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Porous flow fields distribute fuel and oxygen for the electrochemical reactions of proton exchange membrane (PEM) fuel cells through their pore network instead of conventional flow channels. This type of flow fields has showed great promises in enhancing reactant supply, heat removal, and electrical conduction, reducing the concentration performance loss and improving operational stability for fuel cells. This review presents the research and development progress of porous flow fields with insights for next-generation PEM fuel cells of high power density (e.g., ∼9.0 kW L–1). Materials, fabrication methods, fundamentals, and fuel cell performance associated with porous flow fields are discussed in depth. Major challenges are described and explained, along with several future directions, including separated gas/liquid flow configurations, integrated porous structure, full morphology modeling, data-driven methods, and artificial intelligence-assisted design/optimization. [ABSTRACT FROM AUTHOR]

The electrochemical CO 2 reduction reaction (CO 2 RR) into high-value carbon compounds such as CO and HCOOH is a promising strategy for the utilization and conversion of emitted CO 2 . However, the selectivity of the CO 2 RR for HCOOH is typically less than 90% and operates within a narrow voltage range, which limits its practical application. Herein, we propose a novel heterostructural aerogel as a highly efficient electrocatalyst for CO 2 RR to HCOOH. This catalyst consists of Cu-Sn-O x solid solutions embedded in a reduced graphene oxide matrix (Cu-Sn-O x /rGO). The incorporation of Cu 2+ into the SnO 2 matrix enhances HCOOH production by improving the adsorption of the *OCHO intermediate and inhibiting H 2 evolution, as confirmed by in situ measurements and computational studies. As a result, Cu-Sn-O x /rGO achieves a remarkable Faradaic efficiency (FE) of up to 91.4% for HCOOH and maintains high selectivity over a broad operating voltage range (-0.8 to -1.1 V). Additionally, the assembled Zn-CO 2 batteries demonstrated an excellent power density of 1.14 mW/cm 2 and exceptional stability for over 25 h.

Excitonic insulators are long-sought-after quantum materials predicted to spontaneously open a gap by the Bose condensation of bound electron-hole pairs, namely, excitons, in their ground state. Since the theoretical conjecture, extensive efforts have been devoted to pursuing excitonic insulator platforms for exploring macroscopic quantum phenomena in real materials. Reliable evidence of excitonic character has been obtained in layered chalcogenides as promising candidates. However, owing to the interference of intrinsic lattice instabilities, it is still debatable whether those features, such as the charge density wave and gap opening, are primarily driven by the excitonic effect or by the lattice transition. Herein, we develop an intercalation chemistry strategy for obtaining a novel charge-transfer excitonic insulator in organic-inorganic superlattice interfaces that serves as an ideal platform to decouple the excitonic effect from the lattice effect. In this system, we observe a narrow excitonic gap, formation of a charge density wave without periodic lattice distortion, and metal-insulator transition, providing visualized evidence of exciton condensation occurring in thermal equilibrium. Our findings identify self-assembly intercalation chemistry as a new strategy for developing novel excitonic insulators.

Extensive use of renewable and clean energy is one of the promising ways to solve energy/environmental problems and promote the sustainable development of our society. As inexhaustible energy sources, the photothermal (PT) and radiative cooling (RC) energy from the sun and outer space have recently attracted tremendous interest. However, these two kinds of energy utilization have distinctly opposite spectral properties, especially in the infrared range, making it extremely difficult to integrate these two energy harvesting modes within a fixed device for continuous energy collection. Thus, in the current study, we have proposed a spectrally self-adaptive broadband absorber/emitter (SSBA/E) based on vanadium dioxide (VO 2 ), a typical phase transition material, to achieve continuous energy harvesting via collecting solar thermal energy in PT mode during the day and obtaining cool energy in wide-band RC mode at night. Experimental results show that owing to the phase transition property of the VO 2 layer, these two energy collection modes can be adaptively switched. Specifically, the VO 2 -based device shows a broadband infrared emissivity modulation from 0.21 to 0.75 and low critical temperatures (58.4 and 49.2 °C) during the phase transition, leading to continuous energy harvesting with high efficiency. Due to the broadband infrared emission, the RC maximum power of the SSBA/E device was estimated to be 58 W m -2 . The proposed VO 2 smart coatings are also applicable for many other applications such as thermal management of spacecraft, infrared camouflage, or adaptive optical devices.

As a typical correlated metal oxide, vanadium dioxide (VO 2 ) shows specific metal-insulator transition (MIT) properties and demonstrates great potential applications in ultrafast optoelectronic switch, resistive memory, and neuromorphic devices. Effective control of the MIT process is essential for improving the device performance. In the current study, we have first proposed a photoassisted ion-doping method to modulate the phase transition of the VO 2 layer based on the photovoltaic effect and electron-ion synergic doping in acid solution. Experimental results show that, for the prepared n-VO 2 /p-GaN nanojunction, this photoassisted strategy can effectively dope the n-VO 2 layer by H + , Al 3+ , or Mg 2+ ions under light radiation and trigger consecutive insulator-metal-insulator transitions. If combined with standard lithography or electron beam etching processes, selective doping with nanoscale size area can also be achieved. This photoassisted doping method not only shows a facile route for MIT modulation via a doping route under ambient conditions but also supplies some clues for photosensitive detection in the future.

Ammonia borane (AB) is regarded as a highly promising candidate for chemical hydrogen-storage materials. Developing low-cost yet efficient catalysts for the dehydrogenation of AB is central to achieving hydrogen conversion. Here a heterostructure of Ni/Ni 2 P nanoparticles deposited on a defective carbon framework for the hydrolysis of AB is developed by elaborately controlling phosphorization conditions. The electronic structure and interfacial interaction of the ternary components are probed by synchrotron-based X-ray absorption fine structure and further simulated via density functional theory. By adjusting the content of Ni and Ni 2 P in the hetrostructure, the optimized hybrid exhibits catalytic performance of H 2 generation from the hydrolysis of AB under ambient conditions with a turnover frequency of 68.3 mol (H 2 ) mol -1 (Cat) min -1 and an activation energy ( E a ) of 44.99 kJ mol -1 , implying its high potential as an efficient supplement for noble-metal-based catalysts in hydrogen energy applications.

Na-O 2 batteries are emerging rechargeable batteries due to their high theoretical energy density and abundant resources, but they suffer from sluggish kinetics due to the formation of large-size discharge products with cubic or irregular particle shapes. Here, we report the unique growth of discharge products of NaO 2 nanowires inside Na-O 2 batteries that significantly boosts the performance of Na-O 2 batteries. For this purpose, a high-spin Co 3 O 4 electrocatalyst was synthesized via the high-temperature oxidation of pure cobalt nanoparticles in an external magnetic field. The discharge products of NaO 2 nanowires are 10-20 nm in diameter and ∼10 μm in length, characteristics that provide facile pathways for electron and ion transfer. With these nanowires, Na-O 2 batteries have surpassed 400 cycles with a fixed capacity of 1000 mA h g -1 , an ultra-low over-potential of ∼60 mV during charging, and near-zero over-potential during discharging. This strategy not only provides a unique way to control the morphology of discharge products to achieve high-performance Na-O 2 batteries but also opens up the opportunity to explore growing nanowires in novel conditions.

A combinatorial approach was used to systematically investigate the effect of trace Pr(3+), Tb(3+), or Sm(3+) on the VUV photoluminescence of Eu(3+) in the Pr(3+), Tb(3+), or Sm(3+) co-doped (Y(0.65)Gd(0.35))BO(3):E(3+)(0.05). We found that Pr(3+) and Tb(3+)increases the VUV photoluminescent efficiency, while Sm(3+) decreases the efficiency. The optimized composition was identified to be between 7 x 10(-6) and 3 x 10(-4), and the corresponding efficiency improvement is about 15%. Scale-up experiments confirmed the results in the combinatorial materials libraries.