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

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.

Fabrication of γ-Fe2O3 Nanowires from Abundant and Low-cost Fe Plate for Highly Effective Electrocatalytic Water Splitting

“…Finally, the current density of the obtained Fe 2 O 3 nanowires was measured by applying the materials as working electrode for electrocatalytic water splitting and the current density has reached as 10 mA/cm 2 at 1.88 V vs. RHE. The value obtained from bare Fe 2 O 3 is comparable with previous results, where chemical modifications or doping is necessary [20][21][22][23][24] .…”

“…7, the linear sweep voltammograms (LSV) of Fe 2 O 3 -1 and Fe 2 O 3 -2 illustrate the enriched current density of 10 mA/cm 2 at the potentials of 1.88 and 1.91 V vs. RHE with 50 mV/sec scan rate. Even though the applied potential is higher than previous results obtained from chemically modified or doped γ-Fe 2 O 3 nanostructures, no one has reported improved performance for bare Fe 2 O 3 electrode (Table 1) [20][21][22][23][24] . Specifically, three important factors such as, (i) highly dense and ordered growth of nanowires, (ii) more abundant of γ-phase and (iii) single crystalline structure played essential role to improve the performance of the as-prepared Fe 2 O 3 electrodes.…”

“…(1) Adsorption of 'OH − ' (present in alkaline electrolyte solution) onto γ-Fe 2 O 3 catalyst surface. Moreover, it is value to mention here that α-Fe 2 O 3 (hematite) offers a favorable combination of good visible light absorption up to 590 nm hence it has been widely used as photoactive material for solar water splitting 46 , but recently few reports are demonstrated the excellent electrocatalytic activity of chemically modified γ-Fe 2 O 3 in electrocatalytic water splitting [20][21][22][23][24] . The morphology of γ-Fe 2 O 3 electrode used for stability measurements was observed by FESEM analysis and the images are shown in Fig.…”

“…Moreover, Ashwani Kumar et al 22 reported the current density of NiFe-NC obtained from the composite of NiO and α/γ-Fe 2 O 3 as 10 mA/cm 2 at the potential of 1.67 V vs. RHE in 1 M KOH. Recently, Davodi et al 23 reported that MWNTs functionalized with nitrogen-rich emeraldine salt (ES-MWNT) as a promising catalyst support to boost the electrocatalytic activity of magnetic maghemite (γ-Fe 2 O 3 ) NPs and the current density of the electrocatalyst (Ni@γ-Fe 2 O 3 /ES-MWNT) was measured as 10 mA/cm 2 at the potential of 1.49 V vs RHE in 1 M NaOH. In addition, Chandrasekaran et al 24 employed γ-Fe 2 O 3 with reduced graphene oxide for PEC water splitting and the photocurrent density of the RGO/γ-Fe 2 O 3 nanocomposite was reported as 6.74 mA/cm 2 at 1.80 V vs RHE in 1 M NaOH.…”

Oxygen Reduction Reaction Electrocatalysis in Alkaline Electrolyte on Glassy-Carbon-Supported Nanostructured Pr6O11 Thin-Films

“…As a result, the sustained hydrogen cycle might only be viable for alkaline systems for which the potential choice of more available and less costly non-noble electrocatalysts is greater (and simply possible) [11]. There are extremely vast numbers of potential non-PGM electrocatalysts for the ORR [12][13][14][15][16][17][18] and OER [19][20][21][22][23][24][25][26][27][28] (these examples being by-no-means comprehensive), and metal oxides in the perovskite structure play a large role in this hot area, owing to their non-negligible activity for the oxygen reduction and evolution reactions, and the extremely large variety of components available [6,11,[29][30][31][32]. Perovskite oxides, usually based on rare-earth component(s), are usually not sufficiently electron-conductive on their own to exhibit sufficient performances, and they are, therefore, generally used in composite electrodes while including some carbon additive [32][33][34][35][36].…”