Composition and electronic structure of Mn3O4 and Co3O4 cathodes in zinc/air batteries: a DFT study

The surface structures of promising cathode materials for zinc-air batteries, Mn3O4 and Co3O4, have been systematically studied under operating conditions by density functional theory calculations. The environment has been taken into account using grand-canonical schemes both for gas-phase and electrochemical conditions. By analysing the structures appearing in the calculated phase diagrams and Pourbaix diagrams in detail, we derive the factors underlying their stability in the gas phase and under electrochemical conditions. Changes in charge, oxidation states and spin states of the metal cations on the surface are discussed and their feasibility as active centers for the oxygen evolution and reduction reaction is thoroughly analyzed.

Origins of the Instability of Non-precious HER Catalysts at Open Circuit Potential

<p>Non-precious hydrogen evolution reaction (HER) catalysts commonly suffer from severe dissolution under open circuit potential (OCP). In this work, using calculated Pourbaix diagrams, we quantitatively analyze the stability of a set of well-known active HER catalysts (MoS₂, MoP, CoP, Pt in acid, and Ni₃Mo in base) under working conditions. We determine that the large thermodynamic driving force towards decomposition created by the electrode/electrolyte interface potential is responsible for the substantial dissolution of non-precious HER catalysts at OCP. Our analysis further shows the stability of HER catalysts in acidic solution is ordered as Pt ∼ MoS₂<i>> </i>MoP <i>> </i>CoP, which is confirmed by the measured dissolution rates using an inductively coupled plasma mass spectrometer. Based on gained insights, we suggest strategies to circumvent the catalyst dissolution in aqueous solution.</p>

Origins of the Instability of Non-precious HER Catalysts at Open Circuit Potential

<p>Non-precious hydrogen evolution reaction (HER) catalysts commonly suffer from severe dissolution under open circuit potential (OCP). In this work, using calculated Pourbaix diagrams, we quantitatively analyze the stability of a set of well-known active HER catalysts (MoS₂, MoP, CoP, Pt in acid, and Ni₃Mo in base) under working conditions. We determine that the large thermodynamic driving force towards decomposition created by the electrode/electrolyte interface potential is responsible for the substantial dissolution of non-precious HER catalysts at OCP. Our analysis further shows the stability of HER catalysts in acidic solution is ordered as Pt ∼ MoS₂<i>> </i>MoP <i>> </i>CoP, which is confirmed by the measured dissolution rates using an inductively coupled plasma mass spectrometer. Based on gained insights, we suggest strategies to circumvent the catalyst dissolution in aqueous solution.</p>

Novel Application of Pourbaix Diagrams to Model Precipitation in Upstream Biomanufacturing Process Solutions

Commercial production of therapeutic proteins using mammalian cells requires complex process solutions, and consistency of these process solutions is critical to maintaining product titer and quality between batches. Inconsistencies between process solutions prepared at bench and commercial scale may be due to differences in mixing time, temperature, and pH which can lead to precipitation and subsequent removal via filtration of critical solution components such as trace metals. Pourbaix diagrams provide a useful tool to model the solubility of trace metals and were applied to troubleshoot the scale-up of nutrient feed preparation after inconsistencies in product titer were observed between bench- and manufacturing-scale batches. Pourbaix diagrams modeled the solubility of key metals in solution at various stages of the nutrient feed preparation and identified copper precipitation as the likely root cause of inconsistent media stability at commercial scale. Copper precipitation increased proportionally with temperature in bench-scale preparations of nutrient feed and temperature was identified as the root cause of copper precipitation at the commercial scale. Additionally, cell culture copper titration studies performed in bench-scale bioreactors linked copper-deficient mammalian cell culture to inconsistent titers at the commercial scale. Pourbaix diagrams can predict when trace metals are at risk of precipitating and can be used to mitigate risk during the scale-up of complex media preparations.

Hydrometallurgical Leaching of Copper Flash Furnace Electrostatic Precipitator Dust for the Separation of Copper from Bismuth and Arsenic

Flash furnace electrostatic precipitator dust (FF-ESP dust) is a recycle stream in some primary copper production facilities. This dust contains high amounts of copper. In some cases, the FF-ESP dust contains elevated levels of bismuth and arsenic, both of which cause problems during the electrorefining stages of copper production. Because of this, methods for separation of copper from bismuth and arsenic in FF-ESP dust are necessary. Hydrometallurgical leaching using a number of lixiviants, including sulfuric acid, sulfurous acid, sodium hydroxide, and water, were explored. Pourbaix diagrams of copper, bismuth, and arsenic were used to determine sets of conditions which would thermodynamically separate copper from bismuth and arsenic. The data indicate that water provides the best overall separation between copper and both bismuth and arsenic. Sodium hydroxide provided a separation between copper and arsenic. Sulfurous acid provided a separation between copper and bismuth. Sulfuric acid did not provide any separations between copper and bismuth or copper and arsenic.

Electrochemical Pourbaix diagrams of Mg-Zn alloys from first-principles calculations and experimental thermodynamical data

Mg-Zn alloys have attracted much attention as biodegradable alloys owing to their superior mechanical properties and excellent biocompatibility. However, their corrosion/degradation behaviour has become a major issue for various biomedical...