Understanding the charge-transfer and Li-ion-migration mechanisms in complex electrochemical environments is critical to improving the performance of commercial lithium-ion batteries (LIBs). Advanced electron microscopy and the associated characterization techniques have significantly assisted in clarifying the structure–function relationships of commercial LIBs by providing localized nano/atomic-scale information concerning the following aspects: atomic structures of light/heavy elements, spatial distributions of structural phase transitions, Li⁺ occupation, interfacial phase structures, occupation and migration of elements, elemental distribution in the interfacial layer, Li⁺ concentration, and interfacial space charge layer. Besides, the development of various in situ techniques coupled with electron microscopy can enable comprehensive understanding of the structural evolution, growth of lithium dendrites at the anode, as well as the ion transport and charge accumulation at the electrode–electrolyte interface in LIBs during charging and discharging. This review summarizes the recent progress of how advanced electron microscopy contributes to elucidating key structural information and evolution in commercial LIBs. Emphasis is placed on (1) the discussions of transition metal dissolution and charge-transfer mechanisms during charging and discharging of LIB cathodes; (2) the morphologies, structures, and compositions of solid-electrolyte-interphase (SEI)/cathode– electrolyte-interface (CEI) films, along with their influence on battery performance; (3) the effects of crystal structures, internal crystal defects, and interface structure on ion transport. The lithiation and delithiation processes in LIBs are scrutinized, and strategies for optimizing ion migration are proposed. This information has been collated to enable a deeper understanding of the charge-transfer and ion-migration mechanisms in commercial LIBs, and to provide guidance for improving battery performance.

Design and fabrication of highly efficient and stable electrocatalysts remain key challenges in green energy technologies such as low-temperature direct liquid fuel cells. Based on in-depth theoretical calculations, here we demonstrate that surface Pd atoms with high coordination numbers (HCNs) can effectively modulate their adsorption energies for CO and OH, and thus achieve very high performance for formic acid electro-oxidation reaction (FAOR). Based on epitaxial coating Pd atomic layers onto nanoporous gold (NPG) thin membranes and a slight further decoration of Au clusters on top, the resulted core-shell structured NPG-Pd-Au electrocatalyst can demonstrate Pd intrinsic and mass activities of 8.62 mA·cm^-2 and 27.25 A·mg^-1 respectively at the peak potential around 0.33 V versus saturated calomel electrode toward FAOR, which are far better than those of commercial Pd/C catalysts (1.09 mA·cm^-2 and 0.32 A·mg^-1) tested under the same conditions. Moreover, the membrane electrode assemblies based on these low precious metal loading electrodes can achieve an anode Pd power efficiency over 10 W·mg^-1 in a direct formic acid fuel cell, which is two orders of magnitude higher than that of the commercial Pd/C. These results provide new inspirations for the development of revolutionary electrodes for energy technologies in a rational manner.

Design of catalyst layers (CLs) with high proton conductivity in membrane electrode assemblies (MEAs) is an important issue for proton exchange membrane fuel cells (PEMFCs). Herein, an ultrathin catalyst layer was constructed based on Pt-decorated nanoporous gold (NPG-Pt) with sub-Debye-length thickness for proton transfer. In the absence of ionomer incorporation in the CLs, these integrated carbon-free electrodes can deliver maximum mass-specific power density of 198.21 and 25.91 kW·g_Pt^-1 when serving individually as the anode and cathode, at a Pt loading of 5.6 and 22.0 μg·cm^-2, respectively, comparable to the best reported nano-catalysts for PEMFCs. In-depth quantitative experimental measurements and finite-element analyses indicate that improved proton conduction plays a critical role in activation, ohmic and mass transfer polarizations.

Plasmonic metal–semiconductor nano-heterojunctions (NHJs), with their superior photocatalytic performance, provide opportunities for the efficient utilization of solar energy. However, scientific significance and technical challenges remain in the development of suitable metal–semiconductor NHJ photoelectrodes for new generation flexible optoelectronic devices, which often require complex processing. Herein, we report integrated three-dimensional (3D) NHJ photoelectrodes by conformally coating cadmium sulfide (CdS) nanolayers onto ultrathin nanoporous gold (NPG) films via a facile electrodeposition method. Localized surface plasmon resonance (LSPR) of NPG enhances the electron–hole pair generation and separation. Moreover, the direct contact interface and high conductive framework structure of the NHJs boosts the photogenerated carrier separation and transport. Hence, the NHJs exhibit evidently enhanced photocurrent density and hydrogen evolution rate relative to CdS deposited on either gold (Au) foil or fluorine-doped tin oxide (FTO) at 0 V vs. SCE (saturated calomel electrode) under visible-light irradiation. Moreover, they demonstrate a surprisingly stable photoelectrochemical hydrogen evolution (PEC-HE) activity over 104 s of continuous irradiation.

The oxygen evolution reaction (OER) is a pivotal process for water-splitting and many other energy technologies involving oxygen electrodes. Herein, a new synthesis strategy is proposed to prepare OER catalysts based on a simple yet flexible in situ decomposition of Co-based acetate hydroxide metal-organic frameworks (MOFs). This process allows straightforward fabrication of various 2D hydroxide ultrathin nanosheets (UNSs) with excellent component controllability. The as-obtained Co-based hydroxide UNSs demonstrate superior catalytic activity for the OER due to the exposure of numerous active sites. In particular, the CoNi hydroxide UNSs exhibit low overpotentials (η) of 324 and 372 mV at current densities of 10 and 100 mA·cm^–2, respectively; a large turnover frequency (TOF) of 0.16 s^–1 at η = 380 mV; and a small Tafel slope of 33 mV·dec^–1 in an alkaline environment. Importantly, these values are superior to those of the state-of-theart IrO₂ commercial electrocatalyst. This facile strategy enables the exploration of more efficient and economic OER electrocatalysts with various constituents and opens a promising avenue for large-scale fabrication of functional nanocatalysts for use in clean energy technologies.

A general method is developed to prepare durable hybrid nanocatalysts by nanostructuring the surface of gold wires via simple alloying and dealloying. The resulting nanoporous gold/Au (NPG/Au) wire catalysts possess nanoporous skins with their thicknesses on robust metal wires specified in a highly controllable manner. As a demonstration, the as-obtained NPG/Au was shown to be a highly active, chemo-selective, and recyclable catalyst for the reduction of nitro compounds and azides using organosilanes as reducing agents.