| Summary: | Exploring low-cost and eco-friendly bifunctional electrocatalysts of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline electrolytes is still highly desired, and is crucial for water electrolysis and sustainable hydrogen generation. In this work, we report a facile pyrolysis–oxidation strategy to convert by-product lignin into bifunctional OER/HER electrocatalysts (Co/Co<sub>3</sub>O<sub>4</sub>-NPC-400) composed of Co/Co<sub>3</sub>O<sub>4</sub> anchored on N-doped carbon with a surface of rich oxygen vacancies and oxygen-containing groups. The co-pyrolysis of lignin and NH<sub>4</sub>Cl can achieve a N-doped carbon matrix with a hierarchical pore structure, while the air-annealing process can induce the formation of oxygen-containing groups and oxygen vacancies. Owing to its surface properties, hierarchical pore structure and multiple active components, the constructed Co/Co<sub>3</sub>O<sub>4</sub>-NPC-400 possesses bifunctional catalytic activity and superior stability for OER/HER, especially for unexpected OER activity with a high current density of about 320 mA∙cm<sup>−2</sup> at a potential of 1.8 V (vs. RHE). Water electrolysis using Co/Co<sub>3</sub>O<sub>4</sub>-NPC-400 as both the anode and the cathode needs a cell voltage of 1.95 and 2.5 V to attain about 10 and 400 mA∙cm<sup>−2</sup> in 1 M KOH. This work not only provides a general strategy for the preparation of carbon-supported electrocatalysts for water splitting, but also opens up a new avenue for the utilization of lignin.
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