Constructing High Efficiency CoZn_xMn_2–xO₄ Electrocatalyst by Regulating the Electronic Structure and Surface Reconstruction

Abstract

with high purity. [5,6] However, compared with two-electron hydrogen evolution reaction (HER), oxygen evolution reaction (OER) with sluggish kinetics restricts seriously the efficiency of water splitting. [7] Therefore, many efforts have been made to improve OER efficiency by synergistic regulating the electronic structures, which can increase significantly electrocatalytic activity. [8,9] Generally, noble metal-based materials are widely utilized as catalysts due to their low overpotential and excellent cycling stability. But the high cost and scarcity hinder their commercial applications.Recently, transition metal oxides CoMn 2 O 4 have attracted one's attention due to tunable d-electron orbitals and abundant chemical states. [10,11] In previous reports, multi-shelled CoMn 2 O 4 hollow structured catalysts showed rich oxygen vacancies with an overpotential of 240 mV at 10 mA cm −2 . [12] Kang et al. fabricated flower-like CoMn 2 O 4 nanospheres showing an overpotential (HER) of 132 mV at −10 mA cm −2 . [13] Gong and coworkers prepared CoMn 2 O 4 /carbon hollow nanofibers, demonstrating an overpotential of 337 mV for OER and 157 mV for HER. [14] However, a single catalyst possesses poor intrinsic activity and conductivity. To boost the electrocatalytic performance, one modulates the electronic structures of the catalysts by doping heterogeneous atoms into host materials. [15] It is a benefit to inducing the generation of vacancies, which can affect the adsorption performance of reaction intermediates, and facilitate the conversion of the intermediates to products. Simultaneously, theoretical calculation demonstrates that the rich defects can regulate electron density close to Fermi level, and then improve the catalytic activity of the catalysts. [16] In this work, we synthesize several Zn-doped CoMn 2 O 4 catalysts through a facile hydrothermal growth route. As OER electrocatalysts, the as-fabricated Zn-CoMn 2 O 4 -1.5 products show the overpotential of 280 mV (50 mA cm −2 ) and a Tafel slope of 69.1 mV dec −1 . Meanwhile, the above catalysts can deliver a current density of −10 mA cm −2 with an overpotential of 146 mV and low Tafel slopes for HER. Moreover, water splitting results present a voltage of 1.63 V and a cycle stability of 12 h. Density functional theory (DFT) calculations further confirm that Zn doping can improve efficiently the intrinsic electrocatalytic activity by optimizing the adsorption free energy of reaction intermediates. It also tunes the relative ratio of different valence states. It is an effective strategy to develop novel electrocatalysts with controllable defects to enhance their electrocatalytic activity and stability. However, how to precisely design these catalysts on the atom scale remains very difficult. Herein, several vacancy-dependent CoZn x Mn 2-x O 4 catalysts are prepared through tailoring the concentration of Zn ions. The in situ activation of the obtained products accelerates the surface reconstruction. The superior electrocatalytic performance can be ascribed to the form...

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