Catalyst Support Effect on the Activity and Durability of Magnetic Nanoparticles: toward Design of Advanced Electrocatalyst for Full Water Splitting.

Fatemeh Davodi,Hua Jiang,Jani Sainio,Mohammad Tavakkoli,Elisabeth Mühlhausen,Tanja Kallio,Bilal Gökce,Galina Marzun

doi:10.1021/acsami.8b08830

Abstract

Earth-abundant element-based inorganic–organic hybrid materials are attractive alternatives for electrocatalyzing energy conversion reactions. Such material structures do not only increase the surface area and stability of metal nanoparticles (NPs) but also modify the electrocatalytic performance. Here, we introduce, for the first time, multiwall carbon nanotubes (MWNTs) functionalized with nitrogen-rich emeraldine salt (ES) (denoted as ES-MWNT) as a promising catalyst support to boost the electrocatalytic activity of magnetic maghemite (γ-Fe2O3) NPs. The latter component has been synthesized by a simple and upscalable one-step pulsed laser ablation method on Ni core forming the core–shell Ni@γ-Fe2O3 NPs. The catalyst (Ni@γ-Fe2O3/ES-MWNT) is formed via self-assembly as strong interaction between ES-MWNT and Ni@γ-Fe2O3 results in NPs’ encapsulation in a thin C–N shell. We further show that Ni does not directly function as an active site in the electrocatalyst but it has a crucial role in synthesizing the maghemite shell. The strong interaction between the NPs and the support improves notably the NPs’ catalytic activity toward oxygen evolution reaction (OER) in terms of both onset potential and current density, ranking it among the most active catalysts reported so far. Furthermore, this material shows a superior durability to most of the current excellent OER electrocatalysts as the activity, and the structure, remains almost intact after 5000 OER stability cycles. On further characterization, the same trend has been observed for hydrogen evolution reaction, the other half-reaction of water splitting.

Highlights

Hydrogen production by electrochemical water splitting is considered a promising route for renewable energy conversion and an enabler for hydrogen utilization as an energy carrier.[1]
Magnetic Ni@γ-Fe2O3 NPs have been synthesized via pulsed laser ablation in liquid (PLAL) from alloy targets in acetone as explained in the synthesis process section
To attach the Ni@γ-Fe2O3 NPs to an electronically conducting support, emeraldine salt (ES)-multiwall carbon nanotubes (MWNTs) have been synthesized as explained in our recent publication[23] and summarized in the Experimental Section (Section 5)

Summary

Introduction

Hydrogen production by electrochemical water splitting is considered a promising route for renewable energy conversion and an enabler for hydrogen utilization as an energy carrier.[1] In a water electrolysis device, the overall water-splitting reactions should be utilized in the same electrolyte. This is one of the challenges in electrocatalyst development because of the difficulty in finding earth-abundant catalysts enhancing the efficiency for both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) in the same electrolyte and under similar pH conditions. Development of an electrocatalyst with bifunctional activity for both water electrolysis half-reactions is of high interest for large-scale device fabrication. One promising strategy to modify the structure and electronic properties of nanoparticulate electro-

Methods

Results

Conclusion