Self-supported lignin-derived carbon coupling with Mo-doped NiO and NiCo alloy heterojunction stimulates lattice tensile strain and electron transfer for boosting ampere-level urea electrolysis.

Developing highly active lignin carbon-based electrocatalysts for urea electrolysis is critical but remains a considerable challenge. Herein, a self-supported lignin-derived carbon coupling with Mo-doped NiO and NiCo alloy heterojunction (Mo-NiO@NiCo/C) has suitable lattice tensile strain and rapid electron transfer, thereby achieving high catalytic performance for urea electrolysis under large current density. The operando electrochemical impedance results demonstrate that Mo-NiO@NiCo/C undergoes an indirect oxidation step during the urea oxidation reaction (UOR) and follows the Volmer-Heyrovsky mechanism during the hydrogen evolution reaction (HER). Consequently, among all prepared catalysts, Mo-NiO@NiCo/C exhibits the best UOR (E = 1.278/1.381/1.430 V) and HER (E = -38/-262/-353 mV) activity in 1.0 M KOH with 0.5 M urea solution. In a UOR//HER electrolysis cell, Mo-NiO@NiCo/C can obtain the potential of 1.313 and 1.607 V at 10 and 1000 mA cm. Meanwhile, benefiting from the self-supported lignin-derived mesoporous carbon structure, it can operate stably for 100 h at 1000 mA cm. This work presents an efficient lignin-derived carbon-based catalyst for urea electrolysis under ampere-level current density and details a practicable method for improving the utilization rate of lignin-derived carbon.