Dissolution Behavior of Ammonia Electrosynthesized in Molten LiCl–KCl–CsCl System

Serizawa, Nobuyuki; Miyashiro, Hajime; Takei, Katsuhito; Ikezumi, Taro; Nishikiori, Tokujiro; Ito, Yasuhiko

doi:10.1149/2.099204jes

“…The delay in peak NH 3 evolution is suggested to be due to the strong absorption of NH 3 by the melt in the presence of N 3− , as reported previously and attributed to the reaction of NH 3 with N 3− to form NH 2 − and NH 2− species [Eq. ]

true normalN^{3 -} + NH_{3} \to NH_{2}^{-} + NH^{2 -}

…”

Section: Resultsmentioning

confidence: 99%

“…[21] However,t od ate the ability of such cells to catalytically produce NH 3 has yet to be carefully confirmed, with only initial rates and non-catalytic conversion of N 3À presented. [22] Results and Discussion Ammonia Synthesis from Li 3 N To confirm that the cell described by Ito and co-workers [10] is truly capable of catalytic ammonia synthesis,w er eproduced their setup in which N 2 and H 2 bubbled through Ni foam electrodes into molten LiCl-KCl eutectic containing Li 3 N( 0.5 mol %). Apotential of 0.7 Vvs.…”

Section: Introductionmentioning

confidence: 99%

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

McPherson

¹

,

Sudmeier

²

,

Fellowes

³

et al. 2019

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Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3− with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li3N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3− to NH3 is grossly over‐simplified. We find that Li3N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H− (H oxidation state −1) and H+ in the form of NH2−/NH2−/NH3 (H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH3. It is further observed that NH2− and NH2− possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3N, N2 can be reduced to N3− while stoichiometric amounts of H− are oxidised to H2. The H2 can then react spontaneously with N3− to form NH3, regenerating H− and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10−8 mol cm−2 s−1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15N2 confirms the resulting NH3 is from catalytic N2 reduction.

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“…The delay in peak NH 3 evolution is suggested to be due to the strong absorption of NH 3 by the melt in the presence of N 3− , as reported previously and attributed to the reaction of NH 3 with N 3− to form NH 2 − and NH 2− species [Eq. ]

true normalN^{3 -} + NH_{3} \to NH_{2}^{-} + NH^{2 -}

…”

Section: Resultsmentioning

confidence: 99%

“…Mechanistic investigation of the reaction with H 2 found that the rate of NH 3 evolution was independent of applied potential, but had a first order dependence on H 2 . However, to date the ability of such cells to catalytically produce NH 3 has yet to be carefully confirmed, with only initial rates and non‐catalytic conversion of N 3− presented …”

Section: Introductionmentioning

confidence: 99%

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

McPherson

¹

,

Sudmeier

²

,

Fellowes

³

et al. 2019

View full text Add to dashboard Cite

Molten LiCl and related eutectic electrolytes are known to permit direct electrochemical reduction of N2 to N3− with high efficiency. It had been proposed that this could be coupled with H2 oxidation in an electrolytic cell to produce NH3 at ambient pressure. Here, this proposal is tested in a LiCl–KCl–Li3N cell and is found not to be the case, as the previous assumption of the direct electrochemical oxidation of N3− to NH3 is grossly over‐simplified. We find that Li3N added to the molten electrolyte promotes the spontaneous and simultaneous chemical disproportionation of H2 (H oxidation state 0) into H− (H oxidation state −1) and H+ in the form of NH2−/NH2−/NH3 (H oxidation state +1) in the absence of applied current, resulting in non‐Faradaic release of NH3. It is further observed that NH2− and NH2− possess their own redox chemistry. However, these spontaneous reactions allow us to propose an alternative, truly catalytic cycle. By adding LiH, rather than Li3N, N2 can be reduced to N3− while stoichiometric amounts of H− are oxidised to H2. The H2 can then react spontaneously with N3− to form NH3, regenerating H− and closing the catalytic cycle. Initial tests show a peak NH3 synthesis rate of 2.4×10−8 mol cm−2 s−1 at a maximum current efficiency of 4.2 %. Isotopic labelling with 15N2 confirms the resulting NH3 is from catalytic N2 reduction.

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“…2,3 Several electrochemical processes have been pursued for consideration as alternative syntheses of NH3. 1,[4][5][6] To this end as illustrated in Figure 1, we utilized Fe2O3 as an electrocatalyst in the molten hydroxide electrolyte synthesis of ammonia directly from air and water, which can driven by sunlight using the STEP solar energy conversion process. Solar Thermal Electrochemical Process (STEP) has demonstrated that sub-band gap solar thermal energy in sunlight is sufficient to heat and drive a variety of chemical reactions that would be energetically forbidden at lower temperature.…”

mentioning

confidence: 99%

Chemical Transformation of Fe, Air & Water to Ammonia: Variation of Reaction Rate with Temperature, Pressure, Alkalinity and Iron

Peng¹,

Li²,

Liu³

et al. 2018

Preprint

0

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The rate of ammonia production by the chemical oxidation of iron, N2(from air or as pure nitrogen) and water is studied as a function of (1) iron particle size, (2) iron concentration, (3) temperature, (4) pressureand (5) concentration of the alkaline reaction medium. The reaction meduium consists of an aqueous solution of equal molal concentrations of NaOH and KOH (Na0.5K0.5OH). We had previously reported on the chemical reaction of iron and nitrogen in alkaline medium to ammonia as an intermediate step in the electrochemical synthesis of ammonia by a nano-sized iron oxide electrocatlyst. Here, the intermediate chemical reaction step is exclusively explored. The ammonia production rate increases with temperature (from 20 to 250°C), pressure (from 1 atm to 15 atm of air or N2), and exhibits a maximum rate at an electrolyte concentration of 8 molal Na0,5K0,5OH in a sealed N2reactor. 1-3 µm particle size Fe drive the highest observed ammonia production reaction rate. The Fe mass normalized rate of ammonia production increases with decreasing added mass of the Fe reactant reaching a maximum observed rate of 2.2x10-4mole of NH3h-1g-1for the reaction of 0.1 g of 1-3 µm Fe in 200°C 8 molal Na0.5K0.5OH at 15 atm. Under these conditions 5.1 wt% of the iron reacts to form NH3via the reaction N2+ 2Fe + 3H2O ®2NH3+ Fe2O3.

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Dissolution Behavior of Ammonia Electrosynthesized in Molten LiCl–KCl–CsCl System

Cited by 32 publications

References 25 publications

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

The Feasibility of Electrochemical Ammonia Synthesis in Molten LiCl–KCl Eutectics

Chemical Transformation of Fe, Air & Water to Ammonia: Variation of Reaction Rate with Temperature, Pressure, Alkalinity and Iron

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