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

The synthesis of fuels using small organic electrocatalysts has gained significant attention in recent years. Un-derstanding how small organic electrocatalysts function is vital to further improve the efficiency and stability towards fuels production. In this work, we have developed a catalyst based on two caffeine units covalently linked to a benzothiadiazole core. This catalyst is able to electrochemically store up to three electrons 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 electroactive 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 electrolysis with no apparent decomposition of the elec-trocatalyst. A reaction mechanism involving a hydride 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.