When MOFs meet MXenes: superior ORR performance in both alkaline and acidic solutions

The oxygen reduction reaction (ORR) plays a key role in many efficient and clean energy systems, specifically in fuel cells and metal-air batteries. As a widely used commercial ORR catalyst, Pt/C has the limitations of high price and scarce reserves. Metal-nitrogen-carbon (M-N-C) is considered as one of the most promising alternatives to replace noble metal catalysts. However, how to balance the high catalytic activity and stability is still a major challenge. In this study, we report a novel non-noble metal composited catalyst, Fe-N-C@Ti 3 C 2 T x , synthesized by a facile separated pyrolysis strategy. The Fe-doped Zeolitic Imidazolate Framework-8 (ZIF-8) was converted to Fe-N-C by carbonization firstly, which was then mixed with few-layered Ti 3 C 2 T x and pyrolyzed together to obtain Fe-N-C@Ti 3 C 2 T x composites. This separated pyrolysis strategy can not only ensure the high carbonization temperature required by Fe-N-C for high catalytic activity but also avoid the damage of MXene caused by high pyrolysis temperature. Thus, Fe-N-C@Ti 3 C 2 T x exhibited excellent ORR activity and stability in alkaline solution, including a half-wave potential of 0.887 V vs. RHE, limiting diffusion current density of 6.3 mA cm −2 , and even no attenuation after 10 000 cycles in 0.1 M KOH. Meanwhile, it also exhibited surprisingly good performance in acidic solution, with a half-wave potential of 0.777 V vs. RHE, limiting diffusion current density of 5.7 mA cm −2 , and only 11 mV attenuation after 10 000 cycles in 0.1 M HClO 4 . The superior ORR performance of the synthesized Fe-N-C@Ti 3 C 2 T x could be attributed to the strong coupling effect between Fe-N-C and MXene, the reduced intrinsic and charge transfer impedance, and the increased electrochemically active surface area. This work here provides a new strategy for the development of M-N-C based non-noble metal-based catalysts with high activity and stability, and a promising future for applications in fuel cells and metal-air batteries. The facilely synthesized Fe-N-C@Ti 3 C 2 T x composite exhibited excellent ORR activity and extraordinary stability in both alkaline and acidic solutions.