Layered Double Hydroxide Nanosheets: Synthesis Strategies and Applications in the Field of Energy Conversion

In recent years, layered double hydroxides (LDH) nanosheets have garnered substantial attention as intriguing inorganic anionic layered clay materials. These nanosheets have captured the attention of researchers due to their unique physicochemical properties. This review aims to showcase the latest advancements in laboratory research concerning LDH nanosheets, with a specific emphasis on their methods of preparation. This review provides detailed insights into the factors influencing the anionic conductivity of LDH, along with delineating the applications of LDH nanosheets in the realm of energy conversion. Notably, the review highlights the crucial role of LDH nanosheets in the oxygen evolution reaction (OER), a vital process in water splitting and diverse electrochemical applications. The review emphasizes the significant potential of LDH nanosheets in enhancing supercapacitor technology, owing to their high surface area and exceptional charge storage capacity. Additionally, it elucidates the prospective application of LDH nanosheets as anion exchange membranes in anion exchange membrane fuel cells, potentially revolutionizing fuel cell performance through improved efficiency and stability facilitated by enhanced ion transport properties.

Oscillatory Reaction Activity of Single Cuprous Oxide Microparticles with NO2

Here, we report on using dark-field microscopy (DFM) as a simple and low-cost imaging platform to visually resolve the kinetics of single cuprous oxide (Cu₂O) microparticles for NO₂ removal in a real-time manner. Unexpectedly, we find that the redox reaction between Cu₂O microparticles and NO₂ is oscillating with the reaction time. Specifically, the oscillatory behavior of single Cu₂O microparticles for NO₂ reduction shows a large particle-to-particle variability, which is also dependent upon the NO₂ pressure and Cu₂O facets. A combined DFM imaging, spectroscopic, scanning electron microscopy, and density functional theory study uncovers that Cu₂O is gradually transformed to copper nitrate hydroxide [Cu₂(NO₃)(OH)₃], and this oscillatory reaction is attributed to the cyclic formation and structural collapse of Cu₂(NO₃)(OH)₃. The present findings open an alternative avenue for probing structure-performance relationships, which are anticipated to benefit the creation of functional materials for air purification.

Advanced electrocatalysts based on two-dimensional transition metal hydroxides and their composites for alkaline oxygen reduction reaction

The electrocatalytic oxygen reduction reaction (ORR) is a crucial part in developing high-efficiency fuel cells and metal-air batteries, which have been cherished as clean and sustainable energy conversion devices/systems to meet the ever-increasing energy demand. ORR electrocatalysts currently employed in the cathodes of fuel cells and metal-air batteries are mainly based on high-cost and scarce noble metal elements. It is thus of great importance to develop cheap and earth-abundant ORR electrocatalysts. In this aspect, redox-active transition metal hydroxides, a class of multifunctional inorganic layered materials, have been proposed as prospective candidates on account of their abundance and high ORR activities. In this article, the preparation and structural evolution of transition metal hydroxides, in particular their exfoliation into two-dimensional (2D) nanosheets, as well as compositing/integrating with catalytic active and/or conductive components to overcome the insulating nature of hydroxides in alkaline ORR, are summarized. Recent advances have demonstrated that 2D transition metal hydroxides with carefully tuned compositions and elaborately designed nanoarchitectures can achieve both high activity and high pathway selectivity, as well as excellent stability comparable to those of commercial Pt/C electrocatalysts. To realize the dream of renewable electrochemical energy conversion, new strategies and insights into rational designing of 2D hydroxide-based nanostructures with further enhanced electrocatalytic performance are still to be vigorously pursued.

Activity enhancement of layered cobalt hydroxide nanocones by tuning interlayer spacing and phosphidation for electrocatalytic water oxidation in neutral solutions

We explored the electrocatalytic performance of cobalt hydroxide nanocones in neutral solutions via tuning the interlayer spacing and phosphidation.