Performance of Reduced Titanium Oxide and Boron Doped Diamond as anodes in hyperthermophilic bioelectrochemical systems

At a Glance

Metadata	Details
Publication Date	2022-01-01
Journal	E3S Web of Conferences
Authors	Laura Malavola, Silvia Franz, Massimiliano Bestetti, Nunzia Esercizio, Giuliana d’Ippolito
Institutions	Ricerca sul Sistema Energetico (Italy), National Research Council
Analysis	Full AI Review Included

Technical Documentation & Analysis: Boron Doped Diamond Anodes in Hyperthermophilic Bioelectrochemical Systems

Source Paper: E3S Web of Conferences 334, 08009 (2022)

Executive Summary

This research validates the critical role of Boron Doped Diamond (BDD) as the benchmark anode material for high-performance, hyperthermophilic bioelectrochemical systems (80 °C).

Superior Inertness: Commercial BDD demonstrated exceptional chemical inertness, exhibiting an overpotential for Oxygen Evolution Reaction (OER) of 1.6 V, significantly lower than RTO or Carbon Cloth (CC).
Stable Biotic Performance: BDD uniquely showed no microbial-induced capacitive effects (0 mC/cm²), confirming its stability and reliability in high-temperature, biotic environments colonized by Thermotoga neapolitana.
High Current Capability: BDD achieved the highest initial current density (1760 µA/cm²), positioning it as the ideal choice for high-voltage regimes and efficient oxidation of organic matter.
Application Validation: The study confirms BDD’s suitability for microbial electrolytic cells where maintaining anaerobic conditions and preventing charge exchange involving the biofilm are paramount.
6CCVD Value Proposition: While the paper notes BDD’s high cost and complex production, 6CCVD specializes in scalable, high-quality MPCVD BDD wafers, addressing these limitations for industrial and research scale-up.

Technical Specifications

The following hard data points were extracted, focusing on the performance of the Boron Doped Diamond (BDD) reference material.

Parameter	Value	Unit	Context
Anode Material Reference	BDD (Commercial)	N/A	Used for comparison against RTO and CC
Initial Current Density (i₀)	1760	µA/cm²	BDD performance in abiotic medium
Final Current Density (i₁₂₀₀)	487	µA/cm²	BDD performance after 1200 seconds
OER Overpotential ($\eta$)	1.6	V	BDD performance (lowest tested)
Operating Temperature	80	°C	Hyperthermophilic system environment
CV Scan Rate	50	mV/s	Anodic region (0-1 V vs Ag/AgCl)
BDD Capacitive Effect	Absent	N/A	Key finding: Stable performance in biotic medium
RTO Capacitive Charge Density	5.58	mC/cm²	Capacitive effect attributed to biofilm formation
RTO Biofilm Thickness (RTO1)	$\approx$250	nm	Observed via SEM
Working Voltage (SEM)	20	KV	SEM analysis instrumentation setting

Key Methodologies

The experiment compared commercial BDD against Reduced Titanium Oxide (RTO) and Carbon Cloth (CC) under hyperthermophilic conditions.

RTO Synthesis: RTO was prepared starting from c.p. titanium plates, followed by Plasma Electrolytic Oxidation (PEO) (150 V, 10 A, 5 min in 1.5 M H₂SO₄ at 0 °C).
Post-Treatment (RTO Sample C): The best-performing RTO sample (C) underwent thermal post-treatment in air (450 °C for 3h) followed by electrochemical reduction (10 mA/cm² for 10 min in 1.5 M H₂SO₄ at 0 °C).
Inoculum and Media: Thermotoga neapolitana subsp. capnolactica (DSM33033) was inoculated into ATCC 1977 culture broth (5 g/L glucose). CO₂ gas was sparged to ensure anaerobic conditions.
System Operation: The double chamber electrochemical bioreactor was operated at 80 °C, applying a voltage of 1.5 $\pm$ 0.1 V between the electrodes.
Electrochemical Testing: Cyclic Voltammetry (CV) was performed in the anodic region (0-1 V vs Ag/AgCl, 50 mV/s) on the anodes, repeated in both abiotic and biotic conditions (24 h post-inoculum).
Capacitive Analysis: Capacitive effects were quantified by integrating the difference in charge density exchanged through anodic current between biotic and abiotic conditions.
Surface Characterization: Scanning Electron Microscopy (SEM) was used to analyze biofilm colonization on all electrode surfaces.

6CCVD Solutions & Capabilities

The research confirms that Boron Doped Diamond (BDD) is the optimal material for stable, high-performance anodes in demanding electrochemical environments, particularly where microbial interaction must be minimized. 6CCVD provides the necessary high-quality, scalable BDD solutions to replicate and advance this research.

Applicable Materials

To replicate the high-performance, inert anode behavior demonstrated by BDD, 6CCVD recommends:

Heavy Boron Doped SCD (Single Crystal Diamond): For applications requiring the highest purity, lowest defect density, and ultra-smooth surface finish (Ra < 1nm). Ideal for fundamental research and high-precision electrochemical sensing.
Heavy Boron Doped PCD (Polycrystalline Diamond): Recommended for scaling up bioelectrochemical systems. 6CCVD offers PCD wafers up to 125mm in diameter, overcoming the size limitations often associated with commercial BDD.

Customization Potential

The successful implementation of BDD in high-current density systems requires precise material engineering and robust electrical integration. 6CCVD offers comprehensive customization capabilities:

Research Requirement	6CCVD Customization Service	Technical Specification Match
Large Area Anodes	Custom PCD Plates/Wafers	Dimensions up to 125mm diameter, enabling scale-up of reactor size.
Optimized Conductivity	Custom Doping Levels	Precise control over boron concentration to achieve specific resistivity (e.g., 10^-3 to 10^-1 $\Omega$$\cdot$cm) for high current density operation (1760 µA/cm²).
Robust Electrical Contact	Custom Metalization	In-house deposition of Au, Pt, Pd, Ti, W, or Cu layers, ensuring low-resistance contacts necessary for high-voltage/high-current regimes.
Thickness Control	SCD/PCD Thickness Control	SCD and PCD layers available from 0.1µm up to 500µm, allowing optimization of material usage and thermal management.
Surface Quality	Precision Polishing	Polishing services to achieve Ra < 1nm (SCD) or Ra < 5nm (PCD), critical for minimizing non-uniform biofilm adhesion.

Engineering Support

The comparison between BDD (inert, no capacitive effect) and RTO (highly capacitive, 5.58 mC/cm²) highlights a key design choice in bioelectrochemical systems: whether the anode should participate in charge transfer via biofilm interaction or remain purely inert.

6CCVD’s in-house PhD team provides expert consultation on material selection, ensuring the chosen diamond material (SCD or PCD BDD) meets the specific electrochemical criteria for hyperthermophilic bioelectrochemical systems and other demanding applications like water treatment or sensing. We assist engineers in defining the optimal doping level and surface preparation to achieve desired OER overpotentials and current densities.

Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

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.

Tech Support

Original Source

DOI: https://doi.org/10.1051/e3sconf/202233408009