A flow-through electrochemical cell for subcritical and supercritical water
systems was developed based on the cell of Lvov [J. Electroanal. Chem. 463
, 146 (1999)]. The cell consisted of two flow-through platinum hydrogen ele
ctrodes and was constructed from a high nickel alloy (Hastelloy-B2). The in
ner surface of electrochemical cell was coated with Al2O3 adhesive and cove
red with the Al2O3 tube for corrosion resistance. Orifices were placed near
the center of the cell to reduce concentration fluctuations around the tes
t electrode. With the cell, a flow apparatus was used to measure the potent
ials for HCl+NaCl aqueous solutions at supercritical conditions. The cell p
otentials were measured at temperatures ranging from 23.9 to 400.2 degreesC
and at pressures ranging from 25.0 to 35.1 MPa and the standard deviations
of measured potentials were less than 0.4 mV for all tests. Comparison of
the experimentally determined and theoretically calculated pH differences a
re better than +/-0.03 logarithmic units over the range of conditions studi
ed. (C) 2001 American Institute of Physics.