Nanoparticle Catalysts Supported on Substitutionally Doped Graphene: Effects on Activity and Stability for Hydrogen Oxidation

Fuel cells represent an important part of a renewable future hydrogen-based energy grid. In particular, hydroxide exchange membrane fuel cells (HEMFCs) offer the advantage of non-noble metals being more stable against dissolution than in the acidic environment. However, the rate of the hydrogen oxidation reaction (HOR) decreases by approximately two orders-of-magnitude when switching from acid to base. As a result, developing more efficient and cheaper HOR catalysts is imperative to advancing the current state-of-the-art fuel cells. In a recent publication, we have demonstrated that Ni nanoparticles supported on nitrogen-doped carbon nanotubes (N-CNT) exhibit a threefold increase in the exchange current density relative to a pristine CNT support, and a factor of 30 increase relative to an amorphous carbon support (Zhuang, Z., et al., Nature Communications 2016, 7, 10141). However, a fundamental study on the synergistic interaction between the supported nanoparticle and doped CNT has yet to be done.

Herein, using graphene as a two-dimensional analog for the CNT support used experimentally, we study from first-principles the impact of graphene and doped graphene supports on the hydrogen oxidation reaction occurring on nanometer-sized catalysts. We consider nickel, copper, and silver nanoparticle compositions, and nitrogen-doped, boron-doped, and phosphorous-doped graphene supports. To understand quantitatively the effect of substitutional doping on the nanoparticle/support interaction, we study: 1) the charge transfer between the nanoparticle and support as a function of dopant and dopant location, 2) the modulation of the nanoparticle's d band center due to the presence of a dopant, 3) the interaction of metal adatoms with graphene and doped-graphene, 4) the hydrogen oxidation activity of the nanoparticle/support systems, and 5) the oxidative stability of the supported copper and nickel nanoparticles.