Advances in research and development of carbon-based metal-free electrocatalysts (C-MFECs) have provided potential alternatives to precious metal catalysts for various reactions important to renewable energy and environmental remediation. This timely but critical review provides an overview of recent breakthroughs (within the past 5 years or so) on C-MFECs in all aspects, including the design and regulation of intrinsic catalytic active sites, design and synthesis of carbon composite and hybrid carbon catalysts, mechanism understanding, and potential applications in clean energy storage and energy/chemical conversion. Current challenges and future opportunities in the field of metal-free carbon electrocatalysis are also discussed to provide forward-looking opportunities for their potential applications in various catalytic processes of practical significance.

Along with the rapid development of flexible and wearable electronic devices, there have been a strong demand for flexible power sources, which has in turn triggered considerable efforts on the research and development of flexible batteries. An ideal flexible battery would have not only just high electrochemical performance but also excellent mechanical deformabilities. Therefore, battery constituent components, chemistry systems, device configurations, and practical applications are all pivotal aspects that should be thoroughly considered. Herein, we systematically and comprehensively review the fundamentals and recent progresses of flexible batteries in terms of these important aspects. Specifically, we first discuss the requirements for constituent components, including the current collector, electrolyte, and separator, in flexible batteries. We then elucidate battery chemistry systems that have been studied for various flexible batteries, including lithium-ion batteries, non-lithium-ion batteries, and high-energy metal batteries. This is followed by discussions on the device configurations for flexible batteries, including one-dimensional fiber-shaped, two-dimensional film-shaped, and three-dimensional structural batteries. Finally, we summarize recent efforts in exploring practical applications for flexible batteries. Current challenges and future opportunities for the research and development of flexible batteries are also discussed.

In this study, we developed a novel confinement-synthesis approach to layered double hydroxide nanodots (LDH-NDs) anchored on carbon nanoparticles, which formed a three-dimensional (3D) interconnected network within a porous carbon support derived from pyrolysis of metal-organic frameworks (C-MOF). The resultant LDH-NDs@C-MOF nonprecious metal catalysts were demonstrated to exhibit super-high catalytic performance for oxygen evolution reaction (OER) with excellent operation stability and low overpotential (~ 230 mV) at an exchange current density of 10 mA·cm^-2. The observed overpotential for the LDH-NDs@C-MOF is much lower than that of large-sized LDH nanosheets (321 mV), pure carbonized MOF (411 mV), and even commercial RuO₂ (281 mV). X-ray absorption measurements and density functional theory (DFT) calculations revealed partial charge transfer from Fe³⁺ through an O bridge to Ni²⁺ at the edge of LDH-NDs supported by C-MOF to produce the optimal binding energies for OER intermediates. This, coupled with a large number of exposed active sides and efficient charge and electrolyte/reactant/product transports associated with the porous 3D C-MOF support, significantly boosted the OER performance of the LDH-ND catalyst with respect to its nanosheet counterpart. Apart from the fact that this is the first active side identification for LDH-ND OER catalysts, this work provides a general strategy to enhance activities of nanosheet catalysts by converting them into edge-rich nanodots to be supported by 3D porous carbon architectures.