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Understanding and improving charge transfer pathways between extracted Photosystem I (PSI) protein complexes and electrodes is necessary for the development of low‐cost PSI‐based devices for energy conversion. We incorporated PSI multilayers within porous indium tin oxide (ITO) electrodes and observed a greater mediated photocurrent in comparison to multilayers on planar ITO. First, the mediated electron transfer (MET) pathway in the presence of 2,6‐dichlorophenolindophenol (DCPIP) and ascorbate (AscH) was studied via photochronoamperometry on planar ITO. ITO nanoparticles were then used to fabricate two porous electrode morphologies; mesoporous (20–100 nm pores) and macroporous (5 μm pores). PSI multilayers within macroporous ITO cathodes produced 42±5 μA cm−2 of photocurrent, three times the photocurrent produced by mesoporous ITO. Additionally, macroporous cathodes are able to utilize twice as much active surface area, when compared to mesoporous cathodes. Our findings show that MET within PSI multilayers is greater in 5 μm macropores than mesoporous ITO due to both an increase in electrode surface area and the location of PSI complexes within the pores. Improving MET in PSI‐based bioelectrodes has applications including improving the total charge transfer achieved in PSI‐based photoelectrochemical cells or even incorporation in bio‐photocatalytic cells.

The design of electrode interfaces to achieve efficient electron transfer to biomolecules is important in many bioelectrochemical processes. Within the field of biohybrid solar energy conversion, constructing multilayered Photosystem I (PSI) protein films that maintain good electronic connection to an underlying electrode has been a major challenge. Previous shortcomings include low loadings, long deposition times, and poor connection between PSI and conducting polymers within composite films. Here, we show that PSI protein complexes can be deposited into monolayers within a 30 min timespan by leveraging the electrostatic interactions between the protein complex and the poly­(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT:PSS) polymer. Further, we follow a layer-by-layer (LBL) deposition procedure to produce up to 9-layer pairs of PSI and PEDOT:PSS with highly reproducible layer thicknesses as well as distinct changes in surface composition. When tested in an electrochemical cell employing ubiquinone-0 as a mediator, the photocurrent performance of the LBL films increased linearly by 83 ± 6 nA/cm2 per PSI layer up to 6-layer pairs. The 6-layer pair samples yielded a photocurrent of 414 ± 13 nA/cm2, after which the achieved photocurrent diminished with additional layer pairs. The turnover number (TN) of the PSI–PEDOT:PSS LBL assemblies also greatly exceeds that of drop-casted PSI multilayer films, highlighting that the rate of electron collection is improved through the systematic deposition of the protein complexes and conducting polymer. The capability to deposit high loadings of PSI between PEDOT:PSS layers, while retaining connection to the underlying electrode, shows the value in using LBL assembly to produce PSI and PEDOT:PSS bioelectrodes for photoelectrochemical energy harvesting applications.

The photosystem I (PSI) protein complex is known to enhance bioelectrode performance for many liquid-based photoelectrochemical cells. A hydrogel as electrolyte media allows for simpler fabrication of more robust and practical solar cells in comparison to liquid-based devices. This paper reports a natural, gel-based dye-sensitized solar cell that integrates PSI to improve device efficiency. TiO2-coated FTO slides, dyed by blackberry anthocyanin, act as a photoanode, while a film of PSI deposited onto copper comprises the photocathode. Ascorbic acid (AscH) and 2,6-dichlorophenolindophenol (DCPIP) are the redox mediator couple inside an agarose hydrogel, enabling PSI to produce excess oxidized species near the cathode to improve device performance. A comparison of performance at low pH and neutral pH was performed to test the pH-dependent properties of the AscH/DCPIP couple. Devices at neutral pH performed better than those at lower pH. The PSI film enhanced photovoltage by 75 mV to a total photovoltage of 0.45 V per device and provided a mediator concentration-dependent photocurrent enhancement over non-PSI devices, reaching an instantaneous power conversion efficiency of 0.30% compared to 0.18% without PSI, a 1.67-fold increase. At steady state, power conversion efficiencies for devices with and without PSI were 0.042 and 0.028%, respectively.

Using a novel hydrothermal synthesis, nitrogen-doped carbon dots were synthesized and shown to exhibit tunable optical and electrochemical properties.

Invited for this month's cover picture is the group of Dr. David E. Cliffel from Vanderbilt University (USA). The Cover Picture shows a Photosystem I (PSI) protein complex converting sunlight into chemical energy through an electron transfer reaction with dichlorophenolindophenol (DCPIP). The PSI is entrapped within a macroporous indium tin oxide (ITO) electrode which leverages its high surface area to produce electrical energy from reacted DCPIP. Read the full text of the Article at 10.1002/celc.201901628

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2020 H. H. Uhlig Summer Research Fellowship – Summary Report