Lignosulfonate-assisted in situ synthesis of Co9S8–Ni3S2 heterojunctions encapsulated by S/N co-doped biochar for efficient water oxidation

The development of highly active and stable earth-rich electrocatalysts remains a major challenge to release the reliance on noble metal catalysts in sustainable (electro)chemical processes. In this work, metal sulfides encapsulated with S/N co-doped carbon were synthesized with a one-step pyrolysis strategy, where S was introduced during the self-assembly process of sodium lignosulfonate. Due to the precise coordination of Ni and Co ions with lignosulfonate, an intense-interacted Co 9 S 8 –Ni 3 S 2 heterojunction was formed inside the carbon shell, causing the redistribution of electrons. An overpotential as low as 200 mV was obtained over Co 9 S 8 –Ni 3 S 2 @SNC to reach a current density of 10 mA cm −2 . Only a slight increase of 14.4 mV was observed in a 50 h chronoamperometric stability test. Density functional theory (DFT) calculations showed that Co 9 S 8 –Ni 3 S 2 heterojunctions encapsulated with S/N co-doped carbon can optimize the electronic structure, lower the reaction energy barrier, and improve the OER reaction activity. This work provides a novel strategy for constructing highly efficient and sustainable metal sulfide heterojunction catalysts with the assistance of lignosulfonate biomass.