Photoelectrochemical Wiring of Paulschulzia pseudovolvox (Algae) to Osmium Polymer Modified Electrodes for Harnessing Solar Energy

Abstract

Studies on biological photovoltaics based on intact organisms are challenging and in most cases include diffusing mediators to facilitate electrochemical communication with electrodes. However, using such mediators is impractical. Instead, surface confined Os‐polymers have been successfully used in electrochemical studies including oxidoreductases and bacterial cells but not with algae. Photoelectrogenic activity of a green alga, Paulschulzia pseudovolvox, immobilized on graphite or Os‐polymer modified graphite is demonstrated. Direct electron transfer is revealed, when no mediator is added, between algae and electrodes with electrons emerging from photolysis of water via the cells to the electrode exhibiting a photocurrent density of 0.02 μA cm−2. Os‐polymers with different redox potentials and structures are used to optimize the energy gap between the photosynthetic complexes of the cells and the Os‐polymers and those of greater solubility, better accessibility with membranes, and relatively higher potentials yielded a photocurrent density of 0.44 μA cm−2. When benzoquinone is included to the electrolyte, the photocurrent density reaches 6.97 μA cm−2. The photocurrent density is improved to 11.50 μA cm−2, when the cells are protected from reactive oxygen species when either superoxide dismutase or catalase is added. When adding an inhibitor specific for photosystem II, diuron, the photocurrent is decreased by 50%.

Redox-Polymers Enable Uninterrupted Day/Night Photo-Driven Electricity Generation in Biophotovoltaic Devices

“…14,22,23 With regards to the polymeric osmium complexes, a considerably higher current generation was observed with Os-1, reaching 320 ± 28 mA m −2 under illumination and 317 ± 29 mA m −2 in the dark, whilst Os-2 systems reached only 93 ± 23 mA m −2 and 89 ± 20 mA m −2 for day/night conditions respectively. These significant differences may be explained by the higher redox potential of Os-1 (+0.428 V vs. SHE) versus Os-2 (+0.188 V vs SHE; see Fig. 2), which may (i) speed up electron harvesting from the photosynthetic electron transport chain 18 and/or (ii) lead to a lower likelihood for Os-1 to get re-oxidized by photosynthetically-evolved oxygen, a problem that severely inhibits EET, as previously demonstrated. 21 Similar effects were previously reported for pure cyanobacterial 17 and algal species.…”

“…21 Similar effects were previously reported for pure cyanobacterial 17 and algal species. 18 Moreover, although the deposition methods and amounts of Os-mediator utilized were identical, it is also possible that (iii) different concentrations of Os-1 and Os-2 were ultimately immobilized onto the studied electrode surfaces (as hinted by the CVs in Fig. S2A).…”

Electrocatalytic Mechanism Involving Michaelis–Menten Kinetics at the Preparative Scale: Theory and Applicability to Photocurrents from a Photosynthetic Algae Suspension With Quinones

“…Such mediators can be grafted at the electrode (redox polymers, nanoparticles or nanotubes) or solubilised in the physiological medium bathing the cells. [10,20,21] In the latter case, exogenous quinones are ap romising electron relayd ue to their PSII acceptorb ehaviour. [22] Of note, all the strategies described above can be used together to enhance the electrons extraction.…”

Extracellular electron transfer in phototrophic microbial communities

“…These significant differences may be explained by the higher redox potential of Os-1 (+0.428 V vs. SHE) versus Os-2 (+0.188 V vs SHE; see Fig. 6.2), which may (i) speed up electron harvesting from the photosynthetic electron transport chain (Hasan et al 2015) and/or (ii) lead to a lower likelihood for Os-1 to get re-oxidised by photosynthetically-evolved oxygen, a problem that severely inhibits EET, as previously demonstrated . Similar effects were previously reported for pure cyanobacterial (Hasan et al 2014) and algal species (Hasan et al 2015).…”

“…polymethylene blue (PMB), polythionine or polymethylene green (PMG)) can be a stable and efficient alternative (see review in Du et al (2014). Indeed, by immobilising polymeric osmium complexes onto working electrodes, the biocatalytic performance of pure cultures of the cyanobacterium Leptolyngbia (Hasan et al 2014) and the microalga Paulschulzia (Hasan et al 2015) have been significantly improved.…”