Performance of Reduced Titanium Oxide and Boron Doped Diamond as anodes in hyperthermophilic bioelectrochemical systems
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | E3S Web of Conferences |
| Authors | Laura Malavola, Silvia Franz, Massimiliano Bestetti, Nunzia Esercizio, Giuliana dâIppolito |
| Institutions | National Research Council, Politecnico di Milano |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the performance of Reduced Titanium Oxide (RTO), Boron Doped Diamond (BDD), and Carbon Cloth (CC) as anodes in hyperthermophilic bioelectrochemical systems (BES) operating at 80 °C using Thermotoga neapolitana.
- Material Comparison: RTO was synthesized via a cost-effective Plasma Electrolytic Oxidation (PEO) and reduction process, offering a promising alternative to expensive BDD and standard CC.
- Biofilm Colonization: T. neapolitana rapidly colonized all tested anodic materials, confirming their strong affinity for positive polarization and feasibility for BES application.
- Capacitive Enhancement (RTO): RTO exhibited a significant capacitive effect (5.58 mC/cm2) upon biofilm formation, attributed to ionic species within the hyperthermophilic toga, which enhance surface conductivity and current exchange.
- Inert Performance (BDD): BDD maintained its inert behavior, showing no capacitive effect, only an increase in faradaic current density. This makes BDD the preferred material for high-voltage regimes where maintaining anaerobic conditions and preventing charge exchange via the biofilm is critical.
- CC Performance: Carbon Cloth showed a lower capacitive contribution (0.77 mC/cm2) compared to RTO, suggesting RTO is superior if leveraging biofilm interaction for conductivity enhancement is desired.
- Engineering Implication: The choice of anode depends on the operational goal: RTO for economic systems benefiting from biofilm-enhanced conductivity, or BDD for high-stability, high-voltage systems requiring minimal biofilm interaction.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| BES Operating Temperature | 80 | °C | Hyperthermophilic conditions |
| CV Scan Rate | 50 | mV/s | Cyclic Voltammetry measurements |
| CV Potential Range (Anodic) | 0 to 1 | V | vs Ag/AgCl reference electrode |
| RTO Capacitive Charge Density | 5.58 | mC/cm2 | Biofilm contribution (RTO) |
| CC Capacitive Charge Density | 0.77 | mC/cm2 | Biofilm contribution (Carbon Cloth) |
| RTO Film Thickness (PEO) | ~3 | ”m | Porous TiO2 coating thickness |
| RTO Thermal Treatment Temperature | 450 | °C | Post-PEO treatment in air (3 hours) |
| RTO Electrochemical Reduction Current Density | 10 | mA/cm2 | Reduction step duration: 10 minutes |
| BDD OER Overpotential (η) | 1.6 | V | Reference material performance |
| RTO (Sample C) OER Overpotential (η) | 1.8-1.9 | V | Optimized RTO material performance |
| PEO Voltage (TiO2 formation) | 150 | V | Synthesis of RTO precursor |
| Biofilm Thickness (RTO1, cracked) | ~250 | nm | Observed post-experiment biofilm layer |
Key Methodologies
Section titled âKey MethodologiesâThe optimized Reduced Titanium Oxide (RTO, Sample C) was prepared and tested alongside commercial Boron Doped Diamond (BDD) and Carbon Cloth (CC) in a hyperthermophilic bioelectrochemical system.
- RTO Synthesis (Three Steps):
- Plasma Electrolytic Oxidation (PEO): C.p. titanium plates were oxidized in 1.5 M H2SO4 at 0 °C, applying 150 V (maximum current 10 A) for 5 minutes to form a porous TiO2 coating.
- Thermal Treatment: Samples were heat-treated in an air environment at 450 °C for 3 hours.
- Electrochemical Reduction: Samples were reduced at a current density of 10 mA/cm2 for 10 minutes in 1.5 M H2SO4 at 0 °C (using a Pt counter electrode).
- Culture Preparation: 250 mL of ATCC 1977 culture broth (containing 5 g/L glucose) was sparged with CO2 to ensure anaerobic conditions.
- Inoculation: The electrochemical bioreactor was inoculated with 7 mL of pre-acclimated Thermotoga neapolitana subsp. capnolactica (DSM33033) batch culture.
- Electrochemical Testing: Cyclic Voltammetry (CV) was performed 24 hours after inoculation in the anodic region (0-1 V vs Ag/AgCl) at a scan rate of 50 mV/s.
- Capacitive Contribution Analysis: The capacitive charge density generated by the biofilm was estimated by integrating the 4th CV cycle and subtracting the charge density measured in abiotic conditions from the charge density measured in biotic conditions.
- Surface Characterization: Electrodes were dried and analyzed using Scanning Electron Microscopy (SEM, Tescan Mira 3) at 20 kV to visualize biofilm colonization and morphology.
Commercial Applications
Section titled âCommercial ApplicationsâThe tested materials and system design are relevant to several high-performance electrochemical and bioenergy sectors:
- Microbial Electrolysis Cells (MECs): Direct application in MECs for enhanced biohydrogen production, leveraging the high kinetics achieved by T. neapolitana at 80 °C.
- High-Temperature Bio-Reactors: Design and implementation of robust electrode materials (RTO, BDD) for industrial fermentation or bio-conversion processes operating under hyperthermophilic conditions (80 °C and greater).
- Wastewater Treatment (Advanced Oxidation): Utilizing BDD anodes for the efficient electrochemical oxidation of recalcitrant organic matter in wastewater, benefiting from BDDâs high chemical inertness and OER overpotential.
- Cost-Effective Electrode Manufacturing: The RTO synthesis method (PEO followed by reduction) offers a scalable and economical route for producing high-surface-area, conductive titanium-based anodes compared to complex BDD production.
- Bio-Integrated Energy Systems: Developing RTO electrodes that actively utilize the capacitive properties of the adherent biofilm to improve overall charge transfer and system conductivity in bioelectrochemical devices.
View Original Abstract
This work investigates Reduced Titanium Oxide (RTO) in comparison with Carbon Cloth (CC) and commercial Boron Doped Diamond (BDD) as anodes in hyperthermophilic bioelectrochemical systems operating at 80°C by Thermotoga neapolitana . Two samples of RTO were synthesized by plasma electrolytic oxidation (PEO) of titanium plates and subsequent electrochemical reduction. Electrochemical performance of CC, BDD, and RTO are tested by performing cyclic voltammetry in the anodic region (0-1V, 50 mV/s), in abiotic and biotic conditions. The surface of colonized materials is observed by SEM microscopy. Results show that bacteria fast settle on all tested material, significantly affecting their electrochemical conductivity. The integration of voltammetric cycles reveals that biofilm generates capacitive effects on the anodic surfaces, particularly evident in RTO, less in CC and absent in BDD. Charge densities provided by capacitive response of RTO and CC are of the order of 5.58 and 0.77 mC/cm 2 , respectively.