Recycling spent water treatment adsorbents for efficient electrocatalytic water oxidation reaction

Abstract Heavy metal contaminated adsorbents are of great environmental concern due to their hazardous effects and large-scale accumulation in the natural environment. Converting massive adsorbents into efficient with a facile strategy can address the challenge of growing energy demand and achieving carbon neutral goal. Herein, we demonstrated a spent adsorbents to heterostructured electrocatalysts conversion strategy based on the waste-to-wealth principle. Via a facile boriding process, the metal ions laden biochar-based adsorbents (SA) have been totally transformed into magnetic metal borides/biochar heterostructures, which exhibit excellent activities towards oxygen evolution reaction. The optimized NiCuFeB/SA catalyst takes a low overpotential of 251 mV to drive a current density of 10 mA cm−2, outperforming many Ni/Fe-based catalysts synthesized from commercial material resources. Comprehensive analyses suggest the high catalytic efficiency mainly attributes to the porous biochar confined well-dispersed nano-sized metallic borides, the in-situ evolved active metal (oxy)hydroxides, favourable charge-transfer kinetics, as well as the heterostructure and amorphous feature. This work offers a general strategy to efficiently reutilize the metal-bearing biochar-based adsorbents, which can be extended to advanced energy applications-oriented reutilization of other metal-contaminated solid wastes in an economically and environmental-benign manner.