Removal of left-over catalyst particles from carbon nanomaterials is a significant scientific and technological problem. Here, we present the physical and electrochemical study of application-specific carbon nanofibers grown from Pt-catalyst layers. The use of Pt catalyst removes the requirement for any cleaning procedure as the remaining catalyst particles have a specific role in the end-application. Despite the relatively small amount of Pt in the samples (7.0 ± 0.2%), they show electrochemical features closely resembling those of polycrystalline Pt. In O2-containing environment, the material shows two separate linear ranges for hydrogen peroxide reduction: 1-100 μM and 100-1000 μM with sensitivities of 0.432 μA μM-1 cm-2 and 0.257 μA μM-1 cm-2, respectively, with a 0.21 μM limit of detection. In deaerated solution, there is only one linear range with sensitivity 0.244 μA μM-1 cm-2 and 0.22 μM limit of detection. We suggest that the high sensitivity between 1 μM and 100 μM in solutions where O2 is present is due to oxygen reduction reaction occurring on the CNFs producing a small additional cathodic contribution to the measured current. This has important implications when Pt-containing sensors are utilized to detect hydrogen peroxide reduction in biological, O2-containing environment.