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Published online 18 November 2020 | https://doi.org/10.1007/s40843-020-1511-7

Melamine-assisted synthesis of ultrafine Mo2C/ Mo2N@N-doped carbon nanofibers for enhanced alkaline hydrogen evolution reaction activity 1

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Jing Chen , Anqiang Pan , Wenchao Zhang , Xinxin Cao , Rou Lu , Shuquan Liang and 3* Guozhong Cao ABSTRACT Noble metal-free electrocatalysts with high activity are highly desirable for the large-scale application of hydrogen evolution reaction (HER). Mo2C-based nanomaterials have been proved as a promising alternative to noble metal-based electrocatalysts owing to the Pt-resembled d-band density and optimal intermediates-adsorption properties. However, the aggregation and excessive growth of crystals often occur during their high-temperature synthesis procedure, leading to low catalytic utilization. In this study, the ultrafine Mo2C/Mo2N heterostructure with large surface and interface confined in the N-doped carbon nanofibers (NCNFs) was obtained by a melamine-assisted method. The synergistic effect of Mo2C/Mo2N heterostructure and plenty active sites exposed on the surface of ultrafine nanocrystals improves the electrocatalytic activity. Meanwhile, the N-CNFs ensure fast charge transfer and high structural stability during reactions. Moreover, the in-situ synthesis method strengthens the interfacial coupling interactions between Mo2C/Mo2N heterostructure and N-CNFs, further enhancing the electronic conductivity and electrocatalytic activity. Owing to these advantages, Mo2C/Mo2N@N-CNFs exhibit excellent HER performance with a low overpotential of 75 mV at a current −2 density of 10 mV cm in alkaline solution, superior to the single-phased Mo2C counterpart and recently reported Mo2C/ Mo2N-based catalysts. This study highlights a new effective strategy to design efficient electrocatalysts via integrating heterostructure, nanostructure and carbon modification. Keywords: Mo2C, hydrogen evolution reaction, heterostructure, ultrafine, nanofibers

INTRODUCTION Hydrogen (H2) is a renewable and abundant energy carrier that is regarded as a promising substitute for nonrenewable fossil fuels in the future [1–3]. Electrochemical water splitting is considered as one of the most promising hydrogen production techniques, which can be divided into two half-reactions: the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) [3–7]. However, the practical application of HER is limited by its large overpotential. Interest in searching electrocatalysts has been arising recently. Pt-based electrocatalysts can effectively accelerate the electrochemical process of HER, but it is too scarce and expensive to generalize [8,9]. Therefore, the key challenge to largescale H2 production lies in developing low-cost and highly efficient electrocatalysts based on earth-abundant elements. Transition metal compounds have been widely studied as electrocatalysts for HER in recent years [10,11]. Among these compounds, Mo2C and Mo2N are outstanding due to their similar d-band density with Pt, good hydroph