Mikael Bergelin

Mediatorless sugar/oxygen enzymatic fuel cells based on gold nanoparticle-modified electrodes.

We report on the fabrication and characterisation of a gold-nanoparticle (AuNP)-based mediatorless sugar/oxygen biofuel cell (BFC) operating in neutral sugar-containing buffers and human physiological fluids, such as blood and plasma. First, Corynascus thermophilus cellobiose dehydrogenase (CtCDH) and Myrothecium verrucaria bilirubin oxidase (MvBOx), used as anodic and cathodic bioelements, respectively, were immobilised on gold electrodes modified with 20 nm AuNPs. Detailed characterisation and optimisation of a new CDH/AuNP-based bioanode were performed and the following fundamental parameters were obtained: (i) the redox potential of the haem-containing centre of the enzyme was measured to be 75 mV vs. NHE, (ii) the surface coverage of CtCDH was found to be 0.65 pmol cm(-2) corresponding to a sub-monolayer coverage of the thiol-modified AuNPs by the enzyme, (iii) a turnover number for CtCDH immobilised on thiol-modified AuNPs was calculated to be ca. 0.5 s(-1), and (iv) the maximal current densities as high as 40 μA cm(-2) were registered in sugar-containing neutral buffers. Second, both biomodified electrodes, namely the CtCDH/AuNP-based bioanode and the MvBOx/AuNP-based biocathode, were combined into a functional BFC and the designed biodevices were carefully investigated. The following characteristics of the mediator-, separator- and membrane-less, miniature BFC were obtained: in phosphate buffer; an open-circuit voltage of 0.68 V, a maximum power density of 15 μW cm(-2) at a cell voltage of 0.52 V and in human blood; an open-circuit voltage of 0.65 V, a maximum power density of 3 μW cm(-2) at a cell voltage of 0.45 V, respectively. The estimated half-lives of the biodevices were found to be >12, <8, and <2 h in a sugar-containing buffer, human plasma, and blood, respectively. The basic characteristics of mediatorless sugar/oxygen BFCs were significantly improved compared with previously designed biodevices, because of the usage of three-dimensional AuNP-modified electrodes.

Oxidation of CO adlayers on Pt(111) at low potentials: an impinging jet study in H2SO4 electrolyte with mathematical modeling of the current transients ☆

The constant potential oxidation of adlayers of CO on a bead type Pt(111) electrode created by the impinging jet flow technique has been studied in 0.5 and 0.05 mol dm−3 H2SO4 electrolyte. Washing procedures were developed which allowed work to be carried out for long periods of time without contamination problems. At low potentials (<680 mV vs. RHE) in 0.5 mol dm−3 H2SO4 the compact adlayers were slowly oxidized in a process which first involved a constant current plateau followed by a single symmetric peak. The total oxidation charges of the transients corresponded to that of a compact CO adlayer and the peak charges to that calculated from data reported in the literature for a looser adlayer structure. In 0.05 mol dm−3 H2SO4 the adlayers oxidize much faster and the oxidation process is more complex. The current−time traces for the stronger electrolyte were described well by an equation especially derived for the oxidation kinetics under the particular conditions used in this work. Values for a potential dependent rate constant for the oxidation were determined by means of curve fitting.

Characterization of Pt-based catalyst materials by voltammetric techniques

Catalyst materials in form of inks, as half-MEAs and inside a polymer electrolyte membrane unit cell were characterized by cyclic voltammetry. Laboratory made Pt inks were modified with Ru, Os and Ru + Ir and the methanol oxidation activity of the created surfaces was tested. A novel electrode, which enables the study of the oxygen reduction reaction on the cathode was introduced. With the measuring device it was possible to vary the oxygen content on the ink side and the proton activity of the electrolyte on the membrane side of a half-MEA. Catalyst layers based on Pt, Pt-Ru and Pt-Co inside a PEM-unit cell were also characterized in situ by cyclic voltammetry. The active surface areas were found to be linearly dependent on the Pt mass density in the catalyst layers. Approximately 30% of the Pt loading in the MEAs were electroactive.

Study of carbon monoxide adsorption and oxidation on Pt(111) by using an electrochemical impinging jet cell

Abstract An impinging jet electrochemical flow cell developed for use with bead type electrodes was successfully employed in a surface structure sensitive study involving the processes of CO adsorption and oxidation on Pt(111) in 1.0 mol dm −3 H 2 SO 4 and HClO 4 . The flow cell enabled straightforward CO coverage control by means of varying the dosing time. Anion and hydrogen displacement charge curves with high potential resolution were obtained by means of CO adsorption and an electrolyte dependent fine structure was found. During the dosing of the electrolyte dissolved CO in the potential range 700–800 mV (vs. RHE) a slow delayed oxidation of adsorbed CO was noted and interpreted as being due to adsorption competition between CO and an oxygen containing species. A novel anion–anion displacement method was developed in which adsorbed bisulfate was replaced by perchlorate or water. The negative current transient obtained indicated desorption of bisulfate.

The impinging jet flow method in interfacial electrochemistry: an application to bead-type electrodes

Abstract The details of an impinging jet flow system to be used for interfacial electrochemical studies at smooth bead-type electrodes are described. The 0.7-ml min−1 electrolyte flow was propelled by hydrostatic pressure and accurately controlled by a computer-controlled rotating valve. Carbon monoxide dissolved in 1 mol dm−3 sulfuric acid was dosed onto a polycrystalline platinum surface in a carrier flow of pure electrolyte. The dosing performance of the flow cell was evaluated by electrooxidation of bulk and adsorbed CO, and the effect of dosing potential on the stripping voltammogram and on the charge displacement behaviour was investigated and discussed.

The impinging jet flow cell — a novel method for the study of PEM fuel cell material

Abstract The electrocatalytic properties of a fuel cell catalyst ink in thin film form based on Vulcan XC72/Pt (30%) and Nafion was investigated by means of a flow cell of impinging jet type in flows of H 2 and H 2 +CO dissolved in H 2 SO 4 electrolyte. CO adlayers of different coverages were produced by a dosing procedure and their electrooxidative removal was studied. Ru was deposited onto the ink in situ by electroreduction and the basic voltammetry of such electrodes was investigated as well as the influence on CO adlayers and CO-tolerance. A Nafion film on top of the ink film influenced both the behaviour of CO adlayers and CO-tolerance. The feasibility of the flow cell for investigation and modification of ink electrodes were demonstrated.

Printed Supercapacitor as Hybrid Device with an Enzymatic Power Source

Low cost printable power sources are needed e.g. in sensors and RFID applications. As manufacturing method printing techniques are preferred in order to keep the costs low. The materials should also be easily disposable. Enzymatic bio-fuel cells are an alternative for printable primary batteries. Since one drawback of bio-fuel cells is their low power, we have developed supercapacitors that can be combined with enzymatic bio-fuel cells to provide the power peaks necessary in the applications. The materials for the supercapacitors have been chosen to be compatible with the fuel cell and with printing methods, e.g. the activated carbon powder in the electrodes was bound with chitosan. As printing substrates we have used paperboards. The current collectors have been made of graphite and metal inks. Since the voltage requirement is limited to approximately 1 V, aqueous electrolytes have been used. Printed supercapacitors of various sizes have been prepared. The geometrical electrode areas have been between 0.5 and 2 cm2. The maximum feasible output current has been in the order of 50 mA corresponding to about 50 mW power. When the capacitor is used together with an enzymatic power source, the leakage current must be as low as possible. Typical leakage current values have been in the order of 10 µA.

Electrodeposition of submonolayer amounts of Os onto polycrystalline Pt

Abstract The behaviour of Os submonolayers on polycrystalline Pt was investigated by means of a flow cell of impinging jet type. Os was electrodeposited onto the electrode for various periods of time. From the loss in the hydrogen region charge it was possible to estimate the Os surface coverage. The activity of Os towards hydrogen adsorption was also studied by depositing the metal onto an Au electrode. An estimation of 40% hydrogen coverage for Os was made, which was taken into consideration in the determination of the Os coverage. Another method for estimating the surface coverage was also considered where the oxidation charge of OsO4 was taken as a measure of the amount of Os present on the surface. It was also found that the deposition potential influences the voltammetry in the hydrogen region. A potential dependent preferential deposition onto Pt[110] and Pt[100] surface sites was observed.

Comparison of High-Temperature Oxidation Onset Behavior of Sanicro 28 Steel with KCl, NaCl and K2CO3

This paper presents results from a study regarding the influence of three alkali salts (KCl, NaCl, and K2CO3) on the initial high temperature corrosion behavior of high alloy stainless steel Sanicro 28 (Fe31Cr27Ni) at 535°C. It was found that all three salts were corrosive, however, with clear differences in terms of reaction initiation.