Atomically dispersed Ni/NiS anchored on doped mesoporous networked carbon framework: Boosting the ORR performance in alkaline and acidic media.

Rational and strategic fabrication of cost-effective, active and durable oxygen reduction reaction (ORR) electrocatalyst is the bottle-neck for the commercialization of fuel cells and metal-air batteries. Atomically dispersed nickel (Ni)/nickel sulfide (NiS) anchored on heteroatom doped networked hierarchical porous carbonaceous sheets are synthesized from nickel nitrate and guanidine thiocyanate. The sample annealed at 750 °C followed by acid-treatment (Ni-GT-750-A) emerges as the best performing pH-universal ORR catalyst with an onset potential of 0.91 (0.1 M KOH) and 0.89 V (0.1 M HClO) vs. reversible hydrogen electrode (RHE). It also exhibits better current durability (95.0 and 60%) and methanol tolerance (90.6 and 80.3%) in comparison to the commercial catalyst (65.0, 27, -33.0 and 16.5%) in alkaline and acidic media, respectively. An insight into the microstructure and ORR-active chemical sites is obtained with the aid of electron microscopic (FE-SEM and HR-TEM) and physiochemical (sorption isotherm, XRD, Raman and XPS) studies, respectively. The enhanced activity results from the synergistic influence of metallic ORR-active sites in hierarchical porous doped defective carbon support, which provides the well-interlinked conducting channel for electron transfer and additional ORR-active sites. The introduced electrocatalyst establishes Ni decorated doped carbon systems as potential revolutionary substitutes for commercial systems.