Understanding the Origin of Improved Hydrogen Oxidation Activity of Supported Ni Nanoparticles
Stephen A. Giles, Zhongbin Zhuang, Glen R. Jenness, Stavros Caratzoulas, Dionisios G. Vlachos, Yushan Yan
Department of Chemical and Biomolecular Engineering, Catalysis Center for Energy Innovation, University of Delaware, Newark, DE 19716.
Fuel cells are an important power source for zero emission vehicles. Among low-temperature fuel cells, hydroxide exchange membrane fuel cells enable the use of non-precious metal catalysts, such as nickel, and have received increased attention from the scientific community as a result. Ni nanoparticles supported on carbon nanotubes (CNT) are shown experimentally to exhibit an order of magnitude higher exchange current density for the hydrogen oxidation reaction (HOR) than what is observed using an amorphous carbon support. Furthermore, an additional increase is observed when the carbon nanotube is doped with nitrogen (N-CNT). Similar beneficial effects have been reported for other metals and metal oxide nanoparticles supported on N-CNT and N-graphene [1,2]. However, the origin of this effect is unknown.
In the current study, we employ density functional theory (DFT) along with a data-driven model to investigate both the origin of this support effect and its impact on the electrocatalytic properties of the catalyst. The activity of the nanoparticle was studied with respect to nitrogen dopant concentration and location within the support. The primary classes of support effects were elucidated: superior immobilization and stability of the nanoparticle and local shifts in key electronic properties (e.g., d-band center) of Ni adsorption sites caused by the presence of nitrogen in the support. We conclude that preferential nitrogen dopant location induces favorable metal-support interaction for the promotion of the HOR.
 Gong, M. et al. Nat. Comm. 2014, 5, 4695.
 Ayala, P. et al. Chem. Phys. Letts. 2006, 5, 104.