Interface-tuned Mo-based nanospheres for efficient oxygen reduction and hydrogen evolution catalysis

Developing earth-abundant materials for efficient oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) catalysis in both alkaline and acidic media is of significance for hydrogen fuel cell application. Herein, an interface metal-to-metal coupling strategy was proposed for constructing electrochemically stable and acid resistant Co-coupled MoO2-based hierarchical nanospheres (HNs-Co), which were synthesizedviaanin situconfinement reaction followed by an interface engineering process. Benefiting from the unique hierarchical structure composed of carbon-based nanosheets embedded with rich nano/sub-nano MoO(2)and the strong electronic coupling between Co and Mo, the well-constructed HNs-Co manifested outstanding ORR catalytic activities along with robust catalytic stability in both alkaline and acidic media compared to reported precious metal-free Mo-based ORR catalysts. The half-wave potential of HNs-Co evaluated in alkaline medium is comparable to that of the benchmark Pt/C catalyst and is the highest in acidic medium among the reported values for precious metal-free Mo-based materials. The strong coupling between Co and Mo not only decreased the oxygen binding energy of MoO2, benefiting ORR catalytic activity, but also enhanced the stability of some Co moieties in acidic medium for maintaining the catalytic capacity of HNs-Co. Moreover, HNs-Co manifested considerable HER catalysis with low overpotential even after 5000 cycle scans. This work highlighted the importance of interface tuning for boosting the ORR and HER catalytic activity of Mo-based materials, which can be extended to the rational design of other precious metal-free materials for efficient energy conversion.