Probing Under-Utilized Melem as Host Scaffold with Strategic Modulation of Cobalt Oxidation State to Accelerate...

The potential of cobalt catalysts for sustainable, carbon-neutral hydrogen production through water splitting can be fully achieved by fundamental understanding-driven strategic tuning of metal oxidation states on a uniform scaffold. In pursuit of a stable scaffold that can enhance electrocatalytic activity through metal-N synergism and envisaging that g-C₃N₄ has inherited its properties from its structurally distinct predecessor, Melem; a comprehensive exploration of s-heptazine (Melem, M) is furnished as host for strategic tuning of cobalt electrocatalysts having variable oxidation states. Co(II)-doped heptazine (Co^II@M) catalyzed oxygen evolution reaction (OER) with an overpotential of 302 mV achieving 50 mA cm^-2 current density, with minimal charge-transfer resistance (0.41 Ω). Co(0)-doped heptazine nanotube (Co⁰@M) facilitated the arduous H-O-H bond cleavage for alkaline hydrogen evolution reaction (HER), achieving 50 mA cm^-2 current density at 206 mV overpotential, with low charge-transfer resistance of 0.66 Ω, attesting to the scaffold's assistance to electron transfer. The Co^II@M||Co⁰@M assembly shows low cell voltage (1.637 V @ 10 mA cm^-2) and promising stability (114 h) for total water splitting. s-heptazine scaffold ensured finer dispersion and stabilization of cobalt active sites in a corrosive environment. The scaffold's substantial stability, attributes to its nitrogen-rich core and extensive H-bonding, unlocks the potential of under-explored melem-based systems for electrocatalytic applications.