Two-dimensional triazine-based porous framework as a novel metal-free bifunctional electrocatalyst for zinc-air batty

A metal-free carbon catalyst, melem-cyanuric acid complex (MCAC), was prepared by hydrogen bonding assembly and further explored as a novel bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The proposed MCAC network presented nanosheet-like structure, nitrogen-rich, and large specific surface area, which are close to the natures of graphitic carbon nitride (g-C₃N₄) and N-doped reduced graphene oxide (N-rGO), but giving much more defect active sites and regular framework structure. Compared with the g-C₃N₄, N-rGO and other reported carbon-nitride electrocatalysts, the MCAC nanosheets exhibited a lower overpotential of 1.45 V at a current density of 10 mA cm^-2 for OER, along with a higher half-potential of 0.8 V and larger limit current density of -6.0 mA cm^-2 for ORR. Density functional theory calculation revealed that the melem N atoms bonded with cyanurate greatly enhanced the OER activity by increasing the interaction between catalysts and intermediates. Furthermore, as a metal-free electrocatalyst, MCAC displayed superior reversible oxygen electrocatalytic activity, giving a small overpotential difference (0.76 V). The rechargeable zinc-air battery with MCAC as the air electrode in a two-electrode configuration showed a high open-circuit potential of 1.383 V and a specific capacity of 613.5 mA h g_Zn^-1 at 10 mA cm^-2. This work opens up a new avenue to develop advanced porous solids as metal-free electrocatalysts for the energy storage and conversion applications.