In this study, an unprecedented electrochemically formed proton relay of a paddlewheel Rh2(II,II) hydrogen evolution electrocatalyst, cis-[Rh2(DPhF)2(bncn)2]2+ (Rh2-bncn2, DPhF = diphenylformamidinate, bncn = benzo[c]cinnoline), was investigated. The origin of a reversible prewave at ~ -0.72 V vs Fc/Fc+ in the cyclic voltammograms (CVs) of Rh2-bncn2 in DMF (0.1 M TBAPF6) with the presence of organic acid (TsOH or TFA) was found to be a pre-catalysis transformation. Further analysis revealed that the prewave is originated from a concerted proton-electron transfer (CPET) occurred on the nitrogen atom of the bncn ligand attached to the Rh2(II,II) core. The resulting attached proton on coordinated bncn ligand offers an opportunity to form H-H bond with Rh-H hydride. Through CV simulation and DFT calculation, we proposed a reaction mechanism that the electrochemically formed N-H bond on bncn ligand can serve as a proton relay in hydrogen formation reaction via intra-molecular proton-hydride transfer at around -1.15 V vs Fc/Fc+. In summary, we discovered a new design strategy to incorporate proton relay in molecular hydrogen evolution electrocatalysts for achieving higher efficiency.

New electrochemical strategy of introducing proton relay to a paddlewheel Rh2(II,II) hydrogen evolution electrocatalyst

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.