Ru single atoms and nanoparticles on carbon nanotubes as multifunctional catalysts
In the last decade we have witnessed an increased interest in the production of renewable energy and value-added chemicals through sustainable and low-cost technologies were catalysts play a crucial role. Herein, we report the application of Ru/CNT material containing a mixture of Ru single atoms and Ru nanoparticles as multifunctional catalyst for both the catalytic reduction of nitroarenes and the electrocatalytic oxygen reduction (ORR) and evolution reactions (OER). The catalytic activity of the Ru-CNT material was evaluated in the reduction of 4-nitrophenol (4-NP), 4-nitroaniline (4-NA) and 2-nitrophenol (2-NP) in the presence of sodium borohydride as reducing agent at room temperature, presenting high catalytic activity with normalized rate constants (knor) of 19.0 × 103, 57.7x103 and 16.6 × 103 min-1 mmol-1 respectively. Furthermore, the catalyst could be reused in at least 10 cycles without catalytic activity loss, confirming the material high stability and robustness. The Ru/CNT also showed good ORR electrocatalytic activity in alkaline medium with Eonset of 0.76 V vs. RHE, a diffusion-limited current density of 3.89 mA cm-2 and ñO2 of 3.3. Additionally, Ru/CNT was remarkably insensitive to the methanol with current retention of 93% (51% for Pt/C) and competitive electrochemical stability 80% after 20 000 s. Moreover, the Ru/CNT was active for OER with jmax = 29.5 mA cm-2 at E = 1.86 V vs RHE, a ƞ10 = 0.50 V and good stability (ƞ10 changed 0.01V and jmax only decrease ≈ 12% after 500 cycles).