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

Summary

The paper investigates cathodic corrosion of bismuth in contact with an ionic-liquid electrolyte under CO₂ electroreduction–relevant potentials, combining ReaxFF molecular dynamics and DFT to connect interfacial disorder, charge state, and metal migration into the electric double layer. ReaxFF is used to capture large-scale ionic rearrangements and surface roughening at negative bias, while DFT supports local bonding interpretations (e.g., Bi migration motifs). Adri C. T. van Duin is among the coauthors bridging reactive MD with electrocatalysis-focused collaborators. The study targets a failure mode—metal etching under cathodic bias—that can masquerade as poor catalytic selectivity if interfacial reconstruction is ignored. CO₂RR literature often emphasizes C–C coupling and Faradaic efficiency, but catalyst durability under reducing bias can be limited by metal dissolution when ionic liquids penetrate and destabilize near-surface Bi layers.

Methods

MD application (ReaxFF, electrified Bi–ionic-liquid interface). LAMMPS-style ReaxFF MD treats Bi(001) slabs solvated with ionic-liquid species relevant to CO\(_2\) electroreduction conditions (atom counts and supercell vectors in Chem. Mater. Methods). Cells use three-dimensional periodic boundary conditions (PBC) for the slab/electrolyte geometry unless the article specifies otherwise. Cathodic bias is imposed through charge, field, or excess-electron protocols as defined in the paper—an approximate constant-potential treatment rather than a full ab initio continuum electrode solver (see Limitations). Ensemble: NVT-class trajectories with thermostat parameters and timestep in fs tabulated in Methods/SI (pdf_path); target temperature (often near 300 K unless the article specifies other NVT set points) is defined there. Duration: production segment lengths in ps/ns are given in the peer-reviewed PDF—not duplicated numerically here. Barostat: N/A — NPT isotropic volume fluctuation is not the focus for the quoted interface MD. Pressure / stress: N/A — target hydrostatic pressure (bar/GPa) is not a headline control beyond interfacial stress diagnostics discussed in the article. Shear / strain rate: N/A. Replica / enhanced sampling: N/A — umbrella sampling, metadynamics, or replica exchange is not highlighted in the main text—confirm SI if any rare-event workflow appears.

Static QM / DFT. Complementary DFT uses the functional, basis, and k-mesh choices stated in Chem. Mater. to evaluate adsorption and migration energetics for Bi and electrolyte fragments where ReaxFF needs QM anchors.

Trajectory diagnostics. RMS surface roughness, coordination statistics, and Bi migration metrics versus cathodic severity separate reversible elastic motion from irreversible etching-like events.

Experiments. Synchrotron/spectroscopy-motivated validation and related experimental discussion appear in the article—beamline conditions and sample protocols belong to pdf_path.

Findings

Outcomes. More negative surface charge correlates with increased RMS roughness and Bi migration into the electric double layer, i.e., cathodic corrosion rather than a static passive interface.

Comparisons. DFT fragments and synchrotron/spectroscopy-motivated experiment in the article benchmark the qualitative ReaxFF trends.

Sensitivity. Bias severity and electrolyte composition control how quickly disorder accumulates in the short MD windows shown.

Limitations and PDF grounding. Constant-potential approximations and IL force-field fidelity cap predictive quantitative accuracy; operando imaging remains necessary. All numerical protocols: pdf_path.

Limitations

  • Electrochemical potential control in classical reactive MD is approximate; compare DFT and experiment where quoted in the paper.
  • Ionic liquid force-field fidelity for long-time dynamics may require validation on subset processes.
  • CO₂RR selectivity metrics from experiment can be convolved with cathodic corrosion that roughens Bi; the MD story highlights atomic-scale roughening trends but does not replace operando microscopy for linking surface area evolution to Faradaic efficiency.

Relevance to group

Demonstrates ReaxFF applied to electrified interfaces with ionic liquids, a recurring theme in electrochemistry + reactive MD.

Citations and evidence anchors

  • DOI: https://doi.org/10.1021/acs.chemmater.8b00050 (papers/MedinaRamon_ChemMat_2018.pdf).

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