Tuning Electronic Structures of Nonprecious Ternary Alloys Encapsulated in Graphene Layers for Optimizing Overall Water Splitting Activity

Abstract

Electrochemical water splitting is considered as the most promising technology for hydrogen production. Considering overall water splitting for practical applications, catalysis of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) should be performed in the same electrolyte, especially in alkaline solutions. However, designing and searching for highly active and inexpensive electrocatalysts for both OER and HER in basic media remain significant challenges. Herein, we report a facile and universal strategy for synthesizing nonprecious transition metals, binary alloys, and ternary alloys encapsulated in graphene layers by direct annealing of metal–organic frameworks. Density functional theory calculations prove that with an increase in the degree of freedom of alloys or a change in the metal proportions in FeCoNi ternary alloys, the electronic structures of materials can also be tuned intentionally by changing the number of transferred electrons between alloys and graphene. The optimal material alloys FeCo and FeCoNi exhibited remarkable catalytic performance for HER and OER in 1.0 M KOH, reaching a current density of 10 mA cm–2 at low overpotentials of 149 mV for HER and 288 mV for OER. In addition, as an overall alkaline water electrolysis, they were comparable to that of the Pt/RuO2 couple, along with long cycling stability.

In Situ Coupling Strategy for the Preparation of FeCo Alloys and Co4N Hybrid for Highly Efficient Oxygen Evolution

“…As shown in Figure 1a, the dominant phase is bimetallic FeCo alloy with www.advmat.de www.advancedsciencenews.com diffraction peaks centered at 44.9° and 65.4°, [29] which can be ascribed to the (110) and (200) facets of FeCo alloy (JCPDS No. The structural features of the resultant carbon material (FeCo-Co 4 N/N-C) were first studied by the X-ray diffraction (XRD) technique.…”

Microwave-assisted CVD-like synthesis of dispersed monolayer/few-layer N-doped graphene encapsulated metal nanocrystals for efficient electrocatalytic oxygen evolution

“…As shown in Fig. 3e, those products formed after 2 s of microwave irradiation were already cubic FeNi alloys9,13 and the composition had no obvious change during the following reaction time, indicating that this reaction is indeed an ultrafast process. The Raman spectra in Fig.…”

“…In addition, the N 1s peaks (Fig. 3j) could all be divided into four peaks attributed to pyridinic N (398.4 eV), pyrrolic N (399.5 eV and 400.8 eV) and quaternary N (401.7 eV) 12,13. As displayed in Fig.…”

“…It was clearly observed that the 2p 2/3 peaks of Fe and Ni (Fig. 3h and i) could be deconvoluted into three peaks assigned to M 0 (around 707.1 eV for Fe and 852.4 eV for Ni), M 2+ (around 710.3 eV for Fe 2+ and 853.9 eV for Ni 2+ ) and M 3+ (around 712.9 eV for Fe 3+ and 855.8 eV for Ni 3+ ) 12,13. Obviously, the encapsulation of the metal with graphitized NC prevents the adsorption of oxygen species on the metal and increase the content of M 0 , which was confirmed by the semi-quantitative analysis based on the peak area ratios (Table S1†).…”

“…In addition, XPS results showed that the intensity of oxidized metal increased after CP tests (Fig. 5e), which might be caused by the increased adsorption of oxygen species on the surface of FeNi@NC/RGO induced by the high OER potential and/or a slightly oxidized surface of some of the FeNi alloy that not completely encapsulated 9,13. The four peaks assigned to pyridinic N, pyrrolic N and quaternary N were all be observed in the N 1s spectra after CP tests and only little changes in their peak intensities took place (Fig.…”