The demand for lithium-ion batteries (LIBs) with high mass-specific capacities, high rate capabilities and long-term cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNi_xMn_yCo_1−x−yO₂, $$x \geqslant 0.5$$x⩾0.5 ) cathodes and graphite (Li_xC₆) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid electrolyte interfaces are also reviewed, and trade-offs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions. Graphic The demand for lithium-ion batteries (LIBs) with high mass specific capacities, high rate capabilities and longterm cyclabilities is driving the research and development of LIBs with nickel-rich NMC (LiNi_xMn_yCo_1−x−yO₂, x ≥ 0.5) cathodes and graphite (Li_xC₆) anodes. Based on this, this review will summarize recently reported and widely recognized studies of the degradation mechanisms of Ni-rich NMC cathodes and graphite anodes. And with a broad collection of proposed mechanisms on both atomic and micrometer scales, this review can supplement previous degradation studies of Ni-rich NMC batteries. In addition, this review will categorize advanced mitigation strategies for both electrodes based on different modifications in which Ni-rich NMC cathode improvement strategies involve dopants, gradient layers, surface coatings, carbon matrixes and advanced synthesis methods, whereas graphite anode improvement strategies involve surface coatings, charge/discharge protocols and electrolyte volume estimations. Electrolyte components that can facilitate the stabilization of anodic solid-electrolyte interfaces (SEIs) are also reviewed and tradeoffs between modification techniques as well as controversies are discussed for a deeper understanding of the mitigation strategies of Ni-rich NMC/graphite LIBs. Furthermore, this review will present various physical and electrochemical diagnostic tools that are vital in the elucidation of degradation mechanisms during operation to supplement future degradation studies. Finally, this review will summarize current research focuses and propose future research directions.

Atomic site catalysts (ASCs) have recently gained prominence for their potential in the electrochemical hydrogen evolution reaction (HER) due to their exceptional activity, selectivity, and stability. ASCs with individual atoms dispersed on a support material, offer expanded surface areas and increased mass efficiency. This is because each atom in these catalysts serves as an active site, which enhances their catalytic activity. This review is focused on providing a detailed analysis of ASCs in the context of the HER. It will delve into their properties, types, and performance to provide a comprehensive understanding of their role in electrochemical HER processes. The introduction part underscores HER's significance in transitioning to sustainable energy sources and emphasizes the need for innovative catalysts like ASCs. The fundamentals of the HER section emphasizes the importance of understanding the HER and highlights the key role that catalysts play in HER. The review also explores the properties of ASCs with a specific emphasis on their atomic structure and categorizes the types based on their composition and structure. Within each category of ASCs, the review discusses their potential as catalysts for the HER. The performance section focuses on a thorough evaluation of ASCs in terms of their activity, selectivity, and stability in HER. The performance section assesses ASCs in terms of activity, selectivity, and stability, delving into reaction mechanisms via experimental and theoretical approaches, including density functional theory (DFT) studies. The review concludes by addressing ASC-related challenges in HER and proposing future research directions, aiming to inspire further innovation in sustainable catalysts for electrochemical HER.

Water electrolysis is an important way to produce hydrogen at the cathode, but the oxygen evolution reaction (OER) at the anode has a high overpotential. Using the urea oxidation reaction (UOR) to replace OER has been an energy-saving approach for its lower electrode potential, and also a potential approach for wastewater treatment. In this paper, novel materials of MoP@NiCo-LDH/NF-x (x = 10, 20, 30 minutes) are synthesized and explored as bifunctional catalysts for both the hydrogen evolution reaction (HER) at the cathode and the urea oxidation reaction (UOR) or the oxygen evolution reaction (OER) at the anodes of urea–water or water electrolysis. The morphologies and compositions of such catalyst materials are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The catalytic activity and stability are measured by linear sweep voltammetry, electrochemical impedance spectroscopy, chronoamperometry, etc. The results indicate that MoP@NiCo-LDH/NF-20 has better catalytic performance, and can be used as a bifunctional catalyst for both HER and OER/UOR in the electrolysis. A two-electrode electrolyser (MoP@NiCo-LDH/NF-20‖MoP@NiCo-LDH/NF-20) is constructed. At 100 mA cm⁻², the two-electrode electrolyser needs only 1.405 V, while the precious metal electrolyser Pt/C/NF‖IrO₂/NF needs 1.697 V at the same current density, indicating that MoP@NiCo-LDH/NF-20 could be a promising bifunctional electrocatalyst in water and urea–water electrolysis for the treatment of urea wastewater and hydrogen production.

Integrating renewable electricity and concentrated CO₂ from direct air capture, electrochemical CO₂ reduction reactions (eCO₂RR) offer a promising pathway for converting CO₂ into fuel chemicals, enabling the closure of the carbon loop in a sustainable manner. The clean H₂ produced via the hydrogen evolution reaction (HER) during water electrolysis can replace traditional fossil fuels without additional CO₂ emissions. Achieving large‐scale and high‐efficiency eCO₂RR and HER requires the development of rational electrolyzer designs, which are crucial for industrial implementation. This review examines recent innovations in system designs for eCO₂RR, HER, and the latest advances in in situ cell designs for operando characterization during electrochemical reactions. It focuses on cell improvements in flow patterns, membrane electrode assemblies, and electrolyte engineering to maximize catalytic activities at the industrial level. Besides, the review discusses optimizing counter‐anodic reactions to improve the energy efficiency of eCO₂RR and water electrolysis, offering insights into the design of catalytic systems with efficient energy utilization. Furthermore, it explores the integration of eCO₂RR and HER with other electrochemical systems (e.g., fuel cells), highlighting their potential role in the decarbonization of future industrial processes. Finally, the summary, challenge, and outlook on the industrial‐scale eCO₂RR and water electrolysis system designs are concluded.

Electrochemical CO ₂ reduction technology could solve the CO ₂ -induced climate warming by electrochemically converting atmospheric CO ₂ back into fuel, essentially recycling it and building a low carbon emission economy. However, the electrochemical CO ₂ reduction reaction (CO ₂ RR) poses a significant challenge due to the highly stable and linear CO ₂ molecules, in addition to a proton-coupled multi-electron transfer process. Thus, highly active catalysts, placed on activity bolstering materials, and permeable electrodes are crucial for CO ₂ RR. Single-atom catalysts (SACs) have recently garnered increasing interest in the electrocatalysis community due to their potentially high mass efficiency and cost benefits (every atom is an active center, resulting in nearly 100% utilization) and adjustable selectivity (higher uniformity of the active sites compared to nanoparticles). However, preserving the accessibility and activity of the SACs inside the electrode poses major materials development and electrode design challenges. A conventional layered structure SAC electrode typically consists of a gas diffusion layer (GDL), a microporous layer (MPL) and a SAC catalyst layer (SACCL), fabricated by using a powder bonding process. However, this process usually encounters issues such as delamination and instability of SACs due to the weak binder-catalyst-support interface. Conversely, the free-standing SAC electrode design has the potential to overcome these issues by eliminating the GDL, MPL, and need of a binder, in contrast to the powder bonding process. This work first reviews the latest developments in experimental and modeling studies of powdered SAC electrode by the traditional powder bonding process. Next, it examines the development towards the free-standing SAC electrode for high-performance electrochemical reduction of CO ₂ . The synthesis-structure-fabrication-performance relationships of SAC-based materials and associated electrodes are analyzed. Furthermore, the article presents future challenges and perspectives for high-performance SAC electrodes for CO ₂ RR. Graphical Abstract