HYDROGEN EVOLUTION REACTION OF PALLADIUM SUPPORTED ON SULFUR DOPED ORDERED MESOPOROUS CARBON

Abstract

Minimizing the metal particle size for higher accessibility, exploiting nitrogen and sulfur in support as anchors which hold a metal atom has been studied. In this respect, palladium supported on sulfur-doped ordered mesoporous carbon(SOMC) was proposed. 4,4′-thiosbisbenzenethiol and p-toluenesulfonic acid(p-TSA) were mixed thoroughly with SBA-15, followed by melt infiltration, pyrolysis, and HF treatment to remove the silica template. Palladium was supported on SOMC by incipient wetness impregnation and polyol method. To investigate the physical properties of prepared catalysts, X-ray diffraction(XRD), elemental analysis(EA), High-angle annular dark-field imaging scanning transmission electron microscopy(HAADF-STEM) and N2 adsorption/desorption technique were used. By Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) method, specific surface area and pore volume were measured as ≥1000 m2/g and ≥0.95 cm3/g, respectively. Palladium existed as single ions, sub-nanoparticles and nanoparticles below 2.5 nm. From EA, sulfur content was confirmed about 12 wt.%. For electrochemical characterization, a rotating disk electrode(RDE) was used for hydrogen evolution reaction(HER) in a nitrogen purged 0.1 M perchloric acid. Comparing 0.5 wt.% palladium supported on OMC with catalysts using SOMC, Pd/SOMC showed poorer kinetics for HER. The current densities at -0.15 V were -5.84 mA/cm2 for Pd/OMC and -1.19 mA/cm2 for Pd/SOMC, 4.92 times higher for the former one. Overpotential at -10 mA/cm2 of Pd/OMC was 185 mV and that of Pd/SOMC was 277 mV. This is because palladium-sulfur bonds limit metal particle size growth, which leads to enhancement of reactants accessibility, however, their effect on the surface structure and electronic states might not be adequate for HER activity.