First Principles Study of Cobalt (Hydr)oxides under Electrochemical Conditions

Abstract

Density functional theory (DFT) calculations with on-site Coulomb repulsion are carried out to study the relative stabilities of crystalline cobalt oxides and hydroxidesCoO, Co(OH)2, Co3O4, CoO(OH), and CoO2in electrochemical environment. Co(OH)2 is the thermodynamic ground state under reducing conditions, i.e., at voltages V < 0 relative to the standard hydrogen electrode (SHE) potential in acidic solution, whereas CoO(OH) and CoO2 are stable under oxidizing conditions, i.e., at external voltage larger than 1.23 eV vs SHE in basic solution. These results, combined with surface structure studies of the (0001) natural cleavage surface of CoO(OH), show that a CoO2 x– (x = 0–0.5) layer is present when the surface is exposed to solution under oxidizing conditions, in agreement with recent experimental findings. Study of the energetics of water oxidation at regular surface sites of CoO(OH)(0001) indicates however that water deprotonation to form a surface OH species is energetically very costly. Different active sites, e.g. steps, are thus responsible for the observed high activity of crystalline cobalt oxide for electrochemical oxygen evolution.

A first principles study on structural, dynamical, and mechanical stability of newly predicted delafossite HCoO2 at high pressure

“…The calculated lattice parameters along with experimental and other theoretical data are summarised in Table . The table shows an excellent agreement between the calculated and available experimental and other theoretical data . The deviation in band gap from experimental band gap is 41% and 8%, respectively, for LDA and GGA.…”

“…The heterogenite, like many other delafossites forms two phases: heterogenite‐3R in rhombohedral structure with space group R m and heterogenite‐2H with space group P6 3 /mmc, most common form being the 3R‐heterogenite phase . Up to now, only few attempts have been made to synthesise this newly proposed hydroxide . Chen et al reported the relative stability of crystalline cobalt oxides (CoO 2 ), hydroxides (CoO (OH)) and oxyhydroxides (CoOOH) in electrochemical environment.…”

Water Oxidation at Electrodes Modified with Earth‐Abundant Transition‐Metal Catalysts

“…The authors also argued that the catalytic activity observed in spinel type Co3O4 arises from structural remodeling of the latter to generate a layered double-hydroxide surface, the genuine active structure. [77] This surface transformation as the origin of the high catalytic activity is also supported by theoretical DFT calculations, [28] which confer low activity on the regular sites of CoO(OH) and CoO2, the thermodynamically stable CoOx phases under water oxidation conditions. This is also the case, for example, in the WOC activity found in Co(PO3)2 modified anodes.…”

A highly-efficient oxygen evolution electrode based on defective nickel-iron layered double hydroxide

“…Consequently, the bridge site between Ni and Fe was proposed to be the active site for OER (Fig. S11) [43]. The OER on NiFe catalysts' surface involved a four-electron process, as revealed in Fig.…”