Characterizing efficiency of multi-Enzyme cascade-based biofuel cells by product analysis

pre-printThe performance of biofuel cells with enzyme cascades have normally been characterized with open circuit potential, power density, and current density measurements. In this work, we demonstrate that with the method of quantitative product analysis by mass spectrometry, we can obtain other valuable information about the biofuel cell efficiency. Faradaic efficiency, coulombic efficiency and product efficiency were calculated for a six-enzyme glucose biofuel cell system. Oxidation pathway bottlenecks were determined with quantitative mass spectrometry measurements via direct infusion. These measurements and calculations give an in-depth understanding of the bioelectrocatalytic bottlenecks in the enzyme cascade for the target fuel (glucose)

Nickel cysteine complexes as anodic electrocatalysts for fuel cells

pre-printCompared to platinum, nickel is an inexpensive catalyst that can oxidize methanol in alkaline media. There is a desire to increase nickel loading during electrodeposition for improved performance. In this paper, a nickel cysteine complex (NiCys) is used as the precursor for electrodeposition on glassy carbon electrode surfaces. After optimization of cysteine concentration, the surface concentration of NiOOH on NiCys electrodes characterized by cyclic voltammetry in 0.1 M NaOH can reach 1.28 (± 0.32) × 10−7 mol/cm2. The large amount of NiOOH on NiCys electrodes provide 5 times the methanol oxidation current compared to Ni electrodes prepared without cysteine as demonstrated by chronoamperometry at 0.7 V vs. Hg/HgO. Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy have been applied to examine surface morphologies and structures of NiCys and Ni electrodes. The analysis reveals that cysteine adjusts the solubility of Ni(OH)2 in 0.1 M NaOH, so more uniform and smaller size nanoparticles are electrodeposited on electrode surfaces compared to Ni electrodes

High performance glucose/O2 biofuel cell: effect of utilizing purified laccase with anthracene-modified multi-walled carbon nanotubes

pre-printLaccase, a blue multicopper oxidoreductase enzyme, is a robust enzyme that catalyzes the reduction of oxygen to water and has been shown previously to perform improved direct electron transfer in a biocathode when mixed with anthracene-modified multi-walled carbon nanotubes. Previous cathode construction used crude laccase enzyme isolated as a brown cell extract powder containing both active and inactive proteins. Purification of this enzyme, yielding a blue solution, resulted in greatly improved enzyme activity and removed insulating protein that competed for docking space in this cathodic system. Cyclic voltammetry of the purified biocathodes showed a background subtracted limiting current density of 1.84 (±0.05) mA/cm2 in a stationary air-saturated system. Galvanostatic and potentiostatic stability experiments show that the biocathode maintains up to 75% and 80% of the original voltage and current respectively over 24 hours of constant operation. Inclusion of the biocathode in a glucose/O2 biofuel cell using a mediated glucose oxidase (GOx) anode produced maximum current and power densities of 1.28 (±0.18) mA/cm2 and 281 (±50) μW/cm2 at 25◦C and 1.80 (±0.06) mA/cm2 and 381 (±33) μW/cm2 at 37◦C, respectively. Enzymatic efficiency of this glucose/O2 enzymatic fuel cell is among the highest reported for a glucose/O2 enzymatic fuel cell

Utilizing DNA for electrocatalysis: DNA-Nickel aggregates as anodic electrocatalysts for methanol, ethanol, glycerol, and glucose

pre-printDNA-nickel aggregates were electrodeposited onto glassy carbon electrode surfaces and have shown electrocatalytic activity for oxidation of methanol, ethanol, glycerol, and glucose at room temperature in alkaline solutions. Bulk electrolysis oxidation products identified by 13C NMR include carbonate as methanol, glycerol, and glucose's oxidation products suggesting these three fuels can be deeply oxidized by DNA-nickel aggregates and carbon-carbon bonds can be broken during the oxidation of glycerol and glucose. However, ethanol was only oxidized to acetate. The capability of deep oxidation of methanol, ethanol, glycerol and glucose under relatively moderate conditions makes DNA-nickel a candidate for fuel cell applications

Improved performance of a thylakoid bio-solar cell by incorporation of carbon quantum dots

pre-printCarbon quantum dots (CQDs) were incorporated into thylakoid bioanodes capable of direct photobioelectrocatalysis in order to increase the photocurrent generation. More thylakoids are in contact with the increased surface area which allows for greater direct electron transfer (DET). Additionally, the fluorescent quantum dots redshift the light which allows for the thylakoid/CQD electrodes to use more of the solar spectrum, increasing the photocurrent. The current density was more than twice as large when CQDs were included in a thylakoid bio-solar cell

Photobioelectrochemistry: Solar energy conversion and biofuel production with photosynthetic catalysts

pre-printPhotobioelectrochemical cells are devices which have been developed over the past few decades and use photosynthetic catalysts for solar energy conversion or biofuel production. In this paper, a critical review of reported photobioelectrochemical systems is presented. The systems discussed include several types of photobioelectrocatalysts: whole cells, organelles, and enzymes. Special attention is paid to power or product generation as well as immobilization and electron transfer strategies used. The issues that need to be addressed in order for such systems to compete with current technologies are also discussed

Controlled placement of enzymes on carbon nanotubes using comb-branched DNA

pre-printImmobilization is not only useful for preserving enzyme activity, but also to adhere an enzyme to a surface, such as an electrode, so that the enzyme does not leach into solution during testing. Current immobilization approaches do not readily allow for adjustments to the distance between the enzyme and the electrode or other enzymes. The ability to control the distance of enzymes relative to each other on an electrode can allow for optimal placement and improved current responses. In this report, we investigate the use of comb-branched DNA for enzyme immobilization. A DNA foundation strand was covalently attached to multiwalled carbon nanotubes on a glassy carbon electrode. Comb-branched DNA was then successfully formed using a previously-identified deoxyribozyme to attach DNA strands at specific locations on this foundation strand. By changing the foundation strands, the placement of the DNA strands can be adjusted, allowing for distance changes between the enzyme and the electrode surface. Using standard bioconjugation methods, alcohol dehydrogenase and glucose dehydrogenase were attached to these comb-branched DNA structures, resulting in enzyme immobilization on electrode surfaces. Amperometric analysis revealed both distance and DNA foundation strand length dependence for current response of these enzymes in the presence of their appropriate substrates

Bio-solar cells incorporating catalase for stabilization of thylakoid bioelectrodes during direct photoelectrocatalysis

pre-printThylakoid membranes have been proposed for electrochemical solar energy conversion, but they have been plagued with short term instability. In this paper, thylakoid membranes extracted from Spinacia oleracea were physically adsorbed onto Toray paper electrodes with and without catalase, followed by entrapment in a vapor deposited silica matrix. The bioelectrodes were tested using voltammetry and amperometry and tested in a complete photobioelectrochemical cell. Upon subsequent polarization experiments, a significant decrease in the maximum current density from 1.53 ± 0.13 μAcm−2 to 0.75 ± 0.14 μAcm−2 was observed without catalase present. When catalase was included in the anode, this current decrease was not observed, showing the importance of catalase to scavenge reactive oxygen species produced by the thylakoids during photoelectrocatalysis

Investigating the reversible inhibition model of laccase by hydrogen peroxide for bioelectrocatalytic applications

pre-printThe reversible inhibition of laccase by H2O2 as a bioelectrocatalyst was studied in mediated- and direct electron transfer-based configurations to understand the differences in mechanism. The reversible inhibition of laccase follows a noncompetitive inhibition model when 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) is used as an electron mediator, whereas laccase is inhibited by an uncompetitive inhibition model when anthracene-moieties are used to intelligently "dock" laccase to electrodes (consisting of multi-walled carbon nanotubes, MWCNTs) which afford direct electron transfer (DET). This further confirms the efficient orientation of laccase onto suitably-designed docking moieties for bioelectrocatalysis applications

In recognition of Adam Heller and his enduring contributions to electrochemistry

pre-printRecent progress in diverse scientific fields ranging from bioelectrochemistry to battery technology to photoconversion has been deeply influenced by the contributions of Professor Adam Heller of the University of Texas at Austin to electrochemistry and materials science. This focus issue recognizes Prof. Heller's career and works on the occasion of his 80th birthday. It grew from a special symposium in Heller's honor at the 224th Meeting of ECS in San Francisco in the fall of 2013