We report the production of a hybrid catalyst electrode comprising semicrystalline molybdenum sulfide (MoS2+x) attached on nitrogen-doped carbon nanotubes. The nitrogen-doping of the carbon nanotubes stabilizes a semicrystalline structure of MoS2+x with a high exposure of active sites for HER resulting in enhanced catalytic activity. The results are published in the journal of Advanced Functional Materials.

Joakim Ekspong, Tiva Sharifi, Andrey Shchukarev, Alexey Klechikov, Thomas Wågberg, and Eduardo Gracia-Espino.
Adv. Funct. Mater, 2016.
DOI: 10.1002/adfm.201601994

Finding an abundant and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) is crucial for a global production of hydrogen from water electrolysis. This work reports an exceptionally large surface area hybrid catalyst electrode comprising semicrystalline molybdenum sulfide (MoS2+x) catalyst attached on a substrate based on nitrogen-doped carbon nanotubes (N-CNTs), which are directly grown on carbon fiber paper (CP). It is shown here that nitrogen-doping of the carbon nanotubes improves the anchoring of MoS2+x catalyst compared to undoped carbon nanotubes and concurrently stabilizes a semicrystalline structure of MoS2+x with a high exposure of active sites for HER. The well-connected constituents of the hybrid catalyst are shown to facilitate electron transport and as a result of the good attributes, the MoS2+x/N-CNT/CP electrode exhibits an onset potential of −135 mV for HER in 0.5 m H2SO4, a Tafel slope of 36 mV dec−1, and high stability at a current density of −10 mA cm−2.

We produced an efficient electrocatalyst for both water splitting half reactions in the same medium, where the catalyst compromise Co3O4 nanospheres attached on the surface of nitrogen-doped carbon nanotubes, which in turn are directly grown on conductive carbon paper. The firm and well-established interfaces along the electrode play a crucial role on enhanced stability and electrochemical activity observed for both oxygen evolution reaction and hydrogen reduction reaction. The manuscript has been published in the ACS Applied Materials and Interfaces.

We report efficient electrolysis of both water splitting half reactions in the same medium, by a bifunctional 3D electrode comprising Co3O4 nanospheres nucleated on the surface of nitrogen-doped carbon nanotubes (NCNTs) which in turn are grown on conductive carbon paper (CP). The resulting electrode exhibits high stability and large electrochemical activity for both oxygen and hydrogen evolution reactions (OER and HER). We obtain a current density of 10 mA/cm2 in 0.1 M KOH solution at overpotentials of only 0.47 V and 0.38 V for OER and HER respectively. Additionally, the experimental observations are understood and supported by analyzing the Co3O4:NCNT and NCNT:CP interfaces by ab initio calculations. Both the experimental and the theoretical studies indicate that firm and well-established interfaces along the electrode play a crucial role on the stability and electrochemical activity for both OER and HER.

This time we used density functional theory to compute the stability of SWNT fragments of all chiralities, which we compare to the chiralities of actual CVD products from diverse experiments. We found that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. The manuscript is published in the journal of Scientific Reports and can be download below.

Many nanotechnological applications, using single-walled carbon nanotubes (SWNTs), are only possible with a uniform product. Thus, direct control over the product during chemical vapor deposition (CVD) growth of SWNT is desirable, and much effort has been made towards the ultimate goal of chirality-controlled growth of SWNTs. We have used density functional theory (DFT) to compute the stability of SWNT fragments of all chiralities in the series representing the targeted products for such applications, which we compare to the chiralities of the actual CVD products from all properly analyzed experiments. From this comparison we find that in 84% of the cases the experimental product represents chiralities among the most stable SWNT fragments (within 0.2 eV) from the computations. Our analysis shows that the diameter of the SWNT product is governed by the well-known relation to size of the catalytic nanoparticles, and the specific chirality is normally determined by the product’s relative stability, suggesting thermodynamic control at the early stage of product formation. Based on our findings, we discuss the effect of other experimental parameters on the chirality of the product. Furthermore, we highlight the possibility to produce any tube chirality in the context of recent published work on seeded-controlled growth.