Fabrication of ordered polydopamine-coated carbon nanotube arrays and their electrocatalytic activities towards synergistically enhanced oxidation of ascorbate-monosaccharides and reduction of oxygen

Highlights: • AA and monosaccharides can be synergistically oxidized on SWCNTs@PDA arrays. • Electrocatalytic oxidation response of monosaccharides: glucose > galactose > fructose. • SWCNTs@PDA show electrocatalytic activity towards reduction of O₂ and H₂O₂. • AA-Glu fuel cell performance is remarkably enhanced by PDA films on SWCNTs. -- Abstract: An ordered array of single-walled carbon nanotubes coated with polydopamine (SWCNTs@PDA) is prepared using multiple voltammetry for the oxidation of ascorbate (AA)-monosaccharides, and the reduction of oxygen (O₂) in enzyme-free fuel cells. The SWCNTs@PDA electrode exhibits a pair of redox peaks at the formal potential of 0.145 V (vs. SCE, 0.1 V s⁻¹). The electrocatalytic oxidation of ascorbate enhanced by three monosaccharide isomers on SWCNTs@PDA shows the stereoisomeric effects. Glucose (Glu) has the highest ability to enhance synergistically the oxidation reaction of ascorbate while fructose (Fru) has the lowest with galactose (Gal) in between. The presence of SWCNTs@PDA arrays on carbon felt surface leads to a positive shift of 0.331 V or 0.335 V in the onset potential of O₂ or H₂O₂ reduction. While simultaneously employing SWCNTs@PDA as anode and cathode catalysts to assemble an ascorbate-glucose fuel cell, the short-circuit current density (i_sc) or maximum power density (P_max) shows a 5.2-fold or 12.7-fold increase compared with that using bare SWCNTs. The present study provides an interesting platform for the electrochemical oxidation of ascorbate enhanced recognizably by monosaccharides, as well as illustrates that the redox-active SWCNTs@PDA arrays can act as a signal amplifier to promote remarkably the redox reactions of ascorbate and glucose with O₂ in fuel cells.