EnergyChem最新文献

Ammonia not only serves as a building block for nitrogen-rich fertilizer, but offers a carbon-free energy carrier. At present, industrial ammonia synthesis is dominated by the Hablocker-Bosch process under high temperature and pressure, resulting in high energy consumption and serious environmental issues. Considerable recent at tention has focused on designing electrocatalysts for the N₂ reduction reaction (NRR). However, the ammonia synthesis through electrocatalytic N₂ reduction is still far from practical applications. In this review, recent theoretical and experiment investigations on various catalysts for the ammonia synthesis under mild conditions are highlighted. Firstly, the mechanisms for the electrochemical NRR are reviewed briefly. Then, based on these mechanisms, various catalysts, such as noble metal catalysts, non-noble metal catalysts, metal-free catalysts and even single atoms catalysts, for ammonia production are reviewed, with a particular focus on the improvement of the catalytic activity and selectivity toward ammonia production through optimizing the electrolyte, pH and the structure of the catalyst, etc. Lastly, the challenges and outlook for the ammonia synthesis are shown. This review systematically retrospects recent advances in the electrocatalytic NRR to show the readers a thorough understanding in this field. Most importantly, this review sheds some light toward the future development of electrocatalytic NRR.

Ammonia (NH₃) is one of the most important commodity chemicals in today's chemical industry. Industrially, ammonia is synthesized via the Haber-Bosch process at high temperature and pressure (typically 400 °C and 200 atm). In nature, the nitrogenase enzyme can convert N₂ to NH₃ at ambient conditions, motivating the search for similar sustainable technologies for industrial-scale NH₃ production. Over the past few years, photocatalytic ammonia production using sunlight and photocatalysts has attracted much attention, allowing the reduction of N₂ to NH₃ under very mild reaction conditions. Whilst the rates of photocatalytic ammonia synthesis are still a long way off practical requirements, some promising photocatalytic materials have already been identified which encourage wider research in this field. This review aims to capture recent advances in photocatalytic N₂ fixation to NH₃, by encompassing fundamental aspects of photocatalytic ammonia synthesis, as well as effective photocatalyst and reactor design strategies. Further, the review offers some practical guidelines to researchers regarding the appropriate selection of ammonia detection methods and the performance assessment of ammonia synthesis photocatalysts. The overarching aims of this review are i) to support the development of solar-driven ammonia synthesis, and ii) to assist researchers in moving into this exciting new research space.

Solar hydrogen production from water is a sustainable alternative to traditional hydrogen production route using fossil fuels. However, there is still no existing large-scale solar hydrogen production system to compete with its counterpart. In this Review, recent developments of four potentially cost-effective pathways towards large-scale solar hydrogen production, viz. photocatalytic, photobiological, solar thermal and photoelectrochemical routes, are discussed, respectively. The limiting factors including efficiency, scalability and durability for scale-up are assessed along with the field performance of the selected systems. Some benchmark studies are highlighted, mostly addressing one or two of the limiting factors, as well as a few recent examples demonstrating upscaled solar hydrogen production systems and emerging trends towards large-scale hydrogen production. A techno-economic analysis provides a critical comparison of the levelized cost of hydrogen output via each of the four solar-to-hydrogen conversion pathways.

Lithium metal has been considered as a “Holy Grail” anode for rechargeable batteries due to its ultrahigh theoretical specific capacity and the most negative electrochemical potential. Sodium and potassium, the alkali metals that are more abundant in the earth's crust are also regarded as candidates for next-generation anode materials, considering the low crust abundance and high cost of lithium carbonate. However, all of these alkali metal anodes are susceptible to dendrite growth, causing safety concerns, low energy density, and short lifespan, which severely hampers their practical applications. A number of models have been proposed to describe the dendrite growth mechanism/behavior and offer strategies to render a uniform and dendrite-free deposition behavior. In this review, we summarize the progress in the energy chemistry of alkali metal anodes. Firstly, the similarities and differences among three alkali metals in chemical/physical/electrochemical features are addressed. Then, special attention is paid to the understanding of mechanisms and models for Li dendrite nucleation and growth, including the thermodynamic model, space-charge model, stress and inelastic deformation model, film growth model, and phase field kinetics model. The feasibility of these models to Na and K anode systems is also discussed. Finally, general conclusions and perspectives on the current limitations and future research directions toward the understanding of mechanisms on dendrite growth are presented. This review should provide important insights into alkali metal deposition behaviors and alkali metal anode protection.

As emerging crystalline porous organic-inorganic hybrid materials, metal-organic frameworks (MOFs) have been widely used as sacrificial precursors for the synthesis of carbon materials, metal/metal compounds, and their composites with tunable and controllable nanostructures and chemical compositions for electrochemical energy applications. Herein, recent progress of MOF-derived nanomaterials for various electrochemical energy storage and conversion applications including Li-ion batteries, Li-S batteries, Na-ion batteries, supercapacitors, water splitting, and oxygen reduction reaction is reviewed. Structural and compositional design of MOF-derived nanomaterials is systematically summarized, which may hopefully offer inspirations and guidances for future development of MOF-derived nanomaterials for more efficient and more durable electrochemical energy applications.

Lithium-ion batteries (LIBs) have gradually approached the upper limit of capacity, and yet, they are still far from fulfilling the ambitious targets required to meet the grid's storage needs due to their unsatisfactory cycling stability, limited energy density, high cost, and environmental concerns. Dual-ion batteries (DIBs) with non-aqueous electrolyte, as potential alternatives to LIBs in smart-grid application, have attracted much attention in recent years. DIBs were initially known as dual-graphite batteries, where both anions and cations separately intercalate into graphite electrodes during the charge-discharge process. The anion intercalation into the host material enables DIBs in non-aqueous electrolyte to feature a high operating voltage, which also contributes to their enhanced energy density. Moreover, the use of low-cost and “green” raw electrode materials in DIBs offers huge advantages compared to LIBs, in terms of environmental protection by avoiding problems from the disposal of discarded batteries. In this contribution, we comprehensively summarize the recent progress on DIBs with aqueous and non-aqueous electrolytes as well as the limitations and challenges of current DIB technology. Furthermore, some suggestions that might help to address the current challenges of DIB technology are proposed for future work.

Gases are widely used as energy resources for industry and our daily life. Developing energy cost efficient porous materials for gas storage and separation is of fundamentally and industrially important, and is one of the most important aspects of energy chemistry and materials. Metal-organic frameworks (MOFs), representing a novel class of porous materials, feature unique pore structure, such as exceptional porosity, tunable pore structures, ready functionalization, which not only enables high density energy storage of clean fuel gas in MOF adsorbents, but also facilitates distinct host-guest interactions and/or sieving effects to differentiate different molecules for energy-efficient separation economy. In this review, we summarize and highlight the recent advances in the arena of gas storage and separation using MOFs as adsorbents, including progresses in MOF-based membranes for gas separation, which could afford broader concepts to the current status and challenges in this field.

Metal-organic frameworks (MOFs), also known as porous coordination polymers (PCPs), are a unique class of porous crystalline materials that are constructed by metal ions/clusters and organic ligands. The intriguing, numerous and tailorable structures as well as permanent porosity of MOFs make them very promising for a variety of potential applications, especially in catalysis. In this review, we systematically summarize the recent progress of MOF-based materials (including pristine MOFs, MOF composites, and MOF derivatives) for heterogeneous catalysis, photocatalysis and electrocatalysis, according to the category of active site origin. We clearly indicate the significant strengths (and also weaknesses) of the MOF-based materials, in reference to traditional catalysts, in catalytic studies. The challenges and opportunities in regard to the MOF-based materials for catalysis have also been critically discussed.

Li–S batteries, offering high theoretical energy density of 2600 Wh kg⁻¹, low cost and nontoxicity, are considered as a fascinating next-generation electric energy storage devices. However, the dissolution of the lithium polysulfides (LiPSs), shuttle effect and safety issues of Li anode notoriously pose great challenges for the commercialization of Li–S batteries. These problems derive from the interfacial issues among cathodes, separators, electrolytes and anodes, which in turn can be resolved by rational interface tailoring. This review mainly focuses on these interfacial issues in Li–S batteries with traditional liquid electrolytes and the latest research trend including gel polymer electrolytes, solid polymer electrolytes, solid inorganic electrolytes and hybrid electrolytes. In the liquid electrolyte systems, sulfur cathodes can effectively avoid severe shuttle effects and maintain stable cycling with the interfacial regulations of coatings, freestanding interlayers and separator modifications, while Li anode can be modified by protective layers, functional additives, three-dimensional current collectors and Li alloys. In quasi-solid systems (gel polymer electrolytes and hybrid electrolytes), rational designs are applied considering the utility of active materials, restraining LiPSs and suppressing Li dendrites. In all solid-state electrolyte systems (solid polymer electrolytes and solid inorganic electrolytes), the emphasis is to enhance the ionic conductivities and reduce the interfacial resistances. Mechanisms underlying these interfacial issues and corresponding electrochemical performances are discussed. Recent developments on the interfacial designs of Li–S batteries are summarized and highlighted. Based on the most critical factors of the interfaces proposed, prospectives are presented to pave the avenue for the designs of Li–S batteries.