## 2 Materials and Methods
Electrical resistances of the discharge circuit \(R\) = 0.13 \(\Omega\) and 5.55 \(\Omega\) with the ODP and UDP, respectively, were measured at the natural frequency of discharge current oscillations by the impedance spectrometer RLC-meter AMM-3058 (AKTAKOM, Santa Clara, CA, USA). In this case, current and potential contacts of the device were connected to symmetrically arranged electrodes at ends facing each other. Taking into account these measurements, equivalent electrical resistances of the interelectrode spark gap were 0.27 \(\Omega\) and 0.61 \(\Omega\) for the ODP and UDP, respectively. At the beginning of each experiment, electrodes' surfaces, intended for the electroerosive NP synthesis, were polished on the grinding and polishing machine Digiprep Accura (Metkon, Bursa, Turkey) to a roughness of Ra = 0.5 um. The average electrode roughness was measured by the optical profilometer S neox (Sensorfar, Terrassa, Spain) on the confocal 20\(\times\) lens from the area 800 \(\times\) 800 um\({}^{2}\). In the experiments, electrodes were arranged coaxially and their nearest end faces were located parallel (at the angle of 0\({}^{\circ}\)) and at the angles of 7\({}^{\circ}\) and 15\({}^{\circ}\) for the ODP and parallel (at the angle of 0\({}^{\circ}\)) and at the angles of 3\({}^{\circ}\) and 10\({}^{\circ}\) for the UDP. Assuming that the electrode with a positive potential does not undergo significant erosion in the case of the UDP, only cathode end face was beveled, whereas in the case of the ODP, ends of both electrodes were set at an angle (Figure 1b). NPs were synthesized in the process of electrode erosion by a pulse-periodic SD continuously for 6 h maximum. During this experiment, we studied the statistical size distribution of silver NP agglomerates in the aerosol stream by their differential electrical mobility via the aerosol NP analyzer SMPS 3936 (TSI Inc., Shoreview, MN, USA). The statistical agglomerate size distribution was described by a log-normal distribution. The time dependence of the NP agglomerates modal size during electrode wear was constructed from distributions maxima. In parallel, we recorded changes in the capacitor charging voltage and the frequency of capacitor discharges in the setup by oscillograph readings. In addition, samples of the synthesized NPs were studied by the transmission electron microscope (TEM) JEM-2100 (JEOL, Ltd., Tokyo, Japan) for each regime under the study. For that purpose they were deposited on TEM grids in 5-10 min intervals from the start of experiments and after the establishment of thermodynamic equilibrium in the spark gap. Based on the TEM images, we collected statistics on the NPs size for at least 1000 pieces approximating them by round particles of equivalent cross-sectional area and drew their size distribution. At the end of experiments, we investigated electrodes' end faces after their electrical erosion, and their elemental composition in the scanning electron microscope (SEM) JSM 7001F (JEOL, Ltd., Tokyo, Japan) with the option of energy dispersive X-ray spectroscopy (EDX). At the beginning and in the end of each experiment, we weighed electrodes on the scale SQP-F SECURA 225D-1 ORU (Sartorius Lab Instruments, Goettingen, Germany) with a resolution of 10 ug to estimate the electrodes' mass loss as a result of their erosion.