Short O–O separation in layered oxide Na _0.67 CoO ₂ enables an ultrafast oxygen evolution reaction

Abstract

The layered oxide Na0.67CoO2 with Na+ occupying trigonal prismatic sites between CoO2 layers exhibits a remarkably high room temperature oxygen evolution reaction (OER) activity in alkaline solution. The high activity is attributed to an unusually short O–O separation that favors formation of peroxide ions by O−–O– interactions followed by O2 evolution in preference to the conventional route through surface O–OH– species. The dependence of the onset potential on the pH of the alkaline solution was found to be consistent with the loss of H+ ions from the surface oxygen to provide surface O− that may either be attacked by solution OH− or react with another O−; a short O–O separation favors the latter route. The role of a strong hybridization of the O–2p and low-spin CoIII/CoIV π-bonding d states is also important; the OER on other CoIII/CoIV oxides is compared with that on Na0.67CoO2 as well as that on IrO2.

Utilizing ion leaching effects for achieving high oxygen-evolving performance on hybrid nanocomposite with self-optimized behaviors

“…3f, hybrid BSCF exhibits stable crystalline structures after OER, where the fast Fourier transformed (FFT) pattern is similar to that of reported edge/face-sharing structures [42][43][44] . The edge/face-sharing structures are very stable for electrochemical reactions as reported 30,[42][43][44] , which may account for the slight increase of XRD peak intensity and the good OER stability for hybrid BSCF here ( Supplementary Fig. 11b and Supplementary Fig.…”

“…For example, low-valence Co ions (Co 2+/3+ ) tend to be oxidized to Co 3+/4+ cations under alkaline OER conditions and this change would lead to the reconstruction, collapse and loss of surface crystalline matrix to form amorphous oxy(hydroxide) layers, as known in the cases of H 2 /Ar reduced LCF 4 (Co 2+/3+ ), Li 2 Co 2 O 4 21 (Co 3+ ), and BSCF5582 8 (Co 2+/3+ ) fabricated from liquid-state reaction synthesis method. Contrarily, high-valence transition-metal ions (e.g., Co 3+/4+ couples) could relieve the effects of electro-derived oxidation process for alkaline OER, such as high-valence PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (Co 3+/4+ ) 29 , Ba 4 Sr 4 (Co 0.8 Fe 0.2 ) 4 O 15 (Co 3+/4+ ) 16 , and Na 0.67 CoO 2 (Co 3+/4+ ) 30 with good structural stabilities. To further optimize the pristine ion combination in hybrid materials, we also apply a self-assembly synthesis method.…”

Bulk and Surface Properties Regulation of Single/Double Perovskites to Realize Enhanced Oxygen Evolution Reactivity

“…Similarly, the Mo‐ L 2,3 edge spectra before and after OER catalysis also suggest a high stability of the valence state (Figure S5 b). After OER catalysis the Co‐ L 2,3 and Fe‐ L 2,3 sXAS spectra of the material (Figure b and c) exhibits features only slightly higher in energy, indicating an increase of the valence state of Co and Fe ions in agreement with our hard X‐ray XAS result . By comparing the Co‐ L 3 edge peak position with the given reference samples, the average Co valence state of the SP/DP after OER catalysis was calculated to be +3.49, close to the value of +3.4 in the highly efficient SrCoO 2.7 electrocatalyst .…”

Adaptive Bifunctional Electrocatalyst of Amorphous CoFe Oxide @ 2D Black Phosphorus for Overall Water Splitting

“…[32] Generally speaking,t he OER performance of LOM is highly associated with pH at the RHE scale due to the easier deprotonation process at higher pH. [33] As presented in Figure 5a,a tt he RHE scale,t he onset potential of Co-FeO@BP decreases with increasing pH. In conventional AEM, there are four concerted proton-electron transfer steps on surface metal centers,yielding pH-independent activity at the RHE scale.W hile in LOM, the rate-limiting step is the deprotonation of hydroxyl groups.T he pK a of the surface deprotonation eventually results in the overall pH-dependent kinetics.F urthermore,d istinguished from AEM, during the LOM pathway,t here produce peroxo-like (O 2…”