15 February 2024 | Xin Zhang, Haoyin Zhong, Qi Zhang, Qihan Zhang, Chao Wu, Junchen Yu, Yifan Ma, Hang An, Hao Wang, Yiming Zou, Caozheng Diao, Jingsheng Chen, Zhi Gen Yu, Shibo Xi, Xiaopeng Wang, Junmin Xue
Cobalt oxyhydroxide (CoOOH) is a promising material for oxygen evolution reaction (OER) due to its earth abundance and high electrochemical activity. In this study, the authors report the successful synthesis of high-spin state Co³⁺ CoOOH by introducing coordinatively unsaturated Co atoms, which leads to faster electron transfer in apex-to-apex e_g orbitals compared to the low-spin state CoOOH. This results in superior OER activity, with an overpotential of 226 mV at 10 mA cm⁻², 148 mV lower than that of low-spin state CoOOH. The high-spin state Co³⁺ is confirmed through SQUID, EPR, and XAS measurements, exhibiting ferromagnetic behavior at 300 K with unpaired electrons. Density functional theory (DFT) calculations reveal that the appearance of high-spin state Co³⁺ is attributed to the emergence of coordinatively unsaturated Co and O atoms at the edges of CoOOH. The enhanced OER activity is attributed to the increased electronic states around the Fermi level, facilitating faster electron transfer. The high-spin state CoOOH also shows long-term structural and catalytic stability in alkaline electrolyte. This work highlights the significant impact of the spin state of Co³⁺ on OER activity and provides a new strategy for designing highly efficient electrocatalysts.Cobalt oxyhydroxide (CoOOH) is a promising material for oxygen evolution reaction (OER) due to its earth abundance and high electrochemical activity. In this study, the authors report the successful synthesis of high-spin state Co³⁺ CoOOH by introducing coordinatively unsaturated Co atoms, which leads to faster electron transfer in apex-to-apex e_g orbitals compared to the low-spin state CoOOH. This results in superior OER activity, with an overpotential of 226 mV at 10 mA cm⁻², 148 mV lower than that of low-spin state CoOOH. The high-spin state Co³⁺ is confirmed through SQUID, EPR, and XAS measurements, exhibiting ferromagnetic behavior at 300 K with unpaired electrons. Density functional theory (DFT) calculations reveal that the appearance of high-spin state Co³⁺ is attributed to the emergence of coordinatively unsaturated Co and O atoms at the edges of CoOOH. The enhanced OER activity is attributed to the increased electronic states around the Fermi level, facilitating faster electron transfer. The high-spin state CoOOH also shows long-term structural and catalytic stability in alkaline electrolyte. This work highlights the significant impact of the spin state of Co³⁺ on OER activity and provides a new strategy for designing highly efficient electrocatalysts.