Nanostructured carbon materials doped with a variety of heteroatoms have shown promising electrocatalytic activity in the oxygen reduction reaction (ORR). However, understanding of the working principles that underpin the superior ORR activity observed with doped nanocarbons is still limited to predictions based on theoretical calculations. Herein, we demonstrate, for the first time, that the enhanced ORR activity in doped nanocarbons can be correlated with the variation in their nanoscale work function. A series of doped ordered mesoporous carbons (OMCs) were prepared using N, S, and O as dopants; the triple-doped, N,S,O-OMC displayed superior ORR activity and four-electron selectivity compared to the dual-doped (N,O-OMC and S,O-OMC) and the monodoped (O-OMC) OMCs. Significantly, the work functions of these heteroatom-doped OMCs, measured by Kelvin probe force microscopy, display a strong correlation with the activity and reaction kinetics for the ORR. This unprecedented experimental insight can be used to provide an explanation for the enhanced ORR activity of heteroatom-doped carbon materials.

The role of charge transfer at the metal−oxide interface is a long-standing issue in surface chemistry and heterogeneous catalysis. Previous studies have shown that the flow of hot electrons crossing metal−oxide interfaces correlates with catalytic activity. In this study, we employed ceria-supported gold nanoparticles to identify a correlation between the catalytic activity of CO oxidation and hot electrons generated via light irradiation. We tuned the size of the Au nanoparticles by changing the discharge voltages used in the arc plasma deposition process, thus allowing us to investigate the influence of Au nanoparticle size on changes in catalytic activity. CO oxidation over the Au/CeO X catalysts was carried out, and we found that the activity of the Au nanoparticles increased as the size of the nanoparticles decreased, which is associated with the cationic character of the Au nanoparticles, as demonstrated by X-ray photoelectron spectroscopy analysis. We also show that the activity of the Au nanoparticles decreases under light irradiation and that smaller nanoparticles show a higher change of turnover frequency compared with larger ones, presumably due to the mean free path of the hot electrons. From these results, we conclude that the cationic property of the gold species, induced by interaction with the CeO 2 support, and the flow of hot electrons generated on the interface during light irradiation are mainly responsible for the change in catalytic activity on the Au nanoparticles.

We investigated the subdomain structures of single-layer graphene oxide (GO) by characterizing local friction and conductance using conductive atomic force microscopy. Friction and conductance mapping showed that a single-layer GO flake has subdomains several tens to a few hundreds of nanometers in lateral size. The GO subdomains exhibited low friction (high conductance) in the sp(2)-rich phase and high friction (low conductance) in the sp(3)-rich phase. Current-voltage spectroscopy revealed that the local current flow in single-layer GO depends on the quantity of hydroxyl and carboxyl groups, and epoxy bridges within the 2-dimensional carbon layer. The presence of subdomains with different sp(2)/sp(3) carbon ratios on a GO flake was also confirmed by chemical mapping using scanning transmission X-ray microscopy. These results suggest that spatial mapping of the friction and conductance can be used to rapidly identify the composition of heterogeneous single-layer GO at nanometer scale, which is essential for understanding charge transport in nanoelectronic devices.