Atomically Dispersed Iron-Nitrogen Sites on Hierarchically Mesoporous Carbon Nanotube and Graphene Nanoribbon Networks for CO2 Reduction.

Atomically dispersed metal and nitrogen co-doped carbon (M-N/C) catalysts hold great promise for electrochemical CO2 conversion. However, there is a lack of cost-effective synthesis approaches to meet the goal of economic mass production of single-atom M-N/C with desirable carbon support architecture for efficient CO2 reduction. Herein, we report facile transformation of commercial carbon nanotube (CNT) into isolated Fe-N4 sites anchored on carbon nanotube and graphene nanoribbon (GNR) networks (Fe-N/CNT@GNR). The oxidization-induced partial unzipping of CNT results in the generation of GNR nanolayers attached to the remaining fibrous CNT frameworks, which reticulates a hierarchically mesoporous complex and thus enables a high electrochemical active surface area and smooth mass transport. The Fe residues originating from CNT growth seeds serve as Fe sources to form isolated Fe-N4 moieties located at the CNT and GNR basal plane and edges with high intrinsic capability of activating CO2 and suppressing hydrogen evolution. The Fe-N/CNT@GNR delivers a stable CO Faradaic efficiency of 96% with a partial current density of 22.6 mA cm-2 at a low overpotential of 650 mV, making it one of the most active M-N/C catalysts reported. This work presents an effective strategy to fabricate advanced atomistic catalysts and highlights the key roles of support architecture in single-atom electrocatalysis.

Remarkable charge transfer between CdSe seeded CdS nanorods and its metallic and semiconducting tips and its effect on Rhodamine B photodegradation.

Hybrid colloids (HCs) have shown distinct optical, electric, and optoelectronic properties from the components, mainly because of electronic interplay between the components. Here we investigate different charge transfer behaviors of dumbbell-structured CdSe-seeded CdS nanorods with metallic and semiconducting tip materials respectively studied by UV-vis and photoluminescence (PL) spectra, i.e. gold-tipped CdSe-seeded CdS nanorods and palladium sulfide-tipped CdSe-seeded CdS nanorods. They have shown remarkably different optical properties due to different charge transfer processes, i.e. one is only excited electrons transferred from the CdS shell to gold tips while the other is holes as well as electrons injected from the CdS shell into the palladium sulfide tips. The effect of the charge transfer on Rhodamine B (RhB) photodegradation is further investigated. Very interestingly, totally opposite effects were found, that is gold tips enhanced photodegradation rate while palladium sulfide tips vastly reduced photodegradation. Those phenomena are well explained by our proposed mechanism for the charge transfer. This study enables better design of HCs for improved photocatalysis and better photovoltaics.