The key operating characteristics of biofuel cells, high energy density and low power delivery, make them ideal power choices for military, industrial, and niche wireless sensor network applications. There is virtually universal demand for higher energy power supplies for wireless sensors to enable longer operation, more frequent data capture, and higher bandwidth sensing techniques such as video. Advanced biofuel cell technology has been demonstrated for such applications that is capable of 2 -4Â increase in energy density compared to incumbent batteries of a similar size.

Although biofuel cell research has progressed over the past decade, there were still problems with employing enzymes at air-breathing cathodes, because enzymes need to remain hydrated and most enzyme reactions occur in solution and not in gas phase. This research details an approach to the development of an air-breathing biocathode employing direct electron transfer. This laccase biocathode is studied in two different fuel cell configurations: a proton exchange membrane hydrogen/air fuel cell and a direct methanol fuel cell (DMFC) with an anion exchange membrane. The laccase from the Rhus vernificera biocathode with an enzyme loading of 0.224mg/cm2 provides fuel crossover tolerance and provides a high operational current density of 50.0mA/cm2 and a maximum power density of 8.5mW/cm2 in a 40% methanol DMFC. The laccase biocathode shows a lifetime of 290 h in a DMFC. The hydrogen/air fuel cell provides a stable current for a total of 350 discontinuous hours when operated for 8 h daily.

Voltammetric currents of transition metal complexes in films on electrodes increase with electron self exchange (hopping) rate k11. In films, diffusion coefficients Df∝k11c*f, where k11 sets frequency of electron hopping attempts and c*f film concentration sets distance between probes. Cyclic voltammetry of Nafion films on electrodes for six probes, tris(2,2′-bipyridyl) complexes, M(bpy)z +3 where Mz + is Ru2+, Os2+, Fe2+, Cr3+, Co3+, and Co2+, demonstrates Df varies linearly with kH2O11, literature k11 measured in water. From density of Ru(bpy)2 +3 exchanged Nafion 1.95 g/cm3 and nominal equivalent weight 1100, geometry establishes volume limited, z-independent c*f for all M(bpy)z +3. For concentrations of Ru(bpy)2 +3 in HNO3 where either Ru(bpy)2 +3: HNO3 ratio is fixed or Ru(bpy)2 +3 is 1 mM and HNO3 varies, c*f is statistically invariant. Based on aqueous titrations and dielectric constant sufficient to support ions, electron hopping is confined to hydrated domains of Nafion. From c*f, k11 in Nafion kNaf11 is estimated as k11Naf=0.010k11H2O, consistent with higher ion concentration in Nafion. Measured Df is 2 × 10− 9 cm2/s for Ru(bpy)2 +3 and Os(bpy)2 +3; 1 × 10− 10 cm2/s for Fe(bpy)2 +3 and Cr(bpy)3 +3; and 1.5 × 10− 12 and 5 × 10− 12 cm2/s for Co(bpy)2 +3 and Co(bpy)3 +3. For physical diffusion Dp ≲ 10− 12 cm2/s. A self consistent view of M(bpy)z +3 self exchange in Nafion is outlined. For Os(bpy)2/33, kH2O11 ≈ 4.5 × 108/Ms.

Magnetic fields at electrodes increase flux through dynamics. Magnetically modified electrodes sustain a permanent magnetic field because magnetic materials are either attached to the electrode surface or incorporated into the electronic conductor of the electrode. Thus far, magnetically modified electrodes have been produced by coating electrode surfaces with composites of Nafion and magnetic microparticles. Glassy carbon and platinum electrodes as well as fuel cell electrodes modified with Nafion and magnetic microparticles exhibit enhanced flux as compared to similar nonmagnetic composites. Here, magnet incorporated carbon electrodes (MICEs) are presented. Two examples are described: magnet incorporated carbon paste electrodes (MICE-Ps) and magnet incorporated carbon epoxy electrodes (MICE-Es). Voltammetrically driven fluxes for MICEs are higher than those for the corresponding nonmagnetic controls (carbon paste (CPEs) and carbon epoxy (CEEs) electrodes).

Nitrate contamination of groundwater is a major problem, especially in farming areas where nitrogen-based fertilizers are used. Geobacter sulfurreducens electrodes were electrochemically evaluated for their ability to reduce nitrate with implications for groundwater remediation. G. sulfurreducens were optimized for nitrate reduction by modifying growth media during subculture. The Geobacter were then cast on Toray carbon paper electrodes and immobilized with pectin. Cyclic voltammetry demonstrated that the electrodes bioelectrocatalytically reduce nitrate with an onset potential of −0.25 V vs. SCE. Amperometry was used to evaluate nitrate concentrations between 0.5 and 270 mM. The limit of detection is 8 mM with a linear range of 20 mM to 160 mM. Evaluation by a Michaelis Menten kinetic model yields a K M of 110 ± 10 mM. The Geobacter sulfurreducens electrodes were incorporated into a nitrate reducing microbial fuel cell which was fed nitrate contaminated water by a peristaltic pump and hydrogen from a proton exchange membrane (PEM)-based water electrolysis cell and yielded a remediation rate of 6 mg/cm 2 /day.