With the rapid growth and development of proton exchange membrane fuel cell (PEMFC) technology there has been an increasing demand for clean and sustainable global energy applications.While there are many device-level and infrastructure challenges still to be overcome before wide commercialization can be realized, increasing the PEMFC power density is a critical technical challenge, with ambitious goals proposed globally. For example, the short-term and long-term goals of the Japan New Energy and Industrial Technology Development Organization (NEDO) are 6 kW L -1 by 2030 and 9 kW L -1 by 2040, respectively. To this end, we propose technical development directions required for next-generation high power density PEMFCs. This perspective comprehensively embraces the latest advanced ideas for improvements in the membrane electrode assembly (MEA) and its components, bipolar plate (BP), integrated BP-MEA design, with regard to water and thermal management, and materials. The realization of these ideas is expected to be encompassed in next-generation PEMFCs with the aim of achieving a high power density.

Garnet‐type solid‐state electrolytes (SSEs) have been widely studied as a promising candidate for Li metal batteries. Despite the common belief that inorganic SSEs can prevent dendrite propagation, garnet SSEs suffer from relatively low critical current density (CCD) at which the SSEs are abruptly short‐circuited by Li dendrites. In this study, the short‐circuiting mechanism of garnet Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZN) is investigated. It is found that instead of propagating uniaxially from one electrode to other in a dendritic form, metallic lithium is formed within the SSE. This can be attributed to the fact that electrons combine with Li ions at the grain boundary, which exhibits relatively high electronic conductivity, and then reduce Li+ to Li0 to cause short circuits. In order to reduce the electronic conductivity at the grain boundary, a thin layer of LiAlO2 is coated on the grain surface of LLCZN, which results in an improved CCD value. It is also found that under higher external voltages, the electronic conductivity of SSE becomes more significant, which is believed to be the origin of CCD. These findings not only shed light on the short‐circuiting mechanism of garnet‐type SSEs but also offer a novel perspective and useful guidance on their designs and modifications.

The lithium–sulfur (Li–S) battery is considered a promising candidate for the next generation of energy storage system due to its high specific energy density and low cost of raw materials. However, the practical application of Li–S batteries is severely limited by several weaknesses such as the shuttle effect of polysulfides and the insulation of the electrochemical products of sulfur and Li2S/Li2S2. Here, by doping nitrogen and integrating highly dispersed cobalt catalysts, a porous carbon nanocage derived from glucose adsorbed metal–organic framework is developed as the host for a sulfur cathode. This host structure combines the reported positive effects, including high conductivity, high sulfur loading, effective stress release, fast lithium‐ion kinetics, fast interface charge transport, fast redox of Li2Sn, and strong physical/chemical absorption, achieving a long cycle life (86% of capacity retention at 1C within 500 cycles) and high rate performance (600 mAh g−1 at 5C) for a Li–S battery. By combining experiments and density functional theoretical calculations, it is demonstrated that the well‐dispersed cobalt clusters play an important role in greatly improving the diffusion dynamics of lithium, and enhance the absorption and conversion capability of polysulfides in the host structure.

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A flexible composite solid electrolyte membrane consisting of inorganic solid particles (Li1.3Al0.3Ti1.7(PO4)3), polyethylene oxide (PEO), and boronized polyethylene glycol (BPEG) is prepared and investigated. This membrane exhibits good stability against lithium dendrite, which can be attributed to its well‐designed combination components: the compact inorganic lithium ion conducting layer provides the membrane with good mechanical strength and physically barricades the free growth of lithium dendrite; while the addition of planar BPEG oligomers not only disorganizes the crystallinity of the PEO domain, leading to good ionic conductivity, but also facilitates a “soft contact” between interfaces, which not only chemically enables homogeneous lithium plating/stripping on the lithium metal anode, but also reduces the polarization effects. In addition, by employing this membrane to a LiFePO4/Li cell and testing its galvanostatic cycling performances at 60 °C, capacities of 158.2 and 94.2 mA h g−1 are delivered at 0.1 C and 2 C, respectively.