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Li Ligui et al., ACS Catalysis: Cu(II) Ions Induced Structural Transformation of Cobalt Selenides for Remarkable Enhancement in Oxygen/Hydrogen Electrocatalysis
Time:2021-12-29? ? ? ? Views:375


Abstract: Efficient nonprecious multifunctional catalysts are indispensable to enable the widespread applications of several important electrochemical energy technologies. Herein, catalytically active metastable monoclinic-phase Co3Se4 nanorods supported on carbon hybrids of reduced graphene oxide and carbon nanotubes (Cu-14-Co3Se4/GC) were selectively prepared by adding Cu(II) ions to the precursors that were successively treated by a hydrothermal process and thermal annealing at 300 °C, while only low-activity orthorhombic-phase CoSe2 nanorods were obtained without the addition of Cu(II) ions. The resulting grape-bunch-like Cu-14-Co3Se4/GC sample contained a trace amount of Cu element and showed efficient trifunctional activities, with an oxygen evolution reaction (OER) overpotential of 280 mV and impressively the highest half-wave potential of +0.782 V (i.e., EORR,1/2) for the oxygen reduction reaction (ORR) in 0.1 M KOH as well as the lowest hydrogen evolution reaction (HER) overpotential of 166 mV among the Co3Se4 composites reported to date at 10 mA cm–2 in 1.0 M KOH. Moreover, a voltage difference (ΔE) of only 0.680 V was observed between the potential for OER at 10 mA cm–2 (EOER,10) and EORR,1/2 in 1.0 M KOH, and merely 1.620 V was required to reach 10 mA cm–2 in overall water splitting. X-ray photoelectron spectroscopy measurements and theoretical simulations reveal the evident change of the electronic state after incorporation of Cu atoms onto Co–Se skeletons. Density functional theory calculations suggest that upon structural transformation from orthorhombic CoSe2 to monoclinic Co3Se4, the Gibbs free energies of the rate-determining steps were significantly reduced from 0.43 to ?0.22 eV for ORR, from 2.64 to 1.90 eV for OER, and from 1.08 to 0.23 eV for HER, mainly accounting for the high catalytic activities of Cu-14-Co3Se4/GC. Besides, the presence of abundant open-channel nanocavities in three-dimensional grape-bunch-like Cu-14-Co3Se4/GC helps maximize the exposure of active sites and facilitates mass diffusion, while the GC networks improve electrical conductivity, hence expediting the electrocatalysis process. The results in the present work highlight the importance of structural engineering in electrocatalysis and may pave an avenue for the preparation of low-cost, efficient, and multifunctional electrocatalysts.



This achievement was published in ACS Catalysis ( IF:12.221,details:ACS Catal. 2019,9(12), 10761-10772), The corresponding author is Associate Professor Li Ligui of our college. The first author is Dai Jiale, a graduate student and the co-first author is Zhao Dengke, a doctoral student. Sun Wenming, an associate professor of China Agricultural University.



Figure 1. (a) SEM image; (b) TEM images; inset to panel (b) is the EDS spectrum; (c) HR-TEM images of Cu-14-Co3Se4/GC. (d) SAED pattern of Cu-14-Co3Se4/GC. (e1) High-angle annular dark-field scanning transmission electron microscopy image and the corresponding elemental distribution images for (e2) Co, (e3) Se, (e4) Cu, (e5) C, (e6) O, and (e7) N. (f) TEM image of CoSe2/GC; inset to panel f is an HR-TEM image of CoSe2/GC.


Figure 2. (a) XRD profiles of CoSe2, cobalt selenide/GC composites prepared with 0, 11, 14, and 21 wt % of Cu salt in the precursor. (b) Cu 2p XPS spectra for the Cu-14-Co3Se4/GC sample determined at different Ar ion etching times. (c) High-resolution Co 2p XPS spectra of cobalt selenide/GC composites prepared with 14 and 21 wt % of Cu salt in the precursor.


Figure 3. LSV curves of different catalysts catalyzing (a) ORR in 0.1 M KOH at an electrode rotation rate of 1600 rpm; (b) OER and (c) HER in 1.0 M KOH solution at a potential scanning rate of 10 mV s–1 after iR correction. (d) Plot showing the variation of Eonset for ORR and E10for OER and HER for different samples.


Figure 4. Most stable H* and O* adsorption configurations on the surfaces of (a) CoSe2(111), (b) Cu–Co3Se4(111), and (c) Co3Se4(111) during HER and OER. Co, Se, and Cu atoms are represented by blue, yellow, and green spheres, respectively. (d) Free energy diagrams for the HER process proceeded on the surface of the CoSe2(111) plane (red line), the Cu–Co3Se4(111) plane (blue line), and the Co3Se4(111) plane (green line). (e) Free energy diagrams for the OER process (and the reverse process, i.e., ORR) proceeded on the surface of the CoSe2(111) plane (red line), the Cu–Co3Se4(111) plane (blue line), and the Co3Se4(111) plane (green line). (f) Free energy of the rate-determining steps for HER and OER processes proceeded on the surface of the CoSe2(111) plane, the Cu–Co3Se4(111) plane, and the Co3Se4(111) plane.

 






 



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