TY - JOUR
T1 - Effects of interstitial water and alkali cations on the expansion, intercalation potential, and orbital coupling of nickel hexacyanoferrate from first principles
AU - Liu, Sizhe
AU - Smith, Kyle C.
N1 - This research was funded by the U.S. National Science Foundation (Award No. 1931659) and the Department of Mechanical Science and Engineering at the University of Illinois at Urbana-Champaign. Access to the Blue Waters supercomputer was provided through a Director’s Award from the National Center for Supercomputing Applications (NCSA). Access to the Expanse and Bridges-2 computing platforms, respectively, at the San Diego Supercomputing Center (SDSC) and the Penn State Supercomputing Center (PSC) was supported by the Extreme Science and Engineering Discovery Environment (XSEDE93 Award No. TG-PHY210018), which is supported by the National Science Foundation (NSF) under Grant No. ACI-1548562. We also wish to acknowledge technical support at SDSC and Materials Square (MatSQ) for offering suggestions and help in executing the DFT calculations presented here.
PY - 2022/3/14
Y1 - 2022/3/14
N2 - Prussian blue analogs (PBAs) are an important material class for aqueous electrochemical separations and energy storage owing to their ability to reversibly intercalate monovalent cations. However, incorporating interstitial H 2 O molecules in the ab initio study of PBAs is technically challenging, though essential to understanding the interactions between interstitial water, interstitial cations, and the framework lattice that affect intercalation potential and cation intercalation selectivity. Accordingly, we introduce and use a method that combines the efficiency of machine-learning models with the accuracy of ab initio calculations to elucidate mechanisms of (1) lattice expansion upon intercalation of cations of different sizes, (2) selectivity bias toward intercalating hydrophobic cations of large size, and (3) semiconductor-conductor transitions from anhydrous to hydrated lattices. We analyze the PBA nickel hexacyanoferrate [NiFe (CN) 6] due to its structural stability and electrochemical activity in aqueous electrolytes. Here, grand potential analysis is used to determine the equilibrium degree of hydration for a given intercalated cation (Na+, K+, or Cs+) and NiFe (CN)6 oxidation state based on pressure-equilibrated structures determined with the aid of machine learning and simulated annealing. The results imply new directions for the rational design of future cation-intercalation electrode materials that optimize performance in various electrochemical applications, and they demonstrate the importance of choosing an appropriate calculation framework to predict the properties of PBA lattices accurately.
AB - Prussian blue analogs (PBAs) are an important material class for aqueous electrochemical separations and energy storage owing to their ability to reversibly intercalate monovalent cations. However, incorporating interstitial H 2 O molecules in the ab initio study of PBAs is technically challenging, though essential to understanding the interactions between interstitial water, interstitial cations, and the framework lattice that affect intercalation potential and cation intercalation selectivity. Accordingly, we introduce and use a method that combines the efficiency of machine-learning models with the accuracy of ab initio calculations to elucidate mechanisms of (1) lattice expansion upon intercalation of cations of different sizes, (2) selectivity bias toward intercalating hydrophobic cations of large size, and (3) semiconductor-conductor transitions from anhydrous to hydrated lattices. We analyze the PBA nickel hexacyanoferrate [NiFe (CN) 6] due to its structural stability and electrochemical activity in aqueous electrolytes. Here, grand potential analysis is used to determine the equilibrium degree of hydration for a given intercalated cation (Na+, K+, or Cs+) and NiFe (CN)6 oxidation state based on pressure-equilibrated structures determined with the aid of machine learning and simulated annealing. The results imply new directions for the rational design of future cation-intercalation electrode materials that optimize performance in various electrochemical applications, and they demonstrate the importance of choosing an appropriate calculation framework to predict the properties of PBA lattices accurately.
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U2 - 10.1063/5.0080547
DO - 10.1063/5.0080547
M3 - Article
AN - SCOPUS:85126960696
SN - 0021-8979
VL - 131
JO - Journal of Applied Physics
JF - Journal of Applied Physics
IS - 10
M1 - 105101
ER -