Significant reduction in the operating temperature of the Mn(<scp>ii</scp>)/Mn(<scp>iii</scp>) oxide-based thermochemical water splitting cycle brought about by the use of nanoparticles

Dey, Sunita; Rajesh, S.; Rao, C. N. R.

doi:10.1039/c6ta06271g

Cited by 8 publications

(8 citation statements)

References 28 publications

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“…2). The yield of H 2 at 750°C is ∼40% (over 80 min) with an extended tail due to further H 2 evolution over a period (13). As shown in Fig.…”

Section: Low-temperature Multistep Cyclesmentioning

confidence: 72%

“…2A). Thus, ball-milled samples show a high rate of H 2 production soon after the entry of H 2 O, with an overall increase of 1.5-2 times in comparison with the bulk samples (13). Interestingly, the use of nanoparticles effectively brings down the H 2 evolution temperature to 750°C or 700°C as shown for the 60-min ballmilled (MnNa60) sample in Fig.…”

Section: Low-temperature Multistep Cyclesmentioning

confidence: 82%

“…The CO 2 evolution temperature can be decreased drastically (∼600°C) with the use of nanoparticles of Mn 3 O 4 and Na 2 CO 3 obtained with ball milling (Fig. S1) (13). When nanoparticles of both Mn 3 O 4 and Na 2 CO 3 are used (Fig.…”

Section: Low-temperature Multistep Cyclesmentioning

confidence: 99%

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Solar thermochemical splitting of water to generate hydrogen

Rao

Dey

2017

Proc. Natl. Acad. Sci. U.S.A.

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122

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Solar photochemical means of splitting water (artificial photosynthesis) to generate hydrogen is emerging as a viable process. The solar thermochemical route also promises to be an attractive means of achieving this objective. In this paper we present different types of thermochemical cycles that one can use for the purpose. These include the low-temperature multistep process as well as the high-temperature two-step process. It is noteworthy that the multistep process based on the Mn(II)/Mn(III) oxide system can be carried out at 700°C or 750°C. The two-step process has been achieved at 1,300°C/900°C by using yttrium-based rare earth manganites. It seems possible to render this high-temperature process as an isothermal process. Thermodynamics and kinetics of H 2 O splitting are largely controlled by the inherent redox properties of the materials. Interestingly, under the conditions of H 2 O splitting in the high-temperature process CO 2 can also be decomposed to CO, providing a feasible method for generating the industrially important syngas (CO+H 2 ). Although carbonate formation can be addressed as a hurdle during CO 2 splitting, the problem can be avoided by a suitable choice of experimental conditions. The choice of the solar reactor holds the key for the commercialization of thermochemical fuel production. The impact of global climate change as well as the likely shortage of fossil fuels demand harvesting of energy using renewable sources. Although solar energy captured by the Earth in an hour is expected to satisfy the energy demand of the world for a year, the high energy density and nonpolluting end product renders hydrogen a viable alternative to fossil fuels (1). In this context, conversion of solar power to H 2 and synfuels with the utilization of renewable H 2 O and CO 2 seems to be a sound option. Artificial photosynthesis and photovoltaic-powered electrolysis of water are promising approaches, although their implementation is somewhat restricted because of the low solar-tofuel conversion efficiency (η solar-to-fuel ) of <5% and <15%, respectively (2, 3). The other strategy would be a solarthermochemical process that provides a high theoretical efficiency and enables large-scale production of H 2 by using the entire solar spectrum (4). Research in thermochemical splitting of H 2 O made a beginning in the early 1980s (5, 6) and several thermochemical cycles have been examined. Thermochemical methods come under two main categories, the low-temperature multistep processes and the high-temperature two-step processes. The two-step process involving the thermal decomposition of metal oxides followed by reoxidation by reacting with H 2 O to yield H 2 is an attractive and viable process that can be rendered to become an isothermal process. Thermochemical splitting of H 2 O at low temperatures (<1,000°C) is accomplished by a minimum of three steps as dictated by thermodynamic energy constraints (7,8). In this paper we present the highlights of recent investigations of H 2 O splitting by the low-temperature m...

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“…2). The yield of H 2 at 750°C is ∼40% (over 80 min) with an extended tail due to further H 2 evolution over a period (13). As shown in Fig.…”

Section: Low-temperature Multistep Cyclesmentioning

confidence: 72%

Section: Low-temperature Multistep Cyclesmentioning

confidence: 82%

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Solar thermochemical splitting of water to generate hydrogen

Rao

Dey

2017

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

122

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“…However, the typical dimensions of a thin TEM specimen are 5 μm (length) × 5 μm (width) × 100 nm (thick); therefore oxygen transport to a free surface is much more rapid than in a large bulk specimen and could explain the greater extent of Mn reduction observed at a lower temperature in the EELS experiment. 51 Second, the structural transformations observed during in situ reduction can also be compared to previous literature reports on bulk BCM. Importantly, a recent publication demonstrated a phase transformation of 12R-BCM to a 6H− Ba 3 Ce 0.75 Mn 2.25 O 9 phase (6H fraction = 56 wt %) that had been previously unreported.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Probing Electronic and Structural Transformations during Thermal Reduction of the Promising Water Splitting Perovskite BaCe_0.25Mn_0.75O₃

et al. 2022

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In this report, we investigate the thermal reduction of the octahedral perovskite BaCe 0.25 Mn 0.75 O 3 (BCM) using in situ electron energy loss spectroscopy (EELS) in an aberration-corrected transmission electron microscope (TEM). The 12R-polytype of BCM is known to demonstrate high solar thermochemical hydrogen production capacity. In situ EELS measurements show that Mn is the active redox cation in BCM, undergoing thermal reduction from Mn 4+ to Mn 3+ during heating to 700 °C inside the TEM under a high vacuum. The progressive reduction of Mn 4+ during oxygen vacancy (O v ) formation was monitored as a function of temperature. Additionally, atomic-resolution scanning transmission electron microscopy identified two different types of twin boundaries present in the oxidized and reduced form of 12R-BCM, respectively. These two types of twin boundaries were shown, via computational modeling, to modulate the site-specific O v formation energies in 12R-BCM. It is concluded that these types of atomic defects provide sites more energetically favorable for O v formation during thermal reduction.

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“…In addition to the older three-step sulfur-iodine cycle [104], Mn-oxide based three-step cycles have been more recently proposed [62,105,106]. The use of nanoparticles was also found to have a beneficial effect on lowering the maximum temperature of the cycle [107].…”

Section: Reactor/receivers For Water-splitting Redox Cyclesmentioning

confidence: 99%

Methodologies for the Design of Solar Receiver/Reactors for Thermochemical Hydrogen Production

Murmura

Annesini

2020

Processes

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Thermochemical hydrogen production is of great interest due to the potential for significantly reducing the dependence on fossil fuels as energy carriers. In a solar plant, the solar receiver is the unit in which solar energy is absorbed by a fluid and/or solid particles and converted into thermal energy. When the solar energy is used to drive a reaction, the receiver is also a reactor. The wide variety of thermochemical processes, and therefore of operating conditions, along with the technical requirements of coupling the receiver with the concentrating system have led to the development of numerous reactor configurations. The scope of this work is to identify general guidelines for the design of solar reactors/receivers. To do so, an overview is initially presented of solar receiver/reactor designs proposed in the literature for different applications. The main challenges of modeling these systems are then outlined. Finally, selected examples are discussed in greater detail to highlight the methodology through which the design of solar reactors can be optimized. It is found that the parameters most commonly employed to describe the performance of such a reactor are (i) energy conversion efficiency, (ii) energy losses associated with process irreversibilities, and (iii) thermo-mechanical stresses. The general choice of reactor design depends mainly on the type of reaction. The optimization procedure can then be carried out by acting on (i) the receiver shape and dimensions, (ii) the mode of reactant feed, and (iii) the particle morphology, in the case of solid reactants.

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Significant reduction in the operating temperature of the Mn(ii)/Mn(iii) oxide-based thermochemical water splitting cycle brought about by the use of nanoparticles

Abstract: The use of Mn3O4 and Na2CO3 nanoparticles decreases the temperature of CO2 and H2 evolution with further increase in the reaction rate.

Cited by 8 publications

References 28 publications

Solar thermochemical splitting of water to generate hydrogen

Solar thermochemical splitting of water to generate hydrogen

Probing Electronic and Structural Transformations during Thermal Reduction of the Promising Water Splitting Perovskite BaCe_0.25Mn_0.75O₃

Methodologies for the Design of Solar Receiver/Reactors for Thermochemical Hydrogen Production

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Significant reduction in the operating temperature of the Mn(ii)/Mn(iii) oxide-based thermochemical water splitting cycle brought about by the use of nanoparticles

Abstract: The use of Mn3O4 and Na2CO3 nanoparticles decreases the temperature of CO2 and H2 evolution with further increase in the reaction rate.

Cited by 8 publications

References 28 publications

Solar thermochemical splitting of water to generate hydrogen

Solar thermochemical splitting of water to generate hydrogen

Probing Electronic and Structural Transformations during Thermal Reduction of the Promising Water Splitting Perovskite BaCe0.25Mn0.75O3

Methodologies for the Design of Solar Receiver/Reactors for Thermochemical Hydrogen Production

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Resources

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Probing Electronic and Structural Transformations during Thermal Reduction of the Promising Water Splitting Perovskite BaCe_0.25Mn_0.75O₃