Rewriting Electron-Transfer Kinetics at Pyrolytic Carbon Electrodes Decorated with Nanometric Ruthenium Oxide

Abstract

Platinum is state-of-the-art for fast electron transfer whereas carbon electrodes, which have semimetal electronic character, typically exhibit slow electron-transfer kinetics. But when we turn to practical electrochemical devices, we turn to carbon. To move energy devices and electro(bio)analytical measurements to a new performance curve requires improved electron-transfer rates at carbon. We approach this challenge with electroless deposition of disordered, nanoscopic anhydrous ruthenium oxide at pyrolytic carbon prepared by thermal decomposition of benzene (RuOx@CVD-C). We assessed traditionally fast, chloride-assisted ([Fe(CN)₆]^3-/4-) and notoriously slow ([Fe(H₂O)₆]^3+/2+) electron-transfer redox probes at CVD-C and RuOx@CVD-C electrodes and calculated standard heterogeneous rate constants as a function of heat treatment to crystallize the disordered RuOx domains to their rutile form. For the fast electron-transfer probe, [Fe(CN)₆]^3-/4-, the rate increases by 34× over CVD-C once the RuOx is calcined to form crystalline rutile RuO₂. For the classically outer-sphere [Fe(H₂O)₆]^3+/2+, electron-transfer rates increase by an even greater degree over CVD-C (55×). The standard heterogeneous rate constant for each probe approaches that observed at Pt but does so using only minimal loadings of RuOx.