Modulating nickel-iron active species via dealloying to boost the oxygen evolution reaction.

The surface structure and composition of pre-catalysts play a critical role in the surface reconstruction process toward active species during the anodic oxygen evolution reaction (OER). Surface modified methods can accelerate the OER process of alloy ribbons, but the understanding of pre-catalysts and the structure/reactivity of the reconstruction (active) species is still insufficient. Herein, we report a two-step dealloyed Ni-Fe-P alloy ribbon as a highly efficient OER electrocatalyst. By adjusting the surface-derived component, we could regulate Ni/Fe hydroxide active species on the Ni-Fe-P alloy ribbon, enhancing the OER performance. The oxidation and release of P driven by dealloying plays a key role in constructing optimal ß-NiOOH/FeOOH catalytic species on Ni-Fe-P. The optimal ß-NiOOH/FeOOH active species enables Ni-Fe-P alloy to obtain a 104 mV of reduction in overpotential (at 10 mA cm-2) and a 78-fold increase in current density (at overpotential: 300 mV) compared to undealloyed Ni-Fe-P. Our work provides valuable insights into the relationship between the surface structure/composition of alloy bulk electrocatalysts and surface-reconstructed species and a rational design of a surface treatment process.

Electronic tuning of Ni-Fe-Co oxide/hydroxide as highly active electrocatalyst for rechargeable Zn-air batteries.

As a bifunctional oxygen electrocatalyst (oxygen reduction reaction (ORR) and oxygen evolution reaction (OER)), spinel copper cobaltite (CuCo2O4) is attracting significant research interest owing to the tailored Co, Cu electronic structure and ease of adjusting the electrochemically active area. However, its poor OER performance (>300 mV at 10 mA cm-2) limits its practical application for rechargeable zinc-air batteries. Therefore, we construct a CuCo2O4/NiFe LDH oxide/hydroxide interface to tune the properties of Ni, Fe and Co for enhancing OER activity and decreasing the charging overpotential of rechargeable zinc-air batteries. The obtained electrocatalysts show a low overpotential of 251 mV (10 mA cm-2), which is 91 mV lower than the overpotential (342 mV) of CuCo2O4. By in situ Raman, XPS and electrochemical analyses, we ascribe the enhanced OER activity to the increasing Ni/Fe oxidation state triggered by the charge transfer of Ni/Fe and Co, which prompts CuCo2O4/NiFe LDH to rapidly form an active surface layer. Benefiting from enhanced OER performance, zinc-air batteries with a CuCo2O4/NiFe LDH electrode display a high round-trip efficiency with a low voltage gap of ∼0.78 V (10 mA cm-2) due to the obvious decrease in the charging overpotential. These results suggest the importance of tuning the charge transfer on interfaces for designing high-efficiency electrocatalysts.