Cobalt/Cobalt Oxide Surface for Water Oxidation

Abstract

Water splitting to produce molecular hydrogen is an essential method to store sustainable energies. One of the bottlenecks for water splitting is the availability of an efficient and stable water-oxidizing catalyst. Herein, metallic cobalt foil, after the treatment under high potential (10–60.0 V), was used for water oxidation. The cobalt/cobalt oxide surface was characterized by various spectroscopic, microscopy, X-ray diffraction, and electrochemical methods. Diffuse reflectance infrared Fourier transform spectroscopy showed peaks for Co oxide at 489 and 595 cm–1 attributed to the stretching of Co–O and bending of O–Co–O bonds in the CoO6 octahedra. Small aggregated particles (ca. 50–100 nm) with a spherical morphology were detected by scanning electron microscopy, and high-resolution transmission electron microscopy from the mechanically separated particles indicated spacings of 2.5–2.6 Å corresponding to the interplanar spacings of the (011) plane for Co3O4. Selected area (electron) diffraction showed concentric rings centered on a bright central spot, indicating a polycrystalline material. Each ring is related to planes of different orientation and different interplanar spacing, attributed to metallic cobalt and cobalt oxides. X-ray diffraction resulted in patterns corresponding to Co3O4 and CoO­(OH), and X-ray photoelectron spectroscopy could confirm the formation of metallic cobalt, Co­(II) and Co­(III) oxides on the surface of the electrode. These results suggest that the oxide on the surface of foil could be a mixture of different phases of Co oxide containing Co3O4 and CoO­(OH). Under overpotentials of 460 and 780 mV, current densities of 0.144 and 0.5 A/cm2 were observed at pH-14 without dropping of IR. To the best of our knowledge, the three-dimensional electrode obtained here is among the most efficient cobalt-based water-oxidizing electrodes under alkaline conditions reported so far and may be applied in large scale water-splitting systems.

Electrocatalytic hydrogen evolution using triaryl corrole cobalt complex

“…The N 1s spectra (Figure c) of 1 and 3 deconvoluted into two peaks at 398.9/398.5 and 400.0/398.7 eV, which could be assigned to pyrrolic N and meso‐group N (cyano group and N , N ′‐dimethyl group) . The peak of Co 2p 3/2 and Co 2p 1/2 of 2 was at 778.0/794.8 eV (Figure d), which is consistent with the literature about Co (III) oxidation state . Compared with 2 , the Co 2p 3/2 and Co 2p 1/2 XPS spectra of 1 and 3 shifted to a higher binding energy at 780.0/795.1 and 780.4/795.3 eV, indicating that meso‐group could affect the electronic interaction between the center metal and corrole ligand.…”

Boosting Photocatalytic Activity Using Carbon Nitride Based 2D/2D van der Waals Heterojunctions

“…Since carbon nitride has a poor oxidizing valence band, the amalgamation of CN with water oxidation catalysts is an appropriate approach to enhance reaction kinetics . Cobalt-based catalysts have demonstrated promising oxygen evolution performance, which makes them an ideal candidate for the formation of 2D/2D heterojunctions with carbon nitride. − Interestingly, the growth of cobalt hydroxide (Co­(OH) 2 ) in the presence of carbon nitride sheets can lead to the formation of a layered structure. For example, Zhang et al have fabricated a Co­(OH) 2 /g-C 3 N 4 heterojunction by using a cobalt nitrate precursor in the presence of NH 3 , which demonstrated enhanced visible absorption .…”

One-step synthesis of mesoporous Cobalt sulfides (CoSx) on the metal substrate as an efficient bifunctional electrode for overall water splitting

“…However, to date, only cobalt oxides are directly obtained after anodization process. [23][24][25] Herein, for the first time, a mesoporous cobalt sulfide (CoSx) structure was fabricated via this facile, one-step anodization method, with merely treating the Co foil in the electrolyte for 5 min. This porous, robust, self-grown nanostructure not only brings high surface active sites for catalytic reaction, but also facilitates electron transport across the active material.…”