Bjorn Winther-Jensen

High Rates of Oxygen Reduction over a Vapor Phase–Polymerized PEDOT Electrode

The air electrode, which reduces oxygen (O2), is a critical component in energy generation and storage applications such as fuel cells and metal/air batteries. The highest current densities are achieved with platinum (Pt), but in addition to its cost and scarcity, Pt particles in composite electrodes tend to be inactivated by contact with carbon monoxide (CO) or by agglomeration. We describe an air electrode based on a porous material coated with poly(3,4-ethylenedioxythiophene) (PEDOT), which acts as an O2 reduction catalyst. Continuous operation for 1500 hours was demonstrated without material degradation or deterioration in performance. O2 conversion rates were comparable with those of Pt-catalyzed electrodes of the same geometry, and the electrode was not sensitive to CO. Operation was demonstrated as an air electrode and as a dissolved O2 electrode in aqueous solution.

Direct electro-deposition of graphene from aqueous suspensions

We describe the direct electro-chemical reduction of graphene oxide to graphene from aqueous suspension by applying reduction voltages exceeding -1.0 to -1.2 V. The conductivity of the deposition medium is of crucial importance and only values between 4-25 mS cm(-1) result in deposition. Above 25 mS cm(-1) the suspension de-stabilises while conductivities below 4 mS cm(-1) do not show a measurable deposition rate. Furthermore, we show that deposition can be carried out over a wide pH region ranging from 1.5 to 12.5. The electro-deposition process is characterised in terms of electro-chemical methods including cyclic voltammetry, quartz crystal microbalance, impedance spectroscopy, constant amperometry and potentiometric titrations, while the deposits are analysed via Raman spectroscopy, infra-red spectroscopy, X-ray photoelectron spectroscopy and X-ray diffractometry. The determined oxygen contents are similar to those of chemically reduced graphene oxide, and the conductivity of the deposits was found to be ∼20 S cm(-1).

Conducting Polymer Composite Materials for Hydrogen Generation

A novel conducting polymer/non-conducting polymer composite (PEDOT/PEG), produced by vapor phase polymerization of PEDOT in the presence of PEG, shows stable electrocatalytic reduction of protons to hydrogen with conversion currents and over-potential comparable to platinum. The swelling of the composite by PEG and especially its ability to coordinate protons seems to be essential for the catalytic activity of the composite.

PdNi hollow nanoparticles for improved electrocatalytic oxygen reduction in alkaline environments

Palladium-nickel (PdNi) hollow nanoparticles were synthesized via a modified galvanic replacement method using Ni nanoparticles as sacrificial templates in an aqueous medium. X-ray diffraction and transmission electron microscopy show that the as-synthesized nanoparticles are alloyed nanostructures and have hollow interiors with an average particle size of 30 nm and shell thickness of 5 nm. Compared with the commercially available Pt/C or Pd/C catalysts, the synthesized PdNi/C has superior electrocatalytic performance towards the oxygen reduction reaction, which makes it a promising electrocatalyst for alkaline anion exchange membrane fuel cells and alkali-based air-batteries. The electrocatalyst is finally examined in a H2/O2 alkaline anion exchange membrane fuel cell; the results show that such electrocatalysts could work in a real fuel cell application as a more efficient catalyst than state-of-the-art commercially available Pt/C.

New generation, metal-free electrocatalysts for fuel cells, solar cells and water splitting

New electrocatalysts have become of increasing significance due to the need for inexpensive and effective catalysis in energy generating, converting and storage devices. Intrinsically conducting polymers such as PEDOT have recently been shown to provide an important new family of electrocatalytic materials. Studies thus far have demonstrated effective electrocatalysis in a range of contexts including for example in the iodine/iodide reaction and other similar reactions important in the dye sensitised solar cell, the oxygen reduction reaction fundamental to the fuel cell and metal–air batteries, and proton reduction in water to produce hydrogen. A general catalytic behaviour seems to be emerging in these studies. This article surveys recent progress in this field from our laboratories and others and foreshadows important new areas requiring study.

Development of a Low Cost Printable Chipless RFID Humidity Sensor

A novel low-cost chipless radio frequency identification tag sensor is presented. The tag sensor provides identification data as well as monitors relative humidity (RH) of tagged objects. The tag sensor is made of passive microwave circuit that uses humidity sensitive polymer material for RH sensing. The aim of this paper is to investigate RF sensing properties of moisture absorbing polymer polyvinyl alcohol at microwave frequency. In addition, frequency shifting technique is used to encode data bits for high data capacity. The overall size of the proposed tag sensor is 15 mm × 6.8 mm and has 6 bit data capacity for ID generation and single bit for humidity sensing. Results presented here show ~ 607 MHz frequency deviation for 50% RH increase. The tag sensor has potential to be printed on flexible laminates such as plastic and paper for ultra-low cost item level tagging and ubiquitous sensing.

CdS thin-film electrodeposition from a phosphonium ionic liquid

Thin, adherent films of CdS were electrodeposited on FTO coated glass by reduction of a thiosulfate precursor in the presence of Cd(II) ions in methyltributylphosphonium (P(1,4,4,4)) tosylate ionic liquid at 130-150 degrees C. The structural properties of the deposits have been characterized by profilometry, scanning electron microscopy (SEM) and optical microscopy. Energy dispersive X-ray spectroscopy (EDX) was used to evaluate the chemical composition, which was found to be close to stoichiometric. Semiconductor properties including the band gap and flat band potential were calculated from UV-Vis and impedance spectroscopy measurements. The crystal structure was analyzed by X-ray diffraction (XRD). The data obtained from XRD and band gap measurements suggest the presence of hexagonal CdS crystals. The possible growth mechanism of the films is also addressed.

PEDOT: gelatin composites mediate brain endothelial cell adhesion

Conducting polymers (CPs) are increasingly being used to interface with cells for applications in both bioelectronics and tissue engineering. To facilitate this interaction, cells need to adhere and grow on the CP surface. Extracellular matrix components are usually necessary to support or enhance cell attachment and growth on polymer substrates. Here we show the preparation of PEDOT(TOS):gelatin composites as a new biocompatible substrate for use in tissue engineering. Gelatin, a derivative of the extracellular matrix protein collagen, was incorporated into poly(3,4 ethylenedioxythiophene)-tosylate (PEDOT(TOS)) films via vapour phase polymerisation (VPP) without changing the electrochemical properties of the CP. Further, gelatin, incorporated into the PEDOT(TOS) film, was found to specifically support bovine brain capillary endothelial cell adhesion and growth, indicating that the functionality of the biomolecule was maintained. The biocompatibility of the composite films was demonstrated indicating the significant future potential of biocomposites of this type for use in promoting cell adhesion in electrically active materials for tissue engineering.

Graphene/zinc nano-composites by electrochemical co-deposition

We describe for the first time the electrochemical co-deposition of composites based on a reactive base metal and graphene directly from a one-pot aqueous mixture containing graphene oxide and Zn(2+). In order to overcome stability issues the Zn(2+) concentration was kept below a critical threshold concentration, ensuring stable graphene oxide suspensions in the presence of cationic base metal precursors. This approach ensures the compatibility between the cationic base metal precursor and graphene oxide, which is more challenging compared to previously reported anionic noble metal complexes. Spectroscopic evidence suggests that the reason for destabilisation is zinc complexation involving the carboxylate groups of graphene oxide. The composition of the electrodeposited co-composites can be tuned by adjusting the concentration of the precursors in the starting mixture. The nano-composites show zinc particles (<3 nm) being uniformly dispersed amongst the graphene sheets. It is also demonstrated that the composites are electrochemically active and suitable for energy storage and energy conversion applications. However, a factor limiting the discharge efficiency is the reactivity of the base metal (low reduction potential and small particle size) which undergoes rapid oxidation when exposed to aqueous electrolytes.

Self polymerising ionic liquid gel

A novel self-polymerised ionic liquid (IL) gel was prepared at room temperature (RT), without light or heat or addition of initiator, using a new IL, choline formate (CF), and 2-hydroxyethyl methacrylate (HEMA).