MXenes and MXene-Based Metal Hydrides for Solid-State Hydrogen Storage: A Review.

Hydrogen-driven energy is fascinating among the everlasting energy sources, particularly for stationary and onboard transportation applications. Efficient hydrogen storage presents a key challenge to accomplishing the sustainability goals of hydrogen economy. In this regard, solid-state hydrogen storage in nanomaterials, either physically or chemically adsorbed, has been considered a safe path to establishing sustainability goals. Though metal hydrides have been extensively explored, they fail to comply with the set targets for practical utilization. Recently, MXenes, both in bare form and hybrid state with metal hydrides, have proven their flair in ascertaining the hydrides' theoretical and experimental hydrogen storage capabilities far beyond the fancy materials and current state-of-the-art technologies. This review encompasses the significant accomplishments achieved by MXenes (primarily in 2019-2024) for enhancing the hydrogen storage performance of various metal hydride materials such as MgH2, AlH3, Mg(BH4)2, LiBH4, alanates, and composite hydrides. It also discusses the bottlenecks of metal hydrides for hydrogen storage, the potential use of MXenes hybrids, and their challenges, such as reversibility, H2 losses, slow kinetics, and thermodynamic barriers. Finally, it concludes with a detailed roadmap and recommendations for mechanistic-driven future studies propelling toward a breakthrough in solid material-driven hydrogen storage using cost-effective, efficient, and long-lasting solutions.

Recent Developments on Electroactive Organic Electrolytes for Non-Aqueous Redox Flow Batteries: Current Status, Challenges, and Prospects.

The ever-increasing threat of climate change and the depletion of fossil fuel resources necessitate the use of solar- and wind-based renewable energy sources. Large-scale energy storage technologies, such as redox flow batteries (RFBs), offer a continuous supply of energy. Depending on the nature of the electrolytes used, RFBs are broadly categorized into aqueous redox flow batteries (ARFBs) and non-aqueous redox flow batteries (NARFBs). ARFBs suffer from various problems, including low conductivity of electrolytes, inferior charge/discharge current densities, high-capacity fading, and lower energy densities. NARFBs offer a wider potential window and range of operating temperatures, faster electron transfer kinetics, and higher energy densities. In this review article, a critical analysis is provided on the design of organic electroactive molecules, their physiochemical/electrochemical properties, and various organic solvents used in NARFBs. Furthermore, various redox-active organic materials, such as metal-based coordination complexes, quinones, radicals, polymers, and miscellaneous electroactive species, explored for NARFBs during 2012-2023 are discussed. Finally, the current challenges and prospects of NARFBs are summarized.

Recent Development of Electrolytes for Aqueous Organic Redox Flow Batteries (Aorfbs): Current Status, Challenges, and Prospects.

In recent years, aqueous organic redox flow batteries (AORFBs) have attracted considerable attention due to advancements in grid-level energy storage capacity research. These batteries offer remarkable benefits, including outstanding capacity retention, excellent cell performance, high energy density, and cost-effectiveness. The organic electrolytes in AORFBs exhibit adjustable redox potentials and tunable solubilities in water. Previously, various types of organic electrolytes, such as quinones, organometallic complexes, viologens, redox-active polymers, and organic salts, were extensively investigated for their electrochemical performance and stability. This study presents an overview of recently published novel organic electrolytes for AORFBs in acidic, alkaline, and neutral environments. Furthermore, it delves into the current status, challenges, and prospects of AORFBs, highlighting different strategies to overcome these challenges, with special emphasis placed on their design, composition, functionalities, and cost. A brief techno-economic analysis of various aqueous RFBs is also outlined, considering their potential scalability and integration with renewable energy systems.

Optical Chemical Sensing of Iodide Ions: A Comprehensive Review for the Synthetic Strategies of Iodide Sensing Probes, Challenges, and Future Aspects.

Among several anions, iodide (I- ) ions play a crucial role in human biological activities. In it's molecular form (I2 ), iodine is utilized for several industrial applications such as syntheses of medicines, fabric dyes, food additives, solar cell electrolytes, catalysts, and agrochemicals. The excess or deficiency of I- ions in the human body and environmental samples have certain consequences. Therefore, the selective and sensitive detection of I- ions in the human body and environment is vital for monitoring their overall profile. Amongst various analytical techniques for the estimation of I- ions, optical-chemical sensing possesses the merits of high sensitivity, selectivity, and utilizing the least amount of sensing materials. The distinctive aims of this manuscript are (i) To comprehensively review the development of optical chemical sensors (fluorescent & colorimetric) reported between 2001-2021 using organic fluorescent molecules, supramolecular materials, conjugated polymers, and metal-organic frameworks (MOFs). (ii) To illustrate the design and synthetic strategies to create specific binding and high affinity of I- ions which could help minimize negative consequences associated with its large size and high polarizability. (iii) The challenges associated with sensitivity and selectivity of I- ions in aqueous and real samples. The probable future aspects concerning the optical chemical detection of I- ions have also been discussed in detail.

Photocatalytic Water-Splitting by Organic Conjugated Polymers: Opportunities and Challenges.

The future challenges associated with the shortage of fossil fuels and their current environmental impacts intrigued the researchers to look for alternative ways of generating green energy. Solar-driven water splitting into oxygen and hydrogen is one of those advanced strategies. Researchers have studied various semiconductor materials to achieve potential results. However, it encountered multiple challenges such as high cost, low photostability and efficiency, and required multistep modifications. The conjugated polymers (CPs) have emerged as promising alternatives for conventional inorganic semiconductors. The CPs offer low cost, sufficient light absorption efficiency, excellent photo and chemical stability, and molecular optoelectronic tunable characteristics. Furthermore, organic CPs also present higher flexibility to tune the basic framework of the backbone of the polymers, amendments in the sidechain to incorporate desired functionalities, and much-needed porosity to serve better for photocatalytic applications. This review article summarizes the recent advancements made in visible-light-driven water splitting covering the aspects of synthetic strategies and experimental parameters employed for water splitting reactions with special emphasis on conjugated polymers such as linear CPs, planarized CPs, graphitic carbon nitride (g-C3 N4 ), conjugated microporous polymers (CMPs), covalent organic frameworks (COFs), and conjugated polymer-based nanocomposites (CPNCs). The current challenges and future prospects have also been described briefly.