All workHanan Hakim
Case study · Electrochemical Catalysis · Imperial MSc

Composition engineering of Ni-Co hydroxide for active and stable glycerol oxidation

An MSc thesis at the Henry Royce Institute exploring how Ni–Co bimetallic hydroxides — electrodeposited onto FTO glass — can valorise crude biodiesel glycerol while lowering the energy cost of green hydrogen.

Partner

Henry Royce Institute · Imperial College London — Dr. Reshma Rao

Role

MSc Researcher · Synthesis, characterisation & electrochemical testing

Year

2025

01

Ni₀.₀₇₅Co₀.₀₂₅(OH)₂

Optimal catalyst composition

02

1.01 kΩ

Charge-transfer resistance — minimised

03

≈10×

Rct improvement vs. pure Ni(OH)₂

04

48%

Projected rise in fossil-fuel demand (2012 → 2040, EIA)

Context

Glycerol — a 10%-by-weight byproduct waiting for a job

The Energy Information Administration projects a ~48% rise in global fossil-fuel consumption between 2012 and 2040. Biodiesel offsets part of that demand — but it also produces crude glycerol as ~10% of its mass output. That glycerol has historically been waste, incinerated or sold at depressed prices.

Electrochemical glycerol oxidation flips the script: convert that waste into high-value chemicals (glyceraldehyde, glycolic acid, formate) while simultaneously lowering the energy needed to split water for green hydrogen. The bottleneck has been finding earth-abundant catalysts that are both active and stable.

The challenge

Earth-abundant catalysts, alkaline conditions, real-world durability

Nickel and cobalt hydroxides are known to be active for glycerol electrooxidation in alkaline media — but their performance is exquisitely sensitive to composition, surface state and morphology. The brief: find the Ni : Co ratio that maximises activity and durability while staying within a scalable, low-cost electrodeposition route on FTO glass.

Methodology

From bath to band — electrodeposition, then six characterisation techniques

I fabricated NiₓCo_y(OH)₂ films by chronopotentiostatic electrodeposition (1 mA cm⁻² for 400 s) onto polished FTO substrates from aqueous nickel/cobalt nitrate baths of varying composition. After in-situ activation via CV staircase, each electrode passed through a full electrochemical and surface-state characterisation stack: CV, LSV (with iR correction and Tafel slopes), EIS, chronoamperometry, XPS (survey + high-resolution Ni 2p / Co 2p / O 1s), SEM and EDX.

Schematic of the three-electrode electrodeposition set-up used to fabricate hierarchical Ni(OH)₂/Co(OH)₂ heterostructured nanoarrays on FTO substrate (Pt counter, Hg/HgO reference, Ni–Co/FTO working electrode).
Fig. 3Schematic of the three-electrode electrodeposition set-up used to fabricate hierarchical Ni(OH)₂/Co(OH)₂ heterostructured nanoarrays on FTO substrate (Pt counter, Hg/HgO reference, Ni–Co/FTO working electrode).
Chronopotentiograms during electrodeposition across the five Ni : Co compositions. Pure Ni(OH)₂ required the highest overpotential (~2.4 V) for nucleation onset; cobalt-rich films deposited at lower overpotentials.
Fig. 4Chronopotentiograms during electrodeposition across the five Ni : Co compositions. Pure Ni(OH)₂ required the highest overpotential (~2.4 V) for nucleation onset; cobalt-rich films deposited at lower overpotentials.
Optical images of the as-deposited films — visual confirmation of compositional dependence on film coverage and uniformity.
Fig. 5Optical images of the as-deposited films — visual confirmation of compositional dependence on film coverage and uniformity.
Results

Surface state and structure — what the spectra revealed

XPS confirmed that the bulk cobalt is present as Co(OH)₂ (no spinel signatures), and that increasing Ni content tunes the electronic environment around the active Ni³⁺ states — the species responsible for selective glycerol oxidation. SEM showed a sharp morphology shift from dense Ni(OH)₂ nanosheets to interpenetrating Co(OH)₂ nanoflakes as the Ni : Co ratio is decreased.

Survey + O 1s XPS spectra across compositions — schematic representation of the different components of Ni-Co catalysts.
Fig. 6Survey + O 1s XPS spectra across compositions — schematic representation of the different components of Ni-Co catalysts.
High-resolution XPS spectra of Ni 2p and Co 2p across all Ni–Co bimetallic compositions. Spectral shifts confirm electronic modulation between the two metal centres.
Fig. 7High-resolution XPS spectra of Ni 2p and Co 2p across all Ni–Co bimetallic compositions. Spectral shifts confirm electronic modulation between the two metal centres.
SEM images of electrodeposited (a) Ni(OH)₂, (b) Ni₀.₀₇₅Co₀.₀₂₅(OH)₂, (c) Ni₀.₀₅Co₀.₀₅(OH)₂, (d) Ni₀.₀₂₅Co₀.₀₇₅(OH)₂ films. Morphology transitions visibly from compact nanosheets to interlocking flakes.
Fig. 8SEM images of electrodeposited (a) Ni(OH)₂, (b) Ni₀.₀₇₅Co₀.₀₂₅(OH)₂, (c) Ni₀.₀₅Co₀.₀₅(OH)₂, (d) Ni₀.₀₂₅Co₀.₀₇₅(OH)₂ films. Morphology transitions visibly from compact nanosheets to interlocking flakes.
Results

Activity, kinetics and durability

Cyclic voltammetry and linear-sweep curves showed that Ni₀.₀₇₅Co₀.₀₂₅(OH)₂ achieved the highest current densities at the lowest overpotentials for glycerol oxidation — and a Tafel slope consistent with a more facile rate-determining step. Nyquist analysis quantified the picture: charge-transfer resistance (Rct) dropped from ~10.9 kΩ for pure Ni(OH)₂ to ~1.01 kΩ at the optimal composition.

Chronoamperometric durability tests held the optimised electrode at constant potential for extended periods with negligible activity loss, confirming both intrinsic catalytic improvement and structural stability.

  • Optimal composition: Ni₀.₀₇₅Co₀.₀₂₅(OH)₂ — minimum Rct and best LSV / Tafel performance.
  • Ni acts as the active catalytic centre; Co operates as a promoter via electronic modulation, not via direct oxidation.
  • Open-source workflow documented for reuse as a standard Royce Institute lab protocol.
Cyclic voltammetry and linear-sweep voltammetry of all Ni–Co compositions in 0.1 M KOH + glycerol, showing the activity ordering across the composition series.
Fig. 9Cyclic voltammetry and linear-sweep voltammetry of all Ni–Co compositions in 0.1 M KOH + glycerol, showing the activity ordering across the composition series.
Nyquist plots of the various Ni–Co hydroxide electrodepositions recorded at 10 mV AC amplitude in 0.1 M KOH + glycerol electrolyte.
Fig. 10Nyquist plots of the various Ni–Co hydroxide electrodepositions recorded at 10 mV AC amplitude in 0.1 M KOH + glycerol electrolyte.
Fitted equivalent-circuit parameters (Rct, Rs, CPE, Zw) extracted from the Nyquist plots — quantifying the kinetic advantage of Ni₀.₀₇₅Co₀.₀₂₅(OH)₂.
Fig. 11Fitted equivalent-circuit parameters (Rct, Rs, CPE, Zw) extracted from the Nyquist plots — quantifying the kinetic advantage of Ni₀.₀₇₅Co₀.₀₂₅(OH)₂.
Chronoamperometric durability test of Ni₀.₀₇₅Co₀.₀₂₅(OH)₂ — confirming sustained activity and structural integrity over time.
Fig. 12Chronoamperometric durability test of Ni₀.₀₇₅Co₀.₀₂₅(OH)₂ — confirming sustained activity and structural integrity over time.
“Cobalt isn't the catalyst here — it's the lever. The activity lives on nickel; cobalt just changes what nickel is willing to do.”

— Thesis · Henry Royce Institute, Imperial College London (2025)

Methodology

How the work held up.

  • Electrodeposition onto polished FTO at 1 mA cm⁻² for 400 s across five Ni : Co compositions.
  • Electrochemical stack: CV staircase activation, iR-corrected LSV, EIS, Tafel-slope analysis, chronoamperometric stability.
  • Surface and structural characterisation: XPS (survey + high-resolution Ni 2p, Co 2p, O 1s), SEM imaging, EDX elemental quantification.
  • Supervised by Dr. Reshma Rao at the Henry Royce Institute, Department of Materials, Imperial College London.
Next case