Small polaron formation is known to limit ground-state mobilities in metal oxide photocatalysts. However, the role of small polaron formation in the photoexcited state and how this affects the photoconversion efficiency has yet to be determined. Here, transient femtosecond extreme-ultraviolet measurements suggest that small polaron localization is responsible for the ultrafast trapping of photoexcited carriers in haematite (α-FeO). Small polaron formation is evidenced by a sub-100 fs splitting of the Fe 3p core orbitals in the Fe M edge. The small polaron formation kinetics reproduces the triple-exponential relaxation frequently attributed to trap states. However, the measured spectral signature resembles only the spectral predictions of a small polaron and not the pre-edge features expected for mid-gap trap states. The small polaron formation probability, hopping radius and lifetime varies with excitation wavelength, decreasing with increasing energy in the t conduction band. The excitation-wavelength-dependent localization of carriers by small polaron formation is potentially a limiting factor in haematite's photoconversion efficiency.

Natural photosynthesis harnesses solar energy to convert CO 2 and water to value-added chemical products for sustaining life. We present a hybrid bioinorganic approach to solar-to-chemical conversion in which sustainable electrical and/or solar input drives production of hydrogen from water splitting using biocompatible inorganic catalysts. The hydrogen is then used by living cells as a source of reducing equivalents for conversion of CO 2 to the value-added chemical product methane. Using platinum or an earth-abundant substitute, α-NiS, as biocompatible hydrogen evolution reaction (HER) electrocatalysts and Methanosarcina barkeri as a biocatalyst for CO 2 fixation, we demonstrate robust and efficient electrochemical CO 2 to CH 4 conversion at up to 86% overall Faradaic efficiency for ≥7 d. Introduction of indium phosphide photocathodes and titanium dioxide photoanodes affords a fully solar-driven system for methane generation from water and CO 2 , establishing that compatible inorganic and biological components can synergistically couple light-harvesting and catalytic functions for solar-to-chemical conversion.artificial photosynthesis | solar fuels | photocatalysis | carbon dioxide fixation | water splitting M ethods for the sustainable conversion of carbon dioxide to value-added chemical products are of technological and societal importance (1-3). Elegant advances in traditional approaches to CO 2 reduction driven by electrical and/or solar inputs using homogeneous (4-16), heterogeneous (17-26), and biological (7, 27-31) catalysts point out key challenges in this area, namely (i) the chemoselective conversion of CO 2 to a single product while minimizing the competitive reduction of protons to hydrogen, (ii) long-term stability under environmentally friendly aqueous conditions, and (iii) unassisted light-driven CO 2 reduction that does not require external electrical bias and/or sacrificial chemical quenchers. Indeed, synthetic homogeneous and heterogeneous CO 2 catalysts are often limited by product selectivity and/or aqueous compatibility, whereas enzymes show exquisite specificity but are generally less robust outside of their protective cellular environment. In addition, the conversion of electrosynthetic systems to photosynthetic ones is nontrivial owing to the complexities of effectively integrating components of light capture with bond-making and bond-breaking chemistry.Inspired by the process of natural photosynthesis in which lightharvesting, charge-transfer, and catalytic functions are integrated to achieve solar-driven CO 2 fixation (32-35), we have initiated a program in solar-to-chemical conversion to harness the strengths inherent to both inorganic materials chemistry and biology (36). As shown in Fig. 1, our strategy to drive synthesis with sustainable electrical and/or solar energy input (37) interfaces a biocompatible photo(electro)chemical hydrogen evolution reaction (HER) catalyst with a microorganism that uses this sustainably generated hydrogen as an electron donor for CO 2 reduction. Impo...

We present a simple nanopore-electroporation (NanoEP) platform for delivery of nucleic acids, functional protein, and Cas9 single-guide RNA ribonucleoproteins into both adherent and suspension cells with up to 80% delivery efficiency and >95% cell viability. Low-voltage electric pulses permeabilize a small area of cell membrane as a cell comes into close contact with the nanopores. The biomolecule cargo is then electrophoretically drawn into the cells through the nanopores. In addition to high-performance delivery with low cell toxicity, the NanoEP system does not require specialized buffers, expensive materials, complicated fabrication processes, or cell manipulation; it simply consists of a generic nanopore-embedded water-filter membrane and a low-voltage square-wave generator. Ultimately, the NanoEP platform offers an effective and flexible method for universal intracellular delivery.

Recent applications of photoelectrochemistry at the semiconductor/ liquid interface provide a renewable route of mimicking natural photosynthesis and yielding chemicals from sunlight, water, and air. Nanowires, defined as one-dimensional nanostructures, exhibit multiple unique features for photoelectrochemical applications and promise better performance as compared to their bulk counterparts. This article reviews the use of semiconductor nanowires in photoelectrochemistry. After introducing fundamental concepts essential to understanding nanowires and photoelectrochemistry, the review considers answers to the following questions: (1) How can we interface semiconductor nanowires with other building blocks for enhanced photoelectrochemical responses? (2) How are nanowires utilized for photoelectrochemical half reactions? (3) What are the techniques that allow us to obtain fundamental insights of photoelectrochemistry at single-nanowire level? (4) What are the design strategies for an integrated nanosystem that mimics a closed cycle in artificial photosynthesis? This framework should help readers evaluate the salient features of nanowires for photoelectrochemical applications, promoting the sustainable development of solar-powered chemical plants that will benefit our society in the long run.

Microbial electro-and photoelectrochemical CO2 fixation, in which CO2-reducing microorganisms are directly interfaced with a cathode material, represent promising approaches for sustainable fuel production. Although considerable efforts have been invested to optimize microorganism species and electrode materials, the microorganismcathode interface has not been systematically studied. Here, investigation of the interface allowed us to optimize the CO2-reducing rate of silicon nanowire/Sporomusa ovata system. Tuning the bulk electrolyte pH and increasing its buffering capacity supported the formation of a close-packed nanowire-bacteria cathode. Consequently, the resulting closepacked biohybrid achieved a CO2-reducing current density of ~0.65 mA cm-2. When coupled with a photovoltaic device, our system enabled solar-to-acetate production with ~3.6% efficiency over seven days.

Reducing carbon dioxide with a multicomponent artificial photosynthetic system, closely mimicking nature, represents a promising approach for energy storage. Previous works have focused on exploiting light-harvesting semiconductor nanowires (NW) for photoelectrochemical water splitting. With the newly developed CO2 reduction nanoparticle (NP) catalysts, direct interfacing of these nanocatalysts with NW light absorbers for photoelectrochemical reduction of CO2 becomes feasible. Here, we demonstrate a directed assembly of NP catalysts on vertical NW substrates for CO2-to-CO conversion under illumination. Guided by the one-dimensional geometry, well-dispersed assembly of Au3Cu NPs on the surface of Si NW arrays was achieved with facile coverage tunability. Such Au3Cu NP decorated Si NW arrays can readily serve as effective CO2 reduction photoelectrodes, exhibiting high CO2-to-CO selectivity close to 80% at -0.20 V vs RHE with suppressed hydrogen evolution. A reduction of 120 mV overpotential compared to the planar (PL) counterpart was observed resulting from the optimized spatial arrangement of NP catalysts on the high surface area NW arrays. In addition, this system showed consistent photoelectrochemical CO2 reduction capability up to 18 h. This simple photoelectrode assembly process will lead to further progress in artificial photosynthesis, by allowing the combination of developments in each subfield to create an efficient light-driven system generating carbon-based fuels.

Composites, in which two or more material elements are combined to provide properties unattainable by single components, have a historical record dating to ancient times. Few include a living microbial community as a key design element. A logical basis for enabling bioelectronic composites stems from the phenomenon that certain microorganisms transfer electrons to external surfaces, such as an electrode. A bioelectronic composite that allows cells to be addressed beyond the confines of an electrode surface can impact bioelectrochemical technologies, including microbial fuel cells for power production and bioelectrosynthesis platforms where microbes produce desired chemicals. It is shown that the conjugated polyelectrolyte CPE‐K functions as a conductive matrix to electronically connect a three‐dimensional network of Shewanella oneidensis MR‐1 to a gold electrode, thereby increasing biocurrent ≈150‐fold over control biofilms. These biocomposites spontaneously assemble from solution into an intricate arrangement of cells within a conductive polymer matrix. While increased biocurrent is due to more cells in communication with the electrode, the current extracted per cell is also enhanced, indicating efficient long‐range electron transport. Further, the biocomposites show almost an order‐of‐magnitude lower charge transfer resistance than CPE‐K alone, supporting the idea that the electroactive bacteria and the conjugated polyelectrolyte work synergistically toward an effective bioelectronic composite.

Photoelectrochemistry is one of several promising approaches for the realization of efficient solar-to-fuel conversion. Recent work has shown that photoelectrodes made of semiconductor nano-/microwire arrays can have better photoelectrochemical performance than their planar counterparts because of their unique properties, such as high surface area. Although considerable research effort has focused on studying wire arrays, the inhomogeneity in the geometry, doping, defects and catalyst loading present in such arrays can obscure the link between these properties and the photoelectrochemical performance of the wires, and correlating performance with the specific properties of individual wires is difficult because of ensemble averaging. Here, we show that a single-nanowire-based photoelectrode platform can be used to reliably probe the current-voltage (I-V) characteristics of individual nanowires. We find that the photovoltage output of ensemble array samples can be limited by poorly performing individual wires, which highlights the importance of improving nanowire homogeneity within an array. Furthermore, the platform allows the flux of photogenerated electrons to be quantified as a function of the lengths and diameters of individual nanowires, and we find that the flux over the entire nanowire surface (7-30 electrons nm(-2) s(-1)) is significantly reduced as compared with that of a planar analogue (∼1,200 electrons nm(-2) s(-1)). Such characterization of the photogenerated carrier flux at the semiconductor/electrolyte interface is essential for designing nanowire photoelectrodes that match the activity of their loaded electrocatalysts.