Prasanna R Said, Anupa A Kumbhar
Most electrocatalysts reported for the hydrogen evolution reaction (HER) are based on transition-metal composites, nanoparticles, metal-organic frameworks, alloys, sulfides, and metal-nitrogen-carbon frameworks. These materials often require harsh synthetic conditions and generally perform optimally in acidic or alkaline media. In contrast, organic electrocatalysts for HER are relatively rare and are predominantly reported to function under acidic conditions. Thiocarbohydrazones (TCHs) constitute an important class of compounds with applications in coordination and bioinorganic chemistry. The presence of proton-donating and proton-accepting sites, such as NH, SH, and C=N groups, enables them to act as proton relays. Consequently, TCH derivatives can be considered promising candidates for electrocatalytic hydrogen evolution. This work reports the three-step synthesis and characterization of a thiocarbohydrazone derivative, P3. The synthetic procedure is straightforward, affords high yields, and does not require expensive reagents, making it well-suited for educational demonstrations. All compounds were characterized by 1H-NMR, HRMS, UV-Visible, fluorescence, and FTIR spectroscopy. The HER activity of P3 was evaluated by immobilizing it on a 3 mm glassy carbon electrode (GCE) at a loading of 0.4 mgcm⁻2 using perfluorosulfonic acid ionomer binder. Electrochemical measurements were carried out in 100 mM phosphate buffer (pH 7.4) using an Ag/AgCl reference electrode. Linear sweep voltammetry of the P3-modified GCE displayed a pronounced cathodic response at -1.5 V, corresponding to hydrogen evolution, which was confirmed by gas chromatographic analysis. Chronoamperometric measurements performed for more than 2 h showed a stable current response, confirming the stability of P3 on the GCE surface. These results demonstrate the potential of organic thiocarbohydrazone derivatives as promising electrocatalysts for HER in a neutral aqueous medium.