Cu(II) Ions Induced Structural Transformation of Cobalt Selenides for Remarkable Enhancement in Oxygen/Hydrogen Electrocatalysis

• Published in: ACS catalysis 2019-12, Vol.9 (12), p.10761-10772
• Main Authors: Dai, Jiale, Zhao, Dengke, Sun, Wenming, Zhu, Xiaojing, Ma, Li-Jun, Wu, Zexing, Yang, Chenghao, Cui, Zhiming, Li, Ligui, Chen, Shaowei
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.9b04060

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., E ORR,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 (E OER,10) and E ORR,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.