Untreated vs. Treated Carbon Felt Anodes: Impacts on Power Generation in Microbial Fuel Cells.

This research sought to enhance the efficiency and biocompatibility of anodes in bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs), with an aim toward large-scale, real-world applications. The study focused on the effects of acid-heat treatment and chemical modification of three-dimensional porous pristine carbon felt (CF) on power generation. Different treatments were applied to the pristine CF, including coating with carbon nanofibers (CNFs) dispersed using dodecylbenzene sulfonate (SDBS) surfactant and biopolymer chitosan (CS). These processes were expected to improve the hydrophilicity, reduce the internal resistance, and increase the electrochemically active surface area of CF anodes. A high-resolution scanning electron microscopy (HR-SEM) analysis confirmed successful CNF coating. An electrochemical analysis showed improved conductivity and charge transfer toward [Fe(CN)6]3-/4- redox probe with treated anodes. When used in an air cathode single-chamber MFC system, the untreated CF facilitated quicker electroactive biofilm growth and reached a maximum power output density of 3.4 W m-2, with an open-circuit potential of 550 mV. Despite a reduction in charge transfer resistance (Rct) with the treated CF anodes, the power densities remained unchanged. These results suggest that untreated CF anodes could be most promising for enhancing power output in BESs, offering a cost-effective solution for large-scale MFC applications.

Cedar Wood-Based Biochar: Properties, Characterization, and Applications as Anodes in Microbial Fuel Cell.

In this study, the relationship between pyrolysis temperature of woody biomass and physicochemical properties of derived biochar was investigated for microbial fuel cell (MFC) application. Physical and chemical properties of biochar were characterized for different pyrolysis temperatures. Results showed that biochar obtained at 400 °C was not conductor, while biochars prepared at 600 °C, 700 °C, and 900 °C exhibited decreased electrical resistivity of (7 ± 6) × 103 Ω.m, (1.8 ± 0.2) Ω.m, and (16 ± 3) × 10-3 Ω.m, respectively. Rising pyrolysis temperature from 400 to 700 °C exhibited honeycomb-like macroporous structures of biochar with an increase in the specific surface area from 310 to 484 m2.g-1. However, the production of biochar at 900 °C reduced its specific surface area to 136 m2.g-1 and caused the loss of the ordered honeycomb structure. MFCs using anodes based on biochar prepared at 900 °C produced maximum power densities ((9.9 ± 0.6) mW.m-2) higher than that obtained with biochar pyrolyzed at 700 °C ((5.8 ± 0.1) mW.m-2) and with conventional carbon felt anodes ((1.9 ± 0.2) mW.m-2). SEM images of biochar-based anodes indicated the clogging of macropores in honeycomb structure of biochar prepared at 700 °C by growth of electroactive biofilms, which might impede the supply of substrate and the removal of metabolites from the inside of the electrode. These findings highlight that electrical conductivity of biochar is the major parameter for ensuring efficient anodes in microbial fuel cell application. Schematic representation of cedar wood-based biochar and its application as anode in MFC.

A membrane-less Glucose/O2 non-enzymatic fuel cell based on bimetallic Pd-Au nanostructure anode and air-breathing cathode: Towards micro-power applications at neutral pH.

Herein, the authors propose a miniaturized glucose/O2 n-EFC based on a new direct electron transfer. The anode is a screen-printed carbon electrode (SPCE) modified with functionalized carbon nanotubes (f-CNTs) and cauliflower-like PdAu nanostructures (PdAuNS). The PdAuNS/f-CNT biomimetic nanocatalyst was prepared using a cost-effective and straightforward method, which consisted of drop-casting well-dispersed f-CNTs over the SPCE surface before PdAuNS electrodeposition. This enzyme-free interface was used for glucose electrooxidation at neutral medium (pH 7.4). The electrochemical behaviour of the PdAuNS/f-CNT/SPCE was investigated using cyclic voltammetry, linear sweep voltammetry, and amperometry. Several parameters were optimized and discussed, including the metal precursor concentration (HAuCl4, PdCl2) and the electrodeposition conditions. The cathode for oxygen electroreduction is an air-cathode which is composed of Pt-coated carbon cloth. The electrochemical performances of the anode and the cathode were evaluated separately for glucose oxidation and oxygen reduction, respectively. Both electrodes were then assembled in a membrane-less single chamber n-EFC with an innovative architecture. Electrical characterization of the n-EFC supplied with a neutral buffered solution containing 20 mM glucose showed a maximal power output of 129 ± 11 µW cm-2, a current density of 600 ± 39 µA cm-2 with a cell voltage of 0.35 V, and an open circuit potential of 0.56 V. The proposed electrocatalyst possesses several advantages such as fast response, low cost, reusability, poison-free characteristics, and good stability. Hence, glucose/O2 n-EFC could be of great interest in direct glucose fuel cell applications (e.g., powering mountable/implantable biomedical micro-devices running at low electrical power supply) or in self-powered biosensing.

Nanoporous Cauliflower-like Pd-Loaded Functionalized Carbon Nanotubes as an Enzyme-Free Electrocatalyst for Glucose Sensing at Neutral pH: Mechanism Study.

In this work, we propose a novel functionalized carbon nanotube (f-CNT) supporting nanoporous cauliflower-like Pd nanostructures (PdNS) as an enzyme-free interface for glucose electrooxidation reaction (GOR) in a neutral medium (pH 7.4). The novelty resides in preparing the PdNS/f-CNT biomimetic nanocatalyst using a cost-effective and straightforward method, which consists of drop-casting well-dispersed f-CNTs over the Screen-printed carbon electrode (SPCE) surface, followed by the electrodeposition of PdNS. Several parameters affecting the morphology, structure, and catalytic properties toward the GOR of the PdNS catalyst, such as the PdCl2 precursor concentration and electrodeposition conditions, were investigated during this work. The electrochemical behavior of the PdNS/f-CNT/SPCE toward GOR was investigated through Cyclic Voltammetry (CV), Linear Sweep Voltammetry (LSV), and amperometry. There was also a good correlation between the morphology, structure, and electrocatalytic activity of the PdNS electrocatalyst. Furthermore, the LSV response and potential-pH diagram for the palladium-water system have enabled the proposal for a mechanism of this GOR. The proposed mechanism would be beneficial, as the basis, to achieve the highest catalytic activity by selecting the suitable potential range. Under the optimal conditions, the PdNS/f-CNT/SPCE-based biomimetic sensor presented a wide linear range (1-41 mM) with a sensitivity of 9.3 µA cm-2 mM-1 and a detection limit of 95 µM (S/N = 3) toward glucose at a detection potential of +300 mV vs. a saturated calomel electrode. Furthermore, because of the fascinating features such as fast response, low cost, reusability, and poison-free characteristics, the as-proposed electrocatalyst could be of great interest in both detection systems (glucose sensors) and direct glucose fuel cells.

Minimally Invasive Microelectrode Biosensors Based on Platinized Carbon Fibers for in Vivo Brain Monitoring.

The ability to monitor the chemical composition of brain interstitial fluid remains an important challenge in the field of bioanalytical chemistry. In particular, microelectrode biosensors are a promising resource for the detection of neurochemicals in interstitial fluid in both animals and humans. These biosensors can provide second-by-second temporal resolution and enzymatic recognition of virtually any redox or nonredox molecule. However, despite miniaturization of these sensors to 50-250 µm in diameter to avoid vascular and cellular injury, inflammation and foreign-body reactions still occur following their implantation. Here, we fabricated microelectrodes with platinized carbon fibers to create biosensors that have an external diameter that is less than 15 µm. Platinization was achieved with physical vapor deposition, and increased sensitivity to hydrogen peroxide and improved enzymatic detection were observed for these carbon fiber microelectrodes. When these devices were implanted in the brains of rats, no injuries to the parenchyma or brain blood vessels were detected. In addition, these microelectrodes provided different estimates of basal glucose, lactate, and oxygen concentrations compared to conventional biosensors. Induction of spreading depolarization in the cerebral cortex further demonstrated the greater sensitivity of our microelectrodes to dynamic neurochemical changes. Thus, these minimally invasive devices represent a major advance in our ability to analyze brain interstitial fluid.

Investigation of tip-depletion-induced fail in scanning capacitance microscopy for the determination of carrier type.

Scanning capacitance microscopy (SCM) was performed on an n-type Si multilayer structure doped by phosphorus whose concentration ranges from 2×1017 to 2×1019cm-3. Three types of tips were used, i.e. fresh Pt/Ir coated tip, worn Pt/Ir coated tip and non-coated commercial Si tip. The use of fresh Pt/Ir coated tips produces SCM result in good agreement with the doping profile including the correct identification of the carrier type. In contrast, a worn Pt/Ir coated tip which has lost its metal coating and a non-coated tip will fail to recognize successfully the carrier type for phosphorus dopant concentration above 8×1018cm-3 (identifying as p instead of n) due to the tip depletion effect. These results alert us to carefully interpret the SCM results, especially in the case for identification of carrier type inside the sample of interest which is unknown.

Silicon/SU8 multi-electrode micro-needle for in vivo neurochemical monitoring.

Simultaneous monitoring of glucose and lactate is an important challenge for understanding brain energetics in physiological or pathological states. We demonstrate here a versatile method based on a minimally invasive single implantation in the rat brain. A silicon/SU8-polymer multi-sensing needle-shaped biosensor, was fabricated and tested. The multi-electrode array design comprises three platinum planar microelectrodes with a surface area of 40 × 200 µm(2) and a spacing of 200 µm, which were micromachined on a single 3mm long micro-needle having a 100 × 50 µm(2) cross-section for reduced tissue damage during implantation. Platinum micro-electrodes were aligned at the bottom of micro-wells obtained by photolithography on a SU8 photoresist layer. After clean room processing, each micro-electrode was functionalized inside the micro-wells by means of a micro-dispensing device, either with glucose oxidase or with lactate oxidase, which were cross-linked on the platinum electrodes. The third electrode covered with Bovine Serum Albumin (BSA) was used for the control of non-specific currents. The thick SU8 photoresist layer has revealed excellent electrical insulation of the micro-electrodes and between interconnection lines, and ensured a precise localization and packaging of the sensing enzymes on platinum micro-electrodes. During in vitro calibration with concentrations of analytes in the mM range, the micro-wells patterned in the SU8 photoresist proved to be highly effective in eliminating cross-talk signals, caused by H2O2 diffusion from closely spaced micro-electrodes. Moreover, our biosensor was successfully assayed in the rat cortex for simultaneous monitoring of both glucose and lactate during insulin and glucose administration.