Grégory Bataillou defends his PhD on Jan. 31, 2023 at 2:00PM.
Place : Ecole Centrale de Lyon,bâtiment W1, Amphi 202
Jury :
Rapporteurs
Chantal Gondran, Professeure au Département de Chimie Moléculaire de l’Université Grenoble Alpes
Charafeddine Jama, Professeur à l’unité Matériaux et Transformations de l’Institut Centrale de Lille
Examinateurs
Fabrice Martin-Laurent, Directeur de recherches à l’UMR Agroécologie de Dijon, président de séance
Nicolas Forquet, Ingénieur de recherche à l’unité de recherche REVERSAAL à l’INRAE de Lyon
Encadrement
Christian Vollaire, Professeur au laboratoire Ampère, directeur de thèse
Naoufel Haddour, Maître de conférences au laboratoire Ampère, encadrant de thèse
Abstract :
Plant microbial fuel cells are systems that convert solar energy into electrical energy via the growth of plants. In fact, these electrochemical systems can produce electricity from bacterial oxidation of organic compounds released by the roots while the plant is growing. Several plants have been tested, but mostly waterlogged plants : paddy rice, Spartina Anglica, reeds, etc. Maximal power density record was obtained with plants growing in salt marsh and a bio-cathode (dioxygen reduction is catalyzed by an electroactive biofilm).To reduce economic impact of plant microbial fuel cells, many factors are studied and optimized in literature. However, the system is quite complex, which make it difficult to identify real impacts of secluded parameters.
In this context, this thesis aims at the multi-criteria optimization of plant-based biofuel technology according to
an eco-responsible approach, for an application to autonomous sensors.
First, plant microbial fuel cells have been studied as an energy source for supplying autonomous sensors. Given that scale-up of these systems require stacking rather than increasing the size of one microbial fuel cell, multiple configurations are studied. Stacking in series seemed to provide best performances, but it increases internal impedance. Besides, on strong current mode, voltage reversal phenomenon appeared at the weakest microbial fuel cell, as described in literature. Moreover, ionic connection between pots create short-circuits when plan microbial fuel cells are stacked in series. It is then better to opt for parallel connection when plants share the same soil. Once stacking study has been realized, the rest of this chapter focuses on the coupling with electronics. Multiple power management systems have been tested from literature, but quite a few of them adapt their impedance with the “Fractional Open Circuit Voltage” algorithm, which is not adapted to capacitive systems such as plant microbial fuel cells. Solutions have been proposed/tested to tackle this issue.
The previous study revealed some challenges in getting reproducible results. Based on that observation, a novel optimization methodology based on a multiparametric study of an electrochemical system using a simple redox couple as a model, potassium ferricyanide/ferrocyanide is proposed and studied. With this model, the impact of main design parameters has been studied more precisely. It has been shown that anode width could be reduced since it is not a limiting parameter. Conductivity is a key parameter for power increase, but beyond 11.5𝑚𝑆. 𝑐𝑚−1, the impedance of the system is mainly driven by electrodes/collectors’ resistivities. Besides, inter-electrode distance can be a major parameter in ohmic resistance, provided that ionic conductivity is low. Finally, presence of soil has an impact on ohmic resistance since it alters ionic diffusivity of the electrolyte. This alteration is greater as the soil particles are smaller.
Finally, to keep on the work on environmental and economic cost reduction, a new bio-sourced material is tested, as a substitute for classical oil-sourced carbon felt anodes: monolithic cedarwood-based biochar.
Biochar is the solid fraction of biomass pyrolysis, and it can become electrically conductive in certain pyrolysis conditions. Four different biomasses have been pyrolyzed at multiple temperatures and biochars obtained were characterized physicochemically. Then, based on anode wanted specifications, only cedarwood-based biochars, pyrolyzed at 700°C and 900°C have been selected as promising candidates for anode substitute. 900°C biochar has given better performances, and has been investigated more thoroughly. In soil microbial fuel cells, pots with biochar anodes could produce 27% more power density than pots with carbon felt anodes. Biochar has also been tested as a cathode catalyzer, but without interesting performances, although its selectivity towards 2-electron reduction of dioxygen into hydrogen peroxide could explain its anti-biofouling property.
Keywords :
Microbial fuel cell ; Plant microbial fuel cell ; optimization ; impedance ; Electrochemical
Impedance Spectroscopy ; biochar ; wood-based biochar ; stacking ; energy harvesting
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