Experiments were conducted at room temperature in
the three-electrode radio-electrochemical cell depicted
in Fig. 1. The cell design enables electrolyte exchange
under electrode potential control. An Ag AgCl 3 M
NaCl electrode was used as a reference (E=0.206 V vs.
standard hydrogen electrode), but all potentials are
given with respect to the standard hydrogen electrode
(SHE). Platinum wire was used as a counter electrode.
The bottom of the cell was a radiation detector: a glass
scintillation disk, which was covered with a 7.5 m
thick polyimide film onto which a ca. 500 A layer of
gold was vacuum deposited. The working electrode was
prepared by a uniform distribution of Pt or Pt/Ru
black (50:50 at.%) nanoparticle catalysts (Johnson
Matthey) on top of the gold conducting support. The
specific surface areas were 20 m2 g−1, and 65 m2 g−1
for the Pt and Pt/Ru catalysts, respectively, and the
average particle size was 8 nm and 3 nm (diameters),
respectively. A typical catalyst loading was 0.8 mg
cm−2 (0.08 mg cm−2 in some experiments) and the
load was controlled easily. The method of immobilization
of water dispersed nanoparticles on conducting
substrates will be reported elsewhere [34]; needless to
say the catalyst layers were stable to electrochemical
and radiochemical characterizations. For the Pt catalysts,
the roughness factor (the ratio of the real to
geometric electrode surface area) was obtained from the
hydrogen deposition/stripping charge, and was in the
range from 10 to 180. For the Pt/Ru catalyst the
roughness factor was determined from the mass of the
catalyst used and the specific surface area given by the
manufacturer (65 m2 g−1). The supporting electrolyte
was 0.1 M H2SO4, and all measurements were conducted
at room temperature. Solutions were deoxygenated
using ultrapure argon. The specific activity of
14C-methanol (ICN) was in the range from 0.4 to 4 mCi
mmol−1. The methanol concentration varied from
10−3 to 10−1 M.