Kotaro Sasaki

We demonstrated that platinum (Pt) oxygen-reduction fuel-cell electrocatalysts can be stabilized against dissolution under potential cycling regimes (a continuing problem in vehicle applications) by modifying Pt nanoparticles with gold (Au) clusters. This behavior was observed under the oxidizing conditions of the O2 reduction reaction and potential cycling between 0.6 and 1.1 volts in over 30,000 cycles. There were insignificant changes in the activity and surface area of Au-modified Pt over the course of cycling, in contrast to sizable losses observed with the pure Pt catalyst under the same conditions. In situ x-ray absorption near-edge spectroscopy and voltammetry data suggest that the Au clusters confer stability by raising the Pt oxidation potential.

Not noble but effective: A new class of heterogeneous hydrogen-evolving electrocatalysts based on inexpensive components was developed. The carbon-supported nickel–molybdenum nitride (NiMoNx, see picture) catalyst had a nanoscale sheet structure comprising a few layers and an abundance of highly accessible reactive sites.

In an attempt to tailor low-cost, precious-metal-free electrocatalysts for water electrolysis in acid, molybdenum carbide (β-Mo2C) nanoparticles are prepared by in situ carburization of ammonium molybdate on carbon nanotubes and XC-72R carbon black without using any gaseous carbon source. The formation of Mo2C is investigated by thermogravimetry and in situ X-ray diffraction. X-ray absorption analysis reveals that Mo2C nanoparticles are inlaid or anchored into the carbon supports, and the electronic modification makes the surface exhibit a relatively moderate Mo–H bond strength. It is found that carbon nanotube-supported Mo2C showed superior electrocatalytic activity and stability in the hydrogen evolution reaction (HER) compared to the bulk Mo2C. An overpotential of 63 mV for driving 1 mA cm−2 of current density was measured for the nanotube-supported Mo2C catalysts; this exceeds the activity of analogous Mo2C catalysts. The enhanced electrochemical activity is facilitated by unique effects of the anchored structure coupled with the electronic modification.