N-doped spherical activated carbon from dye adsorption: Bifunctional electrocatalyst for hydrazine oxidation and oxygen reduction

Considering that state-of-the-art on energy conversion devices is focused on the development of efficient and low-cost electrocatalysts, noble metal-free carbon materials have been studied as promising substitutes for commercial platinum-based catalysts. Given the importance of sustainability and minimization of the waste generation, we propose not to adopt an exclusive methodology for the new catalyst preparation, but to use a spherical activated carbon saturated with methylene blue molecules (SAC(sat)) after the adsorption process. A brief thermal treatment of SAC(sat) in N-2 atmosphere at 635 ?degrees C for 30 min was performed to incorporate N atoms on carbon lattice, creating defects and active sites to improve the electron conductivity. The N-doped SAC (N-SAC) showed BET surface area of 661 m(2) g(-1) and 1.1% of nitrogen in its elemental composition, distributed in pyrrolic (51.0%), pyridinic (29.2%) and graphitic groups (19.8%). Electrocatalytic performances of bare SAC and N-SAC were tested over hydrazine oxidation and oxygen reduction reactions. The N-SAC promoted total oxidation of hydrazine and the total reduction of oxygen, since the calculated number of electrons transferred for such reactions was of approximately four. In addition, the N-SAC electrochemical responses as a bifunctional electrocatalysts were comparable or even better than other catalysts containing noble metals.

Automated summary

Given the importance of energy efficiency and cost reduction, this study focuses on the development of noble metal-free carbon materials as alternatives to platinum-based catalysts. A new methodology involving the use of activated carbon and thermal treatment is proposed to enhance the electron conductivity and catalytic properties of the materials. The results show that the nitrogen-doped SAC exhibits excellent electrocatalytic performances comparable to or even better than catalysts containing noble metals.