P4VP makes CoPc a selective CO2-to-CO catalyst
Axial pyridine plus a polyvinylpyridine film together raise CoPc’s CO2-to-CO rate and faradaic efficiency while suppressing hydrogen evolution.
Source
Polymer coordination promotes selective CO<sub>2</sub> reduction by cobalt phthalocyanine
Study at a glance
- Design
- Animal / in-vitro — Controlled-potential electrolysis of CoPc films with coordinating versus non-coordinating polymers
- N
- CPE at −1.25 V vs SCE comparing CoPc, P4VP, pyridine, and P2VP films
- Population
- Cobalt phthalocyanine on edge-plane graphite in aqueous CO2 electrolysis
- Outcome
- Axial pyridine plus polyvinylpyridine raise CO2-to-CO rate and faradaic efficiency while suppressing hydrogen evolution
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Inspect source passages
P4VP makes CoPc a selective CO2-to-CO catalyst
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CoPc-P4VP runs at 2 mA cm–2 with TOF 4.8 s–1 and nearly 90% FE for CO
In particular, we find that CoPc-P4VP is remarkably active for the selective generation of CO, operating in pH 5 solution with an average current density of 2 mA cm –2 and a turnover frequency of 4.8 s –1 with nearly 90% faradaic efficiency for CO production at –1.25 V vs.
Average current densities are 0.62 mA cm–2 (CoPc) and 2.0 mA cm–2 (CoPc-P4VP)
Over the 2 h experiments, current densities averaging 0.62 mA cm –2 and 2.0 mA cm –2 were observed for CoPc and CoPc-P4VP , respectively.
What they did
They drop-cast CoPc on edge-plane graphite, then compared free CoPc, CoPc in P4VP, CoPc(pyridine), CoPc in non-coordinating P2VP, and CoPc(py)-P2VP. CPE at −1.25 V vs SCE in pH ~5 phosphate quantified CO, H2, charge, TON, and TOF.
What they found
CoPc-P4VP averages 2.0 mA cm–2 with nearly 90% FE_CO, TOF 4.8 s–1, TON 34 000, and CO/H2 = 19:1, versus CoPc at 0.62 mA cm–2, TON 4500, CO/H2 = 0.9:1. Axial pyridine alone gives 68% FE_CO; P2VP alone gives 73% FE_CO but does not raise TOF. Both primary (axial) and outer-sphere polymer effects are required.
The limits
What it doesn't show
TON/TOF use total deposited Co (1.3×10–9 mol cm–2), so they are lower bounds. No liquid C2 products were detected to ~10 μM. Long-term electrolyzer tests and in situ spectroscopy of the Co–pyridine bond during catalysis are limited.
Key terms
- CoPc
- Cobalt phthalocyanine, a square-planar molecular catalyst for CO2-to-CO on graphite.
- P4VP
- Poly-4-vinylpyridine: pyridines can bind Co axially and also protonate in the film.
- P2VP
- Poly-2-vinylpyridine: steric hindrance prevents Co–N coordination but keeps a similar polymer environment.
- Faradaic efficiency
- Fraction of charge that makes a given product (here CO versus H2).
- Secondary coordination sphere
- Nearby polymer pyridinium/pyridine groups that H-bond or deliver protons without binding Co.
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Quiz yourself
CoPc-P4VP faradaic efficiency for CO near −1.25 V vs SCE is about
Common questions
Why is P4VP better than dissolved pyridine?
You need both an axial ligand and the polymer film; free pyridine in solution does not mimic CoPc-P4VP.
What does P2VP prove?
Without axial binding, HER is suppressed (73% FE_CO) but CO TOF does not rise—so coordination and the film must act together.
How selective is CoPc-P4VP?
CO/H2 ≈ 19:1 and ~90% FE for CO at −1.25 V vs SCE.
Overpotential versus CO thermodynamics?
About 0.61 V from E° = −0.125 V vs RHE in their accounting.
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