How SUNY Binghamton Achieved 40 nm Nanoporous Silver Without Toxic Chemistry
Silver with a controlled nanoporous structure has established uses in biosensing, electrocatalysis, and electrochemical actuation. The difficulty has always been making it reliably. Metallurgical routes require high temperatures and complex processing; conventional electrochemical co-deposition typically relies on cyanide electrolytes.
A research team at the State University of New York at Binghamton set out to find a cleaner alternative — and high-purity copper and silver from Advent Research Materials played a central role in establishing the validity of their results.
Science Made Simple
Think of nanoporous silver as a tiny metal sponge. Ordinary silver is solid all the way through — but nanoporous silver is riddled with microscopic holes, which means it has an enormous surface area packed into a very small volume. That surface area is what makes it so useful: the more surface a material has, the more places there are for chemical reactions to happen, for biological molecules to bind, or for electrical signals to be detected.
To make the sponge, researchers start with a copper-silver alloy — a mixture of both metals — then selectively dissolve away the copper, leaving behind the silver in a porous, interconnected structure. The problem is that copper and silver naturally refuse to mix. Like oil and water, they tend to separate rather than blend, which means the starting alloy is patchy and uneven — and a patchy alloy produces a coarse, poorly controlled sponge.
The Binghamton team's innovation was to use a third metal — lead — as a temporary go-between. By depositing and stripping thin layers of lead in a carefully controlled electrochemical cycle, they coaxed copper and silver into mixing properly, one atomic layer at a time, within a single cell and without cyanide. The lead is never part of the final product; it acts as a mediator that enables the two metals to co-deposit uniformly. Remove the copper afterwards, and what remains is nanoporous silver with far finer, more uniform pores.
The Research
Zhen Lei, Ksenya Mull, and Professor Nikolay Dimitrov compared two versions of this lead-mediated approach — surface limited redox replacement (SLRR) and defect mediated growth (DMG) — against conventional bulk electrodeposition (OPD). Both new methods were conducted without cyanide electrolytes and within a single electrochemical cell.
To verify that their alloy films genuinely mixed copper and silver more effectively than OPD, the team needed a chemically unambiguous baseline: a pure copper electrode and a pure silver electrode to compare against. Any impurity in those references would have introduced artefacts into the measurements, making it impossible to tell whether differences in the data reflected real improvements in alloy quality or simply variability in the reference materials.
Why Purity Mattered
The team sourced their reference electrodes from Advent Research Materials — flat cylindrical copper and silver electrodes, each 99.99% pure.
Both were used as the baseline against which the linear scanning voltammetry (LSV) dissolution curves of the three alloy types were compared. The SLRR and DMG alloys produced dissolution curves with lower slopes than pure copper, confirming genuine mixing of the two metals.
Their curves also shifted more positively than the OPD alloy, demonstrating that the new deposition methods produced more uniform, better-mixed precursors — a finding that depended on having reliable, high-purity reference materials to compare against.
The Results
After dissolving out the copper, both SLRR and DMG produced nanoporous silver with ligament and pore sizes in the region of 40 nm — around 100 nm finer than structures produced by conventional OPD electrodeposition. Surface area enhancement ratios of up to approximately five times that of flat silver were achieved with SLRR. The paper concludes that DMG is the most effective method overall for producing fine ligament structures.
The work establishes both SLRR and DMG as practical alternatives that avoid both the cyanide electrolytes required by conventional electrochemical co-deposition and the high temperatures and complexity of metallurgical routes — conducted within a single electrochemical cell, and capable of producing structural quality that conventional bulk electrodeposition cannot match.
Journal: Journal of The Electrochemical Society
Authors: Zhen Lei, Ksenya Mull, Nikolay Dimitrov
Published: 11 September 2024
DOI: 10.1149/1945-7111/ad7533