Effect of surface oxygen groups and water on hydrogen spillover in pt-doped activated carbon

The synergistic role of increased oxygen functional groups and water on hydrogen adsorption via hydrogen spillover is explored. A potassium hydroxide (KOH) treatment is used to increase the surface density of oxygen groups on a high surface area-activated carbon (AC), which serves as a secondary receptor for hydrogen spillover after physical mixing with a common Pt-based spillover catalyst. Consistent with previous results, XPS shows that KOH treatment increases atomic concentration of oxygen and the fraction of carbonyl/quinone groups on the surface of the AC. Increased surface density of oxygen groups leads to a significant enhancement of hydrogen spillover at pressures <100 mbar. At 300 K, the hydrogen uptake is 1.1 wt % at 100 mbar and increases to 1.4 wt % at 20 bar. However, only 0.4 wt % of this is desorbable via a pressure reduction at room temperature, and appreciable spillover is observed only when trace water is present during pretreatment. The trace water is believed to affect the development of active surface sites based on characterization of the development of oxygen groups by XPS and FTIR. The synergistic role of oxygen groups and water and a plausible mechanism on the effect on hydrogen isotherms are discussed.