Substrate and pH‐dependent homogeneous electrocatalysis using riboflavin for oxygen reduction

Abstract

Homogeneous, aqueous solutions of the natural compound riboflavin were investigated for their electrocatalytic oxygen to hydrogen peroxide (H 2 O 2 ) reduction performance using cyclic voltammetry and electrolysis. In addition to pH dependencies, interestingly the choice of carbon-based electrode material had a strong impact on the electrocatalytic performance. Therefore, the three electrode materials, glassy carbon, carbon paper (CP), and carbon felt were electrochemically compared and afterwards investigated with scanning electron microscopy. Attributed to the deprotonation of riboflavin, pH = 13 was identified as the best performing condition. Using CP at pH = 13, the addition of riboflavin enhanced the H 2 O 2 production by a factor of 14 up to 355 μmol after 6 h at an average faradaic efficiency of around 80%.

How to use a rotating ring-disc electrode (RRDE) subtraction method to investigate the electrocatalytic oxygen reduction reaction?

“…As illustrated in Fig. S9, † no distracting absorption peaks originating from the catalysts were observed during the H 2 O 2 quantification, as also recently demonstrated, 52 except for 1,4-OH-AQ. Hereby, the H 2 O 2 quantification was not altered.…”

“…Due to this fact, this significant background electrocatalytic activity has to be carefully considered when discussing molecular electrocatalytic activities, as we have recently demonstrated and emphasised. 23,52,55 This electroactivity of pristine GC for O 2 reduction is also present in the CV and LSV studies already discussed in Fig. 2 and 3.…”

“…Due to this reason, only hydroxy derivatives were chosen for this study alongside RF, which is known to be a catalyst for the ORR. 47,49,52 The colour appearance of the material in solutions of 0.1 M NaOH and MeCN, as well as the respective UV-vis absorption spectra, can be seen in Fig. S4.…”

“…[49][50][51] Recently, we have investigated the homogeneous ORR of the naturally-occurring vitamin B 2 , riboflavin (RF), on various carbon electrode materials and now included RF as a catalyst molecule in this comparative study. 52 This work aims to demonstrate the applicability of the novel RRDE subtraction method for homogeneously dissolved electrocatalysts for the ORR as a fast yet powerful tool for electrocatalytic studies.…”

“…49–51 Recently, we have investigated the homogeneous ORR of the naturally-occurring vitamin B 2 , riboflavin (RF), on various carbon electrode materials and now included RF as a catalyst molecule in this comparative study. 52…”