High-spin Co3+ in cobalt oxyhydroxide for efficient water oxidation

Abstract

Cobalt oxyhydroxide (CoOOH) is a promising catalytic material for oxygen evolution reaction (OER). In the traditional CoOOH structure, Co3+ exhibits a low-spin state configuration ($${t}_{2{{{{{\rm{g}}}}}}}^{6}{e}_{{{{{{\rm{g}}}}}}}^{0}$$ t 2 g 6 e g 0 ), with electron transfer occurring in face-to-face $${t}_{2{{{{{\rm{g}}}}}}}^{*}$$ t 2 g * orbitals. In this work, we report the successful synthesis of high-spin state Co3+ CoOOH structure, by introducing coordinatively unsaturated Co atoms. As compared to the low-spin state CoOOH, electron transfer in the high-spin state CoOOH occurs in apex-to-apex $${e}_{{{{{{\rm{g}}}}}}}^{*}$$ e g * orbitals, which exhibits faster electron transfer ability. As a result, the high-spin state CoOOH performs superior OER activity with an overpotential of 226 mV at 10 mA cm−2, which is 148 mV lower than that of the low-spin state CoOOH. This work emphasizes the effect of the spin state of Co3+ on OER activity of CoOOH based electrocatalysts for water splitting, and thus provides a new strategy for designing highly efficient electrocatalysts.

Fe-Doped CoS2 Nanocages as Bifunctional Electrocatalysts for Water Splitting

“…As the Fe doping content increases, the Co 2p of CN/Fe-CoS 2 -0.2 appears as a new diffraction peak corresponding to Co 3+ at 778.8 and 793.5 eV, and Fe doping is facilitated to move Co 2+ to Co 3+ . Co 3+ has been reported to be the active site for the large H 2 O molecule adsorption energy and low coordination number, leading to high-efficiency catalytic activity. , Upon a further increase in the Fe doping level, the promotional effect of Fe on the conversion of Co 2+ to Co 3+ reaches a critical point. The Co 2p spectrum of CN/Fe-CoS 2 -0.3 exhibits a similarity to that of CN/Fe-CoS 2 -0.2.…”

“…50 Co 3+ has been reported to be the active site for the large H 2 O molecule adsorption energy and low coordination number, leading to high-efficiency catalytic activity. 51,52 Upon a further increase in the Fe doping level, the promotional effect of Fe on the conversion of Co 2+ to Co 3+ reaches a critical point. The Co 2p spectrum of CN/Fe-CoS 2 -0.3 exhibits a similarity to that of CN/Fe-CoS 2 -0.2.…”

The spin polarization strategy regulates heterogeneous catalytic activity performance: from fundamentals to applications

“…When the energy of the anti-bonding orbital is higher than that of the Fermi level, the degree of occupation is lower, the adsorption strength is higher, and the spin polarization is higher. 71…”

“…58,75,76 Moreover, the electron transfer rate that occurs in the top-to-top orbital is higher than that in the face-to-face orbital. 77 Hence, Xue et al 71 reported that, compared with the low spin state with the orbital near the Fermi level, the high spin state with the orbital near the Fermi level has a faster electron transfer rate. Thus, the spin transition would impact the rate of electron transfer and regulate the catalytic reaction dynamics (Fig.…”

“…Moreover, Zhang et al 71 utilized the π-donor O 2− ligand to coordinate with an unsaturated Co atom in order to synthesize CoOOH (S-CoOOH) with high-spin Co 3+ . The transition of the spin state results in a change in the electron configuration, giving rise to the manifestation of magnetism (Fig.…”