Developing highly efficient and long-durable electrocatalysts toward the hydrogen evolution reaction (HER) is highly desirable for implementation of the water-splitting to produce high-purity H₂ at large scale.[1] Although Pt-group metals so far have been proven to be superior electrocatalysts for HER, the high-cost and scarcity heavily inhibit their widespread application. To date, a series of HER electrocatalysts based on transition metal carbides have been developed. However, in most of these cases, their catalytic activity and durability still need to be improved to compete with Pt-based electrocatalysts.[2, 3] As a cheaper alternative to Pt, Ru possesses similar bond strength with hydrogen, guaranteeing the promise for catalytic hydrogen evolution.[4, 5] In this study, we demonstrate a novel strategy for the preparation of Ru-functionalized Mo₂C nanoparticles embedded in popcorn-derived three-dimensional (3D) porous carbon framework.

The synthesis mainly involves two steps: (i) the activation of popcorn by KOH and the co-assembly with Ru and Mo precursors. With the help of activation treatment, the popcorn can easily disperse in the solution and absorb Ru and Mo precursor. (ii) freeze-drying followed by in situ annealing treatment. The crystallization of Ru nanoparticles, in-site growth of Mo₂C nanoparticles and the carbonization of porous popcorn were simultaneously performed during annealing process. Due to the synergistic effects between Ru and Mo₂C nanoparticles, the composite catalyst showed higher HER activity.

Figure 1. a) A schematic diagram showing the organization of the Mo₂C@Ru. b) HER polarization curves of Mo₂C, Ru and Mo₂C@Ru with the iR drop correction, acquired at a scan rate of 5 mV s^-1 in 0.5 M H₂SO₄.

References
[1] Q. Feng, X.Z. Yuan, G. Liu, B. Wei, Z. Zhang, H. Li, H. Wang, Journal of Power Sources, 366(2017) 33-55.
[2] K.-H. Liu, H.-X. Zhong, S.-J. Li, Y.-X. Duan, M.-M. Shi, X.-B. Zhang, J.-M. Yan, Q. Jiang, Progress in Materials Science, 92 (2018) 64-111.
[3] M. Miao, J. Pan, T. He, Y. Yan, Y. Xia Bao, X. Wang, Chemistry – A European Journal, 23 (2017)10947-10961.
[4] J. Mahmood, F. Li, S.-M. Jung, M.S. Okyay, I. Ahmad, S.-J. Kim, N. Park, H.Y. Jeong, J.-B. Baek,Nature Nanotechnology, 12 (2017) 441.
[5] J. Su, Y. Yang, G. Xia, J. Chen, P. Jiang, Q. Chen, Nature Communications, 8 (2017) 14969.