Lab

X-LAB

About the lab

We are an interdisciplinary research lab at Hasselt University, Belgium, working in cross-exploratory cross-over research. We are mainly a group of physicists working on the understanding of cable bacteria, organic solar cells and wastewater treatment.

Featured projects (1)

Featured research (6)

The plant microbial fuel cell is a fascinating technology that combines plants and bacteria to produce electricity. As sunlight is converted into electric power, plant microbial fuel cells can be compared to photovoltaics on various levels. To investigate to what extent this comparison goes up, a rough upper limit for the energy conversion efficiency of plant microbial fuel cells was calculated and compared to various photovoltaic classes. By examining each step in the process, with the accompanying losses, the maximum power conversion efficiency of a plant microbial fuel cell was estimated to be around 0.92%. Although this efficiency is relatively low, the plant microbial fuel cell does have attractive features making them more interesting than photovoltaics, such as price, simplicity, self-sustainability, working during the night, etc. Moreover, a unique feature is that plant microbial fuel cells can be used as low-power environmental sensors and for environmental remediation. These multidisciplinary features account for the unique place the plant microbial fuel cell currently has in the world of environmental, renewable – and particularly solar – energy research.
This work presents a novel method of local contact openings formation in an Aluminum Oxide (Al2O3) rear surface passivation layer by the selenization of the Lithium Fluoride (LiF) salt on top of the Al2O3 for ultra-thin CIGS solar cells. This study introduces the potentially cost-effective, fast, industrially viable, and environmentally friendly way to create the nano-sized contact openings with the homogeneous distribution in the thick, i.e., up to 30 nm, Al2O3 passivation layer. The passivation layer is deposited by atomic layer deposition (ALD), while the LiF layer is spin-coated. Selenization is done in the H2Se atmosphere and the optimal process parameters are deduced to obtain nano-sized and uniformly allocated openings as confirmed by scanning electron microscopy (SEM) images. The contact openings were produced in the different thicknesses of the alumina layer from 6 nm to 30 nm. Furthermore, the aluminum oxide rear surface passivation layer with the contact openings was implemented into ultra-thin CIGS solar cell design, and one trial set was produced. We demonstrated that the created openings facilitate the effective current collection through the dielectric Al2O3 layer up to 30 nm thick. However, the upper limit of aluminum oxide thickness in which the contact openings can be created by the described method is not established yet. The produced passivated CIGS solar cells show increased EQE response due to the optical enhancement of the passivated cells. However, the production of solar cells on the Al2O3 passivation layer with the openings created by selenization of LiF is not optimized yet.
Cable bacteria are electroactive bacteria that form a long, linear chain of ridged cylindrical cells. These filamentous bacteria perform centimeter-scale long-range electron transport through parallel, interconnected conductive pathways of which the detailed chemical and electrical properties are still unclear. Here, we combine ToF-SIMS (time of flight secondary ion mass spectrometry) and AFM (atomic force microscopy) to investigate the structure and composition of this naturally-occurring electrical network. The enhanced lateral resolution achieved allows differentiation between the cell body and the cell-cell junctions that contain a conspicuous cartwheel structure. Three ToF-SIMS modes were compared in the study of so-called fiber sheaths (i.e., the cell material that remains after removal of cytoplasm and membranes and which embeds the electrical network). Among these, fast imaging delayed extraction (FI-DE) was found to balance lateral and mass resolution, thus yielding multiple benefits in the study of structure-composition relations in cable bacteria: (i) it enables the separate study of the cell body and cell-cell junctions, (ii) by combining FI-DE with in-situ AFM, the depth of Ni-containing protein - key in the electrical transport - is determined with greater precision, and (iii) this combination prevents contamination, which is possible when using an ex-situ AFM. Our results imply that the interconnects in extracted fiber sheaths are either damaged during extraction, or that their composition is different from fibers, or both. From a more general analytical perspective, the proposed methodology of ToF-SIMS in FI-DE-mode combined with in-situ AFM holds great promise for studying the chemical structure of other biological systems.
Abstract Filamentous cable bacteria exhibit long-range electron transport over centimetre-scale distances, which takes place in a parallel fibre structure with high electrical conductivity. Still, the underlying electron transport mechanism remains undisclosed. Here we determine the intrinsic electrical properties of the conductive fibres in cable bacteria from a material science perspective. Impedance spectroscopy provides an equivalent electrical circuit model, which demonstrates that dry cable bacteria filaments function as resistive biological wires. Temperature-dependent electrical characterization reveals that the conductivity can be described with an Arrhenius-type relation over a broad temperature range (− 195 °C to + 50 °C), demonstrating that charge transport is thermally activated with a low activation energy of 40–50 meV. Furthermore, when cable bacterium filaments are utilized as the channel in a field-effect transistor, they show n-type transport suggesting that electrons are the charge carriers. Electron mobility values are ~ 0.1 cm2/Vs at room temperature and display a similar Arrhenius temperature dependence as conductivity. Overall, our results demonstrate that the intrinsic electrical properties of the conductive fibres in cable bacteria are comparable to synthetic organic semiconductor materials, and so they offer promising perspectives for both fundamental studies of biological electron transport as well as applications in microbial electrochemical technologies and bioelectronics.

Lab head

Members (6)

Raghavendran Thiruvallur Eachambadi
  • SEM/Dualbeam (FIB) specialist
Rob Cornelissen
  • Hasselt University
Robin Bonné
  • Aarhus University
Nico Fransaert
  • Hasselt University
Koen Wouters
  • Hasselt University
Thessa Van Limbergen
  • Hasselt University
Jeroen Hustings
Jeroen Hustings
  • Not confirmed yet

Alumni (1)

Ji-Ling Hou
Ji-Ling Hou