Structural and electronic engineering towards high-efficiency metal-free electrocatalysts for boosting oxygen evolution

Due to low price, easy availability, and high durability, metal-free materials have been considered as one of the most promising substitutes of noble metal-based electrocatalysts for oxygen evolution reaction (OER). However, it is a great challenge and still unfulfilled for carbon-based metal-free catalysts to attain outstanding OER catalytic activities which rival those of their metal counterparts. Herein, we report N, O incorporated carbon sponge (2NOC) as an OER catalyst with excellent catalytic activity and stability. Remarkably, the hierarchical metal-free 2NOC carbon catalyst demonstrates an ultralow overpotential of 186 mV at 10 mA cm−2 (274 mV at 50 mA cm−2), Tafel slope as small as 71 mV dec-1, and current density retention of 96 % at 20 mA cm−2 after 50 h, which is beyond the state-of-the-art metal-free carbon materials and the commercial RuO2. The superior OER performance can be attributed to the all-in-one strategy of structural and electronic engineering. Through a facile and economical carbonization of melamine–formaldehyde sponge wastes after undergoing a controllable pre oxidation process, the constructed 2NOC catalyst possesses optimized N, O incorporation, multiscale pores, and interconnected through-hole inside carbon skeleton, which results in fully exposed active sites. Density functional theory calculations reveal that rational incorporation of N and O can optimize the adsorption of oxygen intermediates and greatly reduce the energy barrier of the rate-determining step (from 2.78 eV to 1.78 eV). Significantly, 2NOC||Pt/C electrolyzer achieves stable overall water-splitting at an applied voltage of only 1.47 V to drive 10 mA cm−2. This work proposes a promisingly sustainable strategy toward low-cost, eco-friendly and practicable electrocatalysts.