The development of a low-cost, high-performance platinum-group-metal-free hydroxide exchange membrane fuel cell is hindered by the lack of a hydrogen oxidation reaction catalyst at the anode. Here we report that a composite catalyst, nickel nanoparticles supported on nitrogen-doped carbon nanotubes, has hydrogen oxidation activity similar to platinum-group metals in alkaline electrolyte. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, it increases the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles. Density functional theory calculations indicate that the nitrogen-doped support stabilizes the nanoparticle against reconstruction, while nitrogen located at the edge of the nanoparticle tunes local adsorption sites by affecting the d-orbitals of nickel. Owing to its high activity and low cost, our catalyst shows significant potential for use in low-cost, high-performance fuel cells.

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Adsorption isotherms are a critical tool in determining the transport of environmental contaminants through a particular media. Owing to the inherent heterogeneity of soils, the determination of which soil components are responsible for the adsorption and retention of a particular contaminant remains a challenge. In the current study, we consider several thermodynamic adsorption states in order to predict whether or not 2,4,6-trinitrotoluene (TNT) or 2,4-dinitroanisole (DNAN) would be either a ground-water contaminant or a soil contaminant. In order to reduce the complexity, we only consider two metal oxides (hematite and corundum) that are commonly found in arid regions. We have shown that TNT and DNAN bind favorably across all concentrations, temperatures, and surface hydration considered for α-Al 2 O 3 ; however, only TNT was found to be bound for α-Fe 2 O 3 . Our results indicate that for soils rich in iron oxides, DNAN would be a ground-water contaminant.

Increasing the activity of non-noble catalysts for hydrogen oxidation is crucial in enhancing the efficiency of hydroxide exchange membrane fuel cells. Herein, we study the impact of graphene and nitrogen-and boron-doped graphene supports on the hydrogen oxidation reaction occurring on Ni, Cu, and Ag nanoparticles using first-principles calculations and published experimental data. We find that doping of graphene leads to a stronger interaction between the nanoparticle and the support, consequently weakening hydrogen adsorption. This leads to increased activity of supported Ni nanoparticles, but decreased activity of supported Cu and Ag nanoparticles. The dopant-induced changes in the hydrogen adsorption energies are quantitatively as important as the adsorption site. To describe adsorption energies for each supported nanoparticle, principal component analysis is introduced to systematically identify molecular descriptors of adsorption energy. Finally, a size-dependent activity model is formulated to close the size gap between first-principles calculations and experiments.