Claims:We Claim
1. Solar energy driven ammonia synthesis in wet nitrogen environment using modified perovskite-based photo-catalytic water splitting systemcomprising of :
a composite reactor chamber 1 made of delrin and resin as adhesive, consisting of three isolated cells, the anodic reaction cell 2, filled up with molar concentrated alkaline water, is double the volume of each of the two cathodic cell, one 3 of which is filled up with molar concentrated acidulated water (aqueous HCl) and other 4 with acid-water saturated gas/vapour of nitrogen to produce ammonia, at normal temperature and pressure condition;
a stream of solar energy incident on the sputter deposited gold nano-particle surface of the photo-catalytic perovskite-based structure of niobium doped strontium titanate (Nb-SrTiO3), through a quartz window placed at the anodic cell;
a population of photo-generated electron-hole pair generated at the Au-NP/Nb-SrTiO3interface performs the splitting of alkaline water (aqueous KOH)to generate proton (H+), electron (e-) and molecular oxygen (O2);
a salt bridge/nafion?a proton exchange membrane is employed for the propagation of proton from anodic cell to cathodic cells to maintain charge balance between the cells;
a stream of localized surface plasmon resonance (LSPR) induced electrons propagates through the modified perovskite structure to reach the other surface of the Nb-SrTiO3 substrate, deposited with thin films of transition metal and its oxide by plasma enhanced chemical vapour deposition setup;
a pair of gold nano-particle modified Nb-SrTiO3 structure deposited with thin films of ruthenium and zirconium on other surface of the substrate isolates the anode and cathode cells;
a hydrogen evolution reaction takes place at ruthenium loaded modified perovskite structure to evolve hydrogen;
a specially shaped tube allows evolved molecular hydrogen to pass from the top level of hydrogen evolving cathode cell to the bottom of the other cathode cell filled with acid-water saturated nitrogen gas;
a pressurized N2 gas cylinder 21 supplies wetN2 at the bottom level of the second cathodic cell 4 after getting saturated by acid and water vapour;
a population of energetic LSPR induced electrons propagate to the zirconium loaded surface of modified perovskite structure at the second cathodic cell 4 to dissociate the bonds of molecular N2 and H2;
a recombination reaction takes place between the active atomic hydrogen and nitrogen at the ratio of 3:1 to produce NH3 in second cathodic cell 4;
a caesium sensitized surface of zirconium at the second cathodic cell substantially promotes the ammonia production;
a superior stable and accelerated rate of ammonia synthesis is achieved due to the chemical biasing by the use of acid and water saturated ¬N2 gas;
a plasma enhanced chemical vapour deposition and sputtering setup used to synthesize the thin films of transition metal/transition metal oxides and sputtered deposition of noble metal nano-particles on the perovskite structure under high vacuum condition;
2. A sputter deposited gold nano-particle 6 modified surface of the photo-catalytic perovskite-based structure of niobium doped strontium titanate (Nb-SrTiO3) 5 is exposed under solar radiation, incident through a quartz window 9 placed at the anode cell 2, as claimed in claim 1, forming electron-hole pair (e-?h+) for splitting alkaline water to generate proton (H+), electron (e-) and molecular oxygen (O2);
3. The propagation of proton (H+) from anodic cell 2 to cathodic cells by employing a salt bridge/nafion-a proton exchange membrane 13, as claimed in claim 1, to maintain charge balance between the cells.
4. The photo-generated energetic electrons 31 at the Au-NP/Nb-SrTiO3 interface, propagate through the substrate by inducing localized surface plasmon resonance (LSPR) to arrive at the other surface of the Au-NP/Nb-SrTiO3 structure, deposited with nano-metric film of transition metal or its oxide 8 by the help of plasma enhanced chemical vapour deposition process, as claimed in claim 1;
5. The other surfaces of the pair of Au-NP/Nb-SrTiO3 structure are individually coated with thin films of ruthenium (Ru) and zirconium (Zr) respectively, as claimed in claim 1, isolate anode from two cathode cells;
6. The hydrogen evolution reaction (HER) 42 takes place at ruthenium loaded Au-NP/Nb-SrTiO3, as claimed in claim 1, to evolve hydrogen at one of the cathode cells 3 filled up with acidulated water by reduction of proton (H+) with the help of LSPR induced electrons;
7. The specially shaped tube 14, as claimed in claim 1, is employed to allow the evolved molecular hydrogen from the top level of the hydrogen evolving cathode cell 3 to the bottom level of the other cathode cell 4 filled with acid-water saturated nitrogen gas;
8. The molecular hydrogen and acid-water treated wet nitrogen get dissociated at the zirconium loaded Au-NP/Nb-SrTiO3 substrate in second cathode cell 4 by energetic LSPR induced electrons 31 with a view to recombine the active atomic hydrogen and nitrogen at the ratio of 3:1 for producing ammonia 43, as claimed in claim 1;
9. The zirconia surface of Au-NP/Nb-SrTiO3/Zr is sensitized with caesium (Cs) at the second cathodic cell 4, as claimed in claim 1,enhances the production of negative nitrogen ions that substantially promotes the ammonia production rate due to the strong interaction between active H2;
10. The stable enhanced rate of ammonia synthesis 43 is obtained by creating a difference in pH value (?delpH= ~3-8) to satisfy suitable chemical biasing using acid-water saturated wet nitrogen at ammonia evolving cathode cell. , Description:This invention aims at method and system for ammonia synthesis. The synthesis of ammonia is brought about by the simultaneous solar energy driven photo-catalytic method of namely hydrogen generation by water splitting along with dinitrogen fixation to hydrogen in the apparatus. This ammonia synthesis method and system ensure to meet the demand of ammonia which is one of the most extensively produced chemicals worldwide consuming about 2% of the total world’s energy consumption. This synthesis method also ensures the green energy solution by emission of fresh oxygen that is devoid of greenhouse gases utilizing modified perovskite-based photo-catalytic and co-catalytic nano-structure with relatively efficient yield and lower manufacturing cost. The invention finds application in producing ammonia as a source of chemical energy.
There will be described below the preferred embodiment of the present invention into details with reference to the accompanying drawings. Like members or elements will be designated by like reference characters.
Fig. 1 shows the top view of the solar energy driven ammonia synthesis in wet nitrogen environment using modified perovskite nanostructure-based photo-catalytic water splitting apparatus 1 in accordance with the first and preferred embodiment of the present invention. The apparatus comprises of three cell reactor chamber. The anode cell 2 is contained with alkaline water and one cathode cell3out of the two is filled with acidic water and the other cathode cell 4 with acidic water vapour saturated nitrogen gas at normal temperature and pressure condition. Ammonia is produced in vapour saturated cathodic cell 4 and oxygen is liberated in alkali filled anodic cell 2 which is twice the volume of each of the cathode cells. The solar radiation 10 in the form of photon 11 is incident on the noble metal nano-particles 6 (e.g., Au, Ag, Pt, Ru, Rh, Pd, Os, Ir etc.)modified surface of the perovskite substrate of niobium doped strontium titanate (Nb-SrTiO3)5through the quartz glass window 9. The solar to electrical energy conversion efficiency substantially increases due to the superior electrical conductivity and efficient sunlight trapping property of the noble metal nano-particles 6. The photo-generated energetic electrons 31 at the interface of noble metal nano-particles and Nb-SrTiO3 substrateare transmitted to the other surface of the modified structure by induced localized surface plasmon resonance (LSPR).Nitrogen gas is supplied from a cylinder 21 to the cathodic reaction cell 4. The gas is treated with acid-water 23 filled container 22 employing a gas control valve 24 and then injected into the cathodic reaction cell 4 through a gas pipeline 25 as shown in first andpreferred embodiment of the present invention.
Fig. 2 represents the right side view of the ammonia synthesis apparatus 1 in accordance with the second embodiment of the present invention. The present view of the apparatus 1 in this embodiment shows an anode cell 2 and a cathode cell 3 connected by a salt bridge 13 for proton exchange to maintain charge balance. The oxygen evolution reaction 41 and hydrogen evolution reaction 42 takes place in anodic cell 2 and cathode cell 3, as mentioned in second embodiment.
According to Fig. 3, third embodiment of the present invention, a nano-metric film of zirconia 8 is deposited on the Nb-SrTiO35 nano structures, as mentioned in first embodiment, by an Electron Cyclotron Resonance Plasma Enhanced Chemical Vapour Deposition (ECR-PE-CVD) apparatus. The ammonia synthesis reaction 43 takes place efficiently on caesium oxide (Cs2O) promoted zirconia surface 8. The present view of the apparatus 1 in this embodiment also shows an oxygen gas outlet port 16 and an ammonia gas outlet port 15.
Fig. 4 is a diagram, the fourth embodiment of the present invention, showing the specially shaped tube 14 for the passage of hydrogen produced at the cathodic reaction cell 3 to the ammonia evolving cathodic reaction cell 4. The cathodic cell 3 and 4 are separated by an insulator 12.
The steps of redox reactions take place in this process are mentioned below:
Oxidation reaction41 at Anode: 2H2O (l) ?= O2 (g) + 4H+ (aq) + 4e-
Reduction reaction42 at Cathode: 2H+ (aq) +2e-?= H2 (g)
Ammonia synthesis reaction43 at Cathode: 3H2 (g) + N2 (g) =? 2NH3 (g)
Hence an integrated three cell apparatus using transition metal modified perovskite nanostructure-based photo-catalytic water splitting mechanism in conjunction to Transition Metal co-catalyst ensures an efficient eco-friendly conversion of abundant solar energy to chemical energy (ammonia).