Cobalt-nitride (Co 4 N) nanoparticle-decorated nitrogen-doped graphene sheets were obtained via the nitrogen doping of a graphene-oxide precursor and simultaneous nitride formation. The non-precious metal catalyst formed in this one-step synthesis exhibits high electrocatalytic oxygen reduction activity and hence provides a promising alternative to conventional Pt/C alkaline fuel cell cathode catalysts. The reported composites were formed from the mixture of lyophilized graphene-oxide nanosheets and cobalt(II) acetate in ammonia atmosphere at 600°C. The average Co 4 N particle size increased from 14 to 201 nm with the increase in cobalt content. The oxygen reduction activity of the new catalysts was comparable to that of non-noble metal systems described in the literature, and also to the widely-used carbon black supported platinum catalysts. The highest reduction current density under alkaline conditions was found to be as high as 4.1 mA cm −2 with the corresponding electron transfer number of 3.6. Moreover, the new system outperformed platinum-based composites in terms of methanol tolerance, thus eliminating one of the major drawbacks (besides high price and limited availability), of noble metal catalysts.
Considerable effort
has been devoted recently to replace platinum-based
catalysts with their non-noble-metal counterparts in the oxygen reduction
reaction (ORR) in fuel cells. Nitrogen-doped carbon structures emerged
as possible candidates for this role, and their earth-abundant metal-decorated
composites showed great promise. Here, we report on the simultaneous
formation of nitrogen-doped graphene and iron nitride from the lyophilized
mixture of graphene oxide and iron salt by high-temperature annealing
in ammonia atmosphere. A mixture of FeN and Fe
2
N particles
was formed with average particle size increasing from 23.4 to 127.0
nm and iron content ranging from 5 to 50 wt %. The electrocatalytic
oxygen reduction activity was investigated via the rotating disk electrode
method in alkaline media. The highest current density of 3.65 mA cm
–2
at 1500 rpm rotation rate was achieved in the 20
wt % catalyst via the four-electrode reduction pathway, exceeding
the activity of both the pristine iron nitride and the undecorated
nitrogen-doped graphene. Since our catalysts showed improved methanol
tolerance compared to the platinum-based ones, the formed non-noble-metal
system offers a viable alternative to the platinum-decorated carbon
black (Pt/CB) ORR catalysts in direct methanol fuel cells.
Boron nitride nanospheres
(BNNSs) were functionalized with polyelectrolytes.
The effect of the polyelectrolyte dose and ionic strength on the charging
and aggregation properties was investigated. At appropriate polyelectrolyte
doses, charge neutralization occurred, whereas by increasing the dose,
charge reversal was observed. The complete coating of the particles
was indicated by a plateau in the ζ-potential values, which
do not change significantly beyond the dose corresponding to the onset
of such a plateau. The dispersions were highly aggregated around the
charge neutralization point, while at lower or higher doses, the particles
were stable. The salt-induced aggregation experiments revealed that
the polyelectrolyte coatings contribute to the colloidal stability
of the particles, namely, the critical coagulation concentrations
deviated from the one determined for bare BNNSs. The presence of electrostatic
and steric interparticle forces induced by the adsorbed polyelectrolyte
chains was assumed. The obtained results confirm that the comprehensive
investigation of the colloidal stability of BNNS particles is crucial
to design stable or unstable dispersions and that polyelectrolytes
are suitable agents for both stabilization and destabilization of
BNNS dispersions, depending on the purpose of their application.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.