Studying nickel deposition with EQCM-D and EC-Raman

Studying nickel deposition with EQCM-D and EC-Raman

Significance of the topic

The combination of electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) and in situ Raman spectroscopy provides a powerful platform to study electrodeposition, phase transformations and mechanical properties of thin films under operating electrochemical conditions. This capability is particularly important for research on Ni-based battery electrodes (Ni–MH), electrocatalysts and corrosion studies, where simultaneous mass, viscoelastic and chemical information improves understanding of deposition mechanisms, reversibility and side reactions.

Objectives and overview of the study

The application note demonstrates the use of a 3T analytik eSorptionProbe EQCM-D system integrated with a Metrohm Autolab AUT204 potentiostat (with FRA32M) to:

• Electrodeposit Ni(OH)2 onto a 10 MHz Au QCM crystal and monitor mass and dissipation changes in operando.
• Electrochemically cycle the deposited film to probe reversible mass/structural changes related to the Ni(OH)2 ⇌ NiOOH redox couple.
• Integrate EQCM-D with EC-Raman (using an i-Raman Plus 532H) to obtain complementary vibrational information and to demonstrate in situ chemical identification of the oxidized form NiOOH.

Methodology

Experiments were performed in three parts: deposition, electrochemical cycling (CV), and EC-Raman with a SERS-active roughened surface. Key experimental choices included:

• Working electrode: 10 MHz Au QCM crystal (active area ~19.2 mm2) mounted in a probe compatible with standard electrochemical cells.
• Electrochemical hardware and software: Metrohm Autolab AUT204 with FRA32M; NOVA, qGraph and qGraph Viewer were used to synchronize electrochemical and EQCM-D data.
• Deposition (Part 1): galvanostatic chronopotentiometry at 100 μA for 300 s in a two-electrode configuration (Pt counter) using 50 mmol·L−1 NiSO4 electrolyte.
• Cycling (Part 2): three-electrode cyclic voltammetry with Ag/AgCl reference, electrolyte 0.1 M NaOH, scan limits 0.9 V to −0.2 V at 10 mV·s−1 (0.01 V·s−1 stated in note), to probe Ni(OH)2/NiOOH interconversion.
• Roughening and EC-Raman (Part 3): electrochemical roughening (repeated CA and LSV sequences) in a DRP-RAMANCELL-M cell to produce a SERS-active surface (0.1 M KCl electrolyte). Raman spectra were collected with the i-Raman Plus 532H (100% laser power, 20 s integration, 3 accumulations). Light-induced detuning was managed by collecting spectra at defined potential steps rather than continuously.

Instrument configuration (used instrumentation)

• EQCM-D probe: 3T analytik eSorptionProbe OS measuring fundamental and overtone resonance frequencies and dissipation.
• Potentiostat/galvanostat: Metrohm Autolab AUT204 (PGSTAT204) with FRA32M EIS module; digital I/O used for synchronizing Raman acquisition.
• Raman: i-Raman Plus 532H (Metrohm) and DRP-RAMANCELL-M EC-Raman cell.
• Electrodes and cells: 10 MHz Au QCM crystal (screen-printed-style plastic mount), Pt counter electrode, Ag/AgCl reference; CORR250.CELL.S and DRP-RAMANCELL-M cells were used.

Main results and discussion

Deposition (Part 1):
The chronopotentiometric deposition produced a large negative frequency shift (~−9,500 Hz on the fundamental), corresponding to an areal mass loading of approximately 4.1×10^4 ng·cm−2 when evaluated with the Sauerbrey relation (appropriate because dissipation was <10% of the frequency shift). The dissipation (damping) trace initially increased during early deposition, consistent with island or porous growth, and then decreased toward zero as the islands coalesced to a continuous, relatively rigid film. This behaviour indicates hydrodynamic dissipation from surface roughness rather than viscoelastic losses of a soft film.

Cycling (Part 2):
Cyclic oxidation/reduction of the deposited film produced reversible mass changes linked to the Ni(OH)2 ⇌ NiOOH reaction. The reversible mass change per cycle was roughly 1.5×10^3 ng·cm−2, equivalent to an approximate ±3 nm change in film thickness, attributed to insertion/removal of water and electrolyte cations during redox conversion. The small dissipation changes returning near zero on cycling support the picture of a principally rigid, reversible electrode material under these conditions. The synchronized display of CV and QCM-D signals (via qGraph Viewer) facilitates detection of non-ideal behaviour or parasitic reactions by observing mass/dissipation deviations from expected reversible trends.

EC-Raman (Part 3):
After electrochemical roughening to create a SERS-active surface, Raman spectra collected during potential steps revealed that NiOOH is Raman-active in the 200–800 cm−1 region with characteristic bands at ~476 and ~556 cm−1, whereas Ni(OH)2 showed little Raman signal in this window. Simultaneous EQCM-D and Raman are feasible but require attention to light-induced detuning (LID); the study used timed spectra at stepped potentials to avoid LID artifacts. EQCM confirmed the deposited film thickness in the EC-Raman cell was comparable to that in earlier depositions.

Practical benefits and applications

• Provides quantitative in situ mass monitoring of electrodeposition and redox-driven mass changes with nanoscale sensitivity.
• Dissipation monitoring adds diagnostic information about surface roughness, porous/dendritic growth and mechanical coupling to electrolyte flow, allowing discrimination between rigid and viscoelastic films.
• Integration with Raman spectroscopy enables concurrent chemical identification (e.g., detecting NiOOH formation) to link mass/structural dynamics with chemical state.
• Useful for battery electrode development (Ni–MH), electrocatalyst activation studies, corrosion research and mechanistic investigations of electrode processes.

Future trends and potential uses

• Tighter integration of EQCM-D with operando spectroscopies (Raman, IR, XAS) to achieve multidimensional time-resolved characterization of working electrodes.
• Improved handling of light-induced detuning and other cross-technique artifacts to enable continuous simultaneous acquisition.
• Expanded use of multi-harmonic and viscoelastic modelling for non-rigid films to extract absolute mechanical moduli and layer hydration information.
• Application to advanced battery chemistries, electrode surface engineering (SERS substrate optimization), and coupled hydrodynamic studies of porous electrodes and dendrite formation.

Conclusions

The combination of a Metrohm Autolab AUT204 potentiostat and 3T analytik eSorptionProbe EQCM-D provides a robust, versatile platform for operando study of nickel hydroxide deposition and redox cycling. The deposited Ni(OH)2 behaves largely as a rigid film under the tested conditions, permitting reliable mass quantification via the Sauerbrey relation, while dissipation trends offer insight into growth morphology. Integration with EC-Raman enables direct chemical identification of NiOOH formation, demonstrating the value of coupling mass/viscoelastic and spectroscopic modalities for comprehensive electrode characterization.

References

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