Martin Willett

Lead-free galvanic oxygen sensors — A conceptual approach

Within this paper we present a thermodynamic methodology for the selection of non-toxic metals which could be used as lead-free consumable anodes in electrochemical galvanic oxygen sensors. Starting from thermodynamic nobility theory, metals like copper, bismuth or antimony are proposed to replace lead in future galvanic O2 sensors. The thermodynamic theory provides voltage windows which increase from copper (0.7 V), to bismuth (0.857 V) and antimony (1.076 V). The experimental voltage windows are smaller than the theoretical ones, but these experimental values increase in the same order from Cu, to Bi and Sb, as predicted by our methodology.

Experimental evidence of long life lead-free oxygen galvanic sensors

In this work we present an experimental study of the lifetime of O2 galvanic sensors in KOH aqueous solution, considering bismuth, copper and antimony as the candidates for lead anode replacement in present devices. An initial accelerated ageing test in 100% O2 suggested antimony for the next stage. Further experiments have shown an accelerated ageing factor of 18, which allowed the estimation of a lifetime of more than five years for an O2 galvanic sensor based on Sb anode of large surface area. A scaling law in lifetime as a function surface area (or anode current density) was found, which agreed with electrochemical passivation studies of Sb in alkaline solutions.