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Green plants convert sunlight into high-energy chemicals by coupling solar-driven water oxidation in the Z-scheme and CO2 fixation in the Calvin cycle. In this study, formate dehydrogenase from Clostridium ljungdahlii (ClFDH) is interfaced with a TiO2 -coated CuFeO2 and CuO mixed (ClFDH-TiO2 |CFO) electrode. In this biohybrid photocathode, the TiO2 layer enhances the photoelectrochemical (PEC) stability of the labile CFO photocathode and facilitates the transfer of photoexcited electrons from the CFO to ClFDH. Furthermore, inspired by the natural photosynthetic scheme, the photobiocathode is combined with a water-oxidizing, FeOOH-coated BiVO4 (FeOOH|BiVO4 ) photoanode to assemble a wireless Z-scheme biocatalytic PEC device as a semi-artificial leaf. The leaf-like structure effects a bias-free biocatalytic CO2 -to-formate conversion under visible light. Its rate of formate production is 2.45 times faster than that without ClFDH. This work is the first example of a wireless solar-driven semi-biological PEC system for CO2 reduction that uses water as an electron feedstock.

A robust photovoltaic (PV) is essential for long-term redox biotransformations in biocatalytic photoelectrochemical (PEC) platforms. Here, we report a single Cu(In,Ga)Se2 (CIGS) solar cell for unbiased photobiocatalytic reduction reactions. The photoanode/CIGS/cathode tandem assembly drives cofactor-dependent biocatalytic CO2 reduction under visible light. Our scalable PEC-PV tandem device achieves the longest reaction time of 72 h and the highest ever recorded turnover frequency and total turnover number of the cofactor of 0.236 h−1 and 11.2, respectively, for biocatalytic PEC production of formate through cofactor regeneration. This benchmark performance is attributed to the excellent PEC stability of the CIGS component; the substitution of CIGS with a perovskite solar cell (PSC) results in unstable generation of photocurrent and a lower concentration of formate under high-humidity environments because of the water-induced degradation of PSC. This work demonstrates the propriety of CIGS in robust PEC-PV tandems for artificial photosynthesis.

Redox enzymes catalyze fascinating chemical reactions with excellent regio- and stereo-specificity. Nicotinamide adenine dinucleotide cofactor is essential in numerous redox biocatalytic reactions and needs to be regenerated because it is consumed as an equivalent during the enzymatic turnover. Here we report on unbiased photoelectrochemical tandem assembly of a photoanode (FeOOH/BiVO4) and a perovskite photovoltaic to provide sufficient potential for cofactor-dependent biocatalytic reactions. We obtain a high faradaic efficiency of 96.2% and an initial conversion rate of 2.4 mM h−1 without an external applied bias for the photoelectrochemical enzymatic conversion of α-ketoglutarate to l-glutamate via l-glutamate dehydrogenase. In addition, we achieve a total turnover number and a turnover frequency of the enzyme of 108,800 and 6200 h−1, respectively, demonstrating that the tandem configuration facilitates redox biocatalysis using light as the only energy source. Photoelectrochemical (PEC) cell platforms typically need an electrical bias that drives the electron transfer from the photoanode to the photocathode. Here, the authors report a bias-free PEC tandem device for solar-driven redox biocatalysis.

Natural photosynthesis is an effective route for the clean and sustainable conversion of CO2 into high-energy chemicals. Inspired by the natural process, a tandem photoelectrochemical (PEC) cell with an integrated enzyme-cascade (TPIEC) system was designed, which transfers photogenerated electrons to a multienzyme cascade for the biocatalyzed reduction of CO2 to methanol. A hematite photoanode and a bismuth ferrite photocathode were applied to fabricate the iron oxide based tandem PEC cell for visible-light-assisted regeneration of the nicotinamide cofactor (NADH). The cell utilized water as an electron donor and spontaneously regenerated NADH. To complete the TPIEC system, a superior three-dehydrogenase cascade system was employed in the cathodic part of the PEC cell. Under applied bias, the TPIEC system achieved a high methanol conversion output of 220 μm h−1, 1280 μmol g−1 h−1 using readily available solar energy and water.

Herein, we report a siloxane-encapsulated upconversion nanoparticle hybrid composite (SE-UCNP), which exhibits excellent photoluminescence (PL) stability for over 40 days even at an elevated temperature, in high humidity, and in harsh chemicals. The SE-UCNP is synthesized through UV-induced free-radical polymerization of a sol-gel-derived UCNP-containing oligosiloxane resin (UCNP-oligosiloxane). The siloxane matrix with a random network structure by Si-O-Si bonds successfully encapsulates the UCNPs with chemical linkages between the siloxane matrix and organic ligands on UCNPs. This encapsulation results in surface passivation retaining the intrinsic fluorescent properties of UCNPs under severe conditions (e.g., 85 °C/85% relative humidity) and a wide range of pH (from 1 to 14). As an application example, we fabricate a two-color binary microbarcode based on SE-UCNP via a low-cost transfer printing process. Under near-infrared irradiation, the binary sequences in our barcode are readable enough to identify objects using a mobile phone camera. The hybridization of UCNPs with a siloxane matrix provides the capacity for highly stable UCNP-based applications in real environments.

Redox enzymes are industrially important for catalyzing highly complex reactions because of their excellent regio- and stereo-selectivity; however, broad application of redox enzymes has been often limited by the requirement of stoichiometric supply of cofactors such as β-nicotinamide adenine dinucleotide (NADH). Here, we report light-driven cofactor regeneration coupled with water oxidation by employing a photoelectrochemical cell platform consisted of a FeOOH/Fe2O3 photoanode and a black silicon photocathode. The FeOOH layer deposited on Fe2O3 surface decreased reaction barriers for water oxidation. The black silicon photocathode exhibited high photocurrent response and superior capacity to drive cofactor reduction. The cofactor regeneration yield in the photoelectrochemical cell was almost two-fold higher than that obtained in homogenous system, which demonstrates that photoelectrochemical cell is a promising platform for redox biocatalytic reactions using water as an electron donor.

We present the photoelectrochemical (PEC) regeneration of nicotinamide cofactors (NADH) coupled with the enzymatic synthesis of formate from CO2 towards mimicking natural photosynthesis. The water oxidation-driven PEC platform exhibited high yield and the rate of NADH regeneration was compared to many other homogeneous, photochemical systems. We successfully coupled solar-assisted NADH reduction with enzymatic CO2 reduction to formate under continuous CO2 injection.

Peptide self-assembly is a facile route to the development of bioorganic hybrid materials that have sophisticated nanostructures toward diverse applications. Here, we report the synthesis of self-assembled peptide (Fmoc-diphenylalanine, Fmoc-FF)/graphitic carbon nitride (g-C3N4) hydrogels for light harvesting and biomimetic photosynthesis through noncovalent interactions between aromatic rings in Fmoc-FF nanofibers and tris-s-triazine in g-C3N4 nanosheets. According to our analysis, the photocurrent density of the Fmoc-FF/g-C3N4 hydrogel was 1.8× higher (0.82 μA cm–1) than that of the pristine g-C3N4. This is attributed to effective exfoliation of g-C3N4 nanosheets in the Fmoc-FF/g-C3N4 network, facilitating photoinduced electron transfers. The Fmoc-FF/g-C3N4 hydrogel reduced NAD+ to enzymatically active NADH under light illumination at a high rate of 0.130 mol g–1 h–1 and drove light-responsive redox biocatalysis. Moreover, the Fmoc-FF/g-C3N4 scaffold could well-encapsulate key photosynthetic components,...

We report on a silicon-based photoelectrochemical cell that integrates a formate dehydrogenase from Thiobacillus sp. (TsFDH) to convert CO2 to formate using water as an electron donor under visible light irradiation and an applied bias. Our current study suggests that the deliberate integration of biocatalysis to a light-harvesting platform could provide an opportunity to synthesize valuable chemicals with the use of earth-abundant materials and sustainable resources.