Tim Bobrowski

Cobalt boride modified with N-doped carbon nanotubes as a high-performance bifunctional oxygen electrocatalyst

The development of reversible oxygen electrodes, able to drive both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR), is still a great challenge. We describe a very efficient and stable bifunctional electrocatalytic system for reversible oxygen electrodes obtained by direct CVD growth of nitrogen-doped carbon nanotubes (NCNTs) on the surface of cobalt boride (CoB) nanoparticles. A detailed investigation of the crystalline structure and elemental distribution of CoB before and after NCNT growth reveals that the NCNTs grow on small CoB nanoparticles formed in the CVD process. The resultant CoB/NCNT system exhibited outstanding activity in catalyzing both the OER and the ORR in 0.1 M KOH with an overvoltage difference of only 0.73 V between the ORR at −1 mA cm−2 and the OER at +10 mA cm−2. The proposed CoB/NCNT catalyst showed stable performance during 50 h of OER stability assessment in 0.1 M KOH. Moreover, CoB/NCNT spray-coated on a gas diffusion layer as an air-breathing electrode proved its high durability during 170 galvanostatic charge–discharge (OER/ORR) test cycles (around 30 h) at ±10 mA cm−2 in 6 M KOH, making it an excellent bifunctional catalyst for potential Zn–air battery application.

Rechargeable, flexible and mediator-free biosupercapacitor based on transparent ITO nanoparticle modified electrodes acting in µM glucose containing buffers

We present a transparent and flexible self-charging biosupercapacitor based on an optimised mediator- and membrane-free enzymatic glucose/oxygen biofuel cell. Indium tin oxide (ITO) nanoparticles were spray-coated on transparent conducting ITO supports resulting in a flocculent, porous and nanostructured electrode surface. By this, high capacitive currents caused by an increased electrochemical double layer as well as enhanced catalytic currents due to a higher number of immobilised enzyme molecules were obtained. After a chemical pre-treatment with a silane derivative, bilirubin oxidase from Myrothecium verrucaria was immobilized onto the ITO nanostructured electrode surface under formation of a biocathode, while bioanodes were obtained by either immobilisation of cellobiose dehydrogenase from Corynascus thermophilus or soluble PQQ-dependent glucose dehydrogenase from Acinetobacter calcoaceticus. The latter showed a lower apparent KM value for glucose conversion and higher catalytic currents at µM glucose concentrations. Applying the optimised device as a biosupercapacitor in a discontinuous charge/discharge mode led to a generated power output of 0.030mW/cm2 at 50µM glucose, simulating the glucose concentration in human tears. This represents an enhancement by a factor of 350 compared to the power density obtained from the continuously operating biofuel cell with a maximum power output of 0.086µW/cm2 under the same conditions. After 17h of charging/discharging cycles a remarkable current enhancement was still measured. The entire device was transferred to flexible materials and applied for powering a flexible display showing its potential applicability as an intermittent power source in smart contact lenses.

Transparent, mediator- and membrane-free enzymatic fuel cell based on nanostructured chemically modified indium tin oxide electrodes

We detail a mediator- and membrane-free enzymatic glucose/oxygen biofuel cell based on transparent and nanostructured conducting supports. Chemically modified indium tin oxide nanoparticle modified electrodes were used to substantially increase the active surface area without significantly compromising transparency. Two different procedures for surface nanostructuring were employed, viz. spray-coating and drop-coating. The spray-coated biodevice showed superior characteristics as compared to the drop-coated enzymatic fuel cell, as a result of the higher nanostructured surface area as confirmed by electrochemical characterisation, as well as scanning electron and atomic force microscopy. Subsequent chemical modification with silanes, followed by the immobilisation of either cellobiose dehydrogenase from Corynascus thermophiles or bilirubin oxidase from Myrothecium verrucaria, were performed to obtain the bioanodes and biocathodes, respectively. The optimised biodevice exhibited an OCV of 0.67V and power output of up to 1.4µW/cm2 at an operating voltage of 0.35V. This is considered a significant step forward in the field of glucose/oxygen membrane- and mediator-free, transparent enzymatic fuel cells.

Optimized Ag Nanovoid Structures for Probing Electrocatalytic Carbon Dioxide Reduction Using Operando Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy is a powerful analytical tool and a strongly surface structure-dependent process. Importantly, it can be coupled with electrochemistry to simultaneously record vibrational spectroscopic information during electrocatalytic reactions. Highest Raman enhancements are obtained using precisely tuned nanostructures. The fabrication and evaluation of a high number of different nanostructures with slightly different properties is time-consuming. We present a strategy to systematically determine optimal nanostructure properties of electrochemically generated Ag void structures in order to find the void size providing highest signal enhancement for Raman spectroscopy. Ag-coated Si wafers were decorated with a monolayer of differently sized polymer nanospheres using a Langmuir-Blodgett approach. Subsequently, bipolar electrochemistry was used to electrodeposit a gradient of differently sized void structures. The gradient structures were locally evaluated using Raman spectroscopy of a surface-adsorbed Raman probe, and the surface regions exhibiting the highest Raman enhancement were characterized by means of scanning electron microscopy. High-throughput scanning droplet cell experiments were utilized to determine suitable conditions for the electrodeposition of the found highly active structure in a three-electrode electrochemical cell. This structure was subsequently employed as the working electrode in operando surface-enhanced Raman measurements to verify its viability as the signal amplifier and to spectroscopically rationalize the complex electrochemical reduction of carbon dioxide.

Amperometric Detection of dsDNA using an Acridine-Orange-Modified Glucose Oxidase

Invited for this months cover is the group of Prof. Dr. Wolfgang Schuhmann, Dr. Daliborka Jambrec and Dr. Adrian Ruff at Ruhr-Universität in Bochum, Germany. The cover picture shows a novel procedure for the preferential post-hybridization labeling of double-stranded DNA based on the intercalating compound acridine orange, which was covalently bound to glucose oxidase. Labeling with a highly active biocatalyst allows for a simple and sequence-independent amplification of the signal proportional to the amount of hybridized DNA that may be coupled with other amplification strategies. Read the full text of the article at 10.1002/cplu.201700279.