海底pH的原位探测：镀Nafion膜的Ir/IrO2电极

洋中脊热液流体及大陆斜坡气体水合物区的冷泉中溶解有硫离子.Ir/IrO2电极对硫离子非常敏感.虽然它和Ag/AgCl参比电极配对在pH 0～14中具有优良性能,但在含有2×10-4mol/L Na2S的缓冲溶液(pH=12.6)中无法得到稳定电位.测试初期是高强度假信号,然后是上下波动的信号曲线.为克服硫离子的干扰,在Ir/IrO2电极表面镀上了Nafion膜.Nafion是杜邦公司生产的一种聚合物选择性半透膜.相对于为未镀Nafion膜的Ir/IrO2电极而言,镀膜电极不仅对不同pH值溶液响应良好,而且在含有2×10-4mol/L Na2S的缓冲溶液中信号稳定,表明了硫离子的干扰被有效屏蔽.固态镀膜Ir/IrO2和Ag/AgCl电极对适用于对海底热液和冷泉的pH测定与长期观测.

A resolution for in situ pH sensing on seafloor: Ir/IrO2 electrode with Nafion shielding membrane

Ir/IrO2 electrode is vulnerable to dissolved sulphur anion, which is commonly found in hydrothermal fluid at middle ocean ridge (MOR) and cold seep in gas hydrate area on continental slope. Naked Ir/IrO2 electrode with Ag/AgCl as reference responds linearly with pH standard series, almost the same as predicted by Nernst Equation. The same pairs in a buffered solution (pH=12.6) with 2?10-4 mol/L Na2S failed yield stable signal. Instead there was strong false signal at the beginning and followed by a bumping curve in the rest time of scanning. To overcome the disturb from sulphur anion, the Ir/IrO2 electrode was coated with Nafion, a kind of proton selective substance produced by DuPont. Nafion coated Ir/IrO2 electrode performed well in pH standard series, comparable with the uncoated counterpart. In the buffered solution with 2?10-4 mol/L Na2S, the responding signal is stable. This confirms that the interference from sulphur anion is shield out. Solid state sensing pairs of Ir/IrO2 and Ag/AgCl are suitable for pH measurement and long term monitoring on seafloor, for both hot and cold venting systems.