Ultrasound-assisted transformation from waste biomass to efficient carbon-based metal-free pH-universal oxygen reduction reaction electrocatalysts.

Efficient carbon-based nitrogen-doped electrocatalysts derived from waste biomass are regarded as a promising alternative to noble metal catalysts for oxygen reduction reaction (ORR), which is crucial to fuel cell performance. Here, coconut palm leaves are employed as the carbon source and a series of nitrogen-doped porous carbons were prepared by virtue of a facile and mild ultrasound-assisted method. The obtained carbon material (ANDC-900-10) conveys excellent pH-universal catalytic activity with onset potentials (E) of 1.01, 0.91 and 0.84 V vs. RHE, half-wave potentials (E) of 0.87, 0.74 and 0.66 V vs. RHE and limiting current densities (J) of 5.50, 5.45 and 4.97 mA cm in alkaline, neutral and acidic electrolytes, respectively, prevailing over the commercial Pt/C catalyst and, what's more, ANDC-900-10 displays preeminent methanol crossover resistance and long-term stability in the broad pH range (0-13), thanks to its abundant hierarchical nanopores as well as effective nitrogen doping with high-density pyridinic-N and graphitic-N. This work provides sonochemical insight for underpinning the eco-friendly approach to rationally designing versatile metal-free carbon-based catalysts toward the ORR at various pH levels.