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[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.]

NREL shows graded catalytic-protective layer boosts longevity of high-efficiency photocathodes for renewable hydrogen

January 09, 2017

Researchers at the US Department of Energy’s National Renewable Energy Laboratory (NREL) have developed a method which boosts the longevity of high-efficiency photocathodes in photoelectrochemical water-splitting devices. Their works demonstrates the potential of utilizing a hybridized, heterogeneous surface layer as a cost-effective catalytic and protective interface for solar hydrogen production.

In a paper published in the journal Nature Energy, they show that annealing a bilayer of amorphous titanium dioxide (TiOx) and molybdenum sulfide (MoSx) deposited onto GaInP2 results in a photocathode with high catalytic activity and stability for the hydrogen evolution reaction. The study showed that the annealing results in a graded MoSx/MoOx/TiO2 layer that retains much of the high catalytic activity of amorphous MoSx but with stability similar to crystalline MoS2.

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On the road to solar fuels and chemicals

December 27, 2016

In a new paper in the journal Nature Materials (in an edition focused on materials for sustainable energy), a team from Stanford University and SLAC National Accelerator Laboratory has reviewed milestones in the progress of solid-state photoelectrocatalytic technologies toward delivering solar fuels and chemistry.

Noting the “important advances” in solar fuels research, the review team also noted that the largest scientific and technical milestones are still ahead. Following their review, they listed some of the scientific challenges they see as the most important for the coming years.

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Hydrogen from sunlight, but as a dark reaction; time-delayed photocatalytic H2 production

December 09, 2016

A team at the Max Planck Institute for Solid State Research, Germany, and collaborators at ETH Zurich and the University of Cambridge, have developed a system that enables time-delayed photocatalytic hydrogen generation—essentially, an artificial photosynthesis system that can operate in the dark. A paper on their work is published in the journal Angewandte Chemie International Edition.

The system uses a carbon nitride-based material that can harvest and store sunlight as long-lived trapped electrons for redox chemistry in the dark. More specifically, the system comprises a partially anionic, cyanamide-functionalized heptazine polymer, which, in the presence of an appropriate electron donor, forms a radical species under irradiation that has a lifetime of more than 10 hours. This ultra-long-lived radical can reductively produce hydrogen in the presence of a hydrogen evolution catalyst in the dark on demand.

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Compact pilot plant for solar to liquid fuels production

November 09, 2016

Partners from Germany and Finland in the SOLETAIR project are building a compact pilot plant for the production of gasoline, diesel and kerosene from solar energy, regenerative hydrogen and carbon dioxide. The plant will be compact enough to fit into a shipping container.

The plant consists of three components. A direct air capture unit developed by the Technical Research Center of Finland (VTT) extracts carbon dioxide from air. An electrolysis unit developed by Lappeenranta University of Technology (LUT) produces the required hydrogen by means of solar power. A microstructured, chemical reactor—the key component of the plant—converts the hydrogen produced from solar power together with carbon dioxide into liquid fuels. This reactor was developed by KIT. The compact plant was developed to maturity and is now being commercialized by KIT spin-off INERATEC.

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Stanford team sets record for solar-to-hydrogen efficiency of solar water splitting: >30%

November 02, 2016

Researchers at Stanford University have demonstrated solar water splitting by photovoltaic-electrolysis with a solar-to-hydrogen (STH) efficiency of more than 30%—a new record. The prior record was 24.4%. An open-access paper on their work is published in the journal Nature Communications.

The system consists of two polymer electrolyte membrane electrolyzers in series with one InGaP/GaAs/GaInNAsSb triple-junction solar cell, which produces a large-enough voltage to drive both electrolyzers with no additional energy input. The solar concentration is adjusted such that the maximum power point of the photovoltaic is well matched to the operating capacity of the electrolyzers to optimize the system efficiency. The results, the researchers said, demonstrate the potential of photovoltaic-electrolysis systems for cost-effective solar energy storage.

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DOE seeking input on H2@scale: hydrogen as centerpiece of future energy system; 50% reduction in energy GHGs by 2050

September 11, 2016

Earlier this year, The US Department of Energy (DOE) national laboratories identified the potential of hydrogen to decarbonize deeply a multitude of sectors in a proposal termed “H2@Scale”. Preliminary analysis performed by the national laboratories on the H2@Scale concept indicated that nearly a 50% reduction in greenhouse gas emissions is possible by 2050 via such large-scale hydrogen production and use.

The concept sees hydrogen—a flexible, clean energy-carrying intermediate—having the potential to be a centerpiece of a future energy system where aggressive market penetration of renewables (wind and solar) are coupled with renewable hydrogen production to meet society’s energy demands across industrial, transportation, and power generation sectors using clean, renewable resources and processes.

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SLAC, Stanford team develops new catalyst for water-splitting for renewable fuels production; 100x more efficient than other acid-stable catalysts

September 02, 2016

Researchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have developed a new highly active and stable IrOx/SrIrO3 catalyst for the oxygen evolution reaction (OER).

The new catalyst outperforms known IrOx and ruthenium oxide (RuOx) systems, the only other OER catalysts that have reasonable activity in acidic electrolyte. Because it requires less of the rare and costly metal iridium, the new catalyst could bring down the cost of artifical photosynthetic processes that use sunlight to split water molecules—a key step in a renewable, sustainable pathway to produce hydrogen or carbon-based fuels that can power a broad range of energy technologies. The team published their results in the journal Science.

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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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