Structure Engineering of Lignosulfonate-derived S/N Co-doped Catalyst for Electrocatalytic OER Performance

Oxygen evolution reaction (OER) is a core and rate-control process for the electrocatalytic water splitting. Due to the high energy barrier, the OER kinetics and overall water splitting efficiency are limited. Herein, bimetallic sulfide Co₉S₈-Ni₃S₂/SN-C catalyst was successfully prepared via oxidative ammonolysis of renewable lignosulfonates, and showed excellent electrocatalytic OER performance. The complex structure of sodium lignosulfonate modified with NHCO groups was investigated by comprehensive characterization, and the structural evolution mechanism of the precursor during pyrolysis and carbonization was revealed, with the formation of the active center Co₉S₈-Ni₃S₂ revealed as well. The strong binding of the modified lignin-carbon with metals enhanced the dispersion of active sites Co₉S₈ and Ni₃S₂. The close interaction between Co₉S₈-Ni₃S₂ and the defect doping of N onto the carbon carrier effectively regulated the surface electronic structure, and optimized the adsorption of the reaction intermediate, and thus improved the electrochemical OER reaction performance. The OER activity of Co₉S₈-Ni₃S₂/SN-C catalyst reached the highest level when m(H₂O₂)/m(LS) = 1.5 for oxidative ammonolysis, and showed a lower overpotential (350 mV) than that of commercial Ru/C catalyst (420 mV) at a current density of 50 mA·cm⁻². This work provides an insight into the directional regulation of lignin-based functional materials and its development for highly efficient and stable OER electrocatalysis.