Controllable 1D and 2D Cobalt Oxide and Cobalt Selenide Nanostructures as Highly Efficient Electrocatalysts for the Oxygen Evolution Reaction

Abstract

The relationship between controllable morphology and electrocatalytic activity of Co O and CoSe for the oxygen evolution reaction (OER) was explored in alkaline medium. Based on the time-dependent growth process of cobalt precursors, 1D Co O nanorods and 2D Co O nanosheets were successfully synthesized through a facile hydrothermal process at 180 °C under different reaction times, followed by calcination at 300 °C for 2 h. Subsequently, 1D and 2D CoSe nanostructures were derived by selenization of Co O , which achieved the controllable synthesis of CoSe without templating agents. By comparing the electrocatalytic behavior of these cobalt-based catalysts in 1 m KOH electrolyte toward the OER, both 2D Co O and 2D CoSe nanocrystals have lower overpotentials and better electrocatalytic stability than that of 1D nanostructures. The 2D CoSe nanosheets require overpotentials of 372 mV to reach a current density of 50 mA cm with a small Tafel slope of 74 mV dec . A systematic contrast of the electrocatalytic performances for the OER increase in the order: 1D Co O <2D Co O <1D CoSe <2D CoSe . This work provides fundamental insights into the morphology-performance relationships of both Co O and CoSe , which were synthesized through the same approach, providing a solid guide for designing OER catalysts.

Achieving Increased Electrochemical Accessibility and Lowered Oxygen Evolution Reaction Activation Energy for Co2+ Sites with a Simple Anion Preoxidation

“…The Se 3d spectrum of CoSe 2 (Figure 3d) revealed that it contained Se 2 2− ions in major proportion compared to Se 4+ as surface-oxidized SeO 2 and completely reduced Se 2− . 30,40,41,43,44 This has once again confirmed that the formed phase in the synthesis is CoSe 2 as predicted earlier from TEM analysis. Apart from this, both Figure 3b and Figure 3d 4a).…”

“…Figure a is the high-resolution XPS spectrum of the Co 2p state of CoSeO 3 ·2H 2 O which showed the typical Co 2p 3/2 and Co 2p 1/2 doublet at 781.1 and 797 eV with their respective satellite peaks placed adjacent at slightly higher binding energy values. This indicated the presence of Co 2+ ions in CoSeO 3 ·2H 2 O as expected, and no Co 3+ ions were present. ,,, The Se 3d XPS spectrum (Figure b) upon deconvolution revealed that CoSeO 3 ·2H 2 O had almost all of its Se in the Se 4+ state (at 59.2 eV) with a minor amount of Se 2 2– ions. ,− This indicates that the chemical preoxidation of selenide was successful. Similarly, the exclusive presence of Co 2+ ions was witnessed with the Co 2p XPS spectrum (Figure c) of CoSe 2 as well.…”

“…However, the positions of Co 2p 3/2 and Co 2p 1/2 states were shifted by 0.4 eV to a lower binding energy region which is attributed to the poor electronegativity of Se 2 2– ions (compared to SeO 3 2– ions) coordinated to Co 2+ ions in CoSe 2 . The Se 3d spectrum of CoSe 2 (Figure d) revealed that it contained Se 2 2– ions in major proportion compared to Se 4+ as surface-oxidized SeO 2 and completely reduced Se 2– . ,,,, …”

Inception of Co3O4as Microstructural Support to Promote Alkaline Oxygen Evolution Reaction for Co0.85Se/Co9Se8Network

“…Catalytic performance of our best sample is also compared with the standard RuO 2 and earlier reported cobalt-based electrocatalyst representing akin activity in terms of iR -corrected backward LSV scan (Table S2). − This result also fortifies the bulk scale implementation of the Co 3 O 4 /Co 0.85 Se/Co 9 Se 8 framework as a commercial electrocatalyst for alkaline water oxidation purpose.…”

All-In-One Deep Eutectic Solvent toward Cobalt-Based Electrocatalyst for Oxygen Evolution Reaction

“…The satisfactory OER activity could be ascribed to the following factors: (i) The pre-electrocatalyst [Co­(NH 3 ) 4 CO 3 ]Cl contains abundant Co­(III), which is converted to CoOOH during the activation process. (ii) The enriched Co 3+ ions can not only increase the H 2 O molecules adsorption energy but also promote the deprotonation of OOH species to form O 2 . (iii) The 2D structure of activated [Co­(NH 3 ) 4 CO 3 ]Cl drastically increases the catalytic area and exposes more electrochemical active sites, thus facilitating the ion and electron diffusion during OER.…”