Single-Electrode Electrochemistry: Chemically Engineering Surface Adhesion and Hardness To Maximize Redox Work Extracted from Tribocharged Silicon

Abstract

Recent research has demonstrated that heterogeneous charge-transfer reactions are not restricted to conductors and that electrochemical reactions can occur on the surface of statically charged insulators. However, the exact mechanism by which insulators gain and lose electrical charges remains controversial. Herein we have studied quantitatively the reduction of silver ions on intrinsic amorphous silicon surfaces that are statically charged by contact against plastic polymers. We have quantified the magnitude of the redox work done by the tribocharged silicon surface as a function of its adhesion and hardness, with these two variables being tuned using covalent SiC monolayer chemistries. We observed that metallic particles grow preferentially over surfaces that are relatively soft (low DMT modulus) and highly adhesive, hence indirectly proving that the triboelectrification of an insulator–insulator dynamic contact is caused by the exchange of ionic fragments, rather than by the movement of free electrons. This work clarifies the origin of triboelectricity, devises a surface-chemistry method to maximize tribocharging with immediate scope in single-electrode electrochemistry, and describes a concept potentially suitable for the mask-free and bias-free patterning of metal nanoparticles on photoconductors.

Irreproducibility in the triboelectric charging of insulators: evidence of a non-monotonic charge versus contact time relationship

“…Surface mechanical properties are known to affect material transfer, 5,26 and hence the charge exchange between two polymers. Further, material-specific ion stabilities 22 contribute to define the mosaic pattern of positive and negative domains that sum up to give a tribocharged sample its net (measurable) charge.…”

“…18,20,22 A small and unavoidable asymmetry in the applied mechanical force, and/or a small difference in hardness and adhesion (Fig. S1, ESI †), 5 leads to triboelectrification even of identical materials. 38 The charge measured on each sample is the arithmetic sum of positive and negative charges carried by atoms or molecules being transferred, and very surprisingly for all the non-ionic dielectrics studied here (acetal, PTFE, PVC, PDMS, and nylon) this value reaches a maximum after a finite, and relatively short, charging time.…”

“…[11][12][13][14][15][16][17] Through Kelvin probe force microscopy (KPFM) [18][19][20] and Faraday pail measurements, 21 static charges present on a surface can be accurately mapped and measured. A number of studies have used these types of measurements to highlight the complexity of the triboelectrification process -ionization energy, electron affinity, 22,23 moisture, 24,25 adhesion, 5 hardness, 5,26 contact force, 19 gas dissolution, 27 as well as the exact surface chemistry 23 -all play a role in it. A correct and complete understanding of the process is still lacking.…”

“…A correct and complete understanding of the process is still lacking. A significant amount of material is transferred upon contact, 5,18 and it thus follows that the study of contact charging on insulators will be more easily studied in a single-material model system. Surprisingly, the study of contact electrification has so far mainly focused on dynamic contacts between different materials, [28][29][30] and reports on the contact and charging between identical materials are far less frequent.…”

“…system removes complexity introduced by factors such as differences in surface adhesion, hardness and work function. 5…”