Research | Johnson Group Comp C

Research in the Johnson Group

There are several ongoing projects in the Johnson group. Most of these projects involve some combination of molecular dynamics and density functional theory to study reactions in complex environments.

Ammonia Oxidation

Ammonia has the potential to serve as a transportable, carbon-free fuel. However, extracting protons and electrons from ammonia can be difficult. We study how to do this both electrochemically and using chemical mediators. We also focus on how N–N bonds are formed.

Key Papers

L. Liu, S. I. Johnson, A. M. Appel, R. M. Bullock, Oxidation of Ammonia Catalyzed by a Molecular Iron Complex: Translating Chemical Catalysis to Mediated Electrocatalysis. Angewandte Chemie International Edition. 2024, e202402635.
M. Barona, S. I. Johnson*, M. Mbea, R. M. Bullock and S. Raugei, Computational Investigations of the Reactivity of Metalloporphyrins for Ammonia Oxidation, Topics in Catalysis. 2022, 65, 341-353.
P.L Dunn, B.J. Cook, S.I. Johnson, A.M. Appel, and R.M. Bullock. 2020. "Oxidation of Ammonia with Molecular Complexes." Journal of the American Chemical Society 142, no. 42:17845-17858.
S.I. Johnson, S.P. Heins, C.M. Klug, E.S. Wiedner, R.M. Bullock, S. Raugei. Design and reactivity of pentapyridyl metal complexes for ammonia oxidation. Chemical Communications 55 (35), 5083-5086, 2019

Reactivity in Droplets

Electrospray ionization (ESI) is a critical technique in analytical chemistry, particularly when paired with mass spectrometry. However, the charged droplets generated in ESI have been shown to accelerate reactions relative to bulk solutions of the same components. The source of this acceleration is hotly debated. We aim to create a comprehensive computational model of reactivity.

Key Papers

R.G. Ewing, G.L. Hart, M.K Nims, S.E. Murphy, S.I. Johnson, J. Chun, E.H. Denis, Reducing ion diffusion at atmospheric pressure through intermingled positive and negative ions. International Journal of Mass Spectrometry, 2023, 492, 117115.
S.I. Johnson*, M.D. Baer, S. Raugei, Protonation of Serine in Gas and Condensed and Microsolvated States in Aqueous Solution. Journal of Physical Chemistry A. 2022, 126 (1), 44-52.

Charge Transport and Delivery

Electrochemical reactions often involve proton (H+) and hydrogen atom (H•) transfer, which can be sensitive to the surrounding environment. We use full atomistic molecular dynamics simulations with explicit solvent and counterions to model reactions in homogeneous catalysts and at the surface. Transport of H+/ H• is a key component of this work, both to the catalyst in the bulk and between mediators and the surface of electrodes. Deeper understanding of these processes will help influence the design of moelcules that can use solvent advantageously or engineer their own environments.

Key Papers

N. Kumar, W. Rishko, K. R. Fiedler, A. Hollas, J. Chun, S.I. Johnson*; Correlations between molecular structure, solvation topology, and transport properties of aqueous organic flow battery electrolyte solutions. ACS Materials Letters. 2023, 5, 3050-3057.
S.H.R. Shin, H.-S. Lim, K.S. Han, A.J. Robinson, A. Hollas, B.M. Sivakumar, S.I Johnson, J. Chun, W. Wang, V. Murugesan, P.K. Thallapally; Porous Liquids as Electrolyte: A Case Study of Li+ and Mg2+ Ion Transport in Crown Ether-Based Type-II Porous Liquids. ACS Materials Letters, 2023, 5 (2), 330-335.