Gold as a hydrogen sensing electrode for in situ measurement of dissolved H-2 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 H-2 in aqueous fluids at 375-400 degrees C and 400 bars. Experimental results indicate that the gold electrode responds rapidly and reversibly to variations in dissolved H-2, even at H-2 < 0.1 mmol-kg(-1). Nernstian response of the cell to dissolved H-2 was demonstrated at 400 degrees C and 400 bars Delta E = 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 H-2 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 H-2 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 H-2 in water.