Highly Dispersive Gold Nanoparticles on Carbon Black for Oxygen and Carbon Dioxide Reduction

Abstract

AbstractHighly dispersive Au nanoparticles on carbon black (Au NPs/CB) were synthesized in situ with co‐present two different reducing agents of NaBH4 at various concentrations and citrate at a constant concentration of 3 mM. The average diameters of Au NPs on carbon support were in the range from 5.8 (±2.4) to 2.0 (±0.4) nm, with 50 particles quantified. Electrocatalytic activities of as‐prepared Au NPs/CB were explored for oxygen reduction reaction (ORR) in basic solution with rotating disk electrode (RDE) and rotating ring‐disk electrode (RRDE) voltammetry. In results, the Au NPs/CB synthesized with 0.2 mM NaBH4 (2.0 nm of Au NPs diameter) represented the highest ORR catalytic activity with electron transfer number of 3.9 and mass activity of 0.25 mA cm−2 μg−1as well as a perfect resistance to methanol contamination. Especially, the half‐wave potential of ORR curve which related to the kinetics of oxygen reduction was more positive compared with previously reported Au‐based ORR catalysts. In addition, the Au NPs/CB prepared with 0.2 mM NaBH4 was also examined as a CO2 reduction catalyst in KHCO3 with KCl solution with scanning electrochemical microscopy (SECM). CO2 was reduced to CO selectively without hydrogen evolution at Au NPs/CB substrate electrode, which was directly monitored with an electrochemical CO microsensor as a tip electrode in SECM. In addition, we have identified the products of CO2 reduction through gas chromatography (GC)‐mass spectrometry (MS), flame ionization detector (FID), and thermal conductivity detector (TCD).