Ru single atoms and nanoparticles on carbon nanotubes as multifunctional catalysts

In the last decade we have witnessed increasing interest in the production of renewable energy and value-added chemicals through sustainable and low-cost technologies where catalysts play a crucial role. Herein, we report the application of a Ru/CNT material containing a mixture of Ru single atoms and Ru nanoparticles as a multifunctional catalyst for both the catalytic reduction of nitroarenes and the electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (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 a reducing agent at room temperature, showing high catalytic activity with normalized rate constants (k(nor)) of 19.0 x 10(3), 57.7 x 10(3)and 16.6 x 10(3)min(-1)mmol(-1)respectively. Furthermore, the catalyst could be reused in at least 10 cycles without catalytic activity loss, confirming the high stability and robustness of the material. The Ru/CNT material also showed good ORR electrocatalytic activity in alkaline medium withE(onset)of 0.76 Vvs.RHE, a diffusion-limited current density of 3.89 mA cm(-2)andn(O2)of 3.3. In addition, Ru/CNT was remarkably insensitive to methanol with a current retention of 93% (51% for Pt/C) and competitive electrochemical stability of 80% after 20 000 s. Moreover, Ru/CNT was active for the OER withj(max)= 29.5 mA cm(-2)atE= 1.86 Vvs.RHE,eta(10)= 0.50 V and good stability (eta(10)changed to 0.01 V andj(max)only decreased by approximate to 12% after 500 cycles).