固氮反應，為現今重要的工業及生物程序，其產物氨為製造肥料所需重要原料，而製氨現今仍仰賴十九世紀初期所發展出的哈伯程序(N2(g) + H2(g)  NH3(g))。縱使隨時間推移，投注大量研究，此程序有諸多改善，哈伯法製氨仍是全世界耗能最高的化學程序之一，耗能之主要原因在於製氨過程中須營造高溫及高壓環境(200 atm and 500 Cº)，導致過多的能量耗損並產生大量的溫室氣體。為了在現有基礎上開發出更具效率的固氮反應催化劑，本文選用釕(0001)表面作為研究標的，藉由量子模型(Poisson–Boltzmann solvation model)模擬電化學環境於0.0VS.H.E.，分別搜索釕金屬在電化學及熱化學環境，之於氮氣還原之化學動力學及反應機構。
在電化學(N2ER)及熱化學(N2TR)環境下的氮氣還原反應，大致可劃分為兩種不同基本反應，其一：氮氮鍵於不同氫化程度之斷鍵；其二：氫之加成反應，生成N2HX、NHX等氮氫化合物。氮氮斷鍵在電化學及熱化學環境，具有相似反應熱及活化能；氫之加成反應，在電催化環境下具有較低的活化能。因此，在電化學環境下，氮氣還原反應傾向結合性反應機構(associative reaction pathway)，即是唯有氫加成至滿足配位的情況下，才會誘發氮氮之間的斷鍵；反之，在熱催化環境下，氮氣還原反應傾向解離性反應機構(dissociative reaction pathway)，即是氮氮鍵在還原反應初期即斷鍵。
對於電催化氮氣還原，氮氣先平行吸附於電極表面，氫後加成於平行於電極表面吸附之氮氣(*pN2)為速率決定步驟，總活化能G⧧ = 0.95 eV，其中包含氮氣平行吸附於表面之吸附能G = 0.56 eV，以及吸附後氫化之活化能G⧧ = 0.39 eV。對於熱催化氮氣還原，速率決定步驟為氮氣先平行吸附於電極表面，後氮氮鍵之直接斷鍵，總活化能G⧧ = 2.18 eV，其中包含氮氣平行吸附於表面之吸附能G = 1.09 eV，以及吸附後氮氮鍵斷鍵之活化能G⧧ = 1.09 eV。
由上述能量分析推知，欲改善在釕表面，電化學及熱化學催化之氮氣還原反應效率，需提供氮氣良好的吸附環境，降低氮氣之吸附能，例如：階梯式釕金屬表面，可提供氮氣較平整表面更多配位，使氮氣之吸附能下降，進而獲得較低的總活化能，並藉此加速反應進行。此概念已在熱催化環境下證實，本篇論文目的在於電化學環境下氮氣還原反應之預測，以改善氮氣還原的效率。

In order to provide the basis for developing a new generation of energy efficient processes, we report the detailed atomistic mechanism and kinetics for N2ER on Ru(0001) along with a comparison to N2TR. N2ER favors an associative route where successive hydrogen atoms are added to N2 prior to breaking the NN bonds rather than the dissociative route preferred by N2TR, where the NN bonds are broken first followed by the addition of Hs. Our QM results provided the detailed free energy surfaces for N2ER and N2TR, suggesting a strategy for improving the efficiency of N2ER.

1. Erisman, J. W.; Sutton, M. A.; Galloway, J.; Klimont, Z.; Winiwarter, W. J. N. G., How a century of ammonia synthesis changed the world. 2008, 1 (10), 636.
2. Kang, D. W.; Holbrook, J. H. J. E. R., Use of NH3 fuel to achieve deep greenhouse gas reductions from US transportation. 2015, 1, 164-168.
3. Rees, N. V.; Compton, R. G. J. E.; Science, E., Carbon-free energy: a review of ammonia-and hydrazine-based electrochemical fuel cells. 2011, 4 (4), 1255-1260.
4. Christensen, C. H.; Johannessen, T.; Sørensen, R. Z.; Nørskov, J. K. J. C. T., Towards an ammonia-mediated hydrogen economy? 2006, 111 (1-2), 140-144.
5. Wang, L.; Xia, M.; Wang, H.; Huang, K.; Qian, C.; Maravelias, C. T.; Ozin, G. A. J. J., Greening ammonia toward the solar ammonia refinery. 2018, 2 (6), 1055-1074.
6. Kordali, V.; Kyriacou, G.; Lambrou, C. J. C. C., Electrochemical synthesis of ammonia at atmospheric pressure and low temperature in a solid polymer electrolyte cell. 2000, (17), 1673-1674.
7. Song, Y.; Johnson, D.; Peng, R.; Hensley, D. K.; Bonnesen, P. V.; Liang, L.; Huang, J.; Yang, F.; Zhang, F.; Qiao, R. J. S. a., A physical catalyst for the electrolysis of nitrogen to ammonia. 2018, 4 (4), e1700336.
8. Zhang, Y.; Qiu, W.; Ma, Y.; Luo, Y.; Tian, Z.; Cui, G.; Xie, F.; Chen, L.; Li, T.; Sun, X. J. A. C., High-performance electrohydrogenation of N2 to NH3 catalyzed by multishelled hollow Cr2O3 microspheres under ambient conditions. 2018, 8 (9), 8540-8544.
9. Ren, X.; Zhao, J.; Wei, Q.; Ma, Y.; Guo, H.; Liu, Q.; Wang, Y.; Cui, G.; Asiri, A. M.; Li, B. J. A. C. S., High-performance N2-to-NH3 conversion electrocatalyzed by Mo2C nanorod. 2018, 5 (1), 116-121.
10. Brown, D. E.; Edmonds, T.; Joyner, R. W.; McCarroll, J. J.; Tennison, S. R. J. C. l., The genesis and development of the commercial BP doubly promoted catalyst for ammonia synthesis. 2014, 144 (4), 545-552.
11. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized Gradient Approximation Made Simple. Physical Review Letters 1996, 77 (18), 3865-3868.
12. Blöchl, P. E., Projector augmented-wave method. Physical Review B 1994, 50 (24), 17953-17979.
13. Kresse, G.; Joubert, D., From ultrasoft pseudopotentials to the projector augmented-wave method. Physical Review B 1999, 59 (3), 1758-1775.
14. Kresse, G.; Furthmüller, J., Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Computational Materials Science 1996, 6 (1), 15-50.
15. Kresse, G.; Furthmüller, J., Efficient iterative schemes forab initiototal-energy calculations using a plane-wave basis set. Physical Review B: Condensed Matter 1996, 54 (16), 11169-11186.
16. Kresse, G.; Hafner, J., Ab initiomolecular dynamics for liquid metals. Physical Review B: Condensed Matter 1993, 47 (1), 558-561.
17. Kresse, G.; Hafner, J., Ab initio molecular-dynamics simulation of the liquid-metal--amorphous-semiconductor transition in germanium. Physical Review B 1994, 49 (20), 14251-14269.
18. Clendenen, R. L.; Drickamer, H. J. J. o. P.; Solids, C. o., The effect of pressure on the volume and lattice parameters of ruthenium and iron. 1964, 25 (8), 865-868.
19. Henkelman, G.; Uberuaga, B. P.; Jónsson, H. J. T. J. o. c. p., A climbing image nudged elastic band method for finding saddle points and minimum energy paths. 2000, 113 (22), 9901-9904.
20. Henkelman, G.; Jónsson, H. J. T. J. o. c. p., A dimer method for finding saddle points on high dimensional potential surfaces using only first derivatives. 1999, 111 (15), 7010-7022.
21. Xiao, P.; Sheppard, D.; Rogal, J.; Henkelman, G. J. T. J. o. c. p., Solid-state dimer method for calculating solid-solid phase transitions. 2014, 140 (17), 174104.
22. Zhang, H.; Goddard, W. A.; Lu, Q.; Cheng, M.-J. J. P. C. C. P., The importance of grand-canonical quantum mechanical methods to describe the effect of electrode potential on the stability of intermediates involved in both electrochemical CO 2 reduction and hydrogen evolution. 2018, 20 (4), 2549-2557.
23. Goodpaster, J. D.; Bell, A. T.; Head-Gordon, M. J. T. j. o. p. c. l., Identification of possible pathways for C–C bond formation during electrochemical reduction of CO2: New theoretical insights from an improved electrochemical model. 2016, 7 (8), 1471-1477.
24. Xiao, H.; Cheng, T.; Goddard III, W. A.; Sundararaman, R. J. J. o. t. A. C. S., Mechanistic explanation of the pH dependence and onset potentials for hydrocarbon products from electrochemical reduction of CO on Cu (111). 2016, 138 (2), 483-486.
25. Xiao, H.; Cheng, T.; Goddard III, W. A. J. J. o. t. A. C. S., Atomistic mechanisms underlying selectivities in C1 and C2 products from electrochemical reduction of CO on Cu (111). 2016, 139 (1), 130-136.
26. Steinmann, S. N.; Sautet, P. J. T. J. o. P. C. C., Assessing a first-principles model of an electrochemical interface by comparison with experiment. 2016, 120 (10), 5619-5623.
27. Mathew, K.; Hennig, R. G. J. a. p. a., Implicit self-consistent description of electrolyte in plane-wave density-functional theory. 2016.
28. Donald, W. A.; Leib, R. D.; O'Brien, J. T.; Bush, M. F.; Williams, E. R. J. J. o. t. A. C. S., Absolute standard hydrogen electrode potential measured by reduction of aqueous nanodrops in the gas phase. 2008, 130 (11), 3371-3381.
29. Garza, A. J.; Bell, A. T.; Head-Gordon, M. J. A. C., Mechanism of CO2 reduction at copper surfaces: pathways to C2 products. 2018, 8 (2), 1490-1499.
30. Garza, A. J.; Bell, A. T.; Head-Gordon, M. J. T. j. o. p. c. l., Is subsurface oxygen necessary for the electrochemical reduction of CO2 on copper? 2018, 9 (3), 601-606.
31. Chang, K.; Chen, J. G.; Lu, Q.; Cheng, M.-J. J. T. J. o. P. C. C., Grand Canonical Quantum Mechanical Study of the Effect of the Electrode Potential on N-Heterocyclic Carbene Adsorption on Au Surfaces. 2017, 121 (44), 24618-24625.
32. Nørskov, J. K.; Rossmeisl, J.; Logadottir, A.; Lindqvist, L.; Kitchin, J. R.; Bligaard, T.; Jonsson, H. J. T. J. o. P. C. B., Origin of the overpotential for oxygen reduction at a fuel-cell cathode. 2004, 108 (46), 17886-17892.
33. Jacobsen, C. J.; Dahl, S.; Hansen, P. L.; Törnqvist, E.; Jensen, L.; Topsøe, H.; Prip, D. V.; Møenshaug, P. B.; Chorkendorff, I. J. J. o. M. C. A. C., Structure sensitivity of supported ruthenium catalysts for ammonia synthesis. 2000, 163 (1-2), 19-26.
34. Vitos, L.; Ruban, A.; Skriver, H. L.; Kollar, J. J. S. s., The surface energy of metals. 1998, 411 (1-2), 186-202.
35. Dahl, S.; Logadottir, A.; Egeberg, R.; Larsen, J.; Chorkendorff, I.; Törnqvist, E.; Nørskov, J. K. J. P. R. L., Role of steps in N 2 activation on Ru (0001). 1999, 83 (9), 1814-1817.
36. Hellman, A.; Baerends, E.; Biczysko, M.; Bligaard, T.; Christensen, C. H.; Clary, D.; Dahl, S. v.; Van Harrevelt, R.; Honkala, K.; Jonsson, H., Predicting catalysis: Understanding ammonia synthesis from first-principles calculations. ACS Publications: 2006.
37. Honkala, K.; Hellman, A.; Remediakis, I.; Logadottir, A.; Carlsson, A.; Dahl, S.; Christensen, C. H.; Nørskov, J. K. J. s., Ammonia synthesis from first-principles calculations. 2005, 307 (5709), 555-558.
38. Logadottir, A.; Nørskov, J. K. J. J. o. C., Ammonia synthesis over a Ru (0001) surface studied by density functional calculations. 2003, 220 (2), 273-279.
39. Mortensen, J. J.; Hammer, B.; Nørskov, J. K. J. P. r. l., Alkali promotion of N 2 dissociation over Ru (0001). 1998, 80 (19), 4333-4336.
40. Garden, A. L.; Skúlason, E. J. T. J. o. P. C. C., The mechanism of industrial ammonia synthesis revisited: calculations of the role of the associative mechanism. 2015, 119 (47), 26554-26559.
41. Rod, T. H.; Logadottir, A.; Nørskov, J. K. J. T. J. o. C. P., Ammonia synthesis at low temperatures. 2000, 112 (12), 5343-5347.
42. Diekhöner, L.; Mortensen, H.; Baurichter, A.; Luntz, A.; Hammer, B. J. P. r. l., Dynamics of high-barrier surface reactions: Laser-assisted associative desorption of N 2 from Ru (0001). 2000, 84 (21), 4906-4909.
43. Dietrich, H.; Geng, P.; Jacobi, K.; Ertl, G. J. T. J. o. c. p., Sticking coefficient for dissociative adsorption of N2 on Ru single‐crystal surfaces. 1996, 104 (1), 375-381.
44. Egeberg, R.; Larsen, J. H.; Chorkendorff, I. J. P. C. C. P., Molecular beam study of N 2 dissociation on Ru (0001). 2001, 3 (11), 2007-2011.
45. Romm, L.; Katz, G.; Kosloff, R.; Asscher, M. J. T. J. o. P. C. B., Dissociative chemisorption of N2 on Ru (001) enhanced by vibrational and kinetic energy: Molecular beam experiments and quantum mechanical calculations. 1997, 101 (12), 2213-2217.
46. Shi, H.; Jacobi, K.; Ertl, G. J. T. J. o. c. p., Dissociative chemisorption of nitrogen on Ru (0001). 1993, 99 (11), 9248-9254.
47. Song, T.; Hu, P. J. T. J. o. c. p., Insight into the adsorption competition and the relationship between dissociation and association reactions in ammonia synthesis. 2007, 127 (23), 234706.
48. Zhang, C.; Liu, Z.-P.; Hu, P. J. T. J. o. C. P., Stepwise addition reactions in ammonia synthesis: A first principles study. 2001, 115 (2), 609-611.
49. Zhang, C.; Lynch, M.; Hu, P. J. S. s., A density functional theory study of stepwise addition reactions in ammonia synthesis on Ru (0001). 2002, 496 (3), 221-230.
50. Ertl, G. J. C. R. S.; Engineering, Surface science and catalysis—studies on the mechanism of ammonia synthesis: the PH Emmett award address. 1980, 21 (2), 201-223.
51. Skulason, E.; Bligaard, T.; Gudmundsdóttir, S.; Studt, F.; Rossmeisl, J.; Abild-Pedersen, F.; Vegge, T.; Jonsson, H.; Nørskov, J. K. J. P. C. C. P., A theoretical evaluation of possible transition metal electro-catalysts for N 2 reduction. 2012, 14 (3), 1235-1245.
52. Qian, J.; An, Q.; Fortunelli, A.; Nielsen, R. J.; Goddard III, W. A. J. J. o. t. A. C. S., Reaction mechanism and kinetics for ammonia synthesis on the Fe (111) surface. 2018, 140 (20), 6288-6297.
53. Guidelli, R.; Compton, R. G.; Feliu, J. M.; Gileadi, E.; Lipkowski, J.; Schmickler, W.; Trasatti, S. J. P.; Chemistry, A., Defining the transfer coefficient in electrochemistry: An assessment (IUPAC Technical Report). 2014, 86 (2), 245-258.
54. Arumainayagam, C. R.; Tripa, C. E.; Xu, J.; Yates Jr, J. T. J. S. s., IR spectroscopy of adsorbed dinitrogen: a sensitive probe of defect sites on Pt (111). 1996, 360 (1-3), 121-127.
55. Morgan Jr, G. A.; Sorescu, D. C.; Kim, Y. K.; Yates Jr, J. T. J. S. S., Comparison of the adsorption of N2 on Ru (1 0 9) and Ru (0 0 1)–A detailed look at the role of atomic step and terrace sites. 2007, 601 (17), 3533-3547.
56. Tripa, C. E.; Zubkov, T. S.; Yates Jr, J. T.; Mavrikakis, M.; Nørskov, J. K. J. T. J. o. c. p., Molecular N 2 chemisorption—specific adsorption on step defect sites on Pt surfaces. 1999, 111 (18), 8651-8658.
57. Tripa, C. E.; Zubkov, T. S.; Yates, J. T. J. T. J. o. P. C. B., N2 Chemisorption on Stepped Pt Surfaces. Control by 2-D and 1-D Precursor Behavior. 2001, 105 (18), 3724-3732.
58. Bao, D.; Zhang, Q.; Meng, F. L.; Zhong, H. X.; Shi, M. M.; Zhang, Y.; Yan, J. M.; Jiang, Q.; Zhang, X. B. J. A. M., Electrochemical reduction of N2 under ambient conditions for artificial N2 fixation and renewable energy storage using N2/NH3 cycle. 2017, 29 (3), 1604799.