The
electrochemical gas sensors have been studied on
commercially-available integrated Pt thin-film electrodes (TFEs). Chemically
reversible (but electrochemically quasi-reversible) cyclic voltammetry was
observed in the room temperature ionic liquid (RTIL)
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]),
showing superior behaviour of TFEs compared to screen-printed electrodes for
oxygen sensing.
As a
step towards the preparation of robust gas sensors, the RTIL was mechanically
stabilised on the TFE surface by the addition of poly(methyl methacrylate)
(PMMA). At a PMMA concentration in the RTIL of ca. 50% mass, electrolyte
flow was not evident. O2 reduction peak currents were found to
decrease systematically with increasing PMMA content, reflecting the higher
viscosity of the electrolyte medium. Linear calibration graphs were obtained
for 0–100% vol. oxygen at all PMMA–RTIL mixtures studied.
The
sensitivities decreased as [PMMA] increased, but the limits of detection were
relatively unchanged. Mechanical stability of the sensors was tested in
different orientations (flat, upside down, sideways) with both the neat RTIL
and 50% mass electrolyte. Whilst the electrochemical responses were
dramatically changed for the neat RTIL, the responses in the PMMA–RTIL mixture
were independent of electrode orientation.
Additionally,
the oxygen response in the PMMA–RTIL mixture was less affected by atmospheric
impurities and moisture, compared to the neat RTIL. This suggests that these
low-cost miniaturised devices can successfully be used for oxygen sensing
applications in field situations, especially where portability is essential.
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