In situ time-resolved spectroelectrochemistry reveals limitations of biohybrid photoelectrode performance

•A protein-photoelectrode was investigated with spectroscopy and electrochemistry•We resolved electron flow energy loss channels during biohybrid operation•Continuous intense irradiation exacerbated compromised efficiency•The knowledge will help drive the rational design of more efficient biohybrids Solar fuels life in two ways: through photosynthesis, providing food for virtually all organisms on Earth; by generating electricity photovoltaic devices. Biohybrid photoelectrodes combine best both worlds, coupling natural-light-driven photoenzymes complex artificial materials a bid to achieve sustainable, low-power tools. These may be used wide range applications, from production solar value-added chemicals electricity. However, bridging nature technology often proves challenging, as devices remain inefficient unstable due creation harmful side reactions. Using combined spectroscopic electrochemical tools, we discover origin productivity losses operation state-of-the-art device. A comprehensive quantification processes is provided together blueprint removal these hurdles, bringing us closer zero-carbon economy driven sustainable photoenzymes. Photosynthetic reaction centers catalyze majority conversion Earth. Under low-intensity illumination, this achieved near-unity quantum efficiency, almost every absorbed photon producing photochemical charge separation. technologies seek capture high efficiency natural photoproteins combining them man-made electrodes. transfer their membrane environment into an abiotic architecture invariably results losses. Here, analytical electrochemistry identify reaction-center-based biophotoelectrode. While over 90% under biophotoelectrode dropped ∼11% high-intensity illumination. This stemmed bottlenecks that rendered 60% inactive, well short-circuiting 73% separated active centers. 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All methods produced same maximal amplitude absorbance change diagnostic P870+. QA QB acceptors, post-flash recovery 3A) competition radical pair P870+QA− P870+QB− (simplified P870+Q− below). Consequently, varying concentration free it possible resolve phases S4 associated supplementary text). Complementary measurements, monitored. Upon light-induced formation, c2+ c3+, undock bRC, transport electron-hole causing burst (Jphoto) onset around 20 ms 3A, green). Integration density Faraday’s constant cumulative amount Jphoto order 100 pmol cm−2 cyan). correlated estimate 95 quantity determined extraction experimental procedures). indicated that, event practically electron-holes generated transferred (compare right axes maintained train leading equal amounts c3+ 3B, blue orange). conditions, effective intensity one s−1 bRC−1, reproducibly proceeded near unity turnovers. informative probing comprise 1,000 W fluxes.29Gueymard Myers Emery Proposed irradiance spectra testing.Sol. Energy. 73: 443-467https://doi.org/10.1016/S0038-092X(03)00005-7Crossref (444) approximately 3,500 μmol photons m−2 photosynthetically radiation region 400 900 nm. while mediators equilibrate dark period significantly turnover conditions. electrode-bound therefore examined partition closed changes used. above S3), obtained three approaches. could then compared actinic obtain fraction bRCs; employing multi-turnover, pulses, remaining reduced states. optimal (+160 SHE), oxidized. observed ∼40% became 250 4B, black trace inset). increase multi-turnover pulse reports proportion able form metastable P870+/QB− (or P870+/QBH2 given two-electron carrier) shaded green 4B. stabilized ∼32% 40-s period. accumulation (bearing P870+) depicts donor-side limitation (i.e., ready stable photochemistry, 4B) additional pulses. fraction, colored red constituted population cannot limitation. limitation, long-lived QA− present centers, induces ultrafast bacteriopheophytin anion (HA−) S1G). Over grew, shifting bottlenecked predominantly limited (at s illumination) roughly parts steady-state 4B). get better grasp molecular events taking quantify system terms rates (ETR) “per bRC” basis. ETR (φRC) maximal, light-limited rate (kcs; average absorption, separation):ETR=φRC∗kcs(Equation1) determine kcs, initial rise +360 exponential 4A, allowed determination kcs re-reduction, methodology analogous examination PSI donor, plastocyanin.30Nawrocki W.J. Santabarbara Mosebach State transitions redistribute rather dissipate Chlamydomonas.Nat. Plants. 16031https://doi.org/10.1038/nplants.2016.31Crossref value 110 electrons bRC−1 2,600 irradiance, reasonable agreement theoretical calculated 186 RC-LH1−1 spectrum, spectrum complexes, geometry cuvette S5). Scattering shading taken account, explain discrepancy. Multiplication (φRC per-bRC 4D, line). spectroscopy-derived just 44 after 40 conclusion, 40% photochemistry. window data converting 4C) values apparent procedures. It note electrochemically ETR, called frequency (TOF), since probes flux QH2 4E). contrast, accurately reflect include contributions short-circuiting, quenching, otherwise extracted electrochemically. Strikingly, spectroscopy-based exceeded ETRapp measurements. interpret discrepancy methodological feat allows revealed. contrast e− electrochemistry-based 12 end 4D). indicates ∼73% resulted non-productive primarily circuits. Because types S1C), propose behavior signal least subtypes distinguished. illustrated 4E, expected involving donation (SC2) and/or (SC1). validated decline stirring electrolyte inverted following light-to-dark transition,22Friebe SC2 accounts increasing variance magnitude extrapolated reverse current spike S6A), attributed SC1. Considering SC1 relatively small, major performed illustrate versatility spectroelectrochemistry overcome Lowering clear