The research team, led by Dipali Potdar of Jaysingpur College and Shivaji University together with colleagues including corresponding authors Shivaji Sadale and Prashant Chikode, electrodeposited nickel thin films onto 304-grade stainless steel substrates from simple sulfate baths. They systematically varied three parameters that any plating shop can control: the applied deposition potential, the pH of the electrolyte, and the concentration of nickel ions in solution. By sweeping nickel sulfate concentrations from 25 to 50 millimolar and adjusting pH from 4 to 8 with ammonium hydroxide, they created a matrix of deposition conditions whose effects could be traced all the way from current signatures to crystal structure.

The central analytical tool was the Scharifker-Hills model, a theoretical framework developed in 1983 that remains the workhorse for interpreting nucleation during electrodeposition. The model distinguishes between two limiting behaviors. In instantaneous nucleation, all active sites on the electrode surface are occupied essentially at once, so the number of nuclei is fixed from the start and each nucleus simply grows. In progressive nucleation, new sites continue to activate throughout the deposition, so the population of nuclei keeps increasing. The shape of the current-time transient, recorded when a fixed potential is applied, carries the fingerprint of whichever mechanism dominates, and comparing normalized experimental curves against the model’s dimensionless predictions reveals the mechanism at work.

Before diving into transients, the team used cyclic voltammetry to establish the electrochemical landscape of their bath. Sweeping the potential from 0.7 volts down to minus 1 volt against a silver-silver chloride reference electrode, they observed a stable current until an onset potential near minus 0.7 volts, followed by a rapid rise and a cathodic peak at minus 0.88 volts, which they attribute to the reduction of nickel ions on the stainless steel surface. A further surge at more negative potentials signaled the onset of the hydrogen evolution reaction, the parasitic process that plagues nickel plating by generating gas bubbles at the electrode. Two crossover points on the reverse scan, at minus 0.78 and minus 0.43 volts, marked the initiation of nucleation and the adsorption of nickel ions on the surface, while an anodic peak at minus 0.2 volts reflected nickel oxidation.

The voltammetry also revealed that the deposition reaction is diffusion-controlled. Recording curves at scan rates of 10, 20, and 30 millivolts per second, the researchers found that the anodic peak current density scaled linearly with the square root of the scan rate, exactly the relationship predicted by the Randles-Sevcik equation for a process limited by how fast nickel ions can travel to the electrode. This diffusion control proved crucial for interpreting everything that followed, because when ions arrive at the surface faster than they can be replenished from the bulk solution, the geometry of the depletion zones around growing nuclei shapes both the current response and the final film morphology.

Chronoamperometry, the recording of current as a function of time at a fixed applied potential, then exposed the three-act drama of nickel electrocrystallization. In the first fraction of a millisecond, a sharp spike and decay of current reflects double-layer charging and ion adsorption. A rapid rise follows as new nuclei form and each one draws a hemispherical diffusion zone around itself, pushing the current to a maximum. Beyond that peak, the current decays in a manner governed by the Cottrell equation, the classic signature of diffusion-limited mass transfer, before settling into a plateau where the supply of nickel ions from the bulk solution constrains everything. This characteristic profile confirmed that nickel deposition on stainless steel follows a three-dimensional nucleation process, with hemispherical clusters growing and eventually coalescing into a continuous film.

The comparison with the Scharifker-Hills model produced the study’s most striking finding: the nucleation mechanism is not fixed but shifts with deposition conditions. At underpotentials, where the driving force is modest, the transients tracked the progressive nucleation curve, because the nucleation rate lagged behind the growth rate and new sites kept activating. At overpotentials, the curves aligned closely with instantaneous nucleation, since the nucleation barrier is overcome quickly and a large population of nuclei forms simultaneously. At the reduction potential itself, a mixed mechanism appeared. Raising the bath pH from 4 to 8 pushed the system toward progressive nucleation, which the authors attribute to pH-dependent changes in hydroxide species and surface energetics that favor the continuous creation of new nucleation sites over time.

Concentration played an equally decisive role. Films grown from the most dilute 25 millimolar bath followed the instantaneous nucleation curve, while the 37 and 50 millimolar baths produced mixed instantaneous and progressive behavior, echoing earlier observations of silver deposition on glassy carbon. The team notes that experimental curves deviated from ideal theory in places, with a slower current decay than predicted, which they attribute to side processes such as hydrogen evolution, adsorption, and charge-transfer resistance. These deviations are a reminder that real plating baths are chemically messy systems, and that the clean limiting cases of nucleation theory blend into one another under practical conditions.

What makes the study compelling is that the electrochemical fingerprints translated directly into physical film quality. X-ray diffraction confirmed the cubic crystal structure of nickel in every film, with a prominent reflection from the (111) planes at 44.5 degrees, and the Williamson-Hall analysis of peak broadening revealed compressive microstrain induced by the stainless steel substrate. Notably, crystallite size, lattice constant, and texture coefficient barely changed across the parameter range, but strain and dislocation density dropped to negligible levels at the highest pH and concentration. Meanwhile, field-emission scanning electron microscopy showed a dramatic morphological transition: films from acidic, dilute baths were rough and cracked, riddled with grain boundaries, while films from alkaline, concentrated baths were smooth, uniform, and compact. The culprit behind the cracking is the hydrogen evolution reaction, whose disruptive bubbles and induced internal stress scar the growing film at low pH but are largely suppressed in alkaline conditions.

The practical implications ripple outward from the plating bath. The authors point out that cracked, fine-grained films with abundant grain boundaries resist dislocation movement and are therefore harder, but the same boundaries promote corrosion, whereas the coarser, compact films grown at higher pH and concentration conduct electricity better and resist corrosion. Because nickel coatings serve industries ranging from metal decoration and electronic components to catalysis and energy storage, the ability to dial in a specific nucleation mechanism and morphology through nothing more exotic than pH, concentration, and potential offers a low-cost route to tailored coatings. The researchers acknowledge support from the Mahatma Jyotiba Phule Research and Training Institute, and their work stands as a reminder that some of the most consequential physics in manufacturing happens in the first milliseconds, when a handful of atoms decides what kind of surface the world will see.

Subject of Research: Nucleation and growth kinetics during the electrodeposition of nickel thin films on stainless steel

Article Title: Studies on nucleation and growth kinetics during electrodeposition of nickel thin films

Article References: Potdar, D., Patil, S., Kulkarni, Y., Pawar, N., Banne, S., Sadale, S., & Chikode, P. (2026). Studies on nucleation and growth kinetics during electrodeposition of nickel thin films. Discover Electrochemistry, 3(1), Article 29. https://doi.org/10.1007/s44373-026-00115-4

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00115-4

Keywords: electrodeposition, nickel thin films, nucleation kinetics, Scharifker-Hills model, chronoamperometry, cyclic voltammetry, stainless steel substrate, hydrogen evolution reaction, X-ray diffraction, FESEM, bath pH, crystal growth

The team fabricated a composite counter electrode from activated carbon, Sri Lankan natural vein graphite and a minimal quantity of platinum nanoparticles, all deposited onto a stainless-steel substrate. The choice of substrate is itself significant, because stainless steel is robust, inexpensive and compatible with roll-to-roll manufacturing, opening the door to flexible solar modules that could be produced at industrial scale. Rather than relying on a continuous platinum film, the researchers dispersed tiny amounts of platinum nanoparticles throughout a carbon matrix, letting each nanoparticle act as a catalytic hotspot while the surrounding carbon carries the electrical load.

Structural and morphological analyses confirmed that the composite came together exactly as designed. Raman spectroscopy revealed the characteristic signatures of the graphitic and disordered carbon phases, while scanning electron microscopy and energy-dispersive X-ray analysis verified that the platinum nanoparticles had been successfully incorporated into the composite layer. These characterization steps matter because the performance of a counter electrode depends critically on how well its constituents are integrated; a poorly mixed composite would leave catalytic sites stranded and electrically isolated, squandering the very platinum the design is trying to conserve.

Electrochemical testing then put the composite through its paces. Tafel polarization, cyclic voltammetry and electrochemical impedance spectroscopy all pointed in the same direction: enhanced catalytic activity and efficient charge-transfer behavior at the electrode-electrolyte interface. In a dye-sensitized solar cell, the counter electrode’s job is to catalyze the reduction of triiodide back to iodide, regenerating the redox couple that shuttles electrons through the device. A sluggish counter electrode wastes voltage and throttles current, so the strong electrochemical signatures measured here were an encouraging sign that the composite could hold its own in a working cell.

The photovoltaic results were striking. A reference device using a conventional sputtered platinum counter electrode achieved the highest efficiency in the study, 7.24 percent. The dye-sensitized solar cell built with the activated carbon/vein graphite/platinum nanoparticle composite counter electrode reached 6.87 percent, a figure that comes remarkably close to the platinum benchmark while using only a trace amount of the precious metal. For context, the unmodified activated carbon/graphite electrode without any platinum nanoparticles managed just 5.19 percent. Adding the trace platinum boosted the efficiency by a full 32 percent, transforming a mediocre carbon electrode into a serious contender.

The improvement is not simply a matter of adding more catalyst; it is a story of synergy among three very different materials. The vein graphite contributes high electrical conductivity, providing fast pathways for electrons arriving from the external circuit. The activated carbon contributes an enormous internal surface area, multiplying the number of sites where electrolyte ions can make contact with the electrode. The platinum nanoparticles contribute exceptional electrocatalytic activity toward the triiodide/iodide redox reaction, lowering the energy barrier for the regeneration reaction that keeps the cell running. Together, the three components cover each other’s weaknesses, and the whole ends up far greater than the sum of its parts.

The choice of Sri Lankan vein graphite adds an economic and geopolitical dimension to the work. Vein graphite is a rare, high-purity form of natural graphite found in commercial quantities almost exclusively in Sri Lanka, where it occurs as crystalline veins deposited in rock fissures. Its natural graphitic structure gives it excellent conductivity without the energy-intensive processing required for synthetic graphite, and sourcing it locally reduces transport costs and supply-chain risk. By building a solar cell component around a domestic natural resource, the researchers demonstrate a model of sustainable materials development that other resource-rich developing nations could emulate: rather than exporting raw ore, add value at home by engineering it into advanced energy technology.

The platinum economy of the design deserves particular attention. Platinum is among the most expensive metals on Earth, and its supply is concentrated in a handful of mining regions, making platinum-based components a vulnerability for any technology hoping to scale globally. Because the nanoparticles are so small and so few, the composite electrode captures most of platinum’s catalytic benefit at a tiny fraction of the metal loading of a sputtered film. This approach follows a broader trend in electrocatalysis research, where the goal is not to eliminate platinum entirely but to stretch it as far as physics allows, using carbon scaffolds, alloys or single-atom dispersions to maximize the catalytic turnover per gram of metal.

The study does not claim to have beaten platinum outright, and the authors are candid about that. The sputtered platinum electrode still holds the efficiency record in their own device set. What the composite offers instead is a compelling trade-off: 6.87 percent efficiency at a dramatically lower materials cost, with the added benefits of a durable stainless-steel substrate and locally sourced graphite. For applications where cost per watt matters more than squeezing out the final fraction of a percent, such as building-integrated photovoltaics, rural electrification and low-cost solar modules for emerging markets, that trade-off could be decisive.

Looking ahead, the result suggests several avenues for refinement. Optimizing the ratio of activated carbon to graphite, tuning the platinum nanoparticle loading even further downward, and exploring other low-cost substrates could push the composite closer to or beyond the platinum benchmark. The work also reinforces a lesson that resonates across modern energy research: the future of affordable solar technology may depend less on exotic new materials than on intelligent combinations of abundant ones, arranged so that every atom does the most work it can. In this case, a trace of platinum, a handful of activated carbon and Sri Lanka’s ancient vein graphite have combined to bring low-cost solar power one practical step closer.

Subject of Research: Composite counter electrodes for dye-sensitized solar cells made from activated carbon, Sri Lankan vein graphite and trace platinum nanoparticles

Article Title: Composite counter electrode for dye-sensitized solar cells engineered from trace amounts of platinum nanoparticles and Sri Lankan natural vein graphite

Article References: Dissanayake, M. A. K. L., Sandunika, P. U., Senadeera, G. K. R., Kumari, J. M. K. W., Vedraine, S., Rougier, S., Lakshan, K. L. A. C., Sewwandi, G. G. S., & Senevirathna, M. D. D. S. (2026). Composite counter electrode for dye-sensitized solar cells engineered from trace amounts of platinum nanoparticles and Sri Lankan natural vein graphite. Ionics. https://doi.org/10.1007/s11581-026-07509-9

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07509-9

Keywords: dye-sensitized solar cells, counter electrode, platinum nanoparticles, vein graphite, activated carbon, Sri Lanka, electrocatalysis, photovoltaics, stainless steel substrate, charge transfer, sustainable materials, solar energy