Electrodeposition of Mo-doped NiFex nanospheres on 3D graphene fibers for efficient overall alkaline water splitting

Developing efficient bifunctional catalysts for hydrogen and oxygen evolution reactions (HER/OER) has attracted great interest in hydrogen production from water splitting. In this work, a novel material of Mo-doped NiFe(x )nanospheres on 3D graphene fibers (Mo-NiFex/ 3DGFs) has been successfully fabricated through a simple and cheap one-step electrode-position method. The Mo-NiFex/3DGFs possessed ultra-high conductivity and specific surface area, greatly benefiting to electrocatalytic hydrolysis activity. And it was found that Fe element could obviously promote OER process, while Mo doping facilitated both OER and HER reactions. We proved that there existed synergetic roles between Fe and Mo element, which could realize the control of the electronic structure and optimize the adsorption/ desorption of intermediates. And electrochemical tests showed that the Mo-Ni/3DGFs exhibited a relatively smaller overpotential of 109.9 mV for HER, while the Mo-NiFex/3DGFs presented better OER performance with an overpotential of 240.8 mV at the current density of 100 mA cm(-2) in 1.0 M KOH. Finally, a system for overall water splitting constructed by Mo-Ni/3DGFs||Mo-NiFe0.68/3DGFs electrodes has a low cell voltage of 1.52 V at 10 mA cm(-2) and long-term stability, exceeding most of literature results. Our findings provide insight into possibilities for the simple synthesis of high-performance and cheap catalysts, and laid the foundation for the practical application of transition metal catalysts.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study successfully fabricated a novel material of Mo-doped NiFe(x) nanospheres on 3D graphene fibers, which exhibited excellent conductivity and specific surface area, benefiting the electrocatalytic hydrolysis activity. Fe element was found to promote the oxygen evolution reaction (OER), while Mo doping facilitated both OER and hydrogen evolution reaction (HER). The synergistic roles between Fe and Mo elements were confirmed, controlling the electronic structure and optimizing the adsorption/desorption of intermediates. The Mo-doped Ni/3DGFs showed a smaller HER overpotential of 109.9 mV, and the Mo-doped NiFe(x)/3DGFs exhibited better OER performance with an overpotential of 240.8 mV in 1.0 M KOH at a current density of 100 mA cm(-2). The overall water splitting system constructed by Mo-doped Ni/3DGFs||Mo-doped NiFe0.68/3DGFs electrodes achieved a low cell voltage of 1.52 V at 10 mA cm(-2) and demonstrated long-term stability, surpassing most literature results. These findings provide insights into the simple synthesis of high-performance and cheap catalysts and lay the foundation for practical applications of transition metal catalysts.