Hydrogen evolution via hydride transfer by a small organic benzothiadiazole-caffeine electrocatalyst

Access to multiple redox states in electrocatalysts is vital to enhance the activity and stability of molecular catalysts toward the production of fuels. In this work, we have developed a catalyst based on two caffeine units covalently linked to a benzothiadiazole core. This catalyst can store three electrons in a fully reversible manner. Under reductive conditions and in the presence of strong acids, this molecule forms an organic hydride donor that is electroactive toward H2 evolution at mild potentials in DMSO. Faradaic efficiency up to 92% and a turnover number up to 23 were achieved after 4 h of controlled potential electrolysis with no decomposition of the catalyst. A reaction mechanism involving a hydride transfer step is proposed based on the chemical species found under electrocatalytic conditions and density functional theory (DFT) calculations. The development of this small organic molecule is a step forward in the quest to low-cost, active, and long-term stable electrocatalysts for H2 evolution.