Frontiers in Energy最新文献

Single-atom transition metal-nitrogen-doped carbons (SA M-N-Cs) catalysts are promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, enhancing their performance for practical applications remains a significant challenge. This review summarizes recent advances in enhancing the intrinsic activity of SA M-N-C catalysts through various strategies, such as tuning the coordination environment and local structure of central metal atoms, heteroatom doping, and the creation of dual-/multi metal sites. Additionally, it discusses methods to increase the density of M-N_x active sites, including chelation, defect capture, cascade anchoring, spatial confinement, porous structure design, and secondary doping. Finally, it outlines future directions for developing highly active and stable SA M-N-C catalysts, providing a comprehensive framework for the design of advanced catalysts.

Proton exchange membrane fuel cells (PEMFCs) have attracted significant attention as sustainable energy technologies due to their efficient energy conversion and fuel flexibility. However, several challenges remain, such as low catalytic activity of fuel cell membrane electrode assembly (MEA), insufficient mass transfer performance, and performance degradation caused by catalyst deactivation over long period of operation. These issues are especially significant at high current densities, limiting both efficiency and operational lifespan. Mesoporous carbon materials, characterized by a high specific surface area, tunable pore structure, and excellent electrical conductivity, are emerging as crucial components for enhancing power density, mass transfer efficiency, and durability of PEMFCs. This review first discusses the properties and advantages of mesoporous carbon and outlines various synthetic strategies, including hard template, soft template, and template-free approaches. It then comprehensively examines the applications of mesoporous carbon in PEMFCs, focusing on their effects on the catalyst and gas diffusion layer. Finally, it concludes with future perspectives, emphasizing the need for further research to fully exploit the potential of mesoporous carbon in PEMFCs.

Hydrogen, with its carbon-free composition and the availability of abundant renewable energy sources for its production, holds significant promise as a fuel for internal combustion engines (ICEs). Its wide flammability limits and high flame speeds enable ultra-lean combustion, which is a promising strategy for reducing NO_x emissions and improving thermal efficiency. However, lean hydrogen-air flames, characterized by low Lewis numbers, experience thermo-diffusive instabilities that can significantly influence flame propagation and emissions. To address this challenge, it is crucial to gain a deep understanding of the fundamental flame dynamics of hydrogen-fueled engines. This study uses high-speed planar SO₂-LIF to investigate the evolutions of the early flame kernels in hydrogen and methane flames, and analyze the intricate interplay between flame characteristics, such as flame curvature, the gradients of SO₂-LIF intensity, tortuosity of flame boundary, the equivalent flame speed, and the turbulent flow field. Differential diffusion effects are particularly pronounced in H₂ flames, resulting in more significant flame wrinkling. In contrast, CH₄ flames, while exhibiting smoother flame boundaries, are more sensitive to turbulence, resulting in increased wrinkling, especially under stronger turbulence conditions. The higher correlation between curvature and gradient of H₂ flames indicates enhanced reactivity at the flame troughs, leading to faster flame propagation. However, increased turbulence can mitigate these effects. Hydrogen flames consistently exhibit higher equivalent flame speeds due to their higher thermo-diffusivity, and both hydrogen and methane flames accelerate under high turbulence conditions. These findings provide valuable insights into the distinct flame behaviors of hydrogen and methane, highlighting the importance of understanding the interactions between thermo-diffusive effects and turbulence in hydrogen-fueled engine combustion.

Aqueous zinc metal batteries (ZMBs) are regarded as strong contenders in secondary battery systems due to their high safety and abundant resources. However, the cycling performance of the Zn anode and the overall performance of the cells have often been hindered by the formation of Zn dendrites and the occurrence of parasitic side reactions. In this paper, a surface electron reconfiguration strategy is proposed to optimize the adsorption energy and migration energy of Zn²⁺ for a better Zn²⁺ deposition/stripping process by adjusting the electronic structure of ceric dioxide (CeO₂) artificial interface layer with copper atoms (Cu) doped. Both experimental results and theoretical calculations demonstrate that the Cu₂Ce₇O_x interface facilitates rapid transport of Zn²⁺ due to the optimized electronic structure and appropriate electron density, leading to a highly reversible and stable Zn anode. Consequently, the Cu₂Ce₇O_x@Zn symmetric cell exhibits an overpotential of only 24 mV after stably cycling for over 1600 h at a current density of 1 mA/cm² and a capacity of 1 mAh/cm². Additionally, the cycle life of Cu/Zn asymmetric cells exceeds 2500 h, with an average Coulombic efficiency of 99.9%. This paper provides a novel approach to the artificial interface layer strategy, offering new insights for improving the performance of ZMBs.

Both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for advancing the industrial application of fuel cells and metal-air batteries. This paper reports a bifunctional oxygen catalyst (CoNC@FePc) synthesized by anchoring FePc molecules onto cobalt nanoparticles embedded within a Co-ZIF-derived nitrogen-doped carbon matrix (CoNC). By leveraging the significant electron transfer between Co nanoparticles and FePc molecules, the synthesized catalyst demonstrated outstanding performance for both ORR and OER, further validated by density functional theory (DFT) calculations. The catalyst achieved a half-wave potential of 0.87 V for ORR and a low overpotential of 314 mV at 10 mA/cm² for OER, surpassing the performance of commercial Pt/C and RuO₂, respectively. Additionally, the rechargeable zinc-air batteries incorporating CoNC@FePc exhibited a remarkable peak power density of 150.2 mW/cm² and maintained outstanding cyclic stability for over 100 h. This study offers a straightforward approach to improving the bifunctional oxygen electrocatalytic performance of metal phthalocyanine-based catalysts.

Thermo-mechanical energy storage (TMES) technologies have attracted significant attention due to their potential for grid-scale, long-duration electricity storage, offering advantages such as minimal geographical constraints, low environmental impact, and long operational lifespans. A key benefit of TMES systems is their ability to perform energy conversion steps that enable interaction with both thermal energy consumers and prosumers, effectively functioning as combined cooling, heating and power (CCHP) systems. This paper reviews recent progress in various TMES technologies, focusing on compressed-air energy storage (CAES), liquid-air energy storage (LAES), pumped-thermal electricity storage (PTES, also known as Carnot battery), and carbon dioxide energy storage (CES), while exploring their potential applications as extended CCHP systems for trigeneration. Techno-economic analysis indicate that TMES-based CCHP systems can achieve roundtrip (power-to-power) efficiencies ranging from 40% to 130%, overall (trigeneration) energy efficiencies from 70% to 190%, and a levelized cost of energy (with cooling and heating outputs converted into equivalent electricity) between 70 and 200 $/MWh. In general, the evolution of TMES-based CCHP systems into smart multi-energy management systems for cities or districts in the future is a highly promising avenue. However, current economic analyses remain incomplete, and further exploration is needed, especially in the area “AI for energy storage,” which is crucial for the widespread adoption of TMES-based CCHP systems.

The utilization of solar energy to address energy and environmental challenges has a seen a significant growth in recent years. Metal halides, which offer unique advantages such as tunable bandgaps, high light absorption efficiencies, favorable product release rates, and low exciton binding energies, have emerged as excellent photocatalysts for energy conversion. This paper reviews the recent advancements in both all-inorganic and organic-inorganic hybrid metal halide photocatalytic materials, including the fundamental mechanisms of photocatalytic CO₂ reduction, various synthesis strategies for metal halide photocatalysts, and their applications in the field of photocatalysis. Finally, it examines the current challenges associated with metal halide materials and explores potential solutions for metal halide materials, along with their future prospects in photocatalysis applications.

The use of porous skeletons for encapsulating phase change materials (PCMs) is an effective approach to addressing issues such as leakage, low thermal conductivity, and poor photothermal conversion efficiency. Inspired by the hollow skeletal structure found in birds in nature, high-quality 3D interconnected hollow diamond foam (HDF) was fabricated using a series of processes, including microwave plasma chemical vapor deposition (CVD), laser perforation, and acid immersion. This HDF was then used as a scaffold to encapsulate PEG2000. The results demonstrate that HDF significantly reduces the supercooling degree and latent heat discrepancy of PEG2000. Compared to pure PEG2000, the thermal conductivity of the HDF/PEG increased by 378%, while its latent heat reached 111.48 J/g, accompanied by a photothermal conversion efficiency of up to 86.68%. The significant performance improvement is mainly attributed to the combination of the excellent properties of the diamond with the inherent advantages of the 3D interconnected structure in HDF, which creates a high-conductivity transport network inside. Moreover, the HDF/PEG composite extends the temperature cycling time of electronic components by 4 times for heating and 2.3 times for cooling, thereby prolonging the operational lifetime of electronic devices. HDF/PEG offers an integrated solution for solar energy collection, photothermal conversion, heat dissipation in electronic components, and thermal energy transfer/storage. This innovative approach provides innovative ideas for the design and fabrication of composite PCMs and has great application potential, such as solar energy utilization, thermal management, and thermal energy storage.

Perovskite-based photovoltaic devices have garnered significant interest owing to their remarkable performance in converting light into electricity. Recently, the focus in the field of perovskite solar cells (PSCs) has shifted towards enhancing their durability over extended periods. One promising strategy is the incorporation of two-dimensional (2D) perovskites, known for their ability to enhance stability due to the large organic cations that act as a barrier against moisture. However, the broad optical bandgap and limited charge transport properties of 2D perovskites hinder their efficiency, making them less suitable as the sole light-absorbing material when compared to their three-dimensional (3D) counterparts. An innovative approach involves using 2D perovskite structures to modify the surface properties of 3D perovskite. This hybrid approach, known as 2D/3D perovskites, while enhancing their performance. Beyond solar energy applications, 2D perovskites offer a flexible platform for chemical engineering, allowing for significant adjustments to crystal and thin-film configurations, bandgaps, and charge transport properties through the different organic ligands and halide mixtures. Despite these advantages, challenges remain in integration of 2D perovskites into solar cells without compromising device stability. This review encapsulates the latest developments in 2D perovskite research, focusing on their structural, optoelectronic, and stability attributes, while delving into the challenges and future potential of these materials.