Electrochemical Synthesis of Cation Vacancy-Enriched Ultrathin Bimetallic Oxyhydroxide Nanoplatelets for Enhanced Water Oxidation

Introduction of Cationic Vacancies into NiFe LDH by In Situ Etching To Improve Overall Water Splitting Performance

Nickel-iron layered double hydroxide (NiFe LDH) is still one of the hot catalysts for electrochemical water decomposition applications, despite its drawbacks, such as intrinsic activity and poor stability. In this work, the NiFe LDH-D1 electrocatalyst with cationic vacancies is successfully prepared by alkaline etching of Zn ion-doped NiFe LDH. The tightly arranged flocculated nanosheet structure on its surface provided a large active area. The cationic vacancies formed by strong alkaline etching not only promote the conversion of active phases such as NiOOH but also strengthen the stability of the electrode and the binding ability with oxygen so that the material has excellent catalytic properties along with alkaline long-term stability. At a current density of 10 and 100 mA cm-2, NiFe LDH-D1 shows a small voltage of 1.56 and 1.94 V, and at a current density of 200 mA cm-2, it performs well in a 72 h electrochemical water decomposition stability test. The present work demonstrates a simple etching strategy for cation vacancy engineering and provides an example of the construction of efficient bifunctional electrocatalysts with long-term stability.

Synchronous coupling of defects and a heteroatom-doped carbon constraint layer on cobalt sulfides toward boosted oxide electrolysis activities for highly energy-efficient micro-zinc-air batteries

The sluggish kinetics of oxygen electrocatalysis reactions on cathodes significantly suppresses the energy efficiency of zinc-air batteries (ZABs). Herein, by coupling in situ generated CoS nanoparticles rich in cobalt vacancies (V_Co) with a dual-heteroatom-doped layered carbon framework, a hybrid Co-based catalyst (Co_1-xS@N/S-C) is designed and synthesized from Co-MOF precursor. Experimental analyses, together with density functional theory (DFT)-based calculations, demonstrate that the facilitated ion diffusion enabled by the introduced V_Co, together with the enhanced electron transport benefiting from the well-designed dual-heteroatom-doped laminated carbon framework, synergistically boost the bifunctional electrocatalytic activity of Co_1-xS@N/S-C (ΔE = 0.76 V), which is much superior to that of CoS@N/S-C without V_Co (ΔE = 0.89 V), CoS without V_Co (ΔE = 1.23 V), and the dual-heteroatom-doped laminated carbon framework. As expected, the further assembled ZAB employing Co_1-xS@N/S-C as the cathode electrocatalyst exhibits enhanced energy efficiency in terms of better cycling stability (510 cycles/170 hours) and a higher specific capacity (807 mA h g^-1). Finally, a flexible/stretched solid state micro-ZAB (F/SmZAB) with Co_1-xS@N/S-C as the cathode electrocatalyst and a wave-shaped GaIn-Ni-based liquid metal as the electronic circuit is further designed, which can display excellent electrical properties and long elongation. This work provides a new defect and structure coupling strategy for boosting the oxide electrolysis activities of Co-based catalysts. Furthermore, F/SmZAB represents a promising solution for a compatible micropower source in wearable microelectronics.

Activated MoS2 by Constructing Single Atomic Cation Vacancies for Accelerated Hydrogen Evolution Reaction

Regulating the electronic structure of MoS2 by constructing cationic vacancies is an effective method to activate and improve its intrinsic properties. Herein, we synthesize the MoS2-based composite with abundant single atomic Mo cation vacancies through uniformly loading nickel-cobalt-Prussian blue analogues (NiCoPBA) (NiCoPBA-MoS2-VMo) by immersing a single Ni atom-decorated MoS2 (Ni-MoS2) into K3[Co(CN)6] solution. Subsequently, NiCoP-MoS2-VMo with improved conductivity is obtained by phosphating the composite as a high-efficiency hydrogen evolution reaction (HER) catalyst. Experiments and theoretical calculations indicate that the electrons of NiCoP are spontaneously transferred to the substrate MoS2-VMo nanosheets in NiCoP-MoS2-VMo, and the moderately oxidized NiCoP is beneficial to the adsorption of OH*. Meanwhile, the mono-atomic Mo cation vacancies of the catalyst modulate the electronic structure of S, optimizing the adsorption of hydrogen in the reaction process. Therefore, NiCoP-MoS2-VMo has enhanced chemical adsorption for H* (on MoS2-VMo) and OH*(on NiCoP), expediting the water-splitting step and HER catalysis, and benefiting from the regulation of the electronic structure induced by the construction of metallic Mo vacancies in MoS2, the as-prepared catalyst displays an overpotential of only 67 mV at 10 mA cm-2 with long-term stability (no current decay over 20 h). This work affords not only a kind of efficient HER catalysts but also a new valuable route for developing inexpensive and high-performance catalysts with single atomic cation vacancies.

Fe(Co)OOH Dynamically Stable Interface Based on Self-Sacrificial Reconstruction for Long-Term Electrochemical Water Oxidation

FeOOH on the real catalytic interface for the oxygen evolution reaction (OER) is chemically unstable to dissolve in alkaline media. Herein, based on the perspective of the dynamically stable interface, we purposely design the well-dispersed nanorod arrays of CoMoO₄ as a host on activated iron foam (IF) to realize the optimal redeposition of FeOOH, constructing a self-sacrificial template rich in the FeOOH surface. Notably, at long-time oxidation potential, the precatalyst FeOOH-CoMoO₄ can realize MoO₄^2- dissolution and redeposition of Co oxyhydroxides on FeOOH host simultaneously, constructing a dynamically stable Fe(Co)OOH interface. The introduction of CoOOH improves conductivity and provides synergistic effect with FeOOH to lower the energy barrier for OER and maintain long-time stability, eventually exhibiting a low overpotential of 298 mV to reach the current density of 100 mA cm^-2 and high stability over 60 h. This work demonstrates the feasibility of manipulating metal dissolution-redeposition process for a dynamically stable interface.

Fe-Induced electronic optimization of mesoporous Co–Ni oxide nanosheets as an efficient binder-free electrode for the oxygen evolution reaction

An efficient binder-free OER electrode CoNiFeO_x/NF with mesoporous structure was synthesized by a facile strategy of hydrothermal method and post-annealing.