## 2 Materials and Methods
### Fabrication of Electrodes  
The pure metals to be investigated in this study could not be easily sourced as electrodes in the form needed for precise electrochemical tests. Therefore, electrodes for Sb, Bi, In, Ta, Ag, Dy, Er, Gd, Ho, and Tb were fabricated manually. The fabrication process used the following steps:  
1. Each pure metal was cut into squares with a side length of 0.4 mm using a metal saw. 2. Each piece was filed to form a near square-like shape, roughly having a length of 0.3 mm to 0.4 mm for each side. 3. Copper rod was extracted from a solid core 12-gauge copper wire by removing its outer plastic shield and cut to 12 cm in length. 4. The copper rod is attached to the back side of each piece of metal using conductive silver paste. 5. The silver paste was left to dry at room temperature for one hour and then coated with cyanoacrylate adhesive twice (Figure 1a) to improve the sturdiness of the joint. 6. To cast the electrodes in epoxy resin, polypropylene plastic straws (5 mm diameter) with a length of 10 cm were inserted into a sheet of polystyrene foam (Styrofoam). The straws were then glued from the outside to create a seal. 7. Two-part epoxy resin was mixed and poured to fill each plastic straw, ensuring there were no leaks from the bottom at the polystyrene foam. 8. Each electrode metal attached to the copper rod was then inserted through the straw and resin, making sure to insert the copper end into the polystyrene foam. It is important to ensure that the end surface of the metal is flush with the top of the straw. The resin was then left to cure for at least 48 h at room temperature (Figure 1b). 9. Once the resin had cured, the fabricated metal electrode was removed from the plastic straw shell and using a sterile scalpel any excess resin was trimmed. 10. The metal tips of the electrodes were then polished to remove any irregularities. The metal tips were smoothed, starting with 240 grit sandpaper, and then working up through 320, 400, 600, 800, 1000, 3000, and 5000 grit. The sandpaper was fixed over a tabletop and the standard figure-8 sanding pattern was used during sanding \begin{table}
\begin{tabular}{c c c c} \hline
**Compound/Material** & **Source** & **Purity** & **CAS \#** \\ \hline Reverse-osmosis water (R \(<\) 1.3 μs/cm) & \begin{tabular}{c} High Purity Water Services \\ (Oakville, ON, Canada) \\ \end{tabular} & 100\% & 7732-18-5 \\ \hline Sandpapers, 250 to 5000 grits & 3 M (Saint Paul, MN, USA) & N/A & N/A \\ \hline Silver (rod) & \begin{tabular}{c} Alfa Aesar \\ (Lancashire, UK) \\ \end{tabular} & 99.999\% & 7440-22-4 \\ \hline Sodium chloride & \begin{tabular}{c} Millipore Sigma \\ (Burlington, MA, USA) \\ \end{tabular} & 99.50\% & 7647-14-5 \\ \hline Sodium hydroxide & \begin{tabular}{c} Millipore Sigma \\ (Burlington, MA, USA) \\ \end{tabular} & 98\% & 1310-73-2 \\ \hline Tantalum (foil) & \begin{tabular}{c} Alfa Aesar \\ (Lancashire, UK) \\ \end{tabular} & 99.95\% & 7440-25-7 \\ \hline Terbium (chunks) & \
\begin{tabular}{c} Alfa Aesar \\ (Lancashire, UK) \\ \end{tabular} & 99.9\% & 7440-27-9 \\ \hline Two-part epoxy resin (EPX128 and EPX762) &
\begin{tabular}{c} VViViD (St-Laurent, ON, \\ Canada) \\ \end{tabular} & N/A & N/A \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._operations to ensure an even polishing and as squared as possible polished edges. For the 1000 through 5000 grits, wet sanding was used as well (Figure 1c). * The sanded tips of all the electrodes were placed next to a metric scale and photographed (Figure 2). * Next, the sanded electrodes were wet-polished. A thin microfiber cloth was affixed to a tabletop. Then, 5000, 14,000, and 50,000 grit polishing compounds were applied to the cloth. The standard figure-8 sanding pattern was used again. Polishing was stopped for each electrode as soon as the metal electrode tip formed a mirror-like clean polish (Figure 1d). * An ultrasonic water bath is filled with a solution of 70% isopropanol. The fully polished electrodes were submerged and sonicated for 15 min.