Oriented construction of lignin-derived carbon hybrid electrocatalyst with superwettable surface and Co-based heterostructure for overall water splitting

Converting lignin waste into carbon hybrid catalysts for water electrolysis engenders a beneficial scenario for both the valorization of waste carbon resources and the reduction of hydrogen production costs, which remains a grand challenge. Hence, we report a novel lignin-derived carbon hybrid electrocatalyst as a low-cost and highly efficient bifunctional electrocatalyst for overall water splitting, prepared by a feasible strategy involving NaCl-assisted pyrolysis and subsequent oxidation-phosphorization. Notably, this strategy can not only regulate the composition of CoP/CoO_x nano-heterostructures but also improve the structural properties of porous carbon matrix. Profiting from superwettable surface, ultrafine Co-based heterojunctions and large active area, the optimal CoP/CoO_x-HPC catalyst exhibits exceptional bifunctional catalytic activity in 1 M KOH electrolyte, requiring only small overpotentials of 396 and 522 mV for HER and OER, respectively, to achieve a large current density of 400 mA cm⁻². Meanwhile, the assembled alkali-electrolyzer using CoP/CoO_x-HPC as both cathode and anode needs a relatively low voltage of 2.31 V at 400 mA cm⁻², significantly outperforming the commercial couple of Pt/C || RuO₂. This work can be of value in the design of the low-cost and highly active lignin-derived electrocatalysts and also serve as guidance for the high-value utilization of lignin or even other biomass wastes.