A Computational Approach for Mapping Electrochemical Activity of Multi-principal Element Alloys

Multi principal element alloys (MPEAs) comprise an atypical class of metal alloys. MPEAs have been demonstrated to possess several exceptional properties, including, as most relevant to the present study a high corrosion resistance. In the context of MPEA design, the vast number of potential alloying elements and the staggering number of elemental combinations favours a computational alloy design approach. In order to computationally assess the prospective corrosion performance of MPEA, an approach was developed in this study. A density functional theory (DFT) – based Monte Carlo method was used for the development of MPEA ‘structure’; with the AlCrTiV alloy used as a model. High-throughput DFT calculations were performed to create training datasets for surface activity/selectivity towards different adsorbate species: O2-, Cl- and H+. Machine-learning (ML) with combined representation was then utilised to predict the adsorption and vacancy energies as descriptors for surface activity/selectivity. The capability of the combined computational methods of MC, DFT and ML, as a virtual electrochemical performance simulator for MPEAs was established and may be useful in exploring other MPEAs

Electrochemical Stability of Magnesium Surfaces in an Aqueous Environment

An insight into the electrochemical stability of Mg surfaces is of practical importance for improving the corrosion resistance of Mg as well as its performance as a battery electrode. The present paper employs first-principles density functional theory simulations to study the electrochemical stability of magnesium surfaces in aqueous environments. A number of electrochemical reactions that describe the interactions between the Mg(0001) surface and water were analyzed. It was verified that water dissociation is favored upon the Mg surface, in agreement with recent works; however, it is also shown that the previously unstudied Heyrovsky reaction may play an important role in controlling the surface stability. Furthermore, it was found that the surface stability also crucially depends on the concentration of adsorbed hydroxyl groups. Specifically, the surface work function was determined to vary as the function of hydroxyl coverage, which has ramifications for the catalytic behavior of the Mg surface. The influences of surface doping with Ca (a reactive element) and Fe (a comparatively noble element) were also studied to provide an atomic-level understanding of how the dopants influence surface properties and subsequent electrochemical reactions. With a keen recent empirical interest in Mg surface stability given the industrial relevance of Mg, the present study provides key new insights into the physical processes related to the enhanced catalytic activity of Mg and its alloys

Aqueous electrochemistry of the magnesium surface: Thermodynamic and kinetic profiles

In this study, first-principles density functional theory (DFT) calculations are performed to investigate the contribution of each individual reaction at the magnesium/water interface. Thermodynamic and kinetic models derived from the DFT-calculated parameters are used to describe interdependent reactions at the interface and the resultant magnesium electrochemical activity at different pH and potentials. These models are able to rationalise experimental findings, such as those obtained from polarisation and immersion tests, and provide new insights for defining a complete and viable mechanism of aqueous magnesium electrochemistry.J.A.Y received funding from the Monash International Postgraduate Scholarship (MIPRS), Monash Graduate Scholarship (MGS), Monash Study Away/ Travel Grant and Graduate Research International Travel Award (GRITA). N.B and N.V.M received funding from Australian Research Council DP Scheme (DP160103661). N.B. received support by Woodside Energy

A Computational Approach for Mapping Electrochemical Activity of Multi-Principal Element Alloys

Multi principal element alloys (MPEAs) comprise a unique class of metal alloys. MPEAs have been demonstrated to possess several exceptional properties, including, as most relevant to the present study, a high corrosion resistance. In the context of MPEA design, the vast number of potential alloying elements and the staggering number of elemental combinations favours a computational alloy design approach. In order to computationally assess the prospective corrosion performance of MPEA, an approach was developed in this study. A density functional theory (DFT) based Monte Carlo method was used for the development of MPEA structure, with the AlCrTiV alloy used as a model. High-throughput DFT calculations were performed to create training datasets for surface activity towards different adsorbate species: O2-, Cl- and H+. Machine learning (ML) with combined representation was then utilised to predict the adsorption and vacancy energies as descriptors for surface activity. The capability of the combined computational methods of MC, DFT and ML, as a virtual electrochemical performance simulator for MPEAs was established and may be useful in exploring other MPEAs

Uncovering the CO2 Capture Mechanis of NaNO3-Promoted MgO by O-18 Isotope Labeling

MgO-based CO2 sorbents promoted with molten alkali metal nitrates (e.g., NaNO3) have emerged as promising materials for CO2 capture and storage technologies due to their low cost and high theoretical CO2 uptake capacities. Yet, the mechanism by which molten alkali metal nitrates promote the carbonation of MgO (CO2 capture reaction) remains debated and poorly understood. Here, we utilize O-18 isotope labeling experiments to provide new insights into the carbonation mechanism of NaNO3-promoted MgO sorbents, a system in which the promoter is molten under operation conditions and hence inherently challenging to characterize. To conduct the O-18 isotope labeling experiments, we report a facile and large-scale synthesis procedure to obtain labeled MgO with a high O-18 isotope content. We use Raman spectroscopy and in situ thermogravimetric analysis in combination with mass spectrometry to track the O-18 label in the solid (MgCO3), molten (NaNO3), and gas (CO2) phases during the CO2 capture (carbonation) and regeneration (decarbonation) reactions. We discovered a rapid oxygen exchange between CO2 and MgO through the reversible formation of surface carbonates, independent of the presence of the promoter NaNO3. On the other hand, no oxygen exchange was observed between NaNO3 and CO2 or NaNO3 and MgO. Combining the results of the O-18 labeling experiments, with insights gained from atomistic calculations, we propose a carbonation mechanism that, in the first stage, proceeds through a fast, surface-limited carbonation of MgO. These surface carbonates are subsequently dissolved as [Mg2+center dot center dot center dot CO32-] ionic pairs in the molten NaNO3 promoter. Upon reaching the solubility limit, MgCO3 crystallizes at the MgO/NaNO3 interface.ISSN:2691-370

Understanding H2 Evolution Electrochemistry to Minimize Solvated Water Impact on Zinc-Anode Performance

H2 evolution is the reason for poor reversibility and limited cycle stability with Zn-metal anodes, and impedes practical application in aqueous zinc-ion batteries (AZIBs). Here, using a combined gas chromatography experiment and computation, it is demonstrated that H2 evolution primarily originates from solvated water, rather than free water without interaction with Zn2+. Using linear sweep voltammetry (LSV) in salt electrolytes, H2 evolution is evidenced to occur at a more negative potential than zinc reduction because of the high overpotential against H2 evolution on Zn metal. The hypothesis is tested and, using a glycine additive to reduce solvated water, it is confirmed that H2 evolution and “parasitic” side reactions are suppressed on the Zn anode. This electrolyte additive is evidenced to suppress H2 evolution, reduce corrosion, and give a uniform Zn deposition in Zn|Zn and Zn|Cu cells. It is demonstrated that Zn|PANI (highly conductive polyaniline) full cells exhibit boosted electrochemical performance in 1 M ZnSO4–3 M glycine electrolyte. It is concluded that this new understanding of electrochemistry of H2 evolution can be used for design of relatively low-cost and safe AZIBs for practical large-scale energy storage

The effect of absorbed hydrogen on the dissolution of steel

Atomic hydrogen (H) was introduced into steel (AISI 1018 mild steel) by controlled cathodic pre-charging. The resultant steel sample, comprising about 1 ppmw diffusible H, and a reference uncharged sample, were studied using atomic emission spectroelectrochemistry (AESEC). AESEC involved potentiodynamic polarisation in a flowing non-passivating electrolyte (0.6 M NaCl, pH 1.95) with real time reconciliation of metal dissolution using on-line inductively coupled plasma-atomic emission spectroscopy (ICP-OES). The presence of absorbed H was shown to significantly increase anodic Fe dissolution, as evidenced by the enhanced detection of Fe2+ ions by ICP-OES. We discuss this important finding in the context of previously proposed mechanisms for H-effects on the corrosion of steels