The Water Activity and Free Water Mole Fraction in Perchloric Acid

Abstract

The activity data a H 2 O ¼ p H 2 O . p 0 H2O were plotted against the mole fractions x H 2 O of free water for HClO 4 -H 2 O solutions. It was found that a H 2 O ¼ kÁx H 2 O where k = 1.00 ± 0.01.

Electrocatalyst Performance at the Gas/Electrolyte Interface under High-Mass-Transport Conditions: Optimization of the “Floating Electrode” Method

“…As for the water management (Figure g), the FE allows water generated at the catalyst surface to quickly condense into the bulk electrolyte due to the difference in water activity (see detailed calculation and discussion in the SI). At the flat bulk electrolyte (1 M HClO 4 )/gas interface, the water activity is 0.977 due to the presence of the solute ions, and hence p (H 2 O)/ p sat (H 2 O) is also lowered . At the convex curved surface of a primary catalyst particle (30 nm in diameter, covered with 10 nm ionomer), p (H 2 O)/ p sat (H 2 O) is increased due to the Kelvin effect whereupon higher vapor pressures are seen due to local curvature where p is the actual vapor pressure above the curved interface, p sat is the saturated vapor pressure when the interface is flat, γ is the liquid/vapor surface tension, V m is the molar volume of the liquid, R is the universal gas constant, r is the radius of the droplet, and T is temperature.…”

“…At the flat bulk electrolyte (1 M HClO 4 )/gas interface, the water activity is 0.977 due to the presence of the solute ions, and hence p(H 2 O)/p sat (H 2 O) is also lowered. 71 At the convex curved surface of a primary catalyst particle (30 nm in diameter, covered with 10 nm ionomer), p(H 2 O)/p sat (H 2 O) is increased due to the Kelvin effect whereupon higher vapor pressures are seen due to local curvature i k j j j j j j y…”

Correction to “Electrocatalyst Performance at the Gas/Electrolyte Interface under High Mass Transport Conditions: Optimization of the ‘Floating Electrode’ Method”

“…This means that the water vapour pressure is 4% higher than might be expected above a flat pure water gas-water interface. At the flat bulk electrolyte (1 M HClO4)/gas interface, the water activity is reduced to 0.977 due to the presence of the dissolved acid 8 and hence p(H2O)/p*(H2O) is reduced by the same amount. At 298 K, the saturated water vapor pressure is 3.17 kPa.…”