Lithium-mediated electrochemical ammonia synthesis
In some aspects, the present disclosure pertains to methods for the electrochemical production of NH 3 from nitrogen gas and a hydrogen-containing molecule in an electrochemical cell that comprises a cathode, an anode and a lithium-ion-containing electrolyte disposed between the cathode and the anode. The electrochemical cell is operated under conditions such that lithium ions in the electrolyte are converted to lithium metal at the cathode, the lithium metal reacting with nitrogen gas to form Li 3 N, and the Li 3 N reacting with protons in a proton donor to form NH 3 , lithium ions and a deprotonated proton donor. Moreover, the proton donor has a Kamlet-Taft alpha parameter (α) greater than 0.7 and a Kamlet-Taft beta parameter (β) greater than 0.5. Other aspects of the present disclosure pertain to systems for electrochemical production of NH 3 .
1 . A system for the electrochemical production of NH3 from nitrogen gas and a hydrogen-containing molecule, wherein the system comprises:
(a) an electrochemical cell that comprises a cathode, an anode and a lithium-ion containing electrolyte disposed between the cathode and the anode, and wherein the system is configured to operate the electrochemical cell under conditions such that (i) lithium ions in the electrolyte are converted to lithium metal at the cathode, wherein the lithium metal reacts with nitrogen gas to form Li3N, and wherein the Li3N reacts with protons in a proton donor to form NH3, lithium ions and a proton acceptor and wherein the proton donor has a Kamlet-Taft alpha parameter (α) greater than 0.7 and a Kamlet-Taft beta parameter (β) greater than 0.5 and (ii) protons are generated from the hydrogen-containing molecule at the anode, wherein the protons react with the proton acceptor to produce the proton donor;
(b) a source of the nitrogen gas; and
(c) a source of the hydrogen-containing molecule;
wherein the proton donor is (a) an ionic liquid comprising a cation that has a Kamlet-Taft alpha parameter (α) greater than 0.7 and a Kamlet-Taft beta parameter (β) greater than 0.5, (b) an ionic liquid comprising a anion that has a Kamlet-Taft alpha parameter (α) greater than 0.7 and a Kamlet-Taft beta parameter (β) greater than 0.5, or (c) and an ionic liquid comprising a cation that has a Kamlet-Taft alpha parameter (α) greater than 0.7 and a Kamlet-Taft beta parameter (β) greater than 0.5 and a anion that has a Kamlet-Taft alpha parameter (α) greater than 0.7 and a Kamlet-Taft beta parameter (β) greater than 0.5.
2 . The system of claim 1 , wherein the cation is selected from ammonium, azepanium, benzimidazolium, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), guanidinium, imidazolium, morpholinium, octanium, oxazolidinium, phosphonium, piperidinium, pyrazolium, pyridinium, pyrimidinium, pyrrolidinium, sulfonium and triazolium and/or wherein the anion is selected from sulfonate, sulfate, phosphonate, phosphate, bis(trifluoromethanesulfonyl)imide (NTf2), nitrate, halide, dicyanamide, carboxylate, BF4, acetate, phosphite, perchlorate, tricyanomethanide, thiocyanate, PF6, SbF6, and dimethoxy(oxo)phosphanuide.
3 . The system of claim 1 , wherein the hydrogen-containing molecule is selected from hydrogen gas, water, or an organic hydrogen-containing molecule.
4 . The system of claim 3 , wherein the organic hydrogen-containing molecule is a tetrahydrofuran.
5 . The system of claim 1 , further comprising an ionically conductive separator positioned between the anode and the cathode.
6 . The system of claim 1 , further comprising a voltage source for supplying energy to operate the electrochemical cell.
7 . The system of claim 1 , wherein the electrolyte comprises a lithium salt dissolved in a solvent for the lithium salt.
8 . The system of claim 7 , wherein the lithium salt is selected from lithium tetrafluoroborate (LiBF 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium perchlorate (LiClO 4 ), lithium triflate (LiCF 3 SO 3 ), lithium bisoxalato borate (LiBOB), lithium difluorooxalato borate (LiDFOB), lithium trifluorosulfonylimide (LiTFSI).
9 . The system of claim 7 , wherein the solvent for the lithium salt is selected from ether-containing organic solvents, fluorinated organic solvents and lactones.
10 . The system of claim 7 , wherein the solvent for the lithium salt and the hydrogen-containing molecule are the same.
11 . The system of claim 1 , wherein the cathode is formed from a metal or a metal oxide.
12 . The system of claim 1 , wherein the cathode is selected from transition metals and alloys of transition metals.
13 . The system of claim 1 , wherein the anode is platinum metal.
14 . The system of claim 1 , wherein the electrochemical cell is operated at a current density greater than 300 mA/cm2.