Electronic Modulation of Electrocatalytically Active Center of Cu7S4 Nanodisks by Cobalt-Doping for Highly Efficient Oxygen Evolution Reaction

Aluminum-Tailored Energy Level and Morphology of Co3- x Alx O4 Porous Nanosheets toward Highly Efficient Electrocatalysts for Water Oxidation

Tuning energy levels plays a crucial role in developing cost-effective, earth-abundant, and highly active oxygen evolution catalysts. However, to date, little attention has been paid to the effect of using heteroatom-occupied lattice sites on the energy level to engineer electrocatalytic activity. In order to explore heteroatom-engineered energy levels of spinel Co₃ O₄ for highly-effective oxygen electrocatalysts, herein Al atoms are directly introduced into the crystal lattice by occupying the Co²⁺ ions in the tetrahedral sites and Co³⁺ ions in the octahedral sites (denoted as Co²⁺ _Td and Co³⁺ _Oh , respectively). Experimental and theoretical simulations demonstrate that Al³⁺ ions substituting Co²⁺ _Td and Co³⁺ _Oh active sites, especially Al³⁺ ions occupying the Co²⁺ _Td sites, optimizes the adsorption, activation, and desorption features of intermediate species during oxygen evolution reaction (OER) processes. As a result, the optimized Co_1.75 Al_1.25 O₄ nanosheet exhibit unprecedented OER activity with an ultralow overpotential of 248 mV to deliver a current of 10 mA cm^-2 , among the best Co-based OER electrocatalysts. This work should not only provide fundamental understanding of the effect of Al-occupied different Co sites in Co_3-x Al_x O₄ composites on OER performance, but also inspire the design of low-cost, earth-abundant, and high-active electrocatalysts toward water oxidation.

Synthesis and Anisotropic Electrocatalytic Activity of Covellite Nanoplatelets with Fixed Thickness and Tunable Diameter

Size- and shape-dependent electrochemical activity of nanostructures reveals relationships between nanostructure design and electrochemical performance. However, electrochemical performance of aspect-ratio-tunable quasi-two-dimensional (2D) nanomaterials with anisotropic properties has not been fully investigated. We prepared monodispersed hexagonal covellite (CuS) nanoplatelets (NPls) of fixed thickness (∼2 nm) but broadly tunable diameter (from 8 to >100 nm). These span a range of aspect ratios, from ∼4 to >50, connecting quasi-isotropic and quasi-2D regimes. Tests of electrochemical activity of the NPls for the oxygen reduction reaction in alkaline solution showed improved activity with increasing diameter. Combining experimental results with density functional theory calculations, we attribute size-dependent enhancement to anisotropy of conductivity and electrochemical activity. The lowest computed oxygen adsorption energy was on Cu sites exposed by cleaving covellite along (001) planes through tetrahedrally coordinated Cu atoms. The specific surface area of these planes, which are the top and bottom surfaces of the NPls, remains constant with changing diameter, for fixed NPl thickness. However, charge transport through the electrocatalyst film improves with increasing NPl diameter. These CuS NPl-carbon nanocatalysts provide inspiration for creating well-controlled layered nanomaterials for electrochemical applications and open up opportunities to design new electrocatalysts using transition-metal sulfides.

A Confinement Strategy for Stabilizing ZIF-Derived Bifunctional Catalysts as a Benchmark Cathode of Flexible All-Solid-State Zinc-Air Batteries

Carbon composites with embedded metal/metal oxides represent a group of versatile electrochemical catalysts that has attracted extensive research attention. However, the beauty of this concept is marred by the severe carbon evaporation and the aggregation of metal species during their synthetic process, leading to the diminishment in active sites and catalytic durability. To address this issue, this study demonstrates the feasibility of utilizing Al₂ O₃ nanolayer to trap volatile carbon and nitrogen species and alleviate the aggregation of Co species during the pyrolysis of the Zn/Co-ZIFs (ZIF = zeolitic imidazolate framework). With the confinement effect of an Al₂ O₃ nanolayer, the derived Co₃ O₄ -embedded N-doped porous carbon grown on carbon cloth presents outstanding bifunctional catalytic activity with a small potential difference of 787 mV between the half-wave potential of the oxygen reduction reaction and an overpotential at 10 mA cm^-2 of the oxygen evolution reaction. More impressively, an advanced flexible rechargeable zinc-air battery in all-solid-state configuration is assembled, which achieves the maximum power density of 72.4 mW cm^-3 and good cycling stability. The insights produced in this work will provide guidance for the rational design of metal/carbon hybrid catalysts and low-cost renewable energy systems.

First-principles design of bifunctional oxygen reduction and evolution catalysts through bimetallic centers in metal–organic frameworks

Bi-metallic Fe_xCo_3−x(THT)₂ nanosheets exhibit bifunctional catalytic activity for both the ORR and OER. The ORR occurs on the Co atom, while the active site for the OER is the Fe atom.