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Quinones are dual compounds able to extract photosynthetic electrons from living organisms but with long-term poisoning effects., Plants, algae, and some bacteria convert solar energy into chemical energy by using photosynthesis. In light of the current energy environment, many research strategies try to benefit from photosynthesis in order to generate usable photobioelectricity. Among all the strategies developed for transferring electrons from the photosynthetic chain to an outer collecting electrode, we recently implemented a method on a preparative scale (high surface electrode) based on a Chlamydomonas reinhardtii green algae suspension in the presence of exogenous quinones as redox mediators. While giving rise to an interesting performance (10–60 μA cm–2) in the course of one hour, this device appears to cause a slow decrease of the recorded photocurrent. In this paper, we wish to analyze and understand this gradual fall in performance in order to limit this issue in future applications. We thus first show that this kind of degradation could be related to over-irradiation conditions or side-effects of quinones depending on experimental conditions. We therefore built an empirical model involving a kinetic quenching induced by incubation with quinones, which is globally consistent with the experimental data provided by fluorescence measurements achieved after dark incubation of algae in the presence of quinones.

Photosynthesis can be views as the conversion of carbon dioxide and water into organic matter and dioxygen. Used by algae, plants or some bacteria, photosynthesis efficiency is limited because only 4% of light energy is converted into chemical energy. Under high light conditions, this can induce serious damages of the photosynthetic machinery. Besides, if considering the current environmental context, this limitation is an opportunity to use the part of not converted energy to generate some useable electricity. The aim of the work developed in this manuscript is thus to create an additional pathway for derivating the photosynthetic electrons flow. In this way, the system damages are expected to be reduced under hight light conditions as well as some photocurrent to be generated. This is why an experimental set-up involving carbon working electrode and some quinone type redox mediators has been developed. The quinone ability to accept some electrons from Photosystem II has been studied by the mean of fluorescence techniques. Their ability to be re-oxidised at the carbon electrode surface has been investigated by cyclic voltametry. As a conclusion, the best quinones (selected after the fluorescence investigations) are DCBQ and PPBQ and correspond to photocurrent values about several µA.cm-2. A correlation between experimental data and theoretical predictions helped us to best understand the photosynthetic electrons derivation pathway and to evidence concomitant phenomenon like poisoning and quinone partition effects.; La photosynthèse consiste en la conversion photo-induite du dioxyde de carbone et de l'eau en matière organique et en dioxygène. Utilisée par les algues, les plantes ou certaines bactéries, la photosynthèse est pourtant intrinsèquement bridée puisque seulement 4 % de l'énergie lumineuse sont convertis en énergie chimique. Sous forte irradiation, ceci peut engendrer une dénaturation de l'appareil photosynthétique. Par ailleurs, dans le contexte environnemental actuel, cette limitation représente également une opportunité d'utiliser l'énergie non convertie sous forme d'énergie électrique. Le travail présenté dans ce manuscrit a donc pour but de créer une voie secondaire d'écoulement des électrons photosynthétiques excédentaires afin de réduire l'endommagement du système sous forte irradiation et de les transcrire sous la forme d'un photo-courant. C'est pourquoi un système impliquant une électrode collectrice de carbone et des médiateurs redox de type quinone a été envisagé. La capacité acceptrice de certaines quinones, connues pour être de bons accepteurs du Photosystème II, a été évaluée au moyen d'études de fluorescence. La facilité de restitution des électrons dérivés par les quinones réduites a été quant à elle étudiée par électrochimie. Au bilan, les meilleures quinones (DCBQ, PPBQ) permettent d'obtenir des photo-courants de l'ordre de quelques µA.cm-2. La corrélation entre données expérimentales et théorie a également permis de mieux cerner le mécanisme de dérivation des électrons photosynthétiques par les quinones exogènes mais aussi de mettre en évidence des effets d'empoisonnement et/ou de perte d'accepteur dans les membranes.