posted on 2024-01-26, 19:49authored byEmily
E. A. Robinson, Blair K. Troudt, Philippe Bühlmann
AgCl-coated silver fabricated with the thermal-electrolytic
method
can be used to prepare more reproducible reference electrodes than
Ag/AgCl prepared with alternative methods such as electrolytic and
chemical AgCl deposition or thermal fabrication. However, thermal-electrolytic
fabrication requires a scaffold material upon which to build the layers
upon. Platinum and rhodium have been used for this purpose as they
are mechanically strong and chemically inert, but their cost is prohibitive
for wider application. Herein, we report the stability of Ag/AgCl
reference electrodes built atop a titanium scaffold using the thermal-electrolytic
method and the use of these Ti/Ag/AgCl constructs in capillary-based
reference electrodes. Electrochemical characterization shows that
the probable presence of small amounts of oxygen at the Ti/Ag interface
does not affect the reference electrode performance; in particular,
over a wide pH range, the half-cell potential is pH independent. The
electrical resistance of the Ti/Ag/AgCl/KCl system is dominated by
the charge transfer resistance at the interface of the AgCl to KCl
solution but is kept very small by the large AgCl surface area and
a high solution concentration of chloride. The resulting high exchange
current minimizes the effect of system impurities on the reference
half-cell potential. Capillary-based reference electrodes comprising
Ti/Ag/AgCl show exceptionally low potential drifts (as low as 0.03
± 2.01 μV/h) and standard deviations of the potential at
or below ±0.5 mV over a 60 h period. These capillary-based reference
electrodes are suitable for very small sample volumes while still
providing a free-flowing liquid junction that prevents reference electrode
contamination.