Carbon doping switching on the hydrogen adsorption activity of NiO for hydrogen evolution reaction

Tianyi Kou,Feng Wu,Yuan Ping,Yi-Sheng Liu,Tyler J Smart,Mingpeng Chen,Shengtong Li,Zhonghua Zhang,Yat Li,Yishang Wu,Gongming Wang,Supriya Lall,Ying Zhang,Shanwen Wang,Jinghua Guo

doi:10.1038/s41467-020-14462-2

Abstract

Hydrogen evolution reaction (HER) is more sluggish in alkaline than in acidic media because of the additional energy required for water dissociation. Numerous catalysts, including NiO, that offer active sites for water dissociation have been extensively investigated. Yet, the overall HER performance of NiO is still limited by lacking favorable H adsorption sites. Here we show a strategy to activate NiO through carbon doping, which creates under-coordinated Ni sites favorable for H adsorption. DFT calculations reveal that carbon dopant decreases the energy barrier of Heyrovsky step from 1.17 eV to 0.81 eV, suggesting the carbon also serves as a hot-spot for the dissociation of water molecules in water-alkali HER. As a result, the carbon doped NiO catalyst achieves an ultralow overpotential of 27 mV at 10 mA cm−2, and a low Tafel slope of 36 mV dec−1, representing the best performance among the state-of-the-art NiO catalysts.

Highlights

Hydrogen evolution reaction (HER) is more sluggish in alkaline than in acidic media because of the additional energy required for water dissociation
Since proton rich environment is favorable for hydrogen adsorption on catalyst surface, acidic medium is preferable for hydrogen evolution reaction (HER)
DFT simulations reveal that carbon dopant distorts the local structure of NiO and decreases the coordination number of the top-layer Ni (#1)

Summary

Introduction

Hydrogen evolution reaction (HER) is more sluggish in alkaline than in acidic media because of the additional energy required for water dissociation. We show a strategy to activate NiO through carbon doping, which creates under-coordinated Ni sites favorable for H adsorption. It is critical to develop alkaline HER catalysts that contain both hydrogen adsorption sites as well as water adsorption and dissociation sites[5,6] Transition metal oxides such as NiO are promising alkaline HER catalysts. NiO with metallic Ni, which provides hydrogen adsorption sites, has further decreased the overpotential for alkaline HER to 80 mV at jgeo of 10 mA cm−2 The carbon sites serve as the hot spots for water dissociation with a fairly low energy barrier of 0.81 eV

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