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

The synthesis of fuels using small organic electrocatalysts has gained significant attention in recent years. Understanding the mechanisms governing the reactivity of these molecules is important in order to design better catalysts. In this work, we have developed a catalyst based on two caffeine units cova-lently linked to a benzothiadiazole core. This catalyst is able to electrochemically store up to three elec-trons in a fully reversible manner. Under reductive conditions and in the presence of strong acids such as trifluoroacetic acid and phytic acid, this molecule can form an organic hydride donor that is electroac-tive towards H2 evolution at a mild potential (Ecat/2 = 1.45 V vs Fc+/Fc) in DMSO. Faradaic efficiency up to 92 ± 5 % and turnover number up to 23 ± 4 were achieved after 4-hour controlled potential elec-trolysis with no apparent decomposition of the electrocatalyst. A reaction mechanism involving a hy-dride transfer step is proposed based on the chemical species found under electrocatalytic conditions and DFT calculations. The development of this small organic molecule is a step forward in the quest to find low-cost, active and long-term stable electrocatalysts for H2 evolution.