M. Grdeń

Surface Science and Electrochemical Analysis of Nickel Foams

Open-pore nickel (Ni) foams are characterized using surface science and electrochemical techniques. A scanning electron microscopy analysis reveals interconnected Ni struts that generate small and large pores of ca. 50 and 500 μm in size, respectively. An X-ray photoelectron spectroscopy (XPS) analysis of the surface-chemical composition of the Ni foams shows that there are oxidized and metallic sections within their surfaces despite being prepared by sintering in an oxidizing atmosphere at a high temperature and being stored in moist air. The ratio of the areas of oxidized and metallic sections is evaluated using XPS data. Chemical etching of the Ni foams results in removal of the native surface oxide/hydroxide without altering the three-dimensional structure; it also increases the roughness (R) of the surfaces of Ni struts giving rise to an increase in the electrochemically active surface area (Aecsa). Thermal treatment of Ni foams in an H2(g) atmosphere at 500 °C reduces the native surface oxide/hydroxide but does not increase R or Aecsa. Electrochemical behavior of the Ni foams is examined in 0.5 M aqueous KOH solution using cyclic-voltammetry (CV) and electrochemical impedance spectroscopy (EIS). As-received, chemically etched, thermally reduced and electro-oxidized Ni foams generate distinct CV profiles; their features are assigned to oxidized and metallic surface states. The observations made on the basis of XPS measurements are corroborated by the results of CV analyses. The application of CV and XPS or EIS allows in situ determination of Aecsa and the specific surface area (As) of the chemically etched and thermally reduced Ni foams. The values of As determined on the basis of joint CV and XPS measurements are 227 ± 74 and 149 ± 48 cm(2) g(-1) for the etched and reduced Ni foams, respectively. The values of As determined on the basis of CV, XPS and EIS measurements are 241 ± 80 and 160 ± 23 cm g(-1) for the etched and reduced Ni foams, respectively.

Electrosorption of carbon dioxide on PdPt alloys

The adsorption of carbon dioxide on PdPt alloy electrodes in acidic solution has been studied. The influence of both bulk and surface composition of the alloy on CO2 adsorption is presented. The results obtained suggest that only hydrogen interacting with platinum atoms is active in reaction with CO2. At the same time these platinum atoms are inactive in the hydrogen absorption/desorption process. The latter reaction probably proceeds only with participation of palladium atoms, unblocked by products of adsorption of CO2.

Electrochemical behavior of lead in sulfuric acid solutions

Abstract The electrochemical behavior of the lead electrode has been studied by cyclic voltammetry (CV) in sulfuric acid solutions, with concentrations ranged from 0.05 to 5 M. Also, the effect of a sweep rate, the range of potential polarisation and temperature has been examined. Special attention has been paid to unusual anodic processes, i.e., “anodic excursion” peaks that accompany the main reduction peak. The presence of a small, and previously unrecognized cathodic peak, preceding “anodic excursion” peaks, has been documented. Since all these peaks appear on the CVs only when the electrode potential is cycled in a wide potential range, limited by hydrogen and oxygen evolution, it has been proposed that they are related to the reduction of the lead dioxide to the bare metal, occurring at high negative potentials. The presence of a small reduction peak preceding “anodic excursion” peaks, as well as the presence of the main reduction peak of the lead dioxide has also been related to the exposure of the bare metal. When the lead dioxide, formed at high positive potentials, is reduced (PbO2→PbSO4), a large increase of the molar volume is expected and, as a result, the surface cracks, exposing the bare metal. These parts of the surface are then oxidized in “anodic excursion” peaks. To repeat these redox processes, the electrode has to be reduced again at high negative potentials, i.e., at the conditions when reduction to the metal occurs. The CVs performed only in a positive potential range confirmed that the reduction of PbO2 to PbSO4, which follows the formation of PbO2, is not related to the “anodic excursion” peaks and it also means that no cracks of the surface occur, as long as the potential cycling of the electrode to high negative potentials, and the resulting reduction to the metal, are avoided. Therefore, when the lead electrode is used as a positive electrode in a battery, no corrosion due to the exposure of the bare metal is expected.

Electrochemical behavior of nickel deposited on reticulated vitreous carbon

Abstract The electrochemical performance of nickel deposited on reticulated vitreous carbon (RVC) has been investigated in solutions of KOH. For comparison, the study of sintered nickel and nickel deposited on gold wire behavior were also included. Our results indicate that the RVC covered with nickel is a good carrier for Ni(OH) 2 /NiOOH—an electrode material, used in rechargeable batteries. Ni/RVC saturated with Ni(OH) 2 shows behavior similar or even better than that of sintered Ni saturated with Ni(OH) 2 .

Hydrogen Electrosorption in Pd‐Pt‐Rh Alloys in the Presence of Adsorbed CO

Abstract Electrosorption of hydrogen in Pd‐Pt‐Rh alloys in the presence of adsorbed carbon monoxide has been examined using cyclic voltammetry (CV). CO adsorption has a remarkable influence on both hydrogen adsorption and absorption. Hydrogen adsorption is strongly inhibited by CO adsorption products. The processes of hydrogen absorption and desorption are not totally blocked but proceed much slower than in the absence of CO adsorbates. On electrodes covered with adsorbed CO oxidation of absorbed hydrogen is shifted to higher potentials. †Dedicated to the memory of Professor Harry B. Mark Jr.

Semi-differential analysis of irreversible voltammetric peaks

Voltammetric peaks obtained by simulation of electrochemical reactions under conditions of linear semi-infinite diffusion with an irreversible electron transfer process are analysed using a semi-differentiation procedure. Obtained semi-derivative peaks, separated or overlapped, are fitted with appropriate mathematical functions. The functions used for data fitting include a function describing symmetrical peaks, proposed by several authors for fitting irreversible semi-derivative peaks, and two alternative functions that express asymmetric shape of the irreversible semi-derivative signals. When applied to the overlapped irreversible semi-derivative peaks, the latter two functions allow calculating certain electrochemical parameters with a better accuracy as compared with the function derived for the symmetrical peaks.