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Solar fuels

[Due to the increasing size of the archives, each topic page now contains only the prior 365 days of content. Access to older stories is now solely through the Monthly Archive pages or the site search function.]

Swiss team develops effective and low-cost solar water-splitting device; 14.2% solar-to-hydrogen efficiency

August 25, 2016

Using commercially available solar cells and none of the usual rare metals, researchers at the Swiss Center for Electronics and Microtechnology (CSEM) and École Polytechnique Fédérale de Lausanne (EPFL) have designed an intrinsically stable and scalable solar water splitting device that is fully based on earth-abundant materials, with a solar-to-hydrogen conversion efficiency of 14.2%.

The prototype system is made up of three interconnected, new-generation, crystalline silicon solar cells attached to an electrolysis system that does not rely on rare metals. The device has already been run for more than 100 hours straight under test conditions. The method, which surpasses previous efforts in terms of stability, performance, lifespan and cost efficiency, is published in the Journal of The Electrochemical Society.

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Researchers generate methane from CO2 in one light-driven step using engineered bacteria

Using an engineered strain of the phototropic bacterium Rhodopseudomonas palustris as a biocatalyst, a team from the University of Washington, Utah State University and Virginia Polytechnic Institute and State University have reduced carbon dioxide to methane in one enzymatic step.

The work demonstrates the feasibility of using microbes to generate hydrocarbons (i.e., CH4 in this case) from CO2 in one enzymatic step using light energy. A paper on their work is published in Proceedings of the National Academy of Sciences (PNAS).

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UI, Argonne develop catalyst for more efficient solar-powered reduction of CO2 to CO for conversion to fuel

August 01, 2016

In a new study from the US Department of Energy’s Argonne National Laboratory and the University of Illinois at Chicago, researchers report devising a new transition metal dichalcogenide (TMDC) nanoarchitecture for catalytic electrochemical reduction of CO2 to carbon monoxide (CO) in an ionic liquid.

In their paper published in the journal Science, the researchers found that tungsten diselenide nanoflakes show a current density of 18.95 milliamperes per square centimeter, CO faradaic efficiency of 24%, and CO formation turnover frequency of 0.28 per second at a low overpotential of 54 millivolts. They also applied this catalyst in a light-harvesting artificial leaf platform that concurrently oxidized water in the absence of any external potential.

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Stanford solar tandem cell shows promise for efficient solar-driven water-splitting to produce hydrogen

June 23, 2016

Researchers at Stanford University, with colleagues in China, have developed a tandem solar cell consisting of an approximately 700-nm-thick nanoporous Mo-doped bismuth vanadate (BiVO4) (Mo:BiVO4) layer on an engineered Si nanocone substrate. The nanocone/Mo:BiVO4 assembly is in turn combined with a solar cell made of perovskite.

When placed in water, the device immediately began splitting water at a solar-to-hydrogen conversion efficiency of 6.2%—matching the theoretical maximum rate for a bismuth vanadate cell. Although the efficiency demonstrated was only 6.2%, the tandem device has room for significant improvement in the future, said Stanford Professor Yi Cui, a principal investigator at the Stanford Institute for Materials and Energy Sciences and senior author of an open access paper describing the work published in Scientific Advances.

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Harvard “bionic leaf 2.0” exceeds efficiency of photosynthesis in nature; hydrogen and liquid fuels

June 03, 2016

Researchers at Harvard have created a hybrid water splitting–biosynthetic system based on a biocompatible Earth-abundant inorganic catalyst system to split water into molecular hydrogen and oxygen (H2 and O2) at low driving voltages.

Grown in contact with these catalysts, the bacterium Ralstonia eutropha then consumes the produced H2 to synthesize biomass and fuels or chemical products from low CO2 concentration in the presence of O2. The scalable system has a CO2 reduction energy efficiency of ~50% when producing bacterial biomass and liquid fuel alcohols, scrubbing 180 grams of CO2 per kWh of electricity. Coupling this hybrid device to existing photovoltaic systems would yield a CO2 reduction energy efficiency of ~10%, exceeding that of natural photosynthetic systems, the researchers said in their paper published in the journal Science.

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PSI team demonstrates direct hydrocarbon fuel production from water and CO2 by solar-driven thermochemical cycles

May 26, 2016

Solar-driven thermochemical cycles offer a direct means of storing solar energy in the chemical bonds of energy-rich molecules. By utilizing a redox material such as ceria (CeO2) as a reactive medium, STCs can produce hydrogen and carbon monoxide—i.e., syngas—from water and CO2. The syngas can subsequently be upgraded to hydrocarbon fuels by the Fischer-Tropsch process.

Now, a team from the Paul Scherrer Institute (PSI) in Switzerland has demonstrated the direct production of hydrocarbon fuel—specifically methane—from water and CO2 by incorporating a catalytic process into STCs. A paper on their work is published in the RSC journal Energy & Environmental Science.

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New $30M ARPA-E program to produce renewable liquid fuels from renewable energy, air and water

April 26, 2016

The US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E) announced up to $30 million in funding for a new program for technologies that use renewable energy to convert air and water into cost-competitive liquid fuels. (DE-FOA-0001562)

ARPA-E’s Renewable Energy to Fuels through Utilization of Energy-dense Liquids (REFUEL) program seeks to develop technologies that use renewable energy to convert air and water into Carbon Neutral Liquid Fuels (CNLF). The program is focused in two areas: (1) the synthesis of CNLFs using intermittent renewable energy sources and water and air (N2 and CO2) as the only chemical input streams; and (2) the conversion of CNLFs delivered to the end point to another form of energy (e.g. hydrogen or electricity).

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UTA researchers demonstrate one-step solar process to convert CO2 and H2O directly into renewable liquid hydrocarbon fuels

February 23, 2016

Researchers at the University of Texas at Arlington have demonstrated a new solar process for the one-step, gas-phase conversion of CO2 and H2O to C5+ liquid hydrocarbons and O2 by operating the photocatalytic reaction at elevated temperatures and pressures.

The photothermocatalytic process for the synthesis of hydrocarbons—including liquid alkanes, aromatics, and oxygenates, with carbon numbers (Cn) up to C13—ran in a flow photoreactor operating at elevated temperatures (180–200 °C) and pressures (1–6 bar) using a 5% cobalt on TiO2 catalyst and under UV irradiation. A paper describing the process is published in Proceedings of the National Academy of Sciences (PNAS).

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New photoelectrode with enhanced visible light absorption for improved solar water-splitting for hydrogen production

February 16, 2016

A team of researchers at Ulsan National Institute of Science and Technology (UNIST), Korea University, and the Korea Advanced Institute of Science and Technology (KAIST) has developed a new type of multilayered (Au NPs/TiO2/Au) photoelectrode that could boost the ability of solar water-splitting to produce hydrogen.

This multilayered photoelectrode is a two-dimensional hybrid metal-dielectric structure, comprising three layers of gold (Au) film; an ultrathin TiO2 layer (20 nm), and gold nanoparticles (Au NPs). In a study, reported in the journal Nano Energy, the team reported that the photoelectrode shows high light absorption of about 90% in the visible range 380-700 nm, as well as significant enhancement in photo-catalytic applications.

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Berkeley team develops host-guest nanowires for efficient water splitting and solar energy storage

February 04, 2016

Although metal oxides that absorb visible light are attractive for use as photoanodes in photoelectrosynthetic cells, their performance is often limited by poor charge carrier transport. Researchers from UC Berkeley and colleagues have now addressed this issue by using separate materials for light absorption and carrier transport.

The team reports on their host-guest system of Ta:TiO2|BiVO4 as a photoanode for use in solar water splitting cells in an open-access paper in the journal ACS Central Science. BiVO4 acts as a visible light-absorber and Ta:TiO2 acts as a high surface area electron conductor. The host–guest nanowire architecture allows for simultaneously high light absorption and carrier collection efficiency for efficient solar water oxidation.

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Berkeley Lab team creates “cyborgian” hybrid artificial photosynthesis system; CO2 to acetic acid at high yield

January 05, 2016

Researchers at Berkeley Lab have induced the self-photosensitization of a nonphotosynthetic bacterium—Moorella thermoacetica—with cadmium sulfide nanoparticles (M. thermoacetica–CdS), enabling the photosynthesis of acetic acid from carbon dioxide.

Their hybrid approach combines the highly efficient light harvesting of inorganic semiconductors with the high specificity, low cost, and self-replication and -repair of biocatalysts. Biologically precipitated cadmium sulfide nanoparticles served as the light harvester to sustain cellular metabolism. This self-augmented biological system selectively produced acetic acid continuously over several days of light-dark cycles at relatively high quantum yields, demonstrating a self-replicating route toward solar-to-chemical CO2 reduction. A paper on their work is published in Science.

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Bauhaus Luftfahrt analysis finds solar thermochemical jet fuel production viable only if CO2 captured from renewable sources and not flue gases

December 23, 2015

A team from Bauhaus Luftfahrt in Germany has analyzed the climate impact and economic performance of solar thermochemical jet fuel production. According to their analysis, published in the ACS journal Environmental Science & Technology, favorable assumptions for all involved process steps (30% thermochemical energy conversion efficiency; 3000 kWh/(m2 a) solar irradiation, low CO2 and heliostat costs) result in jet fuel production costs of €1.28/L (US$5.30/gallon) at lifecycle (LC) GHG emissions close to zero (0.10 kgCO2‐equiv/L.

The non-profit Bauhaus Luftfahrt is an internationally-oriented think tank created in November 2005 by the three aerospace companies EADS (today Airbus Group); Liebherr-Aerospace; and MTU Aero Engines as well as the Bavarian Ministry for Economic Affairs. In January 2012, IABG-Industrieanlagen-Betriebsgesellschaft became the latest member of the institution.

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USPTO awards patent to UMD team for process to make gasoline through fermentation; electrofuels

December 22, 2015

The US Patent and Trademark Office issued patent Nº 9,217,161 for a process using naturally occurring microorganisms to ferment biomass or gases directly to hydrocarbons such as hexane and octane. The fuels separate and rise to the surface of the fermentation broth, and are exactly the same as current components of gasoline.

The inventors are Professor Richard Kohn and Faculty Research Associate Dr. Seon-Woo Kim from the University of Maryland (UMD). The team was awarded a separate patent earlier this year (9,193,979) for ethanol-tolerant microorganisms that convert cellulosic biomass to ethanol. (Earlier post.) Both processes were developed based on their theory, described in in a paper published in the Journal of Theoretical Biology, that fermentation systems drive toward thermodynamic equilibrium.

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NREL research advances photoelectrochemical production of hydrogen using molecular catalyst

December 21, 2015

Researchers at the Energy Department’s National Renewable Energy Laboratory (NREL) have made advances toward affordable photoelectrochemical (PEC) production of hydrogen. A paper on their work is published in Nature Materials.

The PEC process uses solar energy to split water into hydrogen and oxygen. The process requires special semiconductors, the PEC materials and catalysts to split the water. Previous work used precious metals such as platinum, ruthenium and iridium as catalysts attached to the semiconductors. A large-scale commercial effort using those precious metals wouldn’t be cost-effective, however.

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Purdue, EPFL team propose Hydricity concept for integrated co-production of H2 and electricity from solar thermal energy

December 16, 2015

Researchers from Purdue University and École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland are proposing a new integrated process involving the co-production of hydrogen and electricity from solar thermal energy—a concept they label “hydricity”. They describe their proposal in a paper in the Proceedings of the National Academy of Sciences (PNAS).

The hydricity process entails integrating solar water power (SWP) cycle and solar thermal hydrogen production technologies and a turbine-based hydrogen power cycle with suitable improvements of each for compatibility and beneficial interaction.

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Stanford team increases power of corrosion-resistant solar cells; advance for solar fuels

November 30, 2015

Researchers at Stanford, with colleagues at University College Cork in Ireland, have shown how to increase the power of corrosion-resistant solar cells, setting a record for solar energy output under water. Instead of pumping electricity into the grid, the power these cells produce would be used in the production of solar fuels.

This new work, published in Nature Materials, was led by Stanford materials scientist Paul McIntyre, whose lab has been a pioneer in the field of artificial photosynthesis. Artificial photosynthesis proposes using the energy from specialized solar cells to combine water with captured carbon dioxide to produce industrial fuels.

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Joule and Red Rock Biofuels intend to merge; solar fuels plus biomass F-T

November 12, 2015

Joule, a pioneer in producing liquid fuels from recycled CO2, and Red Rock Biofuels, a leading developer of renewable jet and diesel fuel bio-refineries using the Fischer-Tropsch process, announced that they intend to merge. Red Rock adds a proven technology pathway to Joule’s own Helioculture technology and strengthens Joule’s platform for global supply of carbon neutral fuels, the two said. The transaction is expected to close during the coming 30 days.

In association with this merger, Joule also announced that President and CEO Serge Tchuruk, will return to his previous board role. Dr. Brian Baynes, a current board member of both Joule and Red Rock and partner at Flagship Ventures, will succeed Tchuruk and will lead Joule as it enters a commercial deployment phase.

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JCAP researchers propose artificial photosynthetic system for high-yield production of ethanol

November 09, 2015

A team at the Joint Center for Artificial Photosynthesis (JCAP) at Lawrence Berkeley National Laboratory and UC Berkeley is proposing an artificial photosynthesis scheme for direct synthesis and separation to almost pure ethanol with minimum product crossover using saturated salt electrolytes.

In a paper in the RSC journal Energy & Environmental Science, Professor Alexis Bell and postdoc Meenesh Singh describe the novel design of an integrated artificial photosynthetic system that continuously produces >90 wt% pure ethanol using a polycrystalline copper cathode and an IrO2 anode at a current density of 0.85 mA cm-2. The annual production rate of > 90 wt% ethanol using such a photosynthesis system operating at 10 mA cm-2 (12% solar-to-fuel (STF) efficiency) can be 15.27 million gallons per year per square kilometer, corresponding to 7% of the industrial ethanol production capacity of California, they suggest.

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Sandia team boosts hydrogen production activity by molybdenum disulfide four-fold; low-cost catalyst for solar-driven water splitting

October 07, 2015

A team led by researchers from Sandia National Laboratories has shown that molybdenum disulfide (MoS2), exfoliated with lithiation intercalation to change its physical structure, performs as well as the best state-of-the-art catalysts for the hydrogen evolution reaction (HER) but at a significantly lower cost. An open access paper on their study is published in the journal Nature Communications.

The improved catalyst has already released four times the amount of hydrogen ever produced by MoS2 from water. To Sandia postdoctoral fellow and lead author Stan Chou, this is just the beginning: “We should get far more output as we learn to better integrate molly with, for example, fuel-cell systems,” he said.

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Rice team demonstrates plasmonic hot-electron solar water-splitting technology; simpler, cheaper and efficient

September 05, 2015

Researchers at Rice have demonstrated an efficient new way to use solar energy for water splitting. The technology, described in a paper in the ACS journal Nano Letters, relies on a novel plasmonic photoelectrode architecture of light-activated gold nanoparticles that harvest sunlight to drive photocatalytic reactions by efficient, non-radiative plasmon decay into “hot carriers”—highly excited electrons.

In contrast to past work, the new architecture does not utilize a Schottky junction—the commonly used building block to collect hot carriers. Instead, the team observed large photocurrents from a Schottky-free junction due to direct hot electron injection from plasmonic gold nanoparticles into the reactant species upon plasmon decay.

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JCAP team reports first complete “artificial leaf”; >10% solar-to-hydrogen conversion efficiency

August 28, 2015

Researchers at the Joint Center for Artificial Photosynthesis (JCAP) report the development of the first complete, efficient, safe, integrated solar-driven system—an “artificial leaf”—for splitting water to produce hydrogen. JCAP is a US Department of Energy (DOE) Energy Innovation Hub established at Caltech and its partnering institutions in 2010.

The new system has three main components: two electrodes—one photoanode and one photocathode—and a membrane. The photoanode uses sunlight to oxidize water molecules, generating protons and electrons as well as oxygen gas. The photocathode recombines the protons and electrons to form hydrogen gas. A key part of the JCAP design is the plastic membrane, which keeps the oxygen and hydrogen gases separate. If the two gases are allowed to mix and are accidentally ignited, an explosion can occur; the membrane lets the hydrogen fuel be separately collected under pressure and safely pushed into a pipeline.

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