Concentrating solar thermal power and thermochemical fuels

Romero, Manuel; Steinfeld, Aldo

doi:10.1039/c2ee21275g

Cited by 617 publications

(329 citation statements)

References 100 publications

(108 reference statements)

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“…Renewable chemical fuels such as hydrocarbons, methanol, hydrogen and ammonia may be synthesized from CO 2 , H 2 O and N 2 by solar-driven photochemical [1,2], electrocatalytic [3,4] or thermochemical processes [5]. The latter approach uses the entire spectrum of concentrated solar energy as the source of high-temperature process heat, and as such provides a thermodynamically favourable path to solar fuels and materials production with high energy conversion efficiencies.…”

Section: Introductionmentioning

confidence: 99%

Rational design of metal nitride redox materials for solar-driven ammonia synthesis

2015

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Fixed nitrogen is an essential chemical building block for plant and animal protein, which makes ammonia (NH 3 ) a central component of synthetic fertilizer for the global production of food and biofuels. A global project on artificial photosynthesis may foster the development of production technologies for renewable NH 3 fertilizer, hydrogen carrier and combustion fuel. This article presents an alternative path for the production of NH 3 from nitrogen, water and solar energy. The process is based on a thermochemical redox cycle driven by concentrated solar process heat at 700–1200°C that yields NH 3 via the oxidation of a metal nitride with water. The metal nitride is recycled via solar-driven reduction of the oxidized redox material with nitrogen at atmospheric pressure. We employ electronic structure theory for the rational high-throughput design of novel metal nitride redox materials and to show how transition-metal doping controls the formation and consumption of nitrogen vacancies in metal nitrides. We confirm experimentally that iron doping of manganese nitride increases the concentration of nitrogen vacancies compared with no doping. The experiments are rationalized through the average energy of the dopant d-states, a descriptor for the theory-based design of advanced metal nitride redox materials to produce sustainable solar thermochemical ammonia.

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Section: Introductionmentioning

confidence: 99%

Rational design of metal nitride redox materials for solar-driven ammonia synthesis

2015

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“…[1][2][3][4] It consists of the reduction of a metal oxide using concentrated solar process heat to liberate O 2 , followed by its reoxidation with H 2 O and/or CO 2 , generating H 2 and/or CO, according to:…”

Section: Introductionmentioning

confidence: 99%

Principles of doping ceria for the solar thermochemical redox splitting of H₂O and CO₂

Muhich

Steinfeld

2017

J. Mater. Chem. A

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Ceria-based metal oxides are promising redox materials for solar H 2 O/CO 2 -splitting thermochemical cycles. Density functional theory (DFT) computations are applied to elucidate the underlying mechanism of the role of dopants in facilitating ceria based redox cycles; specifically, we explain why some dopants increase performance, while others do not. Firstly, we find that Zr and Hf dopants increase the oxygen exchange capacity of ceria because they store energy in tensilely strained Zr-or Hf-O bonds which is released upon O-vacancy formation. This finding corrects a long held assumption that Zr and Hf decrease the O-vacancy formation energy by compensating for ceria expansion upon reduction.Although the released strain energy decreases the O-vacancy formation energy, O-vacancy formation remains sufficiently endothermic to split H 2 O and CO 2 . Secondly, we show that two electrons must be promoted into the high energy Ce f-band during reduction if the O-vacancies are to store sufficient energy to drive the oxidative gas splitting step. This means that di-and trivalent dopants are not suitable for this process. Lastly, we show that dopants which break O bonds due to their small size or strongly covalent character, such as Ti and the pentavalent dopants, substantially decrease the O-vacancy formation energy because only three O bonds must break during reduction. These vacancies, therefore, are too low in energy to drive gas splitting. Based on these findings, we develop guidelines for new ceria doping strategies to facilitate solar thermochemical gas splitting cycles.

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“…Commercial projects use technologies of parabolic troughs with low concentration in two dimensions and linear focus, or systems of central tower and heliostat fields, operating with thermal fluids at relatively modest temperatures [3]. The most immediate consequence of these conservative designs is the use of systems with efficiencies about 20% nominal in the conversion of direct solar radiation to electricity; the tight limitation in the use of efficient energy storage systems; the high water consumption and land extension due to the inefficiency of the integration with the power block; the lack of rational schemes for their integration in distributed generation architectures and the limitation to reach the temperatures needed for the thermochemical routes used to produce solar fuels like hydrogen [4].…”

Section: Introductionmentioning

confidence: 99%

High-flux/high-temperature solar thermal conversion: technology development and advanced applications

Romero

González-Aguilar

2016

Renew. Energy Environ. Sustain.

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Abstract. Solar Thermal Power Plants have generated in the last 10 years a dynamic market for renewable energy industry and a pro-active networking within R&D community worldwide. By end 2015, there are about 5 GW installed in the world, most of them still concentrated in only two countries, Spain and the US, though a rapid process of globalization is taking place in the last few years and now ambitious market deployment is starting in countries like South Africa, Chile, Saudi Arabia, India, United Arab Emirates or Morocco. Prices for electricity produced by today's plants fill the range from 12 to 16 c€/kWh and they are capital intensive with investments above 4000 €/kW, depending on the number of hours of thermal storage. The urgent need to speed up the learning curve, by moving forward to LCOE below 10 c€/kWh and the promotion of sun-to-fuel applications, is driving the R&D programmes. Both, industry and R&D community are accelerating the transformation by approaching high-flux/high-temperature technologies and promoting the integration with high-efficiency conversion systems.

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Concentrating solar thermal power and thermochemical fuels

Cited by 617 publications

References 100 publications

Rational design of metal nitride redox materials for solar-driven ammonia synthesis

Rational design of metal nitride redox materials for solar-driven ammonia synthesis

Principles of doping ceria for the solar thermochemical redox splitting of H₂O and CO₂

High-flux/high-temperature solar thermal conversion: technology development and advanced applications

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Concentrating solar thermal power and thermochemical fuels

Cited by 617 publications

References 100 publications

Rational design of metal nitride redox materials for solar-driven ammonia synthesis

Rational design of metal nitride redox materials for solar-driven ammonia synthesis

Principles of doping ceria for the solar thermochemical redox splitting of H2O and CO2

High-flux/high-temperature solar thermal conversion: technology development and advanced applications

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Principles of doping ceria for the solar thermochemical redox splitting of H₂O and CO₂