Phosphide-Based Electrocatalysts for Urea Electrolysis: Recent Trends and Progress.

Electrolysis is a trend in producing hydrogen as a fuel for renewable energy development, and urea electrolysis is considered as one of the advanced electrolysis processes, where efficient materials still need to be explored. Notably, urea electrolysis came into existence to counter-part the electrode reactions in water electrolysis, which has hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Among those reactions, OER is sluggish and limits water splitting. Hence, urea electrolysis emerged with urea oxidation reaction (UOR) and HER as their reactions to tackle the water electrolysis. Among the explored materials, noble-metal catalysts are efficient, but their cost and scarcity limit the scaling-up of the Urea electrolysis. Hence, current challenges must be addressed, and novel efficient electrocatalysts are to be implemented to commercialize urea electrolysis technology. Phosphides, as an efficient UOR electrocatalyst, have gained huge attention due to their exceptional lattice structure geometry. The phosphide group benefits the water molecule adsorption and water dissociation, and facilitates the oxyhydrate of the metal site. This review summarizes recent trends in phosphide-based electrocatalysts for urea electrolysis, discusses synthesis strategies and crystal structure relationship with catalytic activity, and presents the challenges of phosphide electrocatalysts in urea electrolysis.

Tuning the Structural and Electronic Properties of Zn-Cr LDH/GCN Heterostructure for Enhanced Photodegradation of Estrone in UV and Visible Light.

Estrone is an emerging contaminant found in waters and soils all over the world. Conventional water treatment methods are not suitable for estrone removal due to its nonpolarity and low bioavailability. Heterogeneous photocatalysis is a promising approach; however, pristine semiconductors need optimization for efficient estrone photodegradation. Herein, we compared Zn-Cr LDH/GCN heterostructures obtained by three different synthesis methods. The influence of the GCN content in the heterostructure on photoactivity was also tested. The morphology, structure, and electronic properties of the materials were analyzed and compared. The photocatalytic kinetic tests were conducted with 1 ppm of estrone in both UV and visible light, separately. The HLDH-G50 material, obtained by the hydrothermal route and containing 50 wt % of GCN exhibited the highest photocatalytic efficiency. After 1 h, 99.5% of the estrone was degraded in visible light. In UV light, the pollutant concentration was below the detection limit after 0.5 h. The superior effectiveness was caused by numerous factors such as high homogeneity of the formed heterostructure, lower band gap energy of hydrothermal LDH, and increased photocurrent. These characteristics led to prolonged lifetimes of charge carriers, a wider light absorption range, and uniformity of the material for predictable performance. This study highlights the importance of a proper heterostructure engineering strategy for acquiring highly effective photocatalysts designed for water purification. In particular, this work provides innovative insight into comparing different synthesis methods and their influence on materials' properties.

Recent developments in piezo-photocatalytic CO2 reduction: concepts, mechanism, and advances.

Out of the high number of photocatalytic applications, CO2 reduction has proved to be quite a boon for the present world. Increasing CO2 emissions owing to fossil fuel usage has been a menace to our society. To date, many methods have been developed to redress the situation. One of them is photocatalysis, which has been a well-known branch of energy and environmental applications since 1972. This is due to its low energy consumption and green nature. In recent years, a new phenomenon has come into existence wherein a combination of mechanical energy and photocatalysis can increase the efficiency of any catalytic process. In this regard, this frontier article will discuss the recent developments in piezo-photocatalysis for CO2 reduction. The main focus will be understanding the underlying mechanisms of efficiency enhancements in photocatalytic systems. Initially, the mechanism of CO2 reduction and its current needs will be discussed in the introduction. Further, a collection of recent reports from the literature and various material systems will be discussed to gain insights into the latest developments in the area. Then, literature and references that are purely mechanism-based with deeper analysis will be discussed, along with crucial characterization techniques for piezo-photocatalysts. Many factors need to be factored in for a better understanding of piezo-photocatalysis, e.g., factors such as piezo energy source, material design, and CO2 adsorption, require more attention to increase the CO2 reduction capability of photocatalysts. Based on the discussions in this article, researchers will gain new perceptions on the combination of vibrational energy and light energy to enhance CO2 reduction yields. Moreover, this article can advance understanding of techniques such as Kelvin probe microscopy, the requirement of simulation studies, and CO2 reduction mechanisms to better understand the piezo behavior of materials and ways to improve them for maximum product yield.

Enhancing the Hydrogen Evolution Performance of Tungsten Diphosphide on Carbon Fiber through Ruthenium Modification.

Hydrogen-based energy systems hold promise for sustainable development and carbon neutrality, minimizing environmental impact with electrolysis as the preferred fossil-fuel-free hydrogen generation method. Effective electrocatalysts are required to reduce energy consumption and improve kinetics, given the need for additional voltage (overpotential, η) despite the theoretical water splitting potential of 1.23 V. To date, platinum has been acknowledged as the most effective but expensive hydrogen evolution reaction (HER) catalyst. Hence, we introduce a cost-effective (∼2-fold cheaper) ruthenium-modified tungsten diphosphide (Ru/WP2) catalyst on carbon fiber for HER in ∼0.5 M H2SO4, with η ≈ 34 mV at -10 mA cm-2 which can be comparable (only ∼2-fold higher) to benchmark Pt/C (η ≈ 17 mV). The HER performance of WP2 can be enhanced through the modification of ruthenium, as indicated by the electrochemical characterizations. Considering the Tafel value of ∼40 ± 0.2 mV dec-1, it can be inferred that Ru/WP2 follows the Volmer-Heyrovsky reaction pathway for hydrogen generation. Furthermore, the Faradaic efficiency estimation indicates that Ru/WP2 demonstrates a minimal loss of electrons during the electrochemical reaction with an estimated value of ∼98.7 ± 1.4%. Therefore, this study could emphasize the potential of the Ru/WP2 electrode in advancing sustainable hydrogen production through water splitting.