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The strengths and weaknesses of the technology in the context of specific classes of applications, and areas where additional knowledge is required to properly exploit biological fuel cells are focused. Enzymatic biofuel cells are discussed.

A description of a carbon fiber biofuel cell is presented.

Research applying the method of 'wired' Lacasse cathode to the process of electroreduction of the high current density of oxigen to water at pH5 is presented. Particular attention is given to electrocatalytic reductions of oxygen.

The high efficiency of cascade reactions in supramolecular enzyme nanoassemblies, known as metabolons, has attracted substantial attention in various fields ranging from fundamental biochemistry and molecular biology to recent applications in biofuel cells, biosensors, and chemical synthesis. One reason for the high efficiency of metabolons is the structures formed by sequential enzymes that allow the direct transport of intermediates between consecutive active sites. The supercomplex of malate dehydrogenase (MDH) and citrate synthase (CS) is an ideal example of the controlled transport of intermediates via electrostatic channeling. Here, using a combination of molecular dynamics (MD) simulations and a Markov state model (MSM), we examined the transport process of the intermediate oxaloacetate (OAA) from MDH to CS. The MSM enables the identification of the dominant transport pathways of OAA from MDH to CS. Analysis of all pathways using a hub score approach reveals a small set of residues that control OAA transport. This set includes an arginine residue previously identified experimentally. MSM analysis of a mutated complex, where the identified arginine is replaced by alanine, led to a 2-fold decrease in transfer efficiency, also consistent with experimental results. This work provides a molecular-level understanding of the electrostatic channeling mechanism and will enable the further design of catalytic nanostructures utilizing electrostatic channeling., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

The electrochemical reduction of CO 2 is widely studied as a sustainable alternative for the production of fuels and chemicals. The electrolyte's bulk pH and composition play an important role in the reaction activity and selectivity and can affect the extent of the buildup of pH gradients between the electrode surface and the bulk of the electrolyte. Quantifying the local pH and how it is affected by the solution species is desirable to gain a better understanding of the CO 2 reduction reaction. Local pH measurements can be realized using Scanning Electrochemical Microscopy (SECM); however, finding a pH probe that is stable and selective under CO 2 reduction reaction conditions is challenging. Here, we have used our recently developed voltammetric pH sensor to perform pH measurements in the diffusion layer during CO 2 reduction using SECM, with high time resolution. Using a 4-hydroxylaminothiophenol (4-HATP)/4-nitrosothiophenol (4-NSTP) functionalized gold ultramicroelectrode, we compare the local pH developed above a gold substrate in an argon atmosphere, when only hydrogen evolution is taking place, to the pH developed in a CO 2 atmosphere. The pH is monitored at a fixed distance from the surface, and the sample potential is varied in time. In argon, we observe a gradual increase of pH, while a plateau region is present in CO 2 atmosphere due to the formation of HCO 3 - buffering the reaction interface. By analyzing the diffusion layer dynamics once the sample reaction is turned "off", we gain insightful information on the time scale of the homogeneous reactions happening in solution and on the time required for the diffusion layer to fully recover to the initial bulk concentration of species. In order to account for the effect of the presence of the SECM tip on the measured pH, we performed finite element method simulations of the fluid and reaction dynamics. The results show the significant localized diffusion hindrance caused by the tip, so that in its absence, the pH values are more acidic than when the tip is present. Nonetheless, through the simulation, we can account for this effect and estimate the real local pH values across the diffusion layer., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Electrochemical activation of glassy carbon, carbon paper and functionalized carbon nanotubes via high-applied-potential cyclic voltammetry leads to the formation of adsorbed, redox active functional groups and increased active surface area. Electrochemically activated carbon electrodes display enhanced activity toward nicotinamide adenine dinucleotide (NADH) oxidation, and more importantly, dramatically improved adsorption of bioelectrochemically active azine dyes. Adsorption of methylene green on an electroactivated carbon electrode yields a catalyst layer that is 1.8-fold more active toward NADH oxidation than an electrode prepared using electropolymerized methylene green. Stability studies using cyclic voltammetry indicate 70% activity retention after 4000 cycles. This work further facilitates the electrocatalysis of NADH oxidation for bioconversion, biosensor and bioenergy processes.

We report on the synthesis of thin, transparent, and highly catalytic carbon nanotube films. Nanotubes catalyze the reduction of triiodide, a reaction that is important for the dye-sensitized solar cell, with a charge-transfer resistance as measured by electrochemical impedance spectroscopy that decreases with increasing film thickness. Moreover, the catalytic activity can be significantly enhanced by exposing the nanotubes to ozone in order to introduce defects. Ozone-treated, defective nanotube films could serve as catalytic, transparent, and conducting electrodes for the dye-sensitized solar cell. Other possible applications include batteries, fuel cells, and electroanalytical devices.

Stimulus-responsive, or "smart" protein-based hydrogels are of interest for many bioengineering applications, but have yet to include biological activity independent of structural functionality. We have genetically engineered bifunctional building blocks incorporating fluorescent proteins that self-assemble into robust and active hydrogels. Gelation occurs when protein building blocks are cross-linked through native protein-protein interactions and the aggregation of alpha-helical hydrogel-forming appendages. Building blocks constructed from different fluorescent proteins can be mixed to enable tuning of fluorescence loading and hydrogel strength with a high degree of independence. FRET experiments suggest a macro-homogeneous structure and that intragel and interprotein reactions can be engineered. This design approach will enable the facile construction of complex hydrogels with broad applicability.