Confinement of sulfur-doped NiO nanoparticles into N-doped carbon nanotube/nanofiber-coupled hierarchical branched superstructures: Electronic modulation by anion doping boosts oxygen evolution electrocatalysis

Abstract

The search for non-precious and efficient electrocatalysts towards the oxygen evolution reaction (OER) is of vital importance for the future advancement of multifarious renewable energy conversion/storage technologies. Electronic modulation via heteroatom doping is recognized as one of the most forceful leverages to enhance the electrocatalytic activity. Herein, we demonstrate a delicate strategy for the in-situ confinement of S-doped NiO nanoparticles into N-doped carbon nanotube/nanofiber-coupled hierarchical branched superstructures (labeled as S-NiO@N-C NT/NFs). The developed strategy simultaneously combines enhanced thermodynamics via electronic regulation with accelerated kinetics via nanoarchitectonics. The S-doping into NiO lattice and the 1D/1D-integrated hierarchical branched carbon substrate confer the resultant S-NiO@N-C NT/NFs with regulated electronic configuration, enriched oxygen vacancies, convenient mass diffusion pathways and superior architectural robustness. Thereby, the S-NiO@N-C NT/NFs display outstanding OER properties with an overpotential of 277 mV at 10 mA cm−2 and impressive long-term durability in KOH medium. Density functional theory (DFT) calculations further corroborate that introducing S-dopant significantly enhances the interaction with key oxygenate intermediates and narrow the band gap. More encouragingly, a rechargeable Zn-air battery using an air–cathode of Pt/C + S-NiO@N-C NT/NFs exhibits a lower charge voltage and preferable cycling stability in comparison with the commercial Pt/C + RuO2 counterpart. This study highlighting the concurrent consideration of electronic regulation, architectural design and nanocarbon hybridization may shed light on the future exploration of economical and efficient electrocatalysts.