Morphology and surface chemistry engineering toward pH-universal catalysts for hydrogen evolution at high current density

Yuting Luo,Hui-Ming Cheng,Lei Tang,Xiaolong Zou,Qiangmin Yu,Bilu Liu,Usman Khan

doi:10.1038/s41467-018-07792-9

Abstract

Large-scale implementation of electrochemical hydrogen production requires several fundamental issues to be solved, including understanding the mechanism and developing inexpensive electrocatalysts that work well at high current densities. Here we address these challenges by exploring the roles of morphology and surface chemistry, and develop inexpensive and efficient electrocatalysts for hydrogen evolution. Three model electrocatalysts are flat platinum foil, molybdenum disulfide microspheres, and molybdenum disulfide microspheres modified by molybdenum carbide nanoparticles. The last catalyst is highly active for hydrogen evolution independent of pH, with low overpotentials of 227 mV in acidic medium and 220 mV in alkaline medium at a high current density of 1000 mA cm−2, because of enhanced transfer of mass (reactants and hydrogen bubbles) and fast reaction kinetics due to surface oxygen groups formed on molybdenum carbide during hydrogen evolution. Our work may guide rational design of electrocatalysts that work well at high current densities.

Highlights

Large-scale implementation of electrochemical hydrogen production requires several fundamental issues to be solved, including understanding the mechanism and developing inexpensive electrocatalysts that work well at high current densities
Three model electrocatalysts with different morphologies or/and surface chemistry are used, i.e., a flat Pt foil, MoS2 microspheres made of MoS2 nanosheets, and MoS2 microspheres decorated by Mo2C nanoparticles (MoS2/Mo2C)
Scanning electron microscopy (SEM) images show that the MoS2/Mo2C has a rugged morphology derived from the spherical MoS2 (Fig. 1b, Supplementary Fig. 1)

Summary

Introduction

Large-scale implementation of electrochemical hydrogen production requires several fundamental issues to be solved, including understanding the mechanism and developing inexpensive electrocatalysts that work well at high current densities. Developing electrocatalysts that perform well at high current densities is critical for large-scale use To this end, Chen et al have recently reported that α-MoB2 has decent catalytic activity for HER at very high hydrogen coverage, showing an overpotential less than 400 mV at 1000 mA cm−2 in an acid medium[11]. Features of a catalyst may affect electron transfer rate, the amount and exposure of active sites, accessibility of catalytic surfaces to reactants, bonding strength with hydrogen, and water dissociation kinetics, and would influence their HER performance at high current densities We address these challenges by developing electrocatalysts with an optimized morphology and surface chemistry. Experimental and theoretical investigations show that Mo2C modified by surface oxygen groups formed during the HER promotes the interfacial mass transfer of reactants and hydrogen gas bubbles on MoS2, and speeds up the water dissociation and hydrogen absorption kinetics, resulting in decent HER performance at high current densities

Methods

Results

Conclusion