Modulation of Phase Transition in Cobalt Selenide with Simultaneous Construction of Heterojunctions for Highly‐Efficient Oxygen Electrocatalysis in Zinc–Air Battery

Abstract

Phase‐transformation of cobalt selenide (CoSe2) can effectively modulate its intrinsic electrocatalytic activity. However, enhancing electroconductivity and catalytic activity/stability of CoSe2 still remains challenging. Heterostructure engineering may be feasible to optimize interfacial property to promote the kinetics of oxygen electrocatalysis on CoSe2‐based catalyst. Herein, a heterostructure consisting of CoSe2 and cobalt nitride (CoN) embedded in a hollow carbon‐cage is designed via a simultaneous phase/interface engineering strategy. Notably, phase transition of orthorhombic‐CoSe2 to cubic‐CoSe2 accompanied by in‐situ CoN formation is realized to build the c‐CoSe2/CoN heterointerface, which exhibits excellent/highly‐stable activities for oxygen reduction/evolution reactions (ORR/OER). Notably, heterostructure can modulate local coordination environment and increase Co‐Se/N bond lengths. Theoretical calculations show that Co‐site (c‐CoSe2) with electronic state near Fermi energy level is main active sites for ORR/OER. Energetical tailoring of d‐orbital electronic structure of Co atom of c‐CoSe2 in heterostructure by in‐situ CoN incorporation lowers thermodynamic barriers for ORR/OER. Bader charge analyses reveal that the internal electron transfer from c‐CoSe2 to CoN affords high ORR/OER activities. Attractively, a zinc‐air battery with c‐CoSe2‐CoN cathode displays excellent cycling stability (250 h) and charge/discharge voltage loss (0.953/0.96 V). It highlights that heterointerface engineering provides an option for modulating bifunctional activity of metal selenides with controlled phase‐transformation.This article is protected by copyright. All rights reserved

Asymmetric Coordination of Bimetallic Fe–Co Single-Atom Pairs toward Enhanced Bifunctional Activity for Rechargeable Zinc–Air Batteries

“…The OER polarization curves depicted in Figure e illustrate that FeCo-SAs exhibited a lower overpotential ( η ) of 270 mV compared to the benchmark IrO 2 (348 mV) at 10 mA cm –2 . The reduced η verified the substantial enhancement in catalytic activity due to the presence of Fe–Co bimetallic pairs, suggesting strong chemical interaction and electronic coupling . Correspondingly, the Tafel slope of FeCo-SAs was 35.53 mV dec –1 (Figure f), considerably lower than that of IrO 2 (82.73 mV dec –1 ), suggesting its fast OER kinetics.…”

“…The reduced η verified the substantial enhancement in catalytic activity due to the presence of Fe−Co bimetallic pairs, suggesting strong chemical interaction and electronic coupling. 51 Correspondingly, the Tafel slope of FeCo-SAs was 35.53 mV dec −1 (Figure 4f), considerably lower than that of IrO 2 (82.73 mV dec −1 ), suggesting its fast OER kinetics.…”

ZIF-67-derived Se-doped CoSe2 grown on carbon nanofibers as oxygen electrocatalysts for rechargeable Zn–air batteries

“…S7a (ESI †), the binding energy position of Co 2p of Se-CoSe 2 /CNFs-12 changed significantly, and the Co 3+ peak shifted from 779.0 eV to 780.6 eV, indicating that the Se-CoSe 2 /CNFs-12 component was partially oxidized at high potential. 59 In addition, the Co 3+ /Co 2+ ratio after the OER stability test (E2.69) was higher than that of the original catalyst (E0.86), which was attributed to the generation of CoO(OH). 60,61 Fig.…”

“…In an alkaline solution, the metal ions of CoSe 2 exist in the form of metal hydroxides and are oxidized to form an oxide layer under the applied positive potential. 55 The oxide layer becomes the actual OER catalytic site, and the CoSe 2 under the oxide layer maintains conductivity between the back electrode and the active oxide layer, thereby enhancing catalytic activity. In the second step, the Se site is more easily oxidized than the Co site, and it is difficult to generate OOH*.…”

Controllable Phase Separation Engineering of Iron–Cobalt Alloy Heterojunction for Efficient Water Oxidation

“…The high-resolution Fe 2p XPS spectra (Figure b) of Fe 1 Co 3 /C show the peaks at 711.6 and 714.9 eV, corresponding to Fe 2+ and Fe 3+ in Fe 2p 3/2 , and a pair of peaks at 723.5 and 725.9 eV assigned to Fe 2+ and Fe 3+ in Fe 2p 1/2 . It is worth noting that the Fe 2p 3/2 and Fe 2p 1/2 peaks of Fe 1 Co 3 /C positively shifted by 0.6 and 0.5 eV, respectively, compared with those of Fe/C, implying the electron transfer from iron to cobalt in iron–cobalt alloy and the decreased electron density around iron atoms . It is believed that this phenomenon can be ascribed to the lower electronegativity of Fe.…”