Nitrogen-doped carbon shell armored ‘Janus’ Co/Co9S8 heterojunction as robust bi-functional oxygen reduction reaction/oxygen evolution reaction catalysts in seawater-based rechargeable Zn-air batteries

It is of paramount importance to develop highly efficient and Cl−corrosion-resistant bi-functional catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for application in seawater-based Zn-air batteries (S-ZABs), but the process remains full of challenges. Herein, a facile and effective strategy was adopted to fabricate the N-doped carbon shell armored 'Janus' Co/Co9S8 heterojunction catalyst (denoted as Co/Co9S8-NMC). The well-defined 'Janus' structure endows the catalyst with a 'synergistic effect' between Co and Co9S8 species, which can also accelerate the electron transfer via 'Janus' interfaces, thus boosting ORR/OER performance. Besides, N-doped carbon shells can be considered armor for protecting the catalyst from Cl− corrosion. By virtue of these merits, the resulting Co/Co9S8-NMC catalyst exhibits excellent catalytic activity for ORR and OER in seawater electrolyte, accompanied by a half-wave potential of 0.83 V and a low overpotential of 298 mV to achieve a current density of 10 mA/cm2. Besides, the S-ZABs based on the Co/Co9S8-NMC catalyst deliver a high maximum power density of 162.29 mW/cm2 and robust stability over 600 h. This work advances the development of highly efficient bi-functional catalysts for S-ZABs.