Interfacial band-edge energetics for solar fuels production

Photoelectrochemical (PEC) water splitting has received growing attention as a potential pathway to replace fossil fuels and produce a clean, renewable, and sustainable source of fuel. To achieve overall water splitting and the associated production of solar fuels, complex devices are needed to efficiently capture light from the sun, separate photogenerated charges, and catalyze reduction and oxidation reactions. To date, the highest performing solar fuels devices rely on multi-component systems, which introduce interfaces that can be associated with further performance loss due to thermodynamic and kinetic considerations. In this review, we identify several of the most important interfaces used in PEC water splitting, summarize methods to characterize them, and highlight approaches to mitigating associated loss mechanisms.The authors thank Dr Eric Miller for the inspiration to compile this review, and the members of the U.S. Department of Energy’s Photoelectrochemical Working Group and Task 35 (Renewable Hydrogen) of the International E nergy Agency’s Hydrogen Imple- menting Agreement for helpful comments, suggestions, and dis- cussions, specifically Prof. Shane Ardo, Dr John Turner, Prof. Dunwei Wang, and Prof. Shannon Boettcher. WAS greatly acknowl- edges funding support from the FOM/NWO/Shell Program on CO 2 - neutral Fuels (Project – APPEL). IDS was supported by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. NCS acknowledges start-up funds from Lehigh University. JB thanks financial support from GeneralitatValenciana (ISIC/ 2012/008). A summary version of this review paper (DOI: 10.2172/1209498), and associated summary tables that will be updated as the field progresses, will be available on the working group website (http://energy.gov/eere/fuelcells/ photoelectrochemical-working-group)

Experimental demonstrations of spontaneous, solar-driven photoelectrochemical water splitting

Laboratory demonstrations of spontaneous photoelectrochemical (PEC) solar water splitting cells are reviewed. Reported solar-to-hydrogen (STH) conversion efficiencies range from 10% STH efficiency using potentially less costly materials have been reported. Device stability is a major challenge for the field, as evidenced by lifetimes of less than 24 hours in all but a few reports. No globally accepted protocol for evaluating and certifying STH efficiencies and lifetimes exists. It is our recommendation that a protocol similar to that used by the photovoltaic community be adopted so that future demonstrations of solar PEC water splitting can be compared on equal grounds

High-Transconductance Graphene Solution-Gated Field Effect Transistors

In this work, we report on the electronic properties of solution-gated field effect transistors (SGFETs) fabricated using large-area graphene. Devices prepared both with epitaxially grown graphene on SiC as well as with chemical vapor deposition grown graphene on Cu exhibit high transconductances, which are a consequence of the high mobility of charge carriers in graphene and the large capacitance at the graphene/water interface. The performance of graphene SGFETs, in terms of gate sensitivity, is compared to other SGFET technologies and found to be clearly superior, confirming the potential of graphene SGFETs for sensing applications in electrolytic environments.Comment: The following article has been submitted to Applied Physics Letters. After it is published, it will be found at apl.aip.or

Nanostructured amorphous gallium phosphide on silica for nonlinear and ultrafast nanophotonics

Nanophotonics based on high refractive index dielectrics relies on appreciable contrast between the indices of designed nanostructures and their immediate surrounding, which can be achieved by the growth of thin films on low-index substrates. Here we propose the use of high index amorphous gallium phosphide (a-GaP), fabricated by radio-frequency sputter deposition, on top of a low refractive index glass substrate and thoroughly examine its nanophotonic properties. Spectral ellipsometry of the amorphous material demonstrates the optical properties to be considerably close to crystalline gallium phosphide (c-GaP), with low-loss transparency for wavelengths longer than 650 nm. When nanostructured into nanopatches, the second harmonic (SH) response of an individual a-GaP patch is characterized to be more than two orders of magnitude larger than the as-deposited unstructured film, with an anapole-like resonant behavior. Numerical simulations are in good agreement with the experimental results over a large spectral and geometrical range. Furthermore, by studying individual a-GaP nanopatches through non-degenerate pump-probe spectroscopy with sub-10 fs pulses, we find a more than 5% ultrafast modulation of the reflectivity that is accompanied by a slower decaying free carrier contribution, caused by absorption. Our investigations reveal a potential for a-GaP as an adequate inexpensive and CMOS-compatible material for nonlinear nanophotonic applications as well as for photocatalysis.Fil: Tilmann, Benjamin. Ludwig Maximilians Universitat; AlemaniaFil: Grinblat, Gustavo Sergio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Berté, Rodrigo. Ludwig Maximilians Universitat; AlemaniaFil: Özcan, Mehmet. Ludwig Maximilians Universitat; AlemaniaFil: Kunzelmann, Viktoria F.. Technische Universitat München; AlemaniaFil: Nickel, Bert. Ludwig Maximilians Universitat; AlemaniaFil: Sharp, Ian D.. Ludwig Maximilians Universitat; AlemaniaFil: Cortés, Emiliano. Ludwig Maximilians Universitat; AlemaniaFil: Maier, Stefan A.. Ludwig Maximilians Universitat; AlemaniaFil: Li, Yi. Southern University Of Science And Technology; Chin

Paleoenvironmental and diagenetic evolution of the Aptian Pre-Salt succession in Namibe Basin (Onshore Angola)

The Aptian Pre-Salt sedimentary succession cropping out in Cangulo palaeovalley onshore Namibe Basin (Angola) was studied by a combination of field and analytical techniques to constrain the sedimentary and diagenetic evolution of the uppermost sag sequence of the South Atlantic passive margin. Field observations allows definition of four transgressive-regressive cycles characterised by fluvial to tidal-influenced mixed clastic-carbonate and carbonate-dominated deposits, that locally show evidence of evaporite dissolution; highlighting that evaporite deposition started earlier than deposition of the regional South Atlantic Loeme-Bambata evaporite formations. Two separate pre-salt carbonate units have been differentiated within the Cangulo Fm; i) a lower transitional to marginal marine, and ii) a younger upper non-marine freshwater travertine system, that is documented for the first time in the west African margin. Transgressive-regressive cycles control the early diagenesis of the tidal carbonates that include dolomitization due to mixing fluids during transgressions, and karstification due to evaporite dissolution by meteoric water circulation during regressive events. Clastic supply appears to have been completely shut down during carbonate deposition, suggesting major climatic change associated with carbonate deposition. During the lowstand between the two carbonate units, fluid flow through Cangulo palaeovalley was re-established resulting in extensive karstification and formation of a large-scale erosional unconformity that is interpreted to be time equivalent to an intra Chela-Cuvo Fm. event. The top of the studied succession corresponds to the transgressive deposits of the Bambata evaporites that are not preserved in the Cangulo palaeovalley due to its erosion but are regionally developed. The results of this study can be directly linked to along strike age equivalent Pre-Salt successions cropping out in the Namibe, Benguela and Kwanza basins, and directly offshore Angola and Brazil using well and seismic data. These new data shed important new light and constraints on the depositional and diagenetic evolution of the complex Pre-Salt reservoir systems of the South Atlantic, and the depositional and bathymetric setting at the time of onset of the main south Atlantic evaporite deposition.The geology of Cangulo palaeovalley was characterised through a combination of remote sensing mapping (RSM), fieldwork and laboratory analysis. Remote sensing mapping was performed using Equinor-Digitizer2, software, using very high resolution orthorectified satellite imagery, and a digital elevation model (DEM) with a resolution of 1.0 m. RSM and field mapping were supported by the interpretation of stratal relationships directly onto field photopanoramas.We thank Israel Cruz Orosa and Emilio Casciello for fruitful discussion during the development of the present study. Thanks to Equinor Angola and Rafael's camp staff for logistical support during field work, and all involved in the Equinor-Sonangol onshore field work collaboration program in the Namibe, Benguela and Kwanza basins between 2010 and 2014. Thank you to TGS for permission to use line drawing of seismic in Fig. 2. We thank associate editor Laura Tomassetti, Pierre-Alexandre Teboul and an anonymous reviewer who helped improve the quality of the manuscript. Carbon and oxygen isotopic analyses, and electron microprobe analyses were carried out at the Centre Científics i Tecnològics of the Universitat de Barcelona. XRD analyses were carried out in the laboratories of the Geoscience Barcelona (Geo3BCN–CSIC). This research is a contribution of the Group of Dynamics of the Lithosphere (GDL), Geosciences Barcelona (Geo3Bcn), Consejo Superior de Investigaciones Científicas (CSIC), Spain. The project work was sponsored by Equinor (Norway), ALORBE Project (PIE–CSIC–202030E310), FEIBOB project (PGC2018-093903-B-C22) and ORRI Spanish project (PID2021-122467NB-C22). This research is within the framework of the Grups Consolidats de Recerca “Modelització Geodinàmica de la Litosfera” (2017SGR-847) and “Geologia Sedimentària” (SGR-Cat 2021 349)

Assembly and photocarrier dynamics of heterostructured nanocomposite photoanodes from multicomponent colloidal nanocrystals

Multicomponent oxides and their heterostructures are rapidly emerging as promising light absorbers to drive oxidative chem. To fully exploit their functionality, precise tuning of their compn. and structure is crucial. Here, we report a novel soln.-based route to nanostructured bismuth vanadate (BiVO4) that facilitates the assembly of BiVO4/metal oxide (TiO2, WO3, and Al2O3) nanocomposites in which the morphol. of the metal oxide building blocks is finely tailored. The combination of transient absorption spectroscopy-spanning from picoseconds to second time scales-and photoelectrochem. measurements reveals that the achieved structural tunability is key to understanding and directing charge sepn., transport, and efficiency in these complex oxide heterostructured films

Discovery of Fe–Ce Oxide/BiVO_4 Photoanodes through Combinatorial Exploration of Ni–Fe–Co–Ce Oxide Coatings

An efficient photoanode is a prerequisite for a viable solar fuels technology. The challenges to realizing an efficient photoanode include the integration of a semiconductor light absorber and a metal oxide electrocatalyst to optimize corrosion protection, light trapping, hole transport, and photocarrier recombination sites. To efficiently explore metal oxide coatings, we employ a high-throughput methodology wherein a uniform BiVO_4 film is coated with 858 unique metal oxide coatings covering a range of metal oxide loadings and the full (Ni–Fe–Co–Ce)O_x pseudoquaternary composition space. Photoelectrochemical characterization of the photoanodes reveals that specific combinations of metal oxide composition and loading provide up to a 13-fold increase in the maximum photoelectrochemical power generation for oxygen evolution in pH 13 electrolyte. Through mining of the high-throughput data we identify composition regions that form improved interfaces with BiVO_4. Of particular note, integrated photoanodes with catalyst compositions in the range Fe_((0.4–0.6))Ce_((0.6–0.4))O_x exhibit high interface quality and excellent photoelectrochemical power conversion. Scaled-up inkjet-printed electrodes and photoanodic electrodeposition of this composition on BiVO_4 confirms the discovery and the synthesis-independent interface improvement of (Fe–Ce)O_x coatings on BiVO_4

Two new Wolf-Rayet stars in the LMC

We report the discovery of two previously unknown WN3 stars in the Large Magellanic Cloud. Both are bright (15th magnitude), isolated, and located in regions covered in earlier surveys, although both are relatively weak-lined. We suggest that there may be $\mathcal{O}(10)$ remaining undiscovered WNE stars in the LMC