Annealing and electrochemically activated amorphous ribbons: Surface nanocrystallization and oxidation effects enhanced for oxygen evolution performance

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 β-NiOOH/FeOOH catalytic species on Ni-Fe-P. The optimal β-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.

Amorphous and defective Co-P-O@NC ball-in-ball hollow structure for highly efficient electrocatalytic overall water splitting

Electrochemical water splitting using hollow and defect-rich catalysts has emerged as a promising strategy for efficient hydrogen production. However, the rational design and controllable synthesis of such catalysts with intricate morphology and composition present significant challenges. Herein, we propose a template-engaged approach to fabricate a novel ball-in-ball hollow structure of Co-P-O@N-doped carbon with abundant oxygen vacancies. The synthesis process involves the preparation of uniform cobalt-glycerate (Co-gly) polymer microspheres as precursors, followed by surface coating with ZIF-67 layer, adjustable chemical etching by phytic acid, and controllable pyrolysis at high temperature. The resulting ball-in-ball structure offers a large number of accessible active sites and high redox reaction centers, facilitating efficient charge transport, mass transfer, and gas evolution, which are beneficial for the acceleration of electrocatalytic reaction. Additionally, density functional theory (DFT) calculations indicate that the incorporation of oxygen and the presence of Co-P dangling bonds in CoP significantly enhance the adsorption of oxygenated species, leading to improved intrinsic electroactivity at the single-site level. As a sequence, the titled catalyst exhibits remarkable electrocatalytic activity and stability for water splitting in alkaline media. Notably, it only requires a low overpotential of 283 mV to achieve a current density of 10 mA cm^-2 for the oxygen evolution reaction. This work may provide some new insights into the design of complex hollow structures of phosphides with abundant defects for energy conversion.

Facile formation of Zn-incorporated NiFe layered double hydroxide as highly-efficient oxygen evolution catalyst

Electrochemical water splitting is the primary method to produce green hydrogen, which is considered an efficient alternative to fossil fuels for achieving carbon neutrality. For meeting the increasing market demand for green hydrogen, high-efficiency, low-cost, and large-scale electrocatalysts are crucial. In this study, we report a simple spontaneous corrosion and cyclic voltammetry (CV) activation method to fabricate Zn-incorporated NiFe layered double hydroxide (LDH) on commercial NiFe foam, which shows excellent oxygen evolution reaction (OER) performance. The electrocatalyst achieves an overpotential of 565 mV and outstanding stability of up to 112 h at 400 mA cm^-2. The active layer for OER is shown to be β-NiFeOOH according to the results of in-situ Raman. Our findings suggest that the NiFe foam treated by simple spontaneous corrosion has promising industrial applications as a highly efficient OER catalyst.