Electrochemistry
Bismuth oxyhalide films as photoelectrodes
Open access · cc by · source: Europe PMC
AACVD BiOX films show halide-tuned bandgaps; untreated BiOBr gives about 0.38 mA cm−2 photoanodic current without a sacrificial donor.
Study at a glance
- Design
- Other — AACVD BiOX film deposition with band-structure analysis and photoelectrochemical testing
- N
- Materials photoelectrochemistry — no sample N
- Population
- BiOCl, BiOBr, and BiOI thin-film photoelectrodes
- Outcome
- Photoelectrochemical activity and band-edge positions of BiOX films
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Phase-pure tetragonal matlockite films. Nanoplatelets for Cl/I, nanoflowers for Br. Bandgap narrowing follows halide p orbital energy in the valence band. Untreated BiOCl (p-type) and BiOI (n-type) are unstable for PEC; BiOBr gives ca. 0.38 mA cm−2 at 1 V vs Ag/AgCl, the highest BiOBr photocurrent without a sacrificial donor.
Methodology
Authors deposited BiOCl, BiOBr and BiOI at 300 °C by AACVD, measured XRD/SEM/UV-vis/XPS, computed band structures, and ran PEC in 0.5 M Na2SO4 under 100 mW cm−2 with Mott–Schottky analysis.
Limitations
Long-term tandem-cell solar-to-hydrogen efficiency is not reported; untreated Cl and I films fail stability, so they are not practical photoelectrodes as-made.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
On photoelectrodes, XPS sits beside XRD/SEM/UV-vis rather than replacing them. AACVD BiOCl/Br/I films are phase-pure tetragonal matlockite; untreated BiOCl (p-type) and BiOI (n-type) are unstable for PEC, while BiOBr reaches ca. 0.38 mA cm⁻² at 1 V vs Ag/AgCl without a sacrificial donor. XPS does not by itself explain why Cl and I films fail stability.
Evidence for the claim as stated.
A surface Ni³⁺/Ni²⁺ ratio is a descriptor, not the OER mechanism. NaBH₄-treated LDH correlates Ni³⁺ (0.39 → 1.32) with activity and reports 95.9% O₂ FE, but does not solve the atomic OER cycle. BiOBr's 0.38 mA cm⁻² photocurrent is a different electrochemical question (PEC of a halide film) that XPS characterisation does not make interchangeable with LDH OER.
Evidence for the claim as stated.
SEM distinguishes BiOX film habits that XRD only calls phase-pure tetragonal matlockite: nanoplatelets for Cl and I, nanoflowers for Br, deposited at 300 °C by AACVD. Untreated BiOCl (p-type) and BiOI (n-type) are unstable for PEC; BiOBr gives ca. 0.38 mA cm⁻² at 1 V vs Ag/AgCl under 100 mW cm⁻² in 0.5 M Na₂SO₄ — the highest BiOBr photocurrent in that work without a sacrificial donor.
Evidence for the claim as stated.
An SEM habit (nanoflowers versus pores) does not rank function. BiOBr nanoflowers coincide with 0.38 mA cm⁻² photocurrent but untreated Cl/I films fail stability despite also having SEM-visible nanostructure. Hydrogel SEM porosity coexists with 90.64% DEE that is a loading/release assay. SECCM at 50 nm further shows that a macroscale 'blocked' ITO reading is not a map of dead patches an SEM image would be asked to find.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
A surface Ni³⁺/Ni²⁺ ratio is a descriptor, not the OER mechanism. NaBH₄-treated LDH correlates Ni³⁺ (0.39 → 1.32) with activity and reports 95.9% O₂ FE, but does not solve the atomic OER cycle. BiOBr's 0.38 mA cm⁻² photocurrent is a different electrochemical question (PEC of a halide film) that XPS characterisation does not make interchangeable with LDH OER.
- Supports · NaBH4 raises Ni3+ and speeds NiFe LDH OER
An SEM habit (nanoflowers versus pores) does not rank function. BiOBr nanoflowers coincide with 0.38 mA cm⁻² photocurrent but untreated Cl/I films fail stability despite also having SEM-visible nanostructure. Hydrogel SEM porosity coexists with 90.64% DEE that is a loading/release assay. SECCM at 50 nm further shows that a macroscale 'blocked' ITO reading is not a map of dead patches an SEM image would be asked to find.
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