Silver Tarnishing Mechanism Revealed by Molecular Dynamics Simulations

The mechanism of silver–oxygen and silver–sulfur reactions is revealed by means of molecular dynamics simulations, performed with reactive force fields purposely built and extensively tested against quantum‐chemical results. Different reaction mechanisms and rates for Ag–O and Ag–S emerge. This study solves the long‐lasting question why silver exposed to the environment is strongly vulnerable to sulfur corrosion (tarnishing) but hardly reacts with O₂, despite the thermodynamic prediction that both oxide and sulfide should form. The reliability of the simulation results is confirmed by the agreement with a multitude of experimental results from the literature.     

Quantitative,In Situ Visualization of Metal‐Ion Dissolution and Transport Using 1H Magnetic Resonance Imaging

Quantitative mapping of metal ions freely diffusing in solution is important across a diverse range of disciplines and is particularly significant for dissolution processes in batteries, metal corrosion, and electroplating/polishing of manufactured components. However, most current techniques are invasive, requiring sample extraction, insertion of an electrode, application of an electric potential or the inclusion of a molecular sensor. Thus, there is a need for techniques to visualize the distribution of metal ions non‐invasively, in situ, quantitatively, in three dimensions (3D) and in real time. Here we have used ¹H magnetic resonance imaging (MRI) to make quantitative 3D maps showing evolution of the distribution of Cu²⁺ ions, not directly visible by MRI, during the electrodissolution of copper, with high sensitivity and spatial resolution. The images are sensitive to the speciation of copper, the depletion of dissolved O₂ in the electrolyte and show the dissolution of Cu²⁺ ions is not uniform across the anode.     

In Situ Activating Ubiquitous Rust towards Low‐Cost,Efficient, Free‐Standing,and Recoverable Oxygen Evolution Electrodes

Developing effective ways to recycle rusted stainless steel and to promote the sluggish oxygen evolution reaction (OER), associated with water splitting and metal–air batteries, is important for a resource‐sustainable and environment‐friendly society. Herein, we propose a strategy to enable rusted stainless steel plate to be used as an abundant and low‐cost OER catalyst, wherein a hydrothermal combined in situ electrochemical oxidation–reduction cycle (EORC) method is developed to mimic and expedite the corrosion process, and thus activate stainless steel into free‐standing OER electrodes. Benefiting from the plentiful electrolyte‐accessible Fe/(Ni) oxyhydroxides, high conductivity and mechanical stability, this electrode exhibits remarkable OER performances including low overpotential, fast kinetics, and long‐term durability. The slight degradation in current after long‐term use can be repaired immediately in situ by an EORC.