Jin Jia

Ultrathin N-Doped Mo2C Nanosheets with Exposed Active Sites as Efficient Electrocatalyst for Hydrogen Evolution Reactions

Probing competent electrocatalysts for hydrogen evolution reaction (HER) of water splitting is one of the most hopeful approaches to confront the energy and environmental crisis. Herein, we highlight ultrathin N-doped Mo2C nanosheets (N-Mo2C NSs) in the role of greatly efficient platinum-free-based electrocatalysts for the HER. The transformation of crystal phase and structure between MoO2 nanosheets with a thickness of ∼1.1 nm and N-Mo2C NSs with a thickness of ∼1.0 nm is studied in detail. Structural analyses make clear that the surfaces of the N-Mo2C NSs are absolutely encompassed by apical Mo atoms, hence affording an ideal catalyst prototype to expose the role of Mo atoms for the duration of HER catalysis. Theoretical calculations demonstrate that the nanosheet structure, N doping, and particular crystalline phase of Mo2C produce more exposed Mo active sites, including Mo atoms on the C plane and doped N atoms. Through detailed electrochemical investigations, N-Mo2C NSs possess HER activity with an onset potential of -48.3 mV vs RHE, Tafel slope of 44.5 mV dec-1, and overpotential of 99 mV vs RHE at the cathodic current density of 10 mA cm-2 with excellent long-term stability. Lastly, the calcination temperature and dicyandiamide amount can obviously affect the phase transformation and surface structure of molybdenum carbide, resulting in an adjustable HER activity. This synthesis mechanism will facilitate the understanding and optimization of Mo-based electrocatalysts in the energy conversion field.

Regulated Synthesis of Mo Sheets and Their Derivative MoX Sheets (X: P, S, or C) as Efficient Electrocatalysts for Hydrogen Evolution Reactions

Electrochemical H2 generation from H2O has been focused on the exploration of non-noble metals as well as earth-rich catalysts. In our practical work, we provide a simple cost-efficient fabrication process to prepare large Mo sheets via the controlled equilibrium between sublimation of MoO3 and reduction of H2. Porous MoP sheets were synthesized from the obtained Mo sheets as the Mo source and template which exhibit notable activity in the hydrogen evolution reaction with a low onset potential of -88 mV vs RHE, small Tafel value of 54.5 mV/dec, and strong catalytic stability. With Mo sheets as the universal Mo source and template, MoS2 and Mo2C sheets were synthesized by a similar process, and the corresponding catalytic activities were calculated by density functional theory.