We describe a route to the development of novel PtNiN core-shell catalysts with low Pt content shell and inexpensive NiN core having high activity and stability for the oxygen reduction reaction (ORR). The PtNiN synthesis involves nitriding Ni nanoparticles and simultaneously encapsulating it by 2-4 monolayer-thick Pt shell. The experimental data and the density functional theory calculations indicate nitride has the bifunctional effect that facilitates formation of the core-shell structures and improves the performance of the Pt shell by inducing both geometric and electronic effects. Synthesis of inexpensive NiN cores opens up possibilities for designing of various transition metal nitride based core-shell nanoparticles for a wide range of applications in energy conversion processes.
We synthesized a low-Pt content electrocatalyst consisting of a Pt monolayer placed on carbonsupported thermally treated IrNi core-shell structured nanoparticles using galvanic displacement of a Cu monolayer deposited at underpotentials. The Pt mass activity of the Pt ML /IrNi/C electrocatalyst obtained in a scale-up synthesis is approximately 3 times higher than that of the commercial Pt/C electrocatalyst. The electronic and geometrical effects of the IrNi substrate on the Pt monolayer result in its higher catalytic activity than that of Pt nanoparticles. The structure and composition of the coreshell nanoparticles were verified using transmission electron microscopy and in situ X-ray absorption spectroscopy, while a potential cycling test was employed to confirm the stability of the electrocatalyst. Our experimental results, supported by the density functional calculations using a sphere-like model, demonstrate an effective way of using Pt that can resolve key problems of cathodic oxygen reduction hampering fuel cell commercialization.
Considerable efforts to make palladium and palladium alloys active catalysts and a possible replacement for platinum have had a marginal success. Here we report on a structurally ordered Au 10 Pd 40 Co 50 catalyst that exhibits comparable activity to conventional platinum catalysts in both acid and alkaline media. Electron microscopic techniques demonstrate that, at elevated temperatures, palladium cobalt nanoparticles undergo an atomic structural transition from core-shell to a rare intermetallic ordered structure with twin boundaries forming stable {111}, {110} and {100} facets via addition of gold atoms. The superior stability of this catalyst compared with platinum after 10,000 potential cycles in alkaline media is attributed to the atomic structural order of PdCo nanoparticles along with protective effect of clusters of gold atoms on the surface. This strategy of making ordered palladium intermetallic alloy nanoparticles can be used in diverse heterogeneous catalysis where particle size and structural stability matter.
Given the harsh operating conditions in hydrogen/oxygen fuel cells, the stability of catalysts is one of the critical questions affecting their commercialization. We describe a distinct class of oxygen reduction (ORR) core-shell electrocatalysts comprised of nitride metal cores enclosed by thin Pt shells that is easily synthesized. The synthesis is reproducible and amenable to scale up. Our theoretical analysis and the experimental data indicate that metal nitride nanoparticle cores could significantly enhance the ORR activity as well as the durability of the core-shell catalysts as a consequence of combined geometrical, electronic and segregation effects on the Pt shells. In addition to its fuel cells application, this class of catalysts holds promise to significantly contribute in resolving the problem of platinum scarcity and furthermore indicates the guidelines for future research and development.
The oxygen evolution
reaction (OER) has broad applications in electrochemical
devices, but it often requires expensive and scarce Ir-based catalysts
in acid electrolyte. Presented here is a framework to reduce Ir loading
by combining core–shell iridium/metal nitride morphologies
using in situ experiments and density functional theory (DFT) calculations.
Several group VIII transition metal (Fe, Co, and Ni) nitrides are
studied as core materials, with Ir/Fe4N core–shell
particles showing enhancement in both OER activity and stability.
In situ X-ray absorption fine structure measurements are used to determine
the structure and stability of the core–shell catalysts under
OER conditions. DFT calculations are used to demonstrate adsorbate
binding energies as descriptors of the observed activity trends.
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.