Creating Conjugated C-C Bonds between Commercial Carbon Electrode and Molecular Catalyst for Oxygen Reduction to Hydrogen Peroxide.

Immobilizing molecular catalysts on electrodes is vital for electrochemical applications. However, creating robust electrode-catalyst interactions while maintaining good catalytic performance and rapid electron transfer is challenging. Here, without introducing any foreign elements, we show a bottom-up synthetic approach of constructing the conjugated C-C bond between the commercial Vulcan carbon electrode and an organometallic catalyst. Characterization results from FTIR, XPS, aberration-corrected TEM and EPR confirmed the successful and uniform heterogenization of the complex. The synthesized Vulcan-LN4 -Co catalyst is highly active and selective in the oxygen reduction reaction in neutral media, showing an 80 % hydrogen peroxide selectivity and a 0.72 V (vs. RHE) onset potential which significantly outperformed the homogenous counterpart. Based on single-crystal XRD and NMR data, we built a model for density functional theory calculations which showed a nearly optimal binding energy for the *OOH intermediate. Our results show that the direct conjugated C-C bonding is an effective approach for heterogenizing molecular catalysts on carbon, opening new opportunities for employing molecular catalysts in electrochemical applications.

Dry reforming of methane over single-atom Rh/Al2O3 catalysts prepared by exsolution.

Single-atom catalysts often show exceptionally high performance per metal loading. However, the isolated atom sites tend to agglomerate during preparation and/or high-temperature reaction. Here we show that in the case of Rh/Al2O3 this deactivation can be prevented by dissolution/exsolution of metal atoms into/from the support. We design and synthesise a series of single-atom catalysts, characterise them and study the impact of exsolution in the dry reforming of methane at 700-900 °C. The catalysts' performance increases with increasing reaction time, as the rhodium atoms migrate from the subsurface to the surface. Although the oxidation state of rhodium changes from Rh(iii) to Rh(ii) or Rh(0) during catalysis, atom migration is the main factor affecting catalyst performance. The implications of these results for preparing real-life catalysts are discussed.