The Role of Gold-Adsorbed Photosynthetic Reaction Centers and Redox Mediators in the Charge Transfer and Photocurrent Generation in a Bio-Photoelectrochemical Cell
Bibliographic record
Abstract
Bacterial photosynthetic reaction centers (RCs) are promising materials for solar energy harvesting, due to their high quantum efficiency. A simple approach for making a photovoltaic device is to apply solubilized RCs and charge carrier mediators to the electrolyte of an electrochemical cell. However, the adsorption of analytes on the electrodes can affect the charge transfer from RCs to the electrodes. In this work, photovoltaic devices were fabricated incorporating RCs from purple bacteria, ubiquinone-10 (Q2), and cytochrome c (Cyt c) (the latter two species acting as redox mediators). The adsorption of each of these three species on the gold working electrode was investigated, and the roles of adsorbed species in the photocurrent generation and the cycle of charge transfer were studied by a series of photochronoamperometric, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and cyclic voltammetry (CV) tests. It was shown that both redox mediators were required for photocurrent generation; hence, the RC itself is likely unable to inject electrons into the gold electrode directly. The reverse redox reactions of mediators at the electrodes generates electrical current. Cyclic voltammograms for the RC-exposed gold electrode revealed a redox couple due to the adsorbed RC at ∼ +0.5 V (vs NHE), which confirmed that the RC was still redox active, upon adsorption to the gold. Photochronoamperometric studies also indicated that RCs adsorb, and are strongly bound to the surface of the gold, retaining functionality and contributing significantly to the process of photocurrent generation. Similar experiments showed the adsorption of Q2 and Cyt c on unmodified gold surfaces. It was indicated by the photochronoamperometric tests that the photocurrent derives from Q2-mediated charge transfer between the RCs and the gold electrode, while solubilized Cyt c mediates charge transfer between the P-side of adsorbed RC and the Pt counter electrode. Also, the stability of the adsorbed RCs and mediators was evaluated by measuring the photocurrent response over a period of 1 week. It is found that ∼46% of the adsorbed RCs remain active after a week under aerobic conditions. A significantly extended lifetime is expected by removing oxygen from the electrolyte and sealing the device.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".