in direct path what is explained through ensemble effect induced by Bi-oxide species interrupting Pt domains. Electronic modification of Pt both by surface and sub-surface Bi can play some role as well. Significantly prolonged potential cycling in supporting electrolyte of previously stabilized Pt(Bi)/GC electrodes by Bi oxide, led to considerably lower Bi leaching accompanied by dissolution and redeposition of Pt and the outcome of this treatment was Pt shell over Bi core. These Pt@Bi/GC catalysts also exhibit higher activity for HCOOH oxidation in comparison to Pt/GC depending on the quantity of Bi remained under Pt shell, but in this case the improvement is induced solely by electronic effect of under-laying Bi.

The Metal/Electroactive Polymer Interface Studied by Surface Resistance

The experimental arrangement in this investigation was one in which a poly(o-aminophenol) (POAP) film was supported on a thin gold film electrode whose thickness is of the order of the mean free path of conduction electrons of gold. This arrangement allows one to apply the surface resistance technique to study the electrochemical processes occurring at the metal film surface coated with the polymer film. The dependence of the resistance change of the thin gold film electrode on the external electrolyte composition for polymer thickness lower than 0.25 mC.cm-2, was attributed to a competition, at the gold film surface, between the redox process of the polymer and adsorption of different ion species contained in the electrolyte. This competition reflects a discontinuous character of polymer thickness lower than 0.25 mC.cm-2 at the metal polymer interface. The resistance response of the metal film becomes independent of both the external electrolyte composition and polymer thickness for polymer thickness higher than 0.8 mC.cm-2. Then, POAP thicknesses higher than 0.8 mC.cm-2 seem to be compact enough at the metal polymer interface to prevent the interaction of the species contained in the supporting electrolyte with the gold film surface. The increase of the gold film resistance in going from the reduced to the oxidized state for POAP thicknesses higher than 0.8 mC.cm-2 was attributed to the redox conversion of poly(o-aminophenol) from amine to imine groups. This resistance increase was explained as a transition from specular to diffuse scattering of conduction electrons of gold at the gold poly(o-aminophenol) interface due to a less compact distribution of oxidised sites of POAP as compared with that of the reduced ones. An attenuation of the resistance response of the gold film was observed when the POAP films were deactivated either by contact with a ferric cation solution or prolonged potential cycling. The deactivation of the polymer film was attributed to the creation of inactive gaps within the redox sites configuration of POAP. The surface resistance technique allows one to detect different redox sites configurations of POAP on the gold film, according to the method used to deactivate the polymer films. In this work, it is demonstrated that the surface resistance technique can be employed to study not only the ability of a POAP film to inhibit the interaction of different species in solution with a metal surface but also the deactivation of the polymer film.

First Examples of Hybrids Based on Graphene and a Ring‐Shaped Macrocyclic Polyoxometalate: Synthesis, Characterization, and Properties

AbstractThis work introduces facile synthetic methods of two new classes of green materials based on graphene (G) and the macrocyclic polyoxometalate [H7P8W48O184]33– (P8W48) alone or assembled with an imidazolium‐based poly(ionic liquid) (PIL). The polyoxometalate serves as both an efficient graphite oxide reductant and a stabilizer. Owing to the strong adsorption of P8W48 on the resulting G sheets, water‐dispersible P8W48@G hybrids were obtained without the need for surfactant or polymeric stabilizers. The P8W48@G hybrids were characterized by X‐ray photoelectron spectroscopy, Raman spectroscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, and cyclic voltammetry. The presence of G in these hybrids induces an outstanding enhancement in the electrochemical properties of P8W48 in comparison with those observed with glassy carbon. Moreover, P8W48@G‐ and P8W48@PIL‐G‐based electrodes exhibit remarkable stability during prolonged potential cycling in various aqueous electrolytes. To the best of our knowledge, these are the first examples of successful syntheses of a high nuclearity polyoxometalate and graphene assemblies that might facilitate photoelectrocatalysis of multielectronic reactions.

Graphene Nanoplatelets Outperforming Platinum as the Electrocatalyst in Co-Bipyridine-Mediated Dye-Sensitized Solar Cells

Graphene nanoplatelets (GNP) in the form of thin semitransparent films on F-doped SnO2 (FTO) exhibit high electrocatalytic activity for the Co(bpy)3(3+/2+) redox couple in acetonitrile electrolyte solution. The GNP film is superior to the traditional electrocatalyst, that is, platinum, both in charge-transfer resistance (exchange current) and in electrochemical stability under prolonged potential cycling. The good electrochemical performance of GNP is readily applicable for dye-sensitized solar cells with Y123-sensitized TiO2 photoanodes and Co(bpy)3(3+/2+) as the redox shuttle. The dye-sensitized solar cell with GNP cathode is superior to that with the Pt-FTO cathode particularly in fill factor and in power conversion efficiency at higher illumination intensity.

Dependence on composition of electronic properties and stability of Pt–Fe/C catalysts for oxygen reduction

This work presents studies of electronic characteristics and alloy stability carried out for Pt–Fe/C catalysts of different compositions (10–50% Fe, in atoms) and same particle size. The electronic properties are characterized by in situ dispersive X-ray absorption spectroscopy (DXAS). The results show a steady decrease in Pt d-band occupancy as the amount of Fe in the alloy increases. The alloy stability is evaluated by prolonged potential cycling up to 1.0 V. Catalysts with Fe content up to 30% show good stabilities and keep their activities for oxygen reduction after prolonged cycling. In contrast, catalysts with Fe content above 30% suffer pronounced Fe leaching.

Study of carbon-supported IrO 2 and RuO 2 for use in the hydrogen evolution reaction in a solid polymer electrolyte electrolyzer

Carbon-supported IrO 2 and RuO 2 were prepared using an incipient wetness method and were then calcinated at various temperatures. IrO 2/C and RuO 2/C are less expensive than the conventional Pt/C material and more stable than metal Ni in an acidic electrolyte. Moreover, IrO 2/C and RuO 2/C are not influenced by under potential deposition (UPD) and show lower sensitivity to poisoning by Ni or Fe impurities. The physical properties of IrO 2/C and RuO 2/C were investigated via XRD and TEM. Cyclic voltammograms (CV) and Tafel plots were used to provide information regarding surface redox reaction and electrocatalytic activity. The activity and durability of IrO 2/C and RuO 2/C were studied after prolonged potential cycling between −0.3 and 0.3 V SCE. After comparison of Tafel plots of Pt/C and IrO 2/C after activation, it was observed that they have similar electrocatalytic activities in a hydrogen evolution reaction (HER). A single cell test with solid polymer electrolyte (SPE) proved that the performance of IrO 2/C (0.5 mg cm −2) was similar to that of Pt/C (0.5 mg cm −2).

Stability studies of an electrochemically formed [C60]fullerene-palladium two-component film

The stability of C60 and palladium two-component films, C60/Pd, has been investigated. The effect of different polymerization conditions on the electrochemical stability of the film upon prolonged potential cycling has been studied. Stable voltammetric behavior was observed for polymers formed at potentials less negative than the potential of third C60 reduction step. The incorporation of palladium particles into the structure of C60/Pd polymers increases the polymer stability. The C60/Pd films are doped with supporting electrolyte cations during reduction. The size of these cations is a crucial factor in determining the stability of the film. A strong solvent effect on the potential stability of the film was also observed. The wildest range of stable voltammetric properties was found for acetonitrile and N,N-dimethylformamide. No effect of the temperature on the film stability was observed. The results reported in this work allow for the determination of the optimal conditions for the formation of stable C60/Pd films.

Surface and Subsurface Oxygen on Platinum in a Perchloric Acid Solution

The oxidation of polycrystalline platinum in perchloric acid is studied by cyclic voltammetry at a potential scan rate of 0.1 V s–1 in various potential cycling ranges. The earlier model for the formation of a barrier layer of strong complexes consisting of subsurface oxygen Oss, platinum atoms, and anions adsorbed on the latter is shown to correctly describe experimental results on the platinum oxidation in sulfuric and perchloric acids. The regularities in these acids are on the whole similar. A weaker adsorption of perchlorate anions as compared with bisulfate facilitates chemisorption of oxygen at 0.7–0.85 V and hinders exchange by sites Pt ⇔ O at 0.85–1.35 V. A prolonged potential cycling with a cathodic limit of 0.27 V and low anodic limits leads to the accumulation of surface complexes Oss–Ptn–ClO4, which hinder both the oxygen chemisorption and the exchange Pt ⇔ O below 1 V. At more positive potentials, the complexes are destroyed and oxygen penetrates into subsurface platinum layers.