Gold as a Hydrogen Sensing Electrode for in Situ Measurement of Dissolved H₂ in Supercritical Aqueous Fluid

Potentiometric studies of the Au-YSZ(Hg/HgO) ( YSZ = yttrium stabilized zirconia) cell were conducted to investigate the suitability of gold as a sensing element for in situ determination of dissolved H₂ in aqueous fluids at 375-400°C and 400 bars. Experimental results indicate that the gold electrode responds rapidly and reversibly to variations in dissolved H₂, even at H₂ < 0.1 mmol-kg^-1. Nernstian response of the cell to dissolved H₂ was demonstrated at 400°C and 400 bars ΔE = 0.9815 + 0.0668 log m_H2 In fact, the performance of the gold electrode compares well to that of platinum. Considering the well known difficulties of using platinoid metals in H₂S-bearing fluids, however, the gold electrode holds great promise for in situ measurement of dissolved H₂ in chemically complex natural hydrothermal fluids. The results also suggest that the Au-YSZ(Hg/HgO) cell can be used to determine the solubility behavior of H₂ in aqueous fluid at temperatures and pressures in the vicinity of the critical point of water. At present, such data are lacking, which severely constrains knowledge of the effect of temperature and pressure on the Henry's law constant of H₂ in water.