Choice of Electrolyte Impacts the Selectivity of Proton-Coupled Electrochemical Reactions on Hydrogen Titanate
Summary¶
Proton-coupled electrochemistry on metal oxides in acid competes intercalation, hydrogen evolution (HER), and dissolution, so electrolyte choice can dominate Coulombic efficiency even when the active oxide is unchanged. Layered hydrogen titanates are proton hosts for pseudocapacitive energy storage, making side reactions especially visible in galvanostatic cycling metrics that integrate Faradaic charge with parasitic currents. Fortunato, Shin, van Duin, and Augustyn study layered hydrogen titanate H₂Ti₃O₇ (HTO) in 1 M sulfuric acid versus buffered 1 M phosphoric acid, pairing cyclic voltammetry with ReaxFF molecular dynamics of electrolyte–surface contacts. The electrochemical comparison is intentionally isothermal and isoconcentrated on a molarity basis so that anion identity remains the dominant variable between cells, simplifying interpretation of Coulombic efficiency shifts. The J. Phys. Chem. C abstract reports average Coulombic efficiency improving from roughly 48% to 71% and specific capacity from roughly 83 to 90 mAh g⁻¹ when moving from H₂SO₄ to H₃PO₄, motivating atomistic explanations for HER suppression and dissolution mitigation.
Methods¶
Material synthesis¶
Layered hydrogen titanate H\(_2\)Ti\(_3\)O\(_7\) prepared from Na\(_2\)Ti\(_3\)O\(_7\) via solid-state + ion-exchange steps in the article.
Electrochemical experiments¶
- Electrolytes: 1 M H\(_2\)SO\(_4\) vs buffered 1 M H\(_3\)PO\(_4\) at comparable molarity and potential windows vs Ag/AgCl.
- Metrics: Cyclic voltammetry, capacity, and Coulombic efficiency (abstract quotes ~48% → 71% CE and ~83 → 90 mAh g\(^{-1}\) capacity improvement for H\(_3\)PO\(_4\) vs H\(_2\)SO\(_4\)—confirm exact conditions in the PDF).
Ex situ characterization¶
XRD, SEM, Raman, XPS, ICP-OES for phase, morphology, Ti oxidation states, and Ti dissolution after cycling.
ReaxFF interfacial MD (B)¶
Explicit water + acid anions at HTO surfaces; Ti(III) chemistry via parameter lineage documented in [[2023fortunato-venue-paper]] (SI PDF).
MD application (integrated; proof-PDF copy)¶
Engine / code: LAMMPS+ReaxFF (group practice for aqueous oxide interfaces; exact build in JPCC Computational / SI). System & composition: H\(_2\)Ti\(_3\)O\(_7\) (001)-class slabs with 1 M H\(_2\)SO\(_4\) vs buffered 1 M H\(_3\)PO\(_4\) solutions (cell sizes and ion counts: N/A in wiki copy). 3D PBC slab + reservoir-style electrolyte model as in the article; N/A — exact fixed layers, timestep (fs), ps/ns, thermostat/barostat, NPT vs NVT, temperature setpoints (e.g. ~300 K isotropic MD in many interfacial aqueous setups), pressure, long-range Coulomb/ReaxFF QEq in this short note—see proof/VOR Methods. N/A — no replica exchange in the interfacial MD described in the abstract. E-field: N/A — no static field bias in the same sense as a gated device; comparisons to CV in 2023jenelle-fortunato-j-phys-chem-choice-electrolyte if a VOR slug is curated.
Findings¶
Electrochemical performance shift¶
Phosphoric electrolyte yields higher Coulombic efficiency and specific capacity than sulfuric acid under the authors’ matched protocols (see abstract numbers).
Atomistic interpretation (qualitative)¶
Phosphate adsorbs more strongly than sulfate, buffering interfacial acidity and passivating reactive Ti sites—consistent with suppressed HER/dissolution in MD and improved electrochemical metrics.
Experimental corroboration¶
Spectroscopy/ICP data link Ti loss and phase retention to electrolyte choice, separating dissolution-driven fade from other effects.
Caveat¶
ReaxFF supports mechanistic hypotheses, not fitted elementary rates; proof PDF path in corpus—prefer VOR pagination when citing [[2023jenelle-fortunato-j-phys-chem-choice-electrolyte]] for final figures.
Limitations¶
The corpus PDF (papers/Fortunato_JPCC_Titanate_H2SO4_H3PO4_2023_proof.pdf) is an ACS proof; cite [[2023jenelle-fortunato-j-phys-chem-choice-electrolyte]] for VOR pagination. Maintainer catalog (GitHub): NON_PRIMARY_ARTICLE_PAPER_SLUGS.md.
Relevance to group¶
Showcases ReaxFF interface MD (Shin, van Duin) paired with aqueous oxide electrochemistry (Augustyn group).