Studying nickel deposition with EQCM-D and EC-Raman

Importance of the topic

The combination of electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) and in situ electrochemical Raman (EC‑Raman) provides complementary, time-resolved insight into mass changes, mechanical properties and chemical state of electrodeposited films. This multimodal approach is highly relevant to battery electrode research (e.g., Ni‑MH), electrocatalysis and corrosion science because it links electrochemical activity with film growth morphology and molecular composition in operando.

Objectives and overview of the study

This application note demonstrates use of a Metrohm Autolab potentiostat (AUT204/PGSTAT204 with FRA32M) coupled to a 3T analytik eSorptionProbe EQCM‑D to:

• Electrodeposit nickel hydroxide on a 10 MHz Au QCM crystal and monitor mass and dissipation concurrently.
• Electrochemically cycle the deposited film to probe reversibility and thickness changes relevant to Ni‑MH cathode chemistry.
• Integrate the EQCM‑D probe into an EC‑Raman cell (DRP‑RAMANCELL‑M) to obtain Raman spectra (i‑Raman Plus 532H) of the oxidized species and correlate spectral features with mass/dissipation data.

Methodology

Key experimental workflow and conditions:

• EQCM crystal: 10 MHz Au crystal, active area ~19.2 mm2, mounted in probe compatible with standard electrochemical cells (CORR250.CELL.S and DRP‑RAMANCELL‑M).
Part 1 — galvanostatic deposition: chronopotentiometry at 100 μA for 300 s in 50 mmol·L−1 NiSO4 (two‑electrode cell, Pt counter); simultaneous recording of resonance frequency and dissipation (fundamental and overtones; analysis here focuses on fundamental).
• Part 2 — electrochemical cycling: cyclic voltammetry in 0.1 mol·L−1 NaOH (three‑electrode, Ag/AgCl reference, Pt counter), 0 → 0.9 → −0.2 V at 10 mV·s−1; associate CV with EQCM‑D signals to follow redox‑driven mass changes.
• Part 3 — EC‑Raman and SERS preparation: electrochemical roughening of the QCM Au surface (repeated CA/LSV cycles: −0.3 V CA 30 s, LSV −0.3→1.2 V 10 mV·s−1, CA at 1.2 V 60 s, reverse LSV; repeated 25×) in 0.1 mol·L−1 KCl to generate SERS‑active roughness. Raman acquisition: i‑Raman Plus 532H at 100% laser power, 20 s integration, averaged three spectra; LID (light‑induced detuning) requires careful timing (pre/post spectra or DIO triggering via AUT204 for synchronized steps).

Used instrumentation

The principal instruments and components used:

• Metrohm Autolab AUT204 / PGSTAT204 potentiostat/galvanostat with FRA32M module (NOVA software, DIO triggering available).
• 3T analytik eSorptionProbe OS EQCM‑D (measures resonance frequency and dissipation at fundamental and overtones).
• 10 MHz gold QCM crystals mounted in plastic substrate probe (active area ~19.2 mm2).
• i‑Raman Plus 532H spectrometer (Raman excitation 532 nm), DRP‑RAMANCELL‑M electrochemical Raman cell.

Main results and discussion

Deposition (Part 1):

• Chronopotentiometric deposition produced a resonance frequency shift of ≈ −9500 Hz. Using the Sauerbrey relation with Cf = 4.3 ng·cm−2·Hz−1, this corresponds to an areal mass loading of ≈ 41,000 ng·cm−2.
• Dissipation changes remained small (<10% of the frequency shift), indicating the deposited Ni(OH)2 layer behaves predominantly as a rigid film; therefore the Sauerbrey model is applicable for mass quantification with high confidence.
• Dissipation dynamics provided morphological insight: an initial increase in dissipation followed by return toward baseline was observed, consistent with island growth that coalesces into a continuous rigid layer (hydrodynamic coupling between rough features and electrolyte is responsible for dissipation signal in rigid deposits).

Cycling (Part 2):

• Electrochemical oxidation/reduction follows Ni(OH)2 + OH− ↔ NiOOH + H2O + e−, a reaction central to Ni‑MH battery cathodes.
• EQCM‑D detected reversible mass changes on the order of ±1500 ng·cm−2 during redox cycling, equivalent to approximately ±3 nm thickness change. These changes arise from ion and water intercalation/de‑intercalation during conversion between hydroxide and oxyhydroxide.
• Both frequency and dissipation returned near baseline after cycling in the tested conditions, indicating largely reversible electrochemical behavior and mechanical stability over the limited number of cycles studied.

EC‑Raman (Part 3):

• After electrochemical roughening to create a SERS substrate, Raman spectra collected at potentials favoring NiOOH (0.65 V) showed two diagnostic peaks at ≈ 476 and 556 cm−1, while Ni(OH)2 was essentially Raman‑inactive in the 200–800 cm−1 window under these measurement conditions.
• Combining EC‑Raman with EQCM‑D confirmed that the mass changes measured during oxidation coincide with appearance of NiOOH spectral features, demonstrating synergistic chemical/mechanical monitoring.
• Practical limitations: light‑induced detuning (LID) can perturb simultaneous EQCM and Raman acquisition; the workflow used either DIO triggering for timed acquisitions or pre/post spectral collection to avoid artifacts.

Benefits and practical applications of the method

Combining EQCM‑D with EC‑Raman provides several practical advantages:

• Quantitative mass monitoring (ng·cm−2) linked to electrochemical processes, enabling stoichiometric and ion‑insertion analysis in battery electrodes.
• Dissipation data supplies mechanical and morphological information (rigidity vs viscoelasticity, roughness evolution, dendrite formation) not accessible from electrochemistry alone.
• EC‑Raman adds chemical specificity, distinguishing oxidation states and phases (e.g., NiOOH vs Ni(OH)2), enabling correlation of spectral markers with mass and mechanical behavior.
• The plug‑in probe format and compatibility with standard cells make the workflow adaptable for corrosion tests, electrocatalyst activation, and battery electrode screening.

Future trends and potential uses

Anticipated developments and applications include:

• Broader adoption of synchronized multimodal operando measurements (EQCM‑D + Raman + EIS) for advanced electrode characterization and failure analysis.
• Improved strategies to mitigate light‑induced detuning and enable fully simultaneous EQCM and Raman acquisition (hardware and software solutions, optimized SERS substrates).
• Application to complex, soft or viscoelastic films where combined dissipation modelling and Raman chemical mapping will resolve layered structure and ion/water dynamics.
• Automation and machine‑learning analysis of coupled datasets to extract mechanistic descriptors for electrode design and accelerated materials screening.

Conclusion

The study illustrates that a Metrohm Autolab potentiostat coupled with a 3T analytik eSorptionProbe EQCM‑D and EC‑Raman enables robust, complementary monitoring of nickel hydroxide deposition and electrochemical cycling. Mass and dissipation monitoring validated a rigid Ni(OH)2 deposit and quantified reversible mass/thickness changes during redox cycling, while EC‑Raman identified NiOOH spectral fingerprints during oxidation. The integrated approach is a powerful tool for battery materials research and broader electrochemical studies that require simultaneous mechanical, mass and chemical information.

References

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