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Cathodic Corrosion at the Bismuth–Ionic Liquid Electrolyte Interface under Conditions for CO2 Reduction

In situ X-ray reflectivity on Bi(001) films in ionic-liquid electrolytes under cathodic bias is interpreted with ReaxFF MD and DFT to connect imidazolium adsorption, surface disorder, and bismuth dissolution pathways.

Summary

Combines in situ X-ray reflectivity on Bi(001) thin films in acetonitrile with BMIM-based ionic liquid electrolytes under cathodic scans with ReaxFF MD and DFT to interpret potential-driven thinning, roughening, and partial dissolution of Bi. The modeling emphasizes stronger imidazolium binding vs TBA⁺ as surfaces become more negative and connects Bi···IL motifs to step-edge dissolution at intermediate potentials. The electrochemical context is CO₂ reduction conditions where cathodic corrosion of Bi can compete with catalytic turnover, motivating interface-sensitive probes beyond cyclic voltammetry alone.

Methods

  • Experiment: XR tracking Bi(001) Bragg intensity and domain sizes vs cyclic potential in Ar- and CO₂-saturated electrolytes as reported (see SI figures referenced in the main text).
  • ReaxFF MD: Bi(001) slabs with IL cations to capture disorder and migration trends at negative charge states.
  • DFT: Local bonding and dissolution energetics for Bi···[Im]⁺ motifs and step vs terrace pathways with potential estimates quoted in the article.
  • Integration: Experimental potentials, electrolyte composition, and Bi film thickness ranges should be taken from Chem. Mater. when comparing XR trends to simulation snapshots.

MD application (ReaxFF interface sampling)

Engine / code: ReaxFF molecular dynamics of Bi(001) slabs with BMIM-class imidazolium vs TBA⁺ electrolyte motifs as described in the article; N/A — specific MD engine name not stated in the indexed abstract/excerpt—confirm in Chem. Mater. Methods/SI (papers/MedinaRamon_ChemMat_2018_final.pdf). System & PBC: Bi slab supercells with explicit ionic-liquid ions (atom counts, vacuum, and PBC freeze protocols in Methods). Ensemble: NVT thermal sampling for the ReaxFF interfacial runs unless Methods specify mixed NVE/NVT staging. Timestep / duration / thermostat / barostat: N/A — not transcribed in this excerpt-based note; import from the primary text. Temperature: N/A — explicit MD thermostat K not in the indexed excerpt—likely room-temperature sampling for the interface exploration, but verify in PDF. Pressure: N/A — not used for the classical MD discussion summarized here. Electric field / applied bias in MD: N/A — classical ReaxFF trajectories do not embed continuous Poisson–Boltzmann electrode models; potentials enter via DFT cluster models as quoted below. Enhanced sampling: N/A — not indicated in the abstract for ReaxFF runs.

Findings

  • First cathodic sweep reduces native Bi₂O₃ to Bi⁰; subsequent sweeps show large reflectivity loss attributed to thinning and lateral domain shrinkage partly recovered on anodic return, with cycling increasing damage.
  • ReaxFF predicts greater disorder and Bi migration with [Im]⁺ vs TBA⁺ under increasingly negative surface conditions.
  • DFT suggests step-edge dissolution via Bi···[Im]⁺ complexes at −1.65 to −1.95 V vs Ag/AgCl, while terrace desorption requires more negative potentials (~−2.25 V).
  • Together, the XR and modeling sections argue that cation-specific adsorption steers where Bi atoms leave the surface during cathodic polarization, informing electrolyte design for stable Bi electrodes.

Corpus honesty. XR percent thinning/domain loss and DFT potential windows quoted above follow the Chem. Mater. abstract text; any figure-specific layer electron density details should be checked against the PDF/SI rather than this wiki alone.

Limitations

  • Electrochemical potential mapping to classical MD remains approximate; DFT provides local energetics but not full electrolyte dynamics at long times.
  • CO₂ versus Ar saturation changes interfacial pH and buffering; the XR trends should be read with the electrolyte conditions tabulated in Chem. Mater. when extrapolating to other CO₂RR setups.

Relevance to group

Adri C. T. van Duin-coauthored electrified interface study pairing ReaxFF with DFT and XR.

Citations and evidence anchors

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