Reliable electrochemical phase diagrams of magnetic transition metals and related compounds from high-throughput ab initio calculations

Abstract

Magnetic transition metals (mTM = Cr, Mn, Fe, Co, and Ni) and their complex compounds (oxides, hydroxides, and oxyhydroxides) are highly important material platforms for diverse technologies, where electrochemical phase diagrams with respect to electrode potential and solution pH can be used to effectively understand their corrosion and oxidation behaviors in relevant aqueous environments. Many previous decades-old mTM-Pourbaix diagrams are inconsistent with various direct electrochemical observations, because experimental complexities associated with extracting reliable free energies of formation (Δ f G) lead to inaccuracies in the data used for modeling. Here, we develop a high-throughput simulation approach based on density-functional theory (DFT), which quickly screens structures and compounds using efficient DFT methods and calculates accurate Δ f G values, using high-level exchange-correlation functions to obtain ab initio Pourbaix diagrams in comprehensive and close agreement with various important electrochemical, geological, and biomagnetic observations reported over the last few decades. We also analyze the microscopic mechanisms governing the chemical trends among the Δ f G values and Pourbaix diagrams to further understand the electrochemical behaviors of mTM-based materials. Last, we provide probability profiles at variable electrode potential and solution pH to show quantitatively the likely coexistence of multiple-phase areas and diffuse phase boundaries.

Predicting aqueous stability of solid with computed Pourbaix diagram using SCAN functional

“…In the reaction energy calculation, we neglect the zero-point energy (E ZPE ) and the integrated heat capacity from 0 to 298.15 K (δH) for both solids and gases by assuming that the differences in these quantities between reactants and products are negligible at room temperature. Previous studies in the literature show that E ZPE and δH of solids and gases are comparable [39][40][41] , but we note that estimation of E ZPE and δH is possible, albeit expensive, with phonon or molecular dynamics calculations, and a systematic approach towards these that can further improve our approach merits a study in its own right.…”

Predicting Aqueous Stability of Solid with Computed Pourbaix Diagram using SCAN Functional

“…2,28 In the reaction energy calculation, we neglect the zero-point energy (E ZPE ) and the integrated heat capacity from 0 K to 298.15 K (δ H) for both solids and gases by assuming that the differences in these quantities between reactants and products are negligible at room temperature. Previous studies in the literature show that E ZPE and δ H of solids and gases are comparable, 28,33,34,41 but we note that estimation of E ZPE and δ H is possible, albeit expensive, with phonon or molecular dynamics calculations, and a systematic approach towards these that can further improve our approach merits a study in its own right.…”

“…We note that NiO and/or Ni(OH) 2 was often observed to be stable at pH 5∼15 in experiment. 33,34 This is probably because in practical applications the Ni aqueous ion concentration is much higher than the conventional one ( 10 1.60 V in OER. [36][37][38] In experiment, the formation of high-valence iridium oxides, e.g.…”

A comparative DFT study of Fe3+ and Fe2+ ions adsorption on (100) and (110) surfaces of pyrite: An electrochemical point of view

“…The previous studies have indicated that the DFT is among the most versatile and popular methods to investigate electronic structure of solids . The optimization of bulk FeS 2 and all surface relaxation calculations were performed with the Perdew–Burke–Ernzerhof (PBE) density functional as implemented in the Dmol 3 code .…”