Engineering adjacent N, P and S active sites on hierarchical porous carbon nanoshells for superior oxygen reduction reaction and rechargeable Zn-air batteries.

Heteroatom-doped carbon materials have been regarded as sustainable alternatives to the noble-metal catalysts for oxygen reduction reaction (ORR), while the catalytic performances still remain unsatisfactory. Herein, we develop a metal-free adjacent N, P and S-codoped hierarchical porous carbon nanoshells (NPS-HPCNs) through a novel layer-by-layer template coating method. The NPS-HPCNs is rationally fabricated by crosslinking of polyethyenemine (PEI) and phytic acid (PA) on nano-SiO2 template surface and subsequently coating of viscous sulfur-bearing petroleum pitch, followed by pyrolysis and alkaline etching. Soft X-ray absorption near-edge spectroscopy (XANES) analysis and density functional theory (DFT) calculations prove the engineering of adjacent N, P and S atoms to generate synergistic and reinforced active sites for oxygen electrocatalysis. The NPS-HPCNs manifests excellent ORR activity with a half-wave potential (E1/2) of 0.86 V, as well as promoted durability and methanol tolerance in alkaline medium. Remarkably, the NPS-HPCNs-based Zn-air battery delivers an open-circuit voltage of 1.479 V, a considerable peak power density of 206 mW cm-2 and robust cycling stability (over 200 h), even exceeding the commercial Pt/C catalyst. This study offers fundamental insights into the construction and synergistic mechanism of adjacent heteroatoms on carbon substrate, providing advanced metal-free electrocatalysts for Zn-air batteries and other energy conversion and storage devices.

Engineering controllable oxygen vacancy defects in iron hydroxide oxide immobilized on reduced graphene oxide for boosting visible light-driven photo-Fenton-like oxidation.

Visible light-driven photo-Fenton-like technology is a promising advanced oxidation process for water remediation, while the construction of effective synergetic system remains a great challenge. Herein, iron hydroxide oxide (α-FeOOH) with controllable oxygen vacancy defects were engineered on reduced graphene oxide (rGO) nanosheets (named as OVs-FeOOH/rGO) through an in-situ redox method for boosting visible light-driven photo-Fenton-like oxidation. By adjusting the pH environment to modulate the redox reaction kinetics between graphene oxide (GO) and ferrous salt precursors, the oxygen vacancy concentration in α-FeOOH could be precisely controlled. With optimized oxygen vacancy defects obtained at pH 5, the OVs-FeOOH/rGO displayed superior photo-Fenton-like performance for Rhodamine B degradation (99% within 40 mins, rate constant of 0.2278 mg-1 L min-1) with low H2O2 dosage (5 mM), standing out among the reported photo-Fenton-like catalysts. The catalyst also showed excellent reusability, general applicability, and tolerance ability of realistic environmental conditions, which demonstrates great potential for practical applications. The results reveal that moderate oxygen vacancy defects can not only strengthen absorption of visible light and organic pollutants, but also promote the charge transfer to simultaneously accelerate the photogenerated electron-hole separation and Fe(III)/Fe(II) Fenton cycle, leading to the remarkable photo-Fenton-like oxidation performance. This work sheds light on the controllable synthesis and mechanism of oxygen vacancy defects to develop efficient photo-Fenton-like catalysts for wastewater treatment.