Hydrogen Evolution Reaction Using a Sulfanilamide/Citric Acid Derived N, S-Doped Carbon Dot

Design of metal-free, carbon-based sustainable materials is a hot pursuit for energy conversion studies, particularly for clean hydrogen production. There are some discrete studies of carbon-based materials as cathodes to produce hydrogen through water electrolysis. However, the majority of reported graphene-based or 2-dimensional layered carbon materials often require high heterometal dopants to exhibit fair electrochemical activity. In this work, two carbon dots (CDs) are prepared from citric acid and sulfanilamide precursors by altering their ratio (CD1 and CD2), employed as carbon-based electrocatalysts for the hydrogen evolution reaction (HER) in alkaline medium after depositing them on nickel foam (NF), and used as electrodes that are termed CD1@NF and CD2@NF. These CDs solely demonstrate a better HER efficiency than other carbon-based and composite materials without incorporating CDs with different materials. CD2 delivers a geometric current density (jcathode) of −10 mA cm–2 at an overpotential of 216 mV under alkaline conditions, reasonably lower than the overpotential obtained for CD1 (238 mV) and some previously reported carbon materials. Furthermore, CD2 shows a long-term HER performance under chrono-conditions. The superior and intrinsic activity of CD2 can be correlated to the higher exchange current density (j0) and the electrochemical surface area (ECSA). The low Tafel slope value and charge-transfer resistance (Rct) indicate that the intrinsic HER activity of CD2 is better than that of CD1, due to a higher N/S ratio on the surface, which promotes fast proton adsorption and electrokinetics.