**4. Conclusions**

The electrochemical behavior of the composite electrodes was tested against the ferrocene redox probe. The SWCNT@SiO2 electrodes contain electrocatalytic nanotubes dispersed within its structure, as demonstrated by the improvement of the electrochemical performance in terms of heterogeneous rate constant and the electroactive area. However, the modest improvement of those parameters indicated that a major part of the SWCNT remains electrically isolated from the electrode support. PEDOT-PSS films were synthesized successfully by reactive electrochemical polymerization across SWCNT@SiO2-modified electrodes. The SWCNT@SiO2-PEDOT-PSS composite electrodes obtained a heterogeneous rate constant more than three times higher than the electrode without conducting polymer. Similarly, the electroactive area was also enhanced to almost double of the supporting GC electrode for the SWCNT@SiO2-modified electrodes. A further increase of electroactive area was observed for the SWCNT@SiO2-PEDOT-PSS composite electrodes.

**Author Contributions:** Conceptualization, E.M. and F.M.; methodology, H.D.; software, H.D.; validation, H.D., E.M. and F.M.; formal analysis, H.D.; investigation, H.D.; resources, H.D.; data curation, H.D.; writing-original draft preparation, A.B.; writing-review and editing, E.M. and F.M.; visualization, E.M. and F.M.; supervision, A.B. and F.M.; project administration, F.M.; funding acquisition, E.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Directorate General of Scientific Research and Technological Development (DGRSDT) (Algeria) and by the Ministerio de Ciencia, Innovación y Universidades (MAT2016-76595-R) and by the Conselleria de Educación, Investigación, Cultura y Deporte, Generalitat Valenciana (PROMETEO/2018/087).

**Conflicts of Interest:** The authors declare no conflict of interest.
