Computational Design of Ni-Zn Based Catalyst for Direct Hydrazine Fuel Cell Catalyst Using Density Functional Theory

Abstract

Direct Hydrazine Fuel Cell (DHFC) is a promising alternative for the hydrogen fuel cell because hydrazine (N2H4) is much easier to produce and store than hydrogen. Research into DHFC catalyst has shown that use of Ni-Zn compound as catalyst produces higher power density than using pure Ni as catalyst. This paper presents some findings of our investigation on Ni-Zn based catalyst for DHFC applications by using density functional theory (DFT). Multiple configurations of Ni-Zn DHFC catalysts were modeled using DFT. Hydrazine adsorption onto (111) catalyst surface was studied with adsorption energy and density of states (DOS) collected as data and used in analysis. The supercells consist of 4 layers of 4x4 atoms forming the (111) surface, with structure variation for the top 2 layers and the other 2 bottom layers comprised of Ni atoms to simulate the bulk of the electrodes. The adsorption sites used were the top sites, either Zn or Ni atoms. For every structure variation, adsorption on Ni atoms results in lower adsorption energies than on Zn atoms. Increasing concentration of Zn atoms on catalyst surface raises the adsorption energy of hydrazine on Zn atoms. Adsorption energies of hydrazine were higher on every configurations than on pure Ni (111) surface except for one catalyst surface in which Zn concentration was 25% and hydrazine was adsorbed atop a Ni atom. There was also rotation of hydrazine molecule from its usual anti adsorption conformation for that particular configuration.