In-situ synthesis of heteroatom co-doped mesoporous dominated carbons as efficient electrocatalysts for oxygen reduction reaction

Secondary-Heteroatom-Doping-Derived Synthesis of N, S Co-Doped Graphene Nanoribbons for Enhanced Oxygen Reduction Activity

The rareness and weak durability of Pt-based electrocatalysts for oxygen reduction reactions (ORRs) have hindered the large-scale application of fuel cells. Here, we developed an efficient metal-free catalyst consisting of N, S co-doped graphene nanoribbons (N, S-GNR-2s) for ORRs. GNRs were firstly synthesized via the chemical unzipping of carbon nanotubes, and then N, S co-doping was conducted using urea as the primary and sulfourea as the secondary heteroatom sources. The successful incorporation of nitrogen and sulfur was confirmed by elemental mapping analysis as well as X-ray photoelectron spectroscopy. Electrochemical testing revealed that N, S-GNR-2s exhibited an E_onset of 0.89 V, E_1/2 of 0.79 V and an average electron transfer number of 3.72, as well as good stability and methanol tolerance. As a result, N, S-GNR-2s displayed better ORR property than either N-GNRs or N, S-GNRs, the control samples prepared with only a primary heteroatom source, strongly clarifying the significance of secondary-heteroatom-doping on enhancing the catalytic activity of carbon-based nanomaterials.

Constructing Porous Carbon Electrocatalysts from Cobalt Complex-Decorated Micelles of Mesoporous Silica for Oxygen Reduction/Evolution Reaction

The construction of a porous carbon structure with a high specific surface area is conducive to enhanced electrocatalytic activity due to the accessibility of active sites and improvement of the mass transfer. Herein, we explored the possibility of using micelles of mesoporous silica (MCM-48) as the carbon source to generate porous carbon under the confinement of MCM-48 channels. The complexes formed by Co²⁺ and 4,4'-bipyridine were in situ incorporated into the micelles to derive Co-related active sites (Co-N_x, Co, and Co₃O₄) for catalyzing the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). After pyrolysis in the N₂ atmosphere and subsequent removal of the MCM-48 skeleton, the target porous carbon electrocatalyst was obtained, which exhibited promising performance for both ORR and OER and has great potential as the cathode material for Zn-air battery application. This work not only confirms the effectiveness of using the micelles of MCM-48 as the carbon source for preparing the porous carbon materials, but also provides a new platform for design and synthesis of structurally controllable materials for energy-related electrocatalytic applications.