Category Archives: Chemistry – An Asian Journal:

Improvements in the Electrochemical Performance of Sodium Manganese Oxides by Ti Doping for Aqueous Mg‐Ion Batteries

Posted on 13 September 2023 by

Sodium manganese oxides as positive electrode materials for aqueous magnesium-ion batteries have attracted extensive attention. However, the structural stability of sodium manganese oxides is poor, thus we proposed a production process of titanium-doped sodium manganese oxides and used it as positive electrode materials for aqueous magnesium-ion batteries to obtain good electrochemical performance.

Abstract

In recent times, the research on cathode materials for aqueous rechargeable magnesium ion battery has gained significant attention. The focus is on enhancing high-rate performance and cycle stability, which has become the primary research goal. Manganese oxide and its derived Na−Mn−O system have been considered as one of the most promising electrode materials due to its low cost, non-toxicity and stable spatial structure. This work uses hydrothermal method to prepare titanium gradient doped nano sodium manganese oxides, and uses freeze-drying technology to prepare magnesium ion battery cathode materials with high tap density. At the initial current density of 50 mA g⁻¹, the NMTO-5 material exhibits a high reversible capacity of 231.0 mAh g⁻¹, even at a current density of 1000 mA g⁻¹, there is still 122.1 mAh g⁻¹. It is worth noting that after 180 cycles of charging and discharging at a gradually increasing current density such as 50–1000 mA g⁻¹, it can still return to the original level after returning to 50 mA g⁻¹. Excellent electrochemical performance and capacity stability show that NMTO-5 material is a promising electrode material.

Stoichiometric Control of Guest Recognition of Self‐Assembled Palladium(II)‐Based Supramolecular Architectures

Posted on 11 September 2023 by nJess L. Algar, nJames E. Phillips, nJack D. Evans, nDan Prestonn

Stoichiometry can be used in a flexible system to switch between a 2+2 [Pd₂(L)₂]⁴⁺ macrocycle and a [Pd(L)₂]²⁺ compound where the uncomplexed arms occlude access to the cationic part of the molecule by guests. We can thereby controllably regulate affinity between our host and an aromatic guest.

Abstract

We report flexible [Pd(L)₂]²⁺ complexes where there is self-recognition, driven by π-π interactions between electron-rich aromatic arms and the cationic regions they are tethered to. This self-recognition hampers the association of these molecules with aromatic molecular targets in solution. In one case, this complex can be reversibly converted to an ‘open’ [Pd₂(L)₂]⁴⁺ macrocycle through introduction of more metal ion. This is accomplished by the ligand having two bidentate binding sites: a 2-pyridyl-1,2,3-triazole site, and a bis-1,2,3-triazole site. Due to favourable hydrogen bonding, the 2-pyridyl-1,2,3-triazole units reliably coordinate in the [Pd(L)₂]²⁺ complex to control speciation: a second equivalent of Pd(II) is required to enforce coordination to bis-triazole sites and form the macrocycle. The macrocycle interacts with a molecular substrate with higher affinity. In this fashion we are able to use stoichiometry to reversibly switch between two different species and regulate guest binding.

Temperature‐Dependent Structures of Single‐Atom Catalysts

Posted on 11 September 2023 by

The local structures of Ni single-atom catalysts were regulated by adjusting carbonization temperature of their precursors. The oxidation state, total coordination number, and bond length of the metal center decrease with the increase of the carbonization temperature. The relationship between structure and performance was explored. The structure after regulation could promote the adsorption of CO₂ and improve electrocatalytic CO₂ reduction activity.

Abstract

Single-atom catalysts (SACs) have the unique coordination environment and electronic structure due to the quantum size effect, which plays an essential role in facilitating catalytic reactions. However, due to the limited understanding of the formation mechanism of single atoms, achieving the modulation of the local atomic structure of SACs is still difficult and challenging. Herein, we have prepared a series of Ni SACs loaded on nitrogen-doped carbon substrates with different parameters using a dissolution-and-carbonization method to systematically investigate the effect of temperature on the structure of the SACs. The results of characterization and electrochemical measurements are analyzed to reveal the uniform law between temperature and the metal loading, bond length, coordination number, valence state and CO₂ reduction performance, showing the feasibility of controlling the structure of SACs through temperature to regulate the catalytic performance. This is important for the understanding of catalytic reaction mechanisms and the design of efficient catalysts.

Harnessing Nanomaterials for Enhanced Biohydrogen Generation from Wastewater

Posted on 8 September 2023 by nI. Ihsanullah, nMuhammad Bilal, nMuhammad Tariq Khann

The present review describes an overview of the role of nanomaterials in biohydrogen production from wastewater.

Abstract

Biohydrogen is considered a green fuel due to its eco-friendly nature since it only produces water and energy on combustion. However, their lower yield and production rate is one of the foremost challenges that need an instant sustainable approach. The use of nanotechnology is a potential approach for the enhanced generation of biohydrogen, owing to the significant characteristics of the nanomaterials such as greater specificity, high surface-area-to-volume ratio, better reactivity and dispersibility, enhanced catalytic activity, superb selectivity, greater electron transfer, and better anaerobic microbiota activity. This article explores the recent trends and innovations in the production of biohydrogen from wastewater through the applications of different nanomaterials. The potential of various nanomaterials employed for biohydrogen production from wastewater is evaluated and the impacts of important parameters such as the concentration and size of the nanomaterials, temperature, and pH on the production and yield of biohydrogen are explained in detail. Several pathways involved in the mechanistic approach of biohydrogen generation from wastewater are critically assessed. Lastly, numerous technological challenges are highlighted and recommendations regarding future research are also provided.

Effect of Synthetic Methodology on the Physicochemical Attributes and Electrocatalytic Activity of NiAl‐LDHs for the Oxygen Evolution Reaction

Posted on 30 August 2023 by nAamir Hanif, nM. Yusuf Khan, nM. Ali Ehsan, nAasif Helal, nM. Abdul Aziz, nAbuzar Khann

Exfoliated NiAl LDH synthesized by aqueous miscible organic solvent treatment exhibited a lower overpotential and higher current density than its analogues due to more accessible active catalytic sites.

Abstract

Layered double hydroxides (LDHs) are promising materials for oxygen evolution reactions (OERs), a key component of water splitting to produce hydrogen and oxygen via water electrolysis. However, the performance of LDHs can be limited by their low surface area and poor accessibility of active sites. In this work, we synthesized highly exfoliated 2D NiAl-LDHs by aqueous miscible solvent treatment method (AMOST) and compared its electrocatalytic efficiency with its analogue synthesised via slow urea hydrolysis. We demonstrate that the exfoliated 2D LDHs prepared by AMOST method have a higher surface area and more active sites than the crystalline LDHs obtained through urea hydrolysis, resulting in a superior OER activity and efficiency. The exfoliated 2D LDHs required a lower overpotential of 280 mV to reach a current density of 50 mA cm⁻² and it also outperformed IrO₂, a benchmark OER catalyst, in terms of overpotential and stability. We demonstrate that the physicochemical properties of nanosheets derived from NIAl-LDH-based materials are strongly influenced by the synthetic methodology, which affects the exfoliation degree, surface area and active site density. These factors are crucial for improving the OER catalytic performance of these materials, as shown by our results.

Synergistic Effect of Allium‐like Ni9S8 & Cu7S4 Electrodeposited on Nickel Foam for Enhanced Water Splitting Activity

Posted on 18 August 2023 by

This study investigates a water-splitting process utilizing a biphasic electrodeposited electrode on nickel foam (NF). The *Ni₉S₈/Cu₇S₄/NF electrode, reduced with citric acid, exhibits an ultralow overpotential value of 212 mV for OER and 109 mV for HER at the current density of 10 mA cm⁻². The electrode demonstrated an excellent stability for 80 hours in pure water splitting and 20 hours in seawater splitting.

Abstract

This study explores a water-splitting activity using a biphasic electrodeposited electrode on nickel foam (NF). The *Ni₉S₈/Cu₇S₄/NF electrode with citric acid reduction exhibits superior OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) performance with reduced overpotential and a steeper Tafel slope. The *Ni₉S₈/Cu₇S₄/NF electrode displays the ultra-low overpotential value of 212 mV for OER and 109 mV for HER at the current density of 10 mA cm⁻². The Tafel slope of 25.4 mV dec⁻¹ for OER and 108 mV dec⁻¹ for HER was found from that electrode. The maximum electrochemical surface area (ECSA), lowest series resistance and lowest charge transfer resistance are found in citric acid reduced electrode, showing increased electrical conductivity and quick charge transfer kinetics. Remarkably, the *Ni₉S₈/Cu₇S₄/NF electrode demonstrated excellent stability for 80 hours in pure water splitting and 20 hours in seawater splitting. The synergistic effect of using bimetallic (Cu&Ni) sulfide and enhanced electrical conductivity of the electrode are caused by reduction of metal sulfide into metallic species resulting in improved water splitting performance.