Hybrid NiMn-LDHs as Active Materials for Electro-Oxidation of Organic Pollutants

Electrochemical oxidation of phenol is a promising route for sustainable treatment of wastewater containing toxic aromatic pollutants, but its practical application is limited by sluggish kinetics and competing anodic side reactions. Here, we report NiMn-based layered double hydroxide electrocatalysts (NiMn-LDH) that enhance phenol degradation under mild electrochemical conditions. Mn incorporation into the LDH structure provides accessible higher oxidation states, improving redox flexibility, promoting hydroxyl radical (·OH) generation, and suppressing the competing oxygen evolution reaction. Three variants, NiMn-LDH-CNT, NiMn-LDH-CMC, and NiMn-LDH-Tris, were synthesized to assess the influence of conductive additives and synthesis media. The CNT-supported catalyst showed the highest activity, achieving >95% phenol removal within minutes at current densities up to 20 mA cm^-2, while maintaining a nearly constant cell voltage over approximately 200 h of operation. High removal efficiencies, ca. 90%, were retained even when the Na₂SO₄ concentration was decreased from 100 to 1 mM and under synthetic wastewater conditions, confirming system robustness. The optimized NiMn-LDH electrocatalyst was further integrated as the anode in a hybrid cell coupling phenol oxidation with CO₂ reduction at a Cu/CuO cathode, enabling simultaneous wastewater remediation and CO₂ conversion to value-added hydrocarbons.