Carbon screen-printed electrodes for substrate-assisted electroless deposition of palladium

Five types of carbon-based screen-printed electrodes (SPE) – carbon (C110), mesoporous carbon (MC), single walled carbon nanotubes (SWCNT)-, carbon nanotubes (CNT)-, and carbon nanofibers (CNF)-modified electrodes – are characterized with respect to surface roughness, true surface area (TSA), electrochemical activity and electrochemical impedance (EIS) behavior and further used for electroless deposition of Pd. Structural characterization was performed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Investigation of the surfaces with AFM revealed an increasing root mean square (RMS) roughness in the order C110, SWCNT, CNT, CNF, and MC. EIS studies demonstrate significant difference in the resistance of the SPEs with largest value found for the carbon electrode (C110), followed by the carbon nanofiber (CNF)-modified electrode. MC, CNT- and SWCNT-modified electrodes exhibit close, significantly lower resistance values. The capacitance of the carbon-based SPEs is found to be rather high for all electrodes even if accounting for the TSA which has been determined with AFM. This implies a significant effect of nanoroughness and/or of a large internal porous structure especially for CNF and MC SPEs.

Pd electroless deposition occurs at all carbon-based SPEs after reductive pre-treatment in supporting electrolytes (0.5 mol dm−3 H2SO4 or 0.1 mol dm−3 LiClO4) without using a solute chemical reductant in the metal plating solution. The amount and characteristics of the deposited Pd is estimated by anodic stripping voltammetry, EDX analysis, and SEM. It is established that the type and amount of Pd deposit depends on the structure of the carbon-based electrodes with nanostructured carbon coatings (consisting of CNT, SWCNT, or CNF) providing higher amounts of deposited Pd (in the range of 4.4 to 5.8 µg cm−2) and smaller size of the obtained metal particles.