Engineering of crystalline phase and mesoscale diffusion over hollow MoO2/C nanoreactors toward enhanced hydrogen production

Abstract

Phase and microenvironment engineering are efficient strategies to improve the intrinsic activity of the catalysts, but it is still challenging to grasp the precise regulation strategy and understand the catalytic performance enhancement mechanism. Herein, we report the synergetic regulation of crystalline phase and mesoscale diffusion over monodispersed hollow MoO2/C nanoreactors for enhanced hydrogen evolution reaction (HER). Specially, the hollow MoO2/C (H–MoO2/C) with hexagonal phase is produced via the microemulsion technology, and then is converted to monoclinic phase MoO2/C (M-MoO2/C) nanoreactor by argon annealing treatment. As a result, the HER overpotential (η10) and turnover frequency value (250 mV) of the M-MoO2/C are 109 mV and 0.049 s−1, respectively, showing the improvement of 2-fold and 5.4-fold higher in comparison with the H–MoO2/C. Moreover, under the corresponding potential of 10 mA cm−2, the M-MoO2/C electrode can run stably for more than 30 h. Density functional theory calculations reveal that the carrier density and d-band center of MoO2 which are closely related to the intrinsic activity can be efficiently tailored, leading to improved conductivity and hydrogen adsorption. Benefitting from the modulation of mesopore size from 3.2 to 10.0 nm during the phase transformation process, the flow velocity of electrolyte in the inner of hollow M-MoO2/C model is almost 7-fold higher than that in the H–MoO2/C configuration, according to the finite element analysis simulations. The highly promoted mass transfer in the mesoscale can contribute to the full and rapid connection of electrode and electrolyte, which optimizes the reaction microenvironment around the active sites. Our work inspires to rational design and deep understanding of high-efficiency catalysts for electrosynthesis.